Sunday, December 29, 2013

Goodbye to the AT72ED

Two years ago I purchased a used AT72ED. The scope I wanted was the AT65EDQ, but it was too pricey for my budget.

The AT72 was an able performer when paired with the Orion Field Flattener for Short Refractors (see my Andromeda Galaxy image in this blog post. I didn't care for the mounting foot, but it was easy to replace with rings. The focuser was no Moonlite but it held my heavy CCD + Filter wheel without problems. If it had a fault it was a little blue haloing on brighter stars. (I can't be sure if that wasn't my fault for not being a diligent focuser.)

Eventually a local club member decided to part with his AT65 and I was able to pick it up for not much more than the AT72 cost me. This made the AT72 expendable and I put it up for sale. I let it sit idle for a while on the club's merchandise forum. Finally this fall I listed it on Cloudy Nights and it sold along with the FF. The new owner is interested in using it to get into wide-field DSLR astrophotography, for which it's wonderfully suited.

The AT65 has been great this fall for chasing down the larger Astronomical League Bright Nebula objects. I recommend it to anyone who wants to get into imaging without spending a lot on an expensive telescope.

One of my telescopes is becoming something of an orphan. My old ShortTube 80, originally purchased as a travel scope to take to the 1998 Solar Eclipse in Aruba, doesn't have a role any longer. I'm holding onto it for now because it's still a good travel scope, and it's great as a guide scope. The Orion mini-guider has replaced the ST on my refractors, but I'm uncertain if the little scope will work well with my C925. That determination will have to wait for the summer when the weather is better.

Speaking of the weather, it's not been helpful. I got the usual fall head cold a couple of weeks before Thanksgiving. Then after the holiday the weather turned cold (frequently going sub-zero). I can handle temperatures down to around 10 degrees F, but zero is outside my optimal range of operation. Cold and Clouds have continued all December. I'm hoping for a better 2014!

Oh yes, one more thing. Astrobin did a major reworking of their site code and all my image links are now broken. I'll be fixing them as time permits.

Saturday, November 23, 2013

Astronomical League Bright Nebula List

EDIT: 5/9/15: The lastest version of my corrected ALBN list can be found at THIS post.

Earlier this year the Astronomical League introduced the Bright Nebula Observing Program. As is traditional, this program provides a list of objects to be observed. In this case there is also the option to image objects. For the BN program visual observers are required to acquire 60 objects (non-observations are also accepted). Imagers must capture 100 objects.

The first version of the object list contained quite a few errors and has since been revised. Unfortunately the revised list still has a few errors and some points of confusion, particularly concerning some compound objects:
  • The Heart nebula is given as IC 1805 + IC 1795. NGC 896 is listed as a separate list item, but most references have it as identical to IC 1795. Why is there a distinction here?
  • The Flame nebula is listed as NGC 2024 + NGC 2023. Most references do not include 2023 in the flame, as they're quite distinct from each other
  • Sh 2-8 and NGC 6334 are considered to be the same object (the Cat's Paw nebula), but are listed as separate objects. Possibly the list intends Sh 2-8 to be the extended nebula surrounding NGC 6334, but that distinction is not noted
  • The Gamma Cygni nebula is also referred to as the Butterfly Nebula, which is IC 1318B and C. It's not clear if observations are meant to include IC 1318A
  • The Pelican nebula is generally considered to be made up of two objects, IC 5070 and IC 5067. For some reason the list adds IC 5068 to the Pelican
Some errors give evidence of inadequate proofing:
  • LBN 8 is listed twice
  • The declination of NGC 2174 (Monkey Head nebula) is incorrect, probably because of a cut-and-paste error. It is given the same declination of the object just before it in the list
  • LBN 10 is the probable victim of a typo; its right ascension is off by five hours
  • IC 1287 is placed on the list out of right ascension order
And one error is just plain dumb:
  • IC 425 is on the list, but it is generally considered a fictional object. Another non-existent object was removed from the list's first version but this one persists. Maybe it's there as a test of observers' veracity?
Since it's my intention to do this list through imaging I've been taking a closer look at it. Because I find the published format (PDF) difficult to work with, I've converted it to a Microsoft Word document. As a part of this reformatting:
  • Objects that are also in the Lynds Catalog have had their catalog number and Lynds brightness added. The list fulfillment requirements include giving the Lynds brightness for each object
  • A list index has been added so that each object can be referred to by a sequential number. (For what it's worth, there are 154 real objects on the list. The list originally was said to have 160 objects; it didn't. It now is said to have "over 150," which is correct.)
  • The above-mentioned errors I've spotted have been corrected
Note that I have NOT done a quality check of all the data supplied by the AL--I've only tried to catch obvious errors. Nor have I tried to resolve the issue of multi-component objects, or to reorder the list. Omitted are the chart numbers.

Here is a link to my revised document. Feel free to download it. If you find errors in it, let me know and I'll correct them.

This can be easily converted to spreadsheet form, which I've done. I've also converted it into an observing list for Sky Tools 3.

Final comments: This is a difficult observing program, particularly because many of the objects are very dim. Northern observers will not be able to see many of the objects at all (at least 22 are invisible from my latitude of 45 north). I think that this program would have benefited from having several people examine and field test it before it was announced. Perhaps in time it will get cleaned up.

Working the list: As of today my tally is 47 list objects imaged with 53 remaining to do. After looking at the list it appears there are about 50 reasonably "doable" objects left for imaging, which will leave me three short. It's going to be interesting.

Thursday, October 31, 2013

Sky and Telescope Readership vs. USA Demographics: No Surprises

I stumbled across this page that reports the demographics of S&T readership to advertisers. It's interesting to compare the demographics to that of the United States population. This is S&T's statement about the source of these numbers:

Simmons Research, Inc., June 1998 — all other data from Publisher's Subscriber Survey, May 2005, and ABC Publisher's Statement, June 2012. 

So most of their numbers come from either 1998 or 2005. Probably only the circulation numbers are current. And one must wonder about how meaningful the other numbers are if they were collected from survey cards. I've tried to match the statistical years where it might matter.

The numbers taken from the S&T page are colored RED.

S&T: Male: 95%, Female: 5% (probably from the 2005 subscriber survey)
USA:  Male: 49%, Female: 51%
This statistic varies considerably by age, but a 50-50 split in the general population is a reasonable assumption for the pool from which S&T draws its subscribers.

S&T: 51 (probably from the 2005 subscriber survey)
USA: 35.5 (median, males, 2010 estimate)
Not really a surprise, the S&T readership is older than might be obtained by random sampling of the population.

S&T: 70% (1998)
USA: 57% (2000 est., U.S. Census Bureau)

Graduated from college or higher:
S&T: 77%  (probably from the 2005 subscriber survey)
USA: 41% (2012 est., U.S. Census Bureau)

Professional/technical careers
S&T: 60% (1998)
USA: 38% (Sept. 2013 est. Bureau of Labor Statistics. I might not be comparing apples and oranges here.)

Average household income
S&T: $94,400 (probably from the 2005 subscriber survey)
USA: $46,326 (2005 est.. U.S. Census Bureau)
The 80th percentile in the U.S. for household income is $92,000.

Time in Hobby
40% have been involved in the hobby an average of 20+ years (1998)
26% have been involved less than 5 years (1998)

Experience Level
beginners: 10%, amateurs: 49%, advanced amateurs: 38%, professionals: 3%

So Time in Hobby and Experience Level say that 26% have been in the hobby less than 5 years, and only 10% consider themselves beginners. So for about 15% of the subscribers five years of astronomy moves them past the beginner stage.

Total paid circulation

Pass-along readership
This is the number of people with whom an average subscriber will share an issue. Some publications (such as newspapers) tend to have a large pass-along. The estimation and value of pass-along readership is debated.

Grand total readership

So, what's the bottom line? In general terms, S&T subscribers are older affluent males, well-educated and engaged in professional careers. Few consider themselves beginners in the hobby. They're ready for high quality gear and they can afford it.

Is it any wonder that the upscale portion of the Amateur Astronomy marketplace has blossomed in the last couple of decades?

Saturday, October 26, 2013

2013 Iowa Star Party on Iowa Public Television

Iowa Public Television (IPT) sent their Iowa Outdoors crew to do a segment about the ISP. It just became available for online streaming here (It's episode #305 for you folks reading this long after the post date).

They did a nice job talking about astronomy and the amateurs who love it. I'm not just saying that because I got some face-time:

Me, in all my sweaty glory
(Note the always-chic Aruba 1998 Eclipse T-shirt and goofy forehead light.) Nor am I lauding them because they used my images taken at the event (M8, M33, and the North America / Pelican Nebulae), although that did score them some points.

They did a nice job and treated people with respect. There wasn't any hint of "this is a geekfest," or "this is something that's not accessible to regular people." They spent considerable time talking to attendees and got a good feel for what it was about.

My DEET-soaked hat is tipped to them.

Saturday, September 28, 2013

Working on the AL Bright Nebula List

The last week has been amazing for this part of the world in that it's been clear six nights in a row. This has given me the opportunity to get my AL BN list work underway. Here are some of the results:

The Crescent Nebula
The Crescent is a bi-color shot (Ha and OIII) with synthetic green.

The Propeller
The Propeller is a fairly bright and decidedly strange looking nebula.

The Elephant's Trunk
The Elephant's Trunk is a much-imaged object, and this is one of my poorer efforts. Polar alignment was far off and the drift has caused artifacts in the image.

The Cocoon Nebula

The Cocoon is another popular target because the emission nebula at its heart is so bright. This image was composed to emphasize the dark lane (Barnard 168) extending westward from it.

Details for these images can be found on my AstroBin pages.

Most of my AL BN imaging will be in H alpha only. This is because my sky is very bright (urban/suburban) and some of the nebulae are very dim. So far I've been shooting mostly large objects with my AT65EDQ and will soon move on to smaller targets using my C925.

I've started using PHD guiding to do my polar alignment. All in all it seems to work very well, but I've found that the instructions for doing the alignment are generally incomplete. I'll see if after some experimenting I can write up something better.

Saturday, September 7, 2013

The AstroBin Voting System

Like many web sites that allow people to vote on contributions, AstroBin has run afoul of troll voters.

Currently AstroBin voters use a 5-point scale. The text descriptions of each vote are:

  1. "It's a start, but it needs better data"
  2. "It looks good, but it needs better processing"
  3. "Good data, good processing"
  4. "Great Result!"
  5. "Top Quality!"

Each vote is weighted by a scheme that reduces the effects of outliers, and people aren't allowed to vote for their own images. Salvatore Siovene gives of his own time to comb the votes for those cast by dummy accounts. I have only the highest praise for Salvatore and his efforts regarding AstroBin, which is a labor of love on his part. If some parts of it become commercially successful, more power to him!

In a perfect world, everyone votes on an image based on the image's technical and artistic merit. But we all know how difficult that can be from watching judged sporting events such as skating and gymnastics. In a hobby where egos can run rampant there's little hope of ever doing away with votes cast with dishonest intent. Troll voters adapt quickly to remedies; after it was announced that 1-votes would likely bring scrutiny, the trolls began voting 2s, often for images that were clearly excellent.

Another web site I visit has been plagued by troll voting, and many people have suggested alternative systems for legitimizing voting:

  • Change to a 1 to N scale, usually with N being a number like 10 (This is much like electronic zoom, it accomplishes nothing)
  • Clip the distribution of votes more strongly (Like median stacking, this works well only when there are many votes--usually there aren't)
  • Allow only selected members to vote (Aside from not being very democratic, this leads to other problems, such as favoritism)

I gave the problem quite a bit of thought a few years ago and came to the conclusion that the voting system that would work best was a binary one: a 1 vote indicates that you think the image is above average, and not casting a vote suggests you think it's below average. Note that there is no 0-vote. If you don't think an image is very good, you simply cast no vote.

A binary system is imperfect. Ghost accounts can still pollute the voting. While their effect can reduced by tracking IP numbers, they can never be entirely eliminated .

Another failing of binary voting is that the number of votes depends in part on the interest in the target object. For example, photogenic nebulae may get more attention and more votes. If one image gets 100 1-votes out of 500 "looks," does that mean it's a better image than one that gets 5 votes out of 25 looks? Not really. But 100 votes looks a lot better than 5.

At the moment AstroBin is polling its members to see if it should switch to a simple "like" system. This is basically the binary system that I've been talking about, so I voted for the change. Personally, I wish that the poll had included the option to do away with voting entirely.

All of the above, I suppose, explains why I just opted out of the voting system entirely.

Wednesday, September 4, 2013

Dealing with the Heat

I went to three star parties this summer. While planning for them, I realized they all held the potential to be dangerously hot. Several years ago the Jeffers party had reached a heat index of 117F! What saved us was that the visitor center was open and air conditioned. I would go outside and sit in shade every now and then, but after 20 minutes would have to retreat indoors.

How does one deal with that kind of heat and humidity? The most important thing to do is to avoid direct sunlight. That 117 heat index leaps over 130 and into very dangerous territory if you're not in shade. What I've seen people use at star parties is usually the four-pole canopy. These are nice, but sometimes aren't that sturdy. A strong wind can take them down, perhaps bending a pole and making them useless. For myself I looked for something smaller (and less expensive--it's me, Mr. Cheap). What I found was something from Coleman called the Road Trip Beach Shade.
Coleman Road Trip Beach Shade
It's hard to judge the scale here, but I could easily sit in my chair within the quarter-sphere it provides. The back panel becomes a screen opening to allow air flow, a nice touch. I don't find this shelter the easiest thing to set up, and folding it for storage in its little carrying case is an adventure. Metal stakes are included, which is nice because it needs to be staked down. The biggest con reviewers noted was the fiberglass poles seemed prone to breaking. I've had no problems in two setups and tear downs--but I'm keeping my fingers crossed.

Also, collapse this shelter if you anticipate a storm; If its standing when the winds come, it will be a great wind scoop for a few seconds before it rips or sails off.

$45 from

Number two on the must-have list is water. Keeping yourself hydrated is essential, particularly if the air is dry and there's a wind. Get yourself a large water carrier, a drinking bottle, and chug more than you think you need to.

A nice convenience I found was a small 12V fan:
Coleman Ozark Trail Camping Fan
This normally runs off 8 D-cell batteries, but I had an old 12V 7Ah power supply that was perfect for it. Fortunately the fan has a jack built into its side, and I was able to build a little patch cord to connect it to the battery. The battery is a good ten years old, and it kept the fan running on low for 12 hours. It made a nice breeze, even outside. A steal from Walmart for $16.

And no, I don't work for Coleman. I just like their stuff. Stay cool!

Monday, September 2, 2013

Iowa Star Party 2013

Another star party, and continuing poor weather. This was probably the hottest ISP ever. Thursday: high temperature of 94F, dew point temperature of around 70F (heat index = 100F) Friday: high temperature of 97F, dew point of 72F (heat index = 106F) Saturday (the nice day): 91F and 61F, (heat index = 91F) Speaker's talk in the Barn: 86F and 66F (heat index = 88F) That was a very sticky 88! Some relief was found at midday on Friday in the Oakridge house, but unfortunately the A/C unit was unable to keep pace with the heat: it actually froze up. I bailed out around 3 P.M., preferring to face the heat outside where the air occasionally moved.

Friday was also public night, and the attendance was significantly smaller than I recall from my last visit. Between the heat and the fact that it was the opening night of high school football, it's understandable if people decided to be elsewhere.

And how about the sky? Thursday night was grand, although around 1 A.M. the south wind began shoving clouds northward and the southern sky started to deteriorate. Friday night was great for the public, but about the time they left the clouds moved in. The sky went partly cloudy during the early morning, but at 4 when I woke up it was about 50% cloud cover. Visual observers could deal with that, but imagers not so much.

Saturday night usable sky was all of  90 minutes pinched between the end of twilight and clouds rushing southward ahead of thunderstorms. It never cleared for any substantial time after that, and in fact around 3 A.M. a thunderstorm with heavy rain and gusts to about 44 mph (at Carroll) hit us. From what I saw the next morning no one sustained serious damage from the winds, although a couple of screened sun shades looked like they needed some repair.

Yes, imaging time was scarce, but I managed to get three objects in. Thursday night started with M8 and surroundings:

Messier 8, the "Lagoon"
Click this for a larger version. There are a number of objects here, not just the big old Lagoon. At lower left is globular NGC 6544. At about 10 O'clock from the lagoon and next to a bright double star is the pretty reflection nebula IC 5070. On the left edge of the picture about 1/5 of the way down from the upper left corner is emission/reflection nebula IC 4685. The lagoon itself is a confusing construct of NGC objects.

At this point it was a bit before midnight, and my sense was I didn't have much "awake" left in my tank. Some years ago at Jeffers I'd imaged M33 with my DSLR and TV102, so I  thought I'd try it here with the AT72ED and CCD. Here's the result:

Messier 33, the "Pinwheel"
The AT72 is really too short a scope for this object, but it was the scope at hand. I'm not happy with the color balance of this; judging by the star colors I'd almost say that the green channel is too strong. I'll doubtless reprocess this.

Friday night was clear for a while, and I was able to learn my target's star field while entertaining/educating the public. I  think I collected one frame before having to shut down.

Saturday I raced from the meeting barn to the observing field and was able to get everything running and my target composed in under 30 minutes (a not-so-minor miracle). In fact, I even had to toss my first light frame because it was still twilight. about 90 something minutes later it was over. The NA and Pelican are bright!

Nebulae NGC 7000 "North America" (left) and  IC 5070 "Pelican" (right)
Don't know why the stars bloated so badly in this one. Poor focus, most likely.  Clouds rolled in while there was still plenty of time for another image, so I count this as half a night.

Details for these images, along with their full-size versions can be found on AstroBin.

The last year's star party log sheet runs like this:

HOASP (Autumn 2012): three nights of rain.
WOW: Registered but did not attend; I would have had one good night at best out of three.
Jeffers: 2 good nights out of 3.
South Dakota: 1 out of 3.
Iowa Star Party. 1.5 out of 3

Add those up and it was 5.5 good nights out of 15. Disappointing. Perhaps this autumn will be better? If it is, I'll probably be making more runs to the club's dark-sky sites. Stay tuned.

Sunday, August 11, 2013

M 31 from the South Dakota Star Party

New dew controller in hand (see last entry) I was ready for the South Dakota Star Party. I had a short list of targets--The Iris Nebula, the Lagoon Nebula, the Heart Nebula. The one chosen would depend on the sky conditions. So much for plans.

Thursday night was partly cloudy with heavy dew and fog. I stayed home. Friday night started with high clouds, but went mostly clear as twilight ended. The view to the Lagoon was full of light from Sioux Falls, which was only about 15 miles away. I decided on the northern sky. I did a bore-sight polar align and tried to start with M 103. I switched over to M31 because I wanted to image something prettier. I got everything set up and running, but the first few frames were bad because the autoguider was losing the guide star in the remaining cirrus. There was a bright star at the edge of the autoguider's FOV, so I used that instead.

I set up the camera control to shoot five lights through each of the LRGB filters and then loop. That was at about 11:30. Amazingly, the system continued to run unattended for almost five hours! Focus held steady all that time, and tracking remained solid on all but one frame.

In the end I had to toss 25 frames because of clouds, one for tracking, and a couple because satellites passed right across M 31. Here's the result
Messiers 31, 32, and 110
Click for a larger version. Visit Astrobin for image details and a full-scale version.

I know the cores are overexposed, and maybe I need to do something about the blue fringing on some of the stars, and maybe I left it all a little dark. But I think I like it. Thank goodness I didn't cut the imaging short to chase after another object.

Dew controller and image noise

Well over a year ago I began noticing bands of noise on my images. Here's an example:

Stretched Light Frame showing noise band
And here's a patch of it at full scale (look just below the nebulosity). The appearance of the band will vary from frame to frame, but it's always a horizontal strip of hash. Longer exposures have more bands. Here's what it looks like at full scale:

Noise band at full scale
When that band covers your target, it overlays a great deal of noise that is difficult to remove. ImagesPlus noise removal reduces it, but you can be left with a light band.

I could not figure out what the source was. At first I thought it might be AC line noise (I was running using AC power). Moving to battery power didn't get rid of it. Bad cables to the CCD were suggested by others, but lots of cable swapping didn't fix it. Maybe it was the CCD camera itself? Online searches didn't suggest the camera had any problems like that. I did see some implications of interference from other devices being powered by shared batteries, so I isolated the CCD. The noise remained.

This was an intermittent problem, however. I didn't tumble to the cause until last week at Jeffers, while I was imaging M20/21. Almost every frame was noisy. For some reason I turned off the dew controller, and like magic the noise was gone. I imaged M17 the next night with no dew control (it wasn't needed) and every frame was free of the noise.

A more directed online search led me to a comment about the controller I use, the Model VI:

The Culprit: Kendrick Model VI
I immediately launched into more research and was happy to learn that Kendrick made an RFI-free controller that was in my budget range, the Standard Dual-Channel Controller (SDCC). $114 and shipped free from Astronomics.

The Solution: Kendrick Standard Dual-Channel Controller
A night of imaging with the SDCC keeping everything dry produced images that were all RFI noise-free.
If you're imaging and seeing a lot of horizontal noise bands, it may be your dew controller.

Wednesday, August 7, 2013

Two images from last weekend: M17, M20/21; Processing workflow.

I'm REALLY pleased with how this image of M17 came out:

Messier 17 (Omega or Swan Nebula), click for full size
The previous night's image was not quite as successful--M20 and 21. More about why in the next blog entry.
M20 (Triffid) and M21
Both images are full-frame. For all the gory details of acquisition, look at my gallery on AstroBin. By way of a quick summary, both are LRGB images made with an SBIG ST8300M CCD, TeleVue 102 apo and autoguided CGEM mount under mag 6+ skies. Dark and bias frames only, no flats.

Imaging is SO much faster doing LRGB in the dark than it is to use narrowband filters under light-polluted skies. 

I realize that the colors in the M17 image may look a little muted to you, but I kind of like them this way. What's particularly pleasing about the image from my standpoint is three-fold: The stars are nice and round right out to the edge of the field, meaning that my field flattener is doing its job perfectly; The merging of the LRGB channels seems to be spot-on. And finally, guiding with the Orion mini-guider works great at the 700mm focal length of the TV102 to correct mount errors. I'll eventually try out the mini on my C925.

My processing workflow continues to evolve. These two images were made by ping-ponging back and forth between Images Plus and Photoshop:
  • Calibrate, align and stack using IP
  • Stretch using PS
  • Noise cleanup and star size reduction in IP
  • LRGB combine in PS using Annie's Actions
  • Color balance in IP
  • Masked sharpening in PS
Yes, I know that's a mess, and some will say that all can be done in IP or PS or Maxim or whatever. Good for you if you can function with only one software package, but at this point I can't. I'm using IP 4.5, so probably some of the changes that have gone into later versions would make it a better processing tool. 

Friday, June 14, 2013

Seeing and Saturn

The environment really makes a difference when it comes to planetary imaging. Here are two images of Saturn; the first from a windy night with poor seeing, the second from last night--calm and good seeing.

Windy, Poor Seeing

Calm, Good Seeing
The differences are dramatic. With better conditions the artifacts at the ring-tips are gone, there's more ring structure, Saturn's limb and cloud belts are better defined, and the polar vortex can be seen. Contrast is higher, too. (Differences in color balance are due to processing, not the conditions.)

Now imagine if the seeing had been excellent. Maybe some day I'll have a third image that illustrates that.

(Both images were created using a Point Grey Chameleon, Celestron C925 XLT, and TeleVue 2X Barlow, FireCapture and Registax 6.)

Thursday, June 6, 2013

Clouds, WOW, Focal Reducer

The abysmal spring of 2013 continues with clouds, clouds and more clouds. My plan to attend the Wisconsin Observers Weekend this weekend has fallen through because of weather. The first night is being clouded out as I type this, Tomorrow night is forecast to be partly cloudy (at best) and Saturday night is forecast to be rainy (50% chance) and cloudy.

Worst. Spring. Ever.

But anyway, I did manage last week to shoot some test images with my .63 Celestron Focal Reducer.  I fiddle with my adapters until I got a spacing of about 104mm (I think), and here's what I got:

Flat Field test
This is taken using a Celestron 925 XLT and Celestron 0.63 Focal Reducer/Flattener. The camera is an SBIG-ST8300M with filter wheel (total back focus 38mm). Spacing was provided by a Celestron SCT-to-T adapter #93633-A (about 58mm).

The above full-field image is six 10 second exposures (2x2 binned) aligned and stacked, then given a stretch by Images Plus. The scope was not even roughly polar aligned and was unguided. I was also shooting through overhead power lines. Yechh.

I think it's fairly flat, at least flat enough to make me happy. Some vignetting is present, but it's about the same as found when imaging without the FR. I will probably tinker with the spacing in the future.

What's nice is that this setup gives a much more solid connection between the scope and camera. I look forward to using it SHOULD THE FREAKING SKY EVER CLEAR. Really, no, I'm okay, but thanks for asking.

Monday, May 20, 2013

Messier 3 from April

One advantage of long periods of cloudy weather is the time it gives you to catch up on processing. I've had a shot of M3 sitting around for almost a month. I never processed it because it was an "end of the evening" afterthought. Low priority compared to getting my new planetary imager. Now that that's settled I took a look at it today. My first pass at processing it left it too yellow, and my in my second attempt I may have overcompensated.

Messier 3. Click image for full size.
Image details are here

The way things are going in terms of the weather I may not be able to resume my imaging Messier marathon project until the Wisconsin Observer's Weekend in early June.

Wednesday, May 15, 2013

Third Light with PGR Chameleon: Saturn

First light (5/12): I was using FlyCapture software distributed by Point Grey. The software behaved terribly, crashing repeatedly, but PG support was great in helping me to get the camera online. No .avi files were worth keeping.

Second light (5/13): Now using FireCapture software, which took some work to get going. The creator of the software is an active member of the FireCapture Yahoo group, and he responded to a question I posted almost immediately. Amazing support from both PG and FireCapture. Unfortunately, the night was really windy and the seeing was terrible. No .avi files worth keeping.

Third light (5/14--yes, three semi-clear nights in a row!): Everything was rolling, and the night was a little less windy. Seeing was still not at all good, but I did take some videos. Here's the "first light" f/20 image with my C925:

Saturn, the planet with those big bright rings
Awfully fuzzy, isn't it. And those rings look pretty shabby. Oh well, I'll blame the seeing.

And so another learning curve begins. I have a lot to learn about using FireCapture to optimize my imaging. So far Firecapture is far better than FlyCapture, Both in terms of stability and utility.

Thursday, May 9, 2013

Point Grey Chameleon ready for action (clear skies?)

A long time between updates, but the weather has been incredibly awful. Clouds, Clouds, snow, Clouds.

But it was good for indoor activities like learning how to sell on eBay. My comic book sold for $300, and that along with other sales got me up to what I needed to get the Chameleon, a GSO Crayford focuser for my C925, and a nosepiece so that the Chameleon could use the focuser.

Getting the new camera to work was a brief bit of effort. The camera works well with FlyCapture software, also available from Point Grey. I made a mistake of downloading the latest beta of FlyCap, and it acted like a beta version: no video. As soon as I replaced that with the latest stable version everything worked great. The Crayford will give me zero image shift as I focus. Shift was obviously going to be a problem; the few times I tried video at f/20 it was hard to keep the target in the field of view.

Everything about Point Grey was superb. The camera was shipped via Fed Ex box in box in box; it works great, and when I wrote them asking for advice about the missing video their response was fast and professional.

Last night was the first one with the Chameleon under the stars. FlyCapture software is less than adequate, as it crashed repeatedly, and the GUI is clunky (in my opinion). I'm going to start searching for alternatives.

Monday, March 25, 2013

New camera deferred

Last time I wrote about I comic book that I intended to sell in order to raise some cash for a new video camera:
I submitted it as worth between $300 and $1000. 
I should have my estimate within the week.
Silly me. The grade for the comic came in today, and it was lousy. If I'm lucky I might be able to sell it for enough to pay for the grading and shipping.

Wednesday, March 20, 2013

Comic Relief

Since I purchased a Celestron 9.25" SCT I've been thinking about upgrading from my ToUCam to something a little better. Right now I have my sights on a Point Grey Chameleon. The Chameleon is based on the Sony ICX445 and offers small pixel size, USB 2 compatibility, and a low price. It's frame rate is a little low at 18fps, but that's certainly acceptable. Reviews have been solidly positive.

Yes, there are GigE, firewire, and USB 3 alternatives that could be made to work with my laptop, but those models tend to be higher in price.

But even at $375 (+$20 or so for a 1 1/4" nosepiece), where will the money come from?

One source is an old comic book I have. I'm not a collector, but by coincidence I have one comic that is possibly worth some money--as much as $600, I hope. Not knowing a thing about comics, I have decided to get it professionally graded.

I shipped it to CGC Comics at the end of February. They will grade its condition so that a potential buyer can have confidence in what they are getting, seal it into a container and ship it back.  It's been sitting in their queue since March 1, and today was scheduled for grading. CGC charges for this service on the basis of the comic's estimated worth. If the comic is thought to be worth more than it was submitted as, they will increase the initial grading charge. I submitted it as worth between $300 and $1000. I would love to hear back from them that they plan to charge more!

I should have my estimate within the week.

Wednesday, February 20, 2013

Pixels, Levels and Curves--Oh My!

(I've slowly come to a sort of useful understanding of how some basic tools of image processing work. This is an attempt to put into words those concepts that are elusive to me. I hope these little essays will help a few people starting out with imaging processing. It's meant to be purely introductory)

Pixels, Levels and Curves, Oh My!

Part I

In which a house made of light, dark and bias frames falls on the Wicked Witch of Noise.

Your imaging sensor (whether DSLR or CCD) is a digital device based on discrete bits of information that are either on or off. Most of what it does is an exercise in counting, not measuring.

Sensor pixels act like little buckets, and photons of light as electrons (imagine them as tiny marbles, if you want). For simplicity let’s assume that a pixel can hold 65,536 electrons.  (This capacity will vary from sensor to sensor.) In binary notation, the number of electrons in this pixel can be unambiguously given by a positive 16-bit integer. (In this case we say the bucket has a 16-bit depth.)

We define black as the case where there are zero electrons in the bucket; white is when the pixel is filled to capacity.

Electrons are added to the pixel through a number of effects.  Let’s consider the primary cause: Photons coming from our target object that interact with pixel to liberate an electron.

Imagine two side-by-side pixels, both getting light from a telescope pointed at an object of uniform brightness. You might reasonably assume that both pixels will fill with electrons at the same rate, and after letting a certain amount of time to pass, both pixels would have the same number of electrons in them.  You would be wrong! Let’s do a little thought experiment to find out why.

Take four typical coins and flip them.  Count the number of them that land heads-up and write that down for the contents of Pixel 1. Gather up the coins and flip them again, writing the new number of heads as the contents of Pixel 2. Do this nine more times, adding the new numbers of heads to either Pixel 1 or 2 as appropriate. Knowing that the chance of a coin landing head-up is 50% it’s reasonable to assume that you should have 20 heads in each tally when you’re done. Chances are you don’t, though. In fact, it’s quite likely that the two sums aren’t equal. Why? Because a collection of four coins has other possible outcomes than landing with two heads and two tails showing. The effect of these other possibilities is to change the “perfect” outcome of exactly 20 heads into a distribution peaked near 20 heads, but also having other values.

Light entering a pixel resembles this example. During a given time interval we expect a certain number to enter and produce electrons. But during each interval of time a number of different counts can possibly occur, and by the end we don’t always have the exact amounts suggested by chance.

Now imagine a field of pixels, illuminated by light coming from a uniform source (perhaps an electroluminescent flat panel). We allow light to enter the pixels until they’re about half full and then close the shutter. Do all the pixels have the same exact number of electrons in them, providing an image of uniform intensity? No, they don’t. Some have more electrons, some less, in a very random way that results in intensity that is not uniform.  So the source of uniform illumination is not imaged as uniform; instead it appears a little gritty. This grittiness is called shot noise.

Another process that introduces shot noise is the spontaneous addition of electrons to pixels by dark current. Dark current results from thermal activity in your sensor that occasionally kicks an electron into a pixel bucket. The warmer your sensor is, the faster this process works. Because dark current has nothing to do with the object you’re imaging, it’s something we want to minimize.  The obvious way to do this is to keep the sensor as cool as possible.

There is another way. If we could take an image in which the electrons come only from the dark current, that image would represent a sort of dark image that could be subtracted from our image of the target object. This is what shooting dark frames is all about.  Dark frames are images made with the shutter closed and are essentially images of dark current. Subtracting dark frames from images made with the shutter open (light frames) goes a long way toward removing the noise present. In order to match the amount of dark current present in light frames, the dark and light frames must be made with the sensor at the same temperature and have the same exposure time.
But wait, there’s more! Noise can be generated by random processes in the sensor and its electronics, and more noise can be created during the reading and reporting of pixel counts. These can be lumped together as read noise. Read noise doesn’t depend on exposure time, and is probably not very sensitive to temperature. As for dark current noise, we can image the read noise by making a very short exposure with the shutter closed. We keep it short to minimize the contribution of dark current. These images of read noise are called bias frames.

Conveniently, every dark frame image also contains the bias image, so when dark images are subtracted from light images, the bias image gets removed, too.  When you can rely on the light and dark frame temperatures being the same, bias frames are not needed. Many people apply bias frames regardless.

One more bit of terminology: The application of dark and bias frames to light frames is called calibration. Calibration can also involve flat frames and flat dark frames. We can leave discussion of those to another time.

Ding-dong! The Noisy Witch is dead? Sorry, but it’s impossible to remove her from the picture completely. Using multiple dark and bias frames to better generate the dark and bias images does help to keep her down, though. And she definitely resents increases in total exposure time.

Coming up...
Part II, In which we see that the road to the land of imaging Ahs is a Grayish-Brick Histrogram
Part III, In which we learn that even without a brain we can use Levels
Part IV, In which we find that that the heart of the matter is Curves

Other news... Our astronomy club has decided to go ahead with an Imaging Messier Marathon on April 5. Should be fun!

Tuesday, February 19, 2013

Imaging Messier Marathon list PDF

Here's a PDF I created that is adapted from Don Machholz's Go-To list in his Observing Guide to the Messier Marathon. I have added the multi-object image opportunities for those using a medium-size sensor and 700mm focal length imaging system. Have a suggested change or find an error? Leave a comment and let me know. Here's what a portion of it looks like:

A portion of the IMM list PDF.

Sunday, February 17, 2013

Imaging Messier Marathon: Combining Targets in One Frame

So many objects, so little time. If only there were fewer objects!

Well, in a way there are. Some of the Ms are close enough together that one shot can encompass two or more objects, thus saving us time. Let's see what we can find in the way of grouped Messiers.

I'm going to list the Messier objects in the order given by Don Machholz in his book The Observing Guide to the Messier Marathon--A Handbook and Atlas. This book is available from AmazonBarnes and Noble and other sellers. Frugal? Look to used book stores. I paid $25 for my copy at Half Price Books.

Here are some combined fields for two different focal lengths. If I missed some, please let me know so  that I can add to the list.

These lists depend your go-to running with at least get-it-in-the-finder accuracy. In the lists I'm leaving out all the single-target fields. I'll add a master list of all 110 objects soon.

700 mm Focal Length Combined Fields

Eleven fields saved, five go-to ra/dec actions, four camera orientation checks.

Go-To target is indicated by bold. Tight fits may require camera rotation

M31+32+110:  Check Camera Orientation


M95+96: Target RA 10:45:16, DEC +11:45:54


M81+82: Target RA 9:55:39, DEC +69:23:38

M97+108: Target RA11:13:11, DEC +55:20:23 Check Camera Orientation



M17+18: Target RA 18:20:15, DEC -16:38:38 Check Camera Orientation

M21+20:: Target RA 18:03:23, DEC -23:07:31 Check Camera Orientation

432 mm Focal Length Combined Fields

Fourteen fields saved, four go-to ra/dec actions, five camera orientation checks.

Go-To target is indicated by bold. Tight fits may require camera rotation



M95+96+105 Check Camera Orientation



M97+108: Target RA11:13:11, DEC +55:20:23

M84+86+87: Target RA 12:27:51, DEC +12:38:53 Check Camera Orientation

M58+59+60: Target RA 12:40:25, DEC +11:42:19 Check Camera Orientation

M17+18: Target RA 18:20:15, DEC -16:38:38 Check Camera Orientation

M21+20 Check Camera Orientation

Your choice of imaging focal length(s) may well differ from mine. Focal lengths longer than 700 mm will find that some of the combinations flagged for an orientation check will not work. If your focal length is between 400 and 700mm you're safe if you follow the recommendations for 700mm.

Thursday, February 14, 2013

Imaging Messier Marathon: Imaging Focal Length

Last time I mentioned planning for an imaging Messier marathon (IMM), where the goal was to produce images that recreate the impression a visual observer would have looking through a 6" or 8" telescope. This time I'll look at the choice of a telescope for this task.

Focal Length:

Under ideal circumstances imagers try to choose an imagin focal length that best matches the target object. In the IMM that's not really possible without spending a lot of time on swapping gear around. We need to use one telescope. Since this is quick and dirty imagaing with little concern about "going deep," any reasonable focal ratio from f/5 to f/10 will do, with faster scopes being preferred.

More important in my judgement is the ability to frame the larger of the Ms in single shots. If smaller objects end up looking small, that's fine, for that simulates the eyepiece view.

Since I'm planning this for myself, my calculations will be based the relatively common KAF-8300 sensor (18x13.5mm) that is in my CCD camera. DSLR imagers with APS-C sensors will have somewhat larger fields of view.

You can follow along with what I'm doing if you have a good planetarium program. I recommend Sky Tools 3, a package that is very good for planning. Also helpful is this list of Messier objects sorted by size.

Let's get started by examining some of the Messier objects.

The Ms range from the enormous M31 (about 3°x1°) to the tiny M57 (105"x78"). 400-500mm is about right for the entirety of M31, while M57 probably looks best at 2000mm or longer. This is what M57 looks like at 400 and 700mm FL:

M57 @ 400 mm FL,  5.4um pixel size, enlarged 4X

M57 @ 700mm, 5.4 um pixel size, enlarged 4X
The first image is very pixelated, while the second is smoother. Surrounding stars are better seen in the 700mm image. (We don't care about the central star, since that isn't available to visual observers except using  very large telescopes.)

The second largest Messier object is M45 (M44 is almost as big). Here's what it looks like at 700mm:

M45 @ 700mm, 5.4 um pixels. Red box is FOV in KAF-8300
It fits very nicely. At 800 or 900mm we could still get most of the cluster in, but it would seem a little cramped. (Here we don't care about the nebulosity because it's essentially invisible to the eye of a beginner. We just want to capture the stars with enough dark space around them to make it look like a cluster.) 

We could continue, but there's a balance to be set, and it's a very subjective balance at that. Longer focal lengths favor the more abundant smaller objects, while longer focal lengths favor relatively few objects. Short er focal lengths give us a chance to capture several Ms in single frames, which helps us do the IMM. Longer focal lengths will eat up more time with getting targets centered in the camera's field of view.

 From the above I would suggest any focal length between 600 and 1000mm should serve well. 

The ultimate choice depends on the telescopes you have available to you. In my case only one scope fits: My TV102, which has a FL of 700mm with its flattener attached.

Next time I'll look at which Ms can be combined on single frames given a 700mm FL and KAF-8300 sensor.

Wednesday, February 13, 2013

Imaging Messier Marathon

A plan is being hatched here for an Imaging Messier Marathon or IMM. Just as with the regular visual MM this is all about quantity, not quality.

I have an secondary motive for doing this. I am co-owner of a small (if it was any smaller I'd be the sole owner and employee!) that creates educational software for the earth sciences. One program is an astronomy package, and I'd like to use my images to populate a photo gallery of common objects.

But this isn't about putting together a lot of images for students to ooh and aah over. Nothing I do can compare to what other imagers create, much less resemble something like a HST image.  My goal is to show them what the Ms look like through a small telescope--say a 6" or 8" Dob. I don't want them to be disappointed at the fact that faint fuzzies usually look just like that until you either use a large telescope or view from a really dark site. Sadly, most kids (and teachers) don't have access to either.

I know from experience that showing them the planets (particularly Saturn, Jupiter, crescent Venus and Mars at opposition) and the Moon can really wow them. But often it's the case that they expect galaxies to be just like those bright, colorful spirals seen on the Internet. Sometimes they can't even find a galaxy or globular in the field of view because they're looking for something much more spectacular.

So my goal is to produce a set of images that give teachers and kids an idea of what something will look like in a small telescope operating under a suburban canopy of light. A few of the images will be accompanied by better images, when I'm able to take them.

This means for most objects I would shoot a handful of light frames. Even though most galaxies and nebula show no color visually, I would probably shoot everything with the same scheme: 30 second exposures, binned 2x2, maybe three frames each of RGB, using my ST8300 and TV102. No autoguiding, and only a simple polar align.

Detailed resolution won't be important because untrained eyes have a hard time picking that out, and colors can be muted at best. Quantity, not quality.

As an act of faith that it will eventually be clear at night, I mailed in my registration for Wisconsin Observer's Weekend. Hooray!

Wednesday, February 6, 2013

Hobby on Idle

Still waiting here for clear skies. I've been reprocessing images from last year; you can find them at my page on Astrobin. I'm slowly learning how to use Astrobin, and I think I'm going to like it.

I'll write up my experiences with it, and make a report on the Orion Mini-Guider/StarShoot Autoguider combo. You'll know the weather has improved when you see the latter appear.

It's almost Mid-February, the time it starts warming up around here. This winter has been notable for the abundance of nighttime clouds. Blecch!

Wednesday, January 30, 2013

2013: Star Party Bonanza!

My summer schedule is usually all over the place, and if I can make it to one star party I'm doing well. It seems sometimes like all the new moons fall on busy weekends; if it's not that, there may be several star parties at the same time. Then there's the Minnesota State Fair baked goods entry day, the August Sunday fifteen days before Labor Day.

"Fairchild," mascot of the State Fair.
What, you've never seen a gopher wearing a bow tie?
For a few days leading up to that I'm usually baking furiously in preparation. What can I say, I like baking bread, and I like winning ribbons.

The Ribbon is what it's all about.
Disagree? Get your priorities straight.

And on top of all that, there's earning a living. Oh, to be retired and financially secure! Years to go before that happens, if ever. I teach Friday night and Saturday afternoon science courses that typically run through the end of June. That puts a crimp in attending the usual Thursday through Sunday parties.

Amazingly, this year four parties fall on open dates for me:

  1. Wisconsin Observers Weekend, near Waupaca, WI. This was my only summer party last year, and I really enjoyed it. In 2013 it's in June, on an off weekend for me!
  2. Jeffers Petroglyphs informal party (nee Prairie Grass Stargaze), near Windom, MN. My favorite star party. Hard to do better than the people who stage this and attend, and the setting is made all the more sublime knowing that an ancient Native American observatory has been found nearby.
  3. Northwoods StarFest, near Fall Creek, WI, and hosted by the Chippewa Valley Astronomical Society. Never been to this, but it's close and most people speak highly of it.
  4. Iowa Star Party. I've missed this for the last few years. This is where I was introduced to real astrophotography by some very nice imagers. Someday I hope to exact my revenge.
I don't know if I can handle all this dark site time, but I'll try.

Next time, some words about Astrobin, where I've started posting images. There's not much else to talk about thanks to the clouds and cold weather.

Sunday, January 20, 2013

Another Retirement Location Off the List

Dang, another place I was considering for retirement is off the list. See the big patch of brightness north of Dickinson, North Dakota?

North Dakota at Night

(This is a portion of a NASA Earth At Night image)

The light is coming mainly from the lights on the instrastructure supporting the oil production there. Media reports suggest that this light is mainly from the flaring of natural gas produced by fracking, but the people who fly the satellite suggest that's not the case. Here's a closeup of the field, from an image at the same source:

Bakken Field closeup
I wonder if the effect on viewing is as pronounced as it appears to be in these images? I don't know anyone who lives in that area to ask.

At one point I thought it might be nice to retire to someplace like Watford City and do astronomy outreach at the North Unit of Teddy Roosevelt N.P., and also do some dark-sky imaging too, of course.

The annual North Dakota Badlands Star Party is held at TRNP North Unit, so maybe when they post their dates for 2013 I'll ask about how the light has affected viewing.

Saturday, January 19, 2013

DIY Concrete Pier for a medium-sized SCT

What do you need for imaging with a Celestron 9 1/4" SCT operating at f/10 (FL 2350mm)? A mount with very little flex. In my case this works out to a Celestron CGEM mount. For a couple of years* now I've been working toward building a small observatory. I want to put the mount on a pier, and miracle of miracles I have actually gotten this part of the observatory done! Not without a lot of dithering about what sort of pier to install.

If you go to Cloudy Nights you'll see many people giving their ideas of what constitutes an adequate pier for imaging at a modestly long focal length. The largest telescope I anticipated using was a 9" SCT, so I felt much of the advice, though sound, was meant for larger loads. On the other hand, I decided that some suggestions were a little on the light side.

Some ideas I considered and rejected were for a pier made from 4x4" wood beams (possible polar realignment needed as the humidity changes), steel pipe piers (expensive), 10 or 12" concrete piers (overkill), 4-6" concrete piers (too much flex).

That left me with an 8" concrete pier as the ideal compromise. Cheap in cost, and easy to put together--even for me.

  1. Digging things, such as a hole auger and shovel
  2. A little small gravel to line the hole bottom
  3. Concrete forms
  4. Duct tape
  5. 2x4" lumber for holding the form level
  6. Bagged Concrete (Quikrete, for example) 
  7. Rebar
  8. Pier to mount adapter
  9. "J" bolts with hardware to match adapter
  10. Mixing tub such an old wheelbarrow
  11. Garden hoe for mixing concrete
  12. Bucket to measure water
  13. Water
Now, some lessons learned as applies to each of the above:

The frost line here is 42" down, so the hole must be at least that deep plus a few inches. Fortunately I had an old post hole manual auger that made digging a snap. It looks like this one, which can still be found for sale various places:

Manual Auger
Mine is actually an antique hand-me-down with a decayed wooden hand bar and several layers of rust on the metal parts, but it sliced into my mix of clay and gravel almost like the proverbial warm knife in butter. The only trouble I had was at 42" depth, where it ran into a larger rock (which now sits on a counter in front of me). The hole was deepened to 45" by using a long-handled shovel.

You just need enough gravel to put a few inches in the bottom of the hole for drainage. Pack it down with a 2x4".

Forms are usually available in 4 foot lengths (mine came from Home Depot). Because the total length of my pier was longer than this, I joined two forms by making a 1 foot long external sleeve and putting it all together with duct tape. The length is critical because the adapter will ride atop the form, which will be filled with cement to just below the top of the form. You need to plan things out so that the distance between the adapter bottom and the top of the cement is about 1.5" or so.

The form should fit nicely into the hole with a little wiggle room around it; level it and shore it up with 2x4"s:

Concrete form in place
Then I filled in the gap around the tube with the extracted dirt.  You can use the rebar to get that dirt packed in, and run some water into it to flush it down. (Don't add water unless you're ready to pour concrete; a wet form can lose its integrity in 24 hours).

You will need to know how much concrete to have on hand, calculated from the volume of the pier and the bag weight you're willing to handle. I was able to handle 60 pound bags, but smaller bags will spare you a possible blown back. I would suggest rounding up the amount you need by one bag, just in case. 

This is the fun part. You want everything ready before beginning, so cut the rebar to the right length (an inch or two shorter than the pier. I used one piece of rebar, centered in the pier, but some will say use three. Whatever your choice, make sure the rebar won't interfere with the J bolts.

You have, of course, already determined North, so that you know the way to orient the adapter!

Put together the pier adapter and J bolts so that the assembly is ready to put into the concrete. I used three 1/2" diameter 8" long J bolts (Home Depot) and the Starizona CGEM adapter. In my case the Adapter's diameter was smaller than that of the form tube, so I used shims to hold it in position and maintain reasonable level:

Pier Adapter in place with shims (after has been cement poured)
Now get your bags of quick-mix concrete, mixing tub, mixing tool, and water supply ready at hand. 

Note: Even if you're not using Quick-set concrete  you shouldn't let much time pass between one batch and the next. You won't take any breaks until you've embedded the adapter in the pier top. 

Dump a bag of concrete into the tub, add the manufacturer's suggested amount of water, and mix thoroughly. The common mistake (I've read) is to make the mix too wet, so try not to be tempted into adding more water. In my case I tried to avoid this error so diligently that I made the mix a little dry, but it seems to have worked out. Shovel the concrete into the form, minding the level.

After adding a second bag of concrete push the rebar into the poured concrete so that it's a the right height. You may need to hammer it to the right depth.  

Continue adding more batches of concrete, making sure your rebar remains centered in the form. You may also want to use a long rod from time to time to remove any trapped air pockets that form. When I made my pier I noticed that these pockets tended to form against the inside of the form.

The last batch of concrete should be large enough to complete the pier. Depending on the size of the shim(s), you will fill the form to about an 1.5" from the top. If needed mix in more concrete mix and water. You may want to make the last batch of concrete a little wet so that the J bolts will embed more completely. Shovel this into the form to the level you want and then push the adapter assembly into it. Make sure you have the adapter oriented to north correctly! Level the adapter and you're done!

Clean up your tools and the work site, then take a break. After 24 hours you can rip the form away. At this point inspect the J bolts to make sure they're solid--no wiggling allowed. If they're not, you have a problem. Post a comment if you do and I'll reply how I fixed this when it happened to me. 

Avoid the temptation to put a load on the adapter for at least several days (two weeks would be even better). If the weather is hot and sunny, moisten  the outside of the concrete from time to time and wrap it in plastic.

After a month you can apply a concrete sealer and paint the pier with an outdoor house paint. I went with white, but if fluorescent green is your thing, go for it.


*Why a couple of years on the observatory? The winter of 2011-2012 was so mild here that I found I hardly needed an observatory. And I was so busy during the summer and fall of 2012 that my talent of procrastination bloomed fully. Maybe next summer I'll get to it?


UPDATE, SPRING 2016: Still no observatory. There still seems little need for one; I'm doing more imaging at dark sites as the light pollution, neighbors' absurd "security" lights, and tree blockage all continue to increase. The wood planks on the platform have warped, but the pier continues to serve me well. Factoid: this blog entry is far and away the most viewed of all my posts (which isn't saying much).

Sunday, January 13, 2013

Another Year, Another M42

I've imaged good old M42 a couple of times in the past with my DSLR and ST80. This is a more ambitious try, using my ST8300 monochrome CCD and AT72ED:

M42 (click for full size)
What's ambitious is that it's my first serious attempt at an LRGB image where I've given some thought about how to properly combine luminance and color data. This could definitely use a longer integration time--it was only about 15 minutes per channel at f/6, made worse by fairly substantial light pollution.

Notice those spikes coming out of the brighter stars? They're from overhead power lines!

The next clear night I'll try taking some shorter exposures so that I can mask in the overexposed center of the nebula.

Coming shortly will be a report on the Orion 50mm mini-guider. I will be using it for autoguiding on scopes of different focal lengths. It cuts about five pounds off my mount's load by replacing my ST80, which weighs about 6.4 pounds when guiding. This is particularly significant because that 6.4 pounds rides piggyback on my telescopes and has a substantial moment arm.

Friday, January 4, 2013

Are Baader filters Parfocal?

At a recent star party I made an offhand statement that I doubted that my narrowband filters were parfocal. That set me wondering if I was correct and how would I go about determining this for all my filters. So I did a little experimenting one night by imaging Betelgeuse through all my filters.

I decided to set focus with the luminosity filter in place, and then cycle through all my filters seeing if the focus changed. Sorry, but I don't have a focuser with a digital readout. To get some sense of any focal shift I put a Bahtinov mask on my scope and imaged the results. I used three stars of different spectral types (O, A, and M), just in case the results would be influenced by wavelength. (I was imaging through my TV-102, so I didn't expect to see any significant wavelength dependence.) Here is a test strip for Betelgeuse (click to see full scale image):

Betelgeuse imaged through various filter configurations with no adjustment of focus

I used 5 and 25 s exposures for the broadband and narrowband filters, respectively, and processed only using ImagesPlus digital development. It looks like the central spike produced by the mask moves little if at all as the filter is changed. As expected, the focus shifts significantly when changing to no filter in use. So how much shift is significant? Here is an image resulting from 1/12th turn of my fine-focus knob away from focus:

Appearance when defocused by about 0.3mm

This is approximately an adjustment of 0.3 mm in focus and the central Bahtinov spike has shifted quite a bit. From past imaging experience, I think my final focusing "tweaks" are about 1/5 of this in magnitude.

So are the filters (Baader LRGB and 7 to 8.5 nm Ha/S-II/O-III) parfocal? They look close to being so. To my surprise, the broadband and narrowband filter sets seem to be almost, but not quite, parfocal with each other. The results were the same for the other two stars, Sirius and Altinak. But I'll probably still refocus every time I change filters in the future, particularly when using anything less than an apochromatic telescope or there's been a change in temperature.

Wednesday, January 2, 2013

Photoshop Actions

I spent a little (emphasis on little) of my holiday money on the purchase of two Photoshop action packages for astrophotography. My simple goal for today was using the packages to reprocess one of my old images. Here's my original take on NGC 6781, a small planetary in Aquila. This was shot in June 2012 using H alpha and OIII narrowband filters with my ST8300M CCD and C925. This was my original "final" image:

Original Processing

I used the OIII data for both the blue and green channels, which produced a washed-out cyan in the nebula's interior. Other defects in this image include some uncorrected mild vignetting, a noisy background and almost colorless stars. Using the actions it was an easy task to generate a synthetic green channel, clean up the background, give the stars some color and pretty much obliterate the vignetting (without any flats). Wow! That's not bad for a day's work with new software. Here's the result:

Processed using actions

Not that it's perfect by any means. I think the background is too black and I've lost a lot of the dimmer stars. I'll take it as good enough for the first day of using the actions.

The two packages are Astronomy Tools ($21) and Annie's Astro Actions ($15).  There's some overlap between the packages, but they're so inexpensive that you can get both!