The Importance of Bias Frames

The rule I came to understand for using bias frames was this: Temperature-regulated cameras don't need them when the dark frame exposure time and temperature match those of the light frames. In other words, bias frames are useful only when you're trying to match dark and light frames that differ in exposure time or temperature.

Is this really true? Some people say it's not, and that bias frames should always be used. My experience seems to agree. But is there a way to verify this? That's what I tried to do with some simple analysis using my SBIG ST-8300M CCD camera.

I started by shooting twenty three-minuted dark frames at a temperature of -25C. Ten of these I set aside for later testing. The remaining ten were combined using three different methods (average, median, min/max exclude average). The result was three master dark frames, one for each common method of combining dark frames.

I then shot twenty bias frames at -25C. The ST-8300M's shortest exposure time is 0.04 seconds, so that's what was used. These were averaged to create a master bias frame.

Next, the ten dark frames that were set aside (it's helpful at  this point to think of them as light frames) were calibrated with each of the master dark frames, both with and without the master bias frame. This created six sets of calibrated frames. 

Each set of calibrated frames was then stacked using average, median, min/max excluded average, weighted median and sigma clipping (at 2.55 standard deviations). These are some of the standard stacking methods offered by ImagesPlus. The result is thirty images. ImagesPlus was then used to calculate the noise in each image (represented by the standard deviation of each image's pixels, in this case), and the results are given in the tables below:

Noise in processed images. Top table: noise present when the master bias frame is used. Each column is for a different dark frame combining method (AVG = average, MED= median, MME = min/max exclude). Each row corresponds to a different "light" frame stacking method (WMED = weighted median,  S255 = sigma clipping at 2.55 standard deviations. The row of numbers below each column is the column average. Bottom Table: as in the top table, but the calibration was performed without the master bias frame.

The results show that the exclusion of the master bias frame roughly doubled the standard deviation of the pixel values!

The images below show a comparison between the lowest noise (using min/max for dark combine and light stacking and bias for calibration) and the greatest noise (using median for combine and stacking, with no bias information). ImagesPlus digital development was applied equally to both stacked images.

Best case: Min/max combine and stack, bias included in calibration

Worst case: Median combine and stack, bias not included in calibration.

The lowest noise levels corresponded to combining dark frames using either an average or a min/max exclusion method and then stacking light frames with the min/max exclude method. Because both dark and light frames can be contaminated by cosmic rays, it makes sense to use some sort of rejection combine method in their processing. Both median and min/max perform about the same when the bias information is included. When the bias frame information is not included the min/max method clearly outperforms the median method.

I think that from now on I'll always use bias frames!

Finishing the Astronomical League Bright Nebula list anytime soon? Not very likely.

The ALBN requires 100 objects to be imaged, and I'm in need of 26 more to finish. There are 62 listed objects that I can choose from according to the published list. Let's see how that shakes out.

First eliminate the bogus object on the list, IC 425, although I'm tempted to image its supposed location and count that as one. This leaves 61 Objects.

Next, eliminate all the objects that are too low to image from the locations I plan to use. The southernmost locations are the Iowa and Nebraska star parties at 41.8 and 42.6 degrees north, respectively. As a guess, these allow imaging to about 40 degrees south declination. This eliminates five objects: IC 4628, Gum 12, NGC 2736, NGC 6164, and NGC 6188. There are now 56 objects.

Now let's assume I want to avoid imaging objects that require very dark sites, namely those with Lynd's brightness 6. This includes eleven objects (Sh 2-218, LBN 619, 1064, 683, 8, 10, 1091, 19, 70, 140, and 434). There are now 45 objects available. (Tossing out the brightness 5 objects eliminates another 12 objects, leaving 33.)

Let's see how far I could get just doing the brightest objects. Brightness 1 has 4 objects, 2 has 4, 3 has 5, and 4 has 7. The total without dipping into the 5s is 20. There are some objects without assigned brightness that could add some to this: NGC 2174, Sh 2-264, LBN 962, NGC 2149, NGC 2296, NGC 6357, NGC 6729, and IC 4812. These lift the total to 28! Only two objects to spare!!

Actually, LBN 20 and 22 (brightness 5) share a field, so there are three to spare.

A first pass at the optimum months for imaging these can be found using SkyTools3.

January: IC 2169, LBN 943, Sh 2-280, NGC 2296, IC 468, NGC 2359
February:
March:
April:
May: LBN 1122
June: LBN 20, LBN 22, NGC 6357, Sh 2-12, Sh 2-13
July: IC 4812, NGC 6729, LBN 52, IC 4701
August:
September:
October:
November: IC 360, NGC 1555, NGC 1579
December: LBN 945, NGC 1931, Sh 2-264, NGC 1999, Sh 2-240, LBN 962, NGC 2149, NGC 2174, IC 2162

This is where the bad news rears its ugly head. Sixteen (nineteen minus the three spare) objects must be imaged during the winter months. Given the terribly cloudy (not to mention cold) winters we've had lately, this becomes problematic. It's probably going to be necessary to dip into the dimmer objects that are available in spring and summer. These include LBN 683, 1088, 10, 1091, 19, 11, 8, 70, and 490. That's only 9, though, which means that at least seven of those winter objects will need to be imaged.

Conclusion: I might be at this for a couple of years yet!

Lens Happy

A visit to National Camera Exchange's used lenses page turned up a manual focus 200mm f/4 Olympus Zuiko OM lens. This should work with my ST-8300M, and old reviews suggest that it's got a chance of providing acceptable corner stars even when close to wide open. At a price of $40 it's worth a try. My impression is that the lens sells for $50-60 on the used market, which probably explains why it sat on NatCam's shelf for a long time at $90.

If you get the impression I've got a fixation with lenses, you're right. There have been too many objects that are a bit too large for my 422mm AT65EDQ, and I'm too impatient to make a mosaic for each of them. My telescopes currently give me a nice range of focal lengths:

• 2350mm (C925 @ f/10)
• 1480mm (C925 @ f/6.3)
• 700mm (TV 102 @ f/6.9)
• 422mm (AT65EDQ @ f/6.5)

These very roughly represent steps of two in scale. Extending these to shorter focal lengths with SLR lenses adds:

• 135mm (Tamron OM @ f/5.6)
• 70mm (Canon 17-70mm zoom @ f/5.6)
• 50mm (Zuiko OM lens @ f/1.8)
• 28mm (Tokina @ f/1.8)

The 200 mm lens fills the gap between scopes and lenses, taking the place of an old Tele-Astranar that won't reach focus with my CCD. Granted that these are a bunch of consumer-grade lenses I don't expect miracles from them.

The field of view of a 200mm lens used with an ST-8300 is huge: 5.1 x 3.9 degrees. Here are some objects that fit nicely into that field with a little room around the edges:

IC 1396, which is more extensive than Sky Tools depicts

Lagoon and Trifid Nebulae and vicinity.

Rho Ophiuchi Nebula and vicinity

Orion Nebula and vicinity

M 31 et al.

IC 1318 et al.

Rosette nebula

North America and Pelican Nebulae

The pictures represent the full field of a 200mm lens combined with an ST-8300 CCD camera as illustrated by SkyTools3.

There are more objects than these suitable for the 200mm lens, but this will make a good start!

A New Imaging Telescope, sort of.

Recently I've tried making a couple of mosaic images, but the process is slow. Given my circumstances it's typically a full night's work to make one piece of a mosaic. Wouldn't it be nice to use something that's fast with a much wider field of view?

One way to shoot wide fields is with a camera lens. Consumer-grade lenses tend to be mediocre imaging tools, though; their fields are not very flat and stars at the edges will show a lot of distortion unless the lens is closed down quite a bit. A good reference is Jerry Lodriguss' "Catching the Light" page about lenses. He recommends a number of lenses for imaging, some of which are within the reach of budget-minded imagers.

I'd like to add another lens, a fixed focal length Tamron 135mm Adaptall. It opens up to f/2.5, but it's actually quite decent at f/4. Here's what I mean:

400x400 Corners of a Tamron image

These are the four corners, each 400x400 pixels, from a stretched stack of 10-minute H-alpha exposures. The full frame is 3352x2532. The uneven brightness result from not applying a flat frame. Obviously it needs one!

For reference, here is the frame center:

Center 400x400 area

Center focus is sharp, and the corners are very good.

I originally purchased this lens back in the late 70's or early 80's for my OM-1 and it's been gathering dust since I went digital. Getting this mated with my SBIG ST-8300 was a minor adventure.

The Tamron was sold as a lens that can be used with a number of cameras. It was usually sold along with an adapter for the indended camera, in my case Olympus. SBIG sells a Canon lens adapter for the ST-8300 (A little pricey at $300, but it works). There are a whole bunch of adapter rings available to let OM-1 users put their lenses on their Canons, so the whole thing fits together: Adaptall lens | Adaptall to OM-1 adapter | OM-1 to Canon adapter | Canon adapter | ST-8300. Simple, right?

So now I can go wide. Instead of my AT65EDQ (422mm @ f/6.5) I can image with 135mm @ f/4. That's almost ten times the angular area with exposures that are a factor of 2.5 shorter. Nice.

Targets for this winter will be Barnard's Loop, Sh 2-240 (the Spaghetti Nebula), and whatever else the weather permits.

I'll also be testing an old 200mm lens I used with my OM-1. It only opens to f/6.3 and I suspect the optics are relatively poor. We'll see.

New Images, Projects Done and to Do

Projects Done:

I completed the light shield extension for my AT65, but immediately changed over to imaging with my TV 102 so it's gotten no use.

The electroluminescent flat illuminator is also done, and if the results indicate anything it works great. Just rotate the telescope to looking at the zenith, place the device over the objective, turn off the mount and transfer the 12V power cord to the panel, and start shooting flats.

Images since last time? There's been a few, and you can find them in my gallery on Astrobin. I'll show two of them here in reduced size to save you a trip:

This is IC 348; I really wanted to do a good job with this because I think lately my image quality has suffered as I gather images for the AL Bright Nebula list.

IC 348 and friends

IC 348 is the cluster with nebulosity just below the bright star (Omicron Persei). Note that there are a couple of dark clouds present, one under 348 and the other at image right. 

The evening this was taken was a bit of a marathon, in that it started at dusk and extended until 5:30 A.M. when the Moon rose and I started getting sleep-deprivation punchy. The last image of the night was of the Moon:

I like this image because clouds caused the sunlit side of the Moon to look like it's in a glow... the effect in my mind is of the moon rising like a rocket (complete with exhaust plume) in the morning sky. Well, maybe you had to be there. Given that it's an LRGB image with only one frame per channel it came out well in a goofy sort of way.

Also imaged was M 78, which I think came out a little dark--I'll probably reprocess it.

Next up is fiddling with my DSLR lenses to see how they work with my ST-8300. That's in preparation for some of the big objects coming up: The Witch's Head, Barnard's Loop, Simeis 147, and others. I've got a couple of humble-quality Canon and Olympus lenses that should work (thanks to an adapter) with the Canon adapter sold by SBIG, and I want to see how much they'll need to be stopped down to make decent star shapes.

Imaging at the 4M

The 4M is the MAS (Minnesota Astronomical Society) Mini Messier Marathon. It takes place annually during the fall when it's the second time of the year one can see a large number of Messier objects in one night. In Minnesota the fall marathon usually has much nicer weather; in spring, the observing field can be under a foot or more of snow, or it can be a soggy mess thanks to snow melt. The wind chill can be -25F.

This year the 4M was very nice. Temperatures were in the 60s, the ground was soft but not too wet, and a gentle breeze kept the dew from forming. Mosquitoes were at a minimum--I noticed only a few, and that was only during the early evening. Clouds spread overhead at sunset and persisted until a little before 10 P.M., at which time it was a scramble to get my imaging gear going before I lost too much more time on the southern objects I was going for.
Because the transparency was poor and time was limited I opted to go for only one of my southern targets, Sh 2-46, a fairly bright (LBN brightness 3) emission nebula in Serpens Cauda. With almost no time for it I opted to image it only in luminance. I had to end imaging after 39 minutes because it was sinking into the low-altitude murk and starting to lose brightness.

I stayed west of the meridian to get LBN 113, another emission nebula that almost three hours of Ha could not catch in my back yard. This time I went with a different plan, L binned 2x2 and RGB binned 3x3. I used equal total exposure times for L and RGB, 15x180s. The results were better than I expected:

Top: Sh 2-46. Bottom: LBN 113.

2-46 is the unimpressive light patch just below the center of the image. 113 straddles the yellow star near the image's center. The bright blue star to its right is theta Aql.

These took me to almost midnight, so the evening was still young. By that time M45 was well up, and a difficult object  I wanted, IC 353, was right beside it. It didn't take long to acquire the object and begin shooting. 

However, I made a bad mistake at this time. The scope and camera had to move quite a bit to swing from west to east of the meridian, and in that flip the camera's sensor plane went out of orthogonality with the optical axis. Focus was no longer anything like crisp across the field, and there was some astigmatism introduced. I should have checked everything over, but in my haste I didn't.

After I was done with IC 353, I was getting tired and decided to image something bright. IC 405 in Auriga was up now, and that became my target:

Top: IC 353. Bottom: IC 405 (Flaming Star Nebula)

IC 405 deserves more exposure time, but that will have to wait until another night. By the time I was done with 405 it was 2:44 A.M., and I was ready to call it a night. all but a handful of marathoners had packed it in for the night by this time, so I decided to join them.

Three of these are new AL Bright nebula list images for me, and the image of LBN 113 replaces my earlier attempt. I'm left with only one shaky image, in my opinion, that of Barnard's Loop. It's plainly in the image, but it could look so much nicer!

What's next? The seasonal dry spell in AL Bright Nebular list objects will last for another month or so. Things really start to pick up in November. If there are some clear nights another trip to Cherry Grove may allow me to pick up some fading summer objects. Cherry Grove is only modestly dark, but it's dark enough to allow LRGB imaging. 

PHD Version 2 review and the Little Dumbbell (Messier 76)

It's another time out for the Bright Nebula list this week. There was some discussion about polar alignment methods in our club's forum, which reminded me about the new PA wizard in PHD 2. Which reminded me that I hadn't upgraded from version 1 yet.

A few clicks later the upgrade was finished. The first time you start PHD 2 it will ask you to set up your default autoguiding configuration. You can create a number of configurations to invoke upon later runs, which can save some time. You'll need to know the name of the autoguiding camera you'll be using, the focal length of your guide telescope, and the way you'll be communicating with your mount. That last one is a little tricky. I tried ASCOM, assuming that because I connect the guider to my CGEM through the aux port. It turns out the correct option is "On Camera." My camera is an Orion StarShoot Autoguider, and the mini autguider telescope has a focal length of 162mm--A thank you to Orion for listing this in the product specs.

In point of fact, saving your time is what version 2 seems to be all about. When you start it, it will assume you're using your default configuration. You can do the camera and mount connection with one click or do them separately. (I experience some problems with the all at once connection, but I think this was a problem with the actual physical connection, not PHD.)

What follows is base on one experience using PHD 2. I'll be using it this weekend (fingers crossed for clear skies) and will update this with corrections if any emerge.

Start it scanning, stop it, select a candidate star, and you see the first surprise. The familiar green square is much smaller. I don't know if that's because of my short FL min guider, or is the case for all hardware.

As you did with PHD 1, you next click the little PHD icon and it begins calibration. Now the really nice surprise hits you... PHD 2 is fast! I didn't time it, but it takes probably 1/3 to 1/4 of the time the older version did. You'll be rolling in almost no time, so don't wander off for a sip of coffee or hot chocolate.

The gain control is more important now. If you switch exposure time the display may wash out in a way that might remind you of what version 1 did when it lost hardware connection. If this happens, adjusting the gain setting may restore the display.

And now the Polar Alignment Wizard. It's basically a camera-assisted drift alignment, which means the quality it provides depends to some extent on your patience. Here's how you use it:

1. Find a star at south azimuth that's near the celestial equator
2. Calibrate PHD using it. Center the star in your field of view and resume tracking it.
3. Start the wizard and allow it to watch the star drift (basically it will begin tracking with declination corrections disabled, and then watch the star drift in declination). It will try to estimate the rate and direction of dec drift. This estimate will bounce around for a while, but eventually it will steady itself--the greater your patience, the better your handle will be on the drift rate. 
4. Shift to Adjust mode, in which you change the azimuth of your mount. PHD gives you an estimate of how far you should move the mount, which is nice. I would suggest not moving it the full distance PHD suggests (indicated by a magenta circle).
5. Jump back to Drift mode (PHD will automatically reacquire your guide star!) and see if your correction was adequate. Chances are you'll have to iterate in order to get the right adjustment.

At this point you repeat the entire process for a star near the eastern horizon (adjusting the mount's altitude in this case). The instructions don't suggest recalibrating for the new orientation.

Chances are that at this point your alignment is good enough for long exposure photography. If you want it even better, repeat the azimuth process. If you have absolutely nothing else to do, iterate the night away until your PA alignment is almost perfect.

If there's a trick to this, it's the same one that causes confusion for the drift mode: The direction to adjust the azimuth and altitude for a northward or southward dec drift. PHD lets you enter notes to remind yourself of how this is done for your mount. If you've done drift before, a northward dec drift reported by PHD, indicated by an upward sloped red trend line, is handled the same way as a northward visual drift.

What PHD 2 PA offers is freedom from needing a reticle eyepiece; freedom from trying to establish the direction of dec drift, and a sort of entertainment factor as the program display shows the trend line being updated and the magenta adjustment circle resize.

One other feature that I think is a wonderful improvement is the ability to have PHD put the calibration start back where it was in your field of view before you started calibration. PHD 1 could often leave an offset. Usually this is so small that it's unimportant, but for long focal length imaging--like solar system imaging it can be a bother). I haven't tried this out yet, but when we get some planets back I will.

The image from two nights ago was M 76. Here is an improved version of what I posted on AstroBin:

Messier 76

This is a Ha/OIII bicolor image using almost six hours of data. The center is burned out, but because this is narrowband it's not actually saturated in the light frames. I'll try doing a reprocess to generate a less stretched version to act as a second input to Photoshop's High Dynamic Range merge tool.

Coming up on Friday, it's the fall Mini Messier Marathon. The current forecast is for clear skies! I hope to get some imaging done while others are hunting down Ms.

LBN 434 is a no-show.

Last night I went after two AL BN items, IC 1287 and LBN 434. 1287, a dim reflection nebula, was an almost hopeless task thanks to the trees and the very hazy sky. I collected some light frames, but not nearly enough. The frames were so bad looking that I haven't bothered to process them.

LBN 434 is a Lynds brightness 6 nebula, and I'm beginning to think that category 6 means anything dimmer than a 5. Maybe a better classification for 434 would be a scale extension to 7 or 8. Three hours of 5-minute H alpha exposures turned up nothing at all but stars and a couple of galaxies.

The object does show up in the Digitized Sky Survey, which is more than some cat 6 objects can say. (Evidently not all cat 6s are created equal.) After some work I was able to confirm that I was imaging the correct field. Processing the image beyond all reason might show a trace of the brightest part of the nebula, but it's not nearly solid enough to submit as acquired. The object was simply too dim for me to catch under my bright hazy skies.

I may go after 1287 from a dark site, but 434 is now on my list to not revisit unless I'm desperately short of objects on the way to the required 100.

---

My mosaic of LBN 270 proved to be modestly popular on AstroBin, garnering more "likes" than any other image I've made.

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My next backyard target is going to be more fun, going after M 57 to image the outer shells. This will be a multi-night task, with a lot of unbinned H alpha work at various exposure times, and then possibly the same with binned color. I'll use my C 925 without its reducer/flattener for maximum scale, and because at f/10 the ring can sit happily within the central part of the field.

LBN 270 Mosaic

It's done. Spanning four nights (if you include one night's data that I eventually discarded because of poor focus), the four-image mosaic of LBN 270:

LBN 270

The irony of this is that I had to dodge a lot of clouds in order to image clouds. Only one night was clear for long enough that I was able to image two quadrants of the image.

Normally I would be imaging unbinned because of the short focal length used (an AT65EDQ at 422mm) and 5.4 micrometer pixels of the ST-9800M. Instead I did this by using 2x2 binning, which results in a speed gain by a factor of something like 3.6 (depending on who you trust as a reference). Each quadrant of the mosaic is based on about 20x300s light frames for a total time of about 6.6 hours.   

This is an object on the Astronomical League's Bright Nebula list. 

Speaking of which, a corrected list of objects that I made some time ago is now residing on the AL web site at:

https://www.astroleague.org/files/u3/BrightNebulaRev1.pdf

I might complain to the AL about getting no credit for this, but so far as I can tell they don't publicize this document.

The "official" list, still with errors, continues to be linked to at

https://www.astroleague.org/files/u3/BrightNebulaRev2.pdf

When is the AL going to fix this list? It's been over a year since the original posting of the list.

But enough about the AL, and more about the mosaic. I actually have two images I could append to the mosaic, one for IC 1318 (butterfly) and DWB 111 (propeller). The former is not oriented well, so I'm thinking that in a year I might revisit this and extend the mosaic down to Sadr so that it includes all of IC 1318.

But for now it's back to the list, and seeing how much binning helps tackle some of the dimmer objects on the list.

Time for Mosaics

I imaged many of the smaller/brighter AL Bright Nebula list objects in this season's sky last year, so this year I'm left to clean up the more difficult objects. These can be more demanding in terms of the sky I have to work with (tree-locked and bright), or by virtue of their larger size. In the former category are reflection nebulae and Lynds brightness category 6 objects.

Here's an example of the former, IC 4954 in Vulpecula:

This was shot in H alpha because it has a weak emission in that, and the narrowband filter helped to reduce the light pollution and moonlight. This is given a 2 for brightness.

For faint there's DG 191, shown in the previous post. There's no official brightness for this, but I estimate it as a Lynds 4. Most of it is visible in weak Ha emission, but the lower right quarter or so has a substantial reflection nebula component. Because I wanted to catch the blue tint I shot this in RGB. I should have gone with HaRGB, but I wanted to complete this in one night.

Sh 2-134 was too large for a single frame at 400mm. I combined two images to create a minimal mosaic using Photoshop:

I used Photoshop's default settings for this and it turned out pretty well. There is a transition line visible along the top of the lower frame, so it could use some reprocessing.

Next up is the huge LBN 270 (3 degrees across) in Cygnus, which will require a 2x2 mosaic. I managed to get the southwest frame last night during a couple of hours of clear sky!

Eventually I'd like to patch together a mosaic of Sh 2-240 (Simeis 147 in Taurus), a large supernova remnant in Taurus. That might take five or six frames!

Two star Parties, Two Images

A sad story.

First, the Iowa Star Party. Another year, another hot and humid run of days, even worse that last year. The weather forecasts were so bad (ditto the satellite loops) that I stayed home the first two nights. Thursday night reports were that there were at most two hours of observing. Friday night (the public night) it rained. Saturday it was hot, with the heat index hitting 113. Around the time of the before-dinner talk the dew point reached up to 82. The compensation was that the evening was clear, and I managed to get one image. Because of the extreme humidity my camera's sensor window fogged over at any temperature under 15C, which curtailed using it in a meaningful way. Sunday: l little cooler and drier, but still very warm and humid. The evening started clear (with clouds to the south from a thunderstorm over Missouri) but ended early when a thunderstorm to the northwest attained a high level of electrical activity--its lightning illuminated the sky to such an extent that observing or imaging was nearly impossible.

Out of four possible nights, one decent one.

Now on to the Northern Nights StarFest. Great Facilities. Amazingly enough almost no mosquitoes or flies. As might be expected for a forest setting, generally poor horizons. Wednesday night, clear, but absurdly heavy dew. One image as I fought the fogging sensor window problem. Thursday night: cloudy. Friday night: cloudy, Saturday night: cloudy with rain.

Four possible nights, one decent one.

No more star parties for this year, unless I opt to go to the Heart of America party. As nice as that one is, it's simply too far to go for a maximum of three nights.

In other news, SBIG sent me the ST-8300 sensor window heater and it was waiting for me when I returned from NNSF. It installed easily, and last night it seemed to work, although conditions didn't test it well. With it running, the camera went down to -15C, a good value for any summer night. It may have used a little more power than it used to, perhaps compensating for the heat source.

 I managed to image one of the objects on my list for ISP/NNSF: DG 191:

DG 191 and vdB 158

This was an ill-conceived RGB image. (I should have had the patience to do a multi-night HaRGB image. But it's just for AL, so it doesn't have to be frame-worthy, or even close.)

Another clear night on Friday? Sadly, the moon will be nearly full, so I'll collect Ha. IC 4954 may be the target.

A Mobile Imaging Setup

This is the first summer of my retirement and I'm using it to go to a number of star parties. For the first time I've traveled to the Nebraska Star Party (just south of Valentine, NE), and coming up are the Iowa Star Party (near Coon Rapids, Iowa) and the Northern Nights Star Fest (northwest of Aitkin, MN). All three of these are intended to be imaging trips, and toward that end I've designed my imaging setup to be self-contained, compact, and reliable. I travel in a mid-sized sedan, so there's a natural limit to what I can carry.

The first thing to do is to leave the bells and whistles at home. Keep your gear simple and you'll be rewarded with less hassle when you set up or break down. Remember, if you forget something and no one can lend you a replacement you may be out of luck for the entire party.

What's the least you need? The essentials for imaging: an imaging telescope (including finder), an autoguiding scope (if you autoguide), a mount and tripod, a camera, an autoguider, cables for all these as needed, and batteries to power everything. If you anticipate a chance of dew, a dew prevention system is good to have on hand. Probably you'll need a laptop if you're using a CCD camera.

Oh, and let's not forget a table to put that laptop on. Like a good observing chair, a table is an important part of imaging. I use one much like this. Mine was purchased about 12 years ago from Target for a scant $20, and is one of the best astronomy accessories I've ever found. The roll-up aluminum table top is particularly nice as it's impervious to dew and frost and when you cook food, it doesn't care if you set a hot pan on it. Sadly, my table is reaching the end of its life and some plastic parts are starting to crack. I'm repairing it with J-B Weld as needed, but sooner or later it will need to be replaced.

Batteries will be the heaviest things you'll have to lug around. While it's certainly possible to use your vehicle battery as the sole power source, that's probably not practical for multi-night imaging. Remember that most car batteries are designed for starting your car, not supplying a several amps for many hours. Deep cycle batteries are better for this. You can pay a lot for these or get them at farm and ranch retail stores for far less, as I did.

I use three batteries, which is almost certainly overkill. Two are lead-acid deep cycle marine batteries with a combined capacity of about 140 Amp hours. These power the mount, laptop and camera. The third is a sealed lead battery with about 20 Amp hours that powers my dew strips and can power things like fans. (This battery has the advantage of being easy to recharge.) These batteries can power everything for at least 15 hours, which is a solid three night's worth of imaging on most trips. It's possible they can go longer, but I've never had that much good luck with consecutive clear nights!

[My CGEM mount draws about 1.5 A when tracking, the ST-8300m CCD about 2 A (that's a guess based on its 3 Amp requirement at peak cooling load), and the laptop about 1.8 A (also a guess based on the AC adapter and having a battery that's pretty much gone dead after all these years. That's a total of 4.3A. My two deep cycle batteries should be able to supply that for about 32 hours, or 16 hours if we only take the batteries down to 50%. So my 15 hour estimate above seems reasonable.]

Imaging Setup at the 2014 Nebraska Star Party

The above picture shows how this all looks, minus the "Y" stalked dual finder mount, CCD, and laptop which are all sitting in the shade at this point. The three batteries are sitting on the ground below the mount.

For this trip I took my little refractor, the AT65EDQ. That's the scope I'll take to ISP, but for NNSF the bulkier C9.25 is making the trip.

Regardless of the scope, all of this gear fits quite nicely in my car with room left over for everything I need to set up camp. Best of all, it seems to work quite well!

Two dark-sky images

Just back from the Nebraska Star Party and the smaller party in SW Minnesota.

First, from Minnesota, the Rho Ophiuchi nebula (IC 4604, the blue reflection nebula at top):

At bottom is the emission nebula IC 4603. This is about 1.5 hours of LRGB data. This will need to be reprocessed to get rid of a distracting satellite track. The image above has been reprocessed to get rid of the satellite tracks and improve the color balance.

The first image from NSP is the Iris (NGC 7023, vdB 139) at right in the image,

The small bright nebula at image left is Sh 2-136. About 3.7 hours of data went into this image. I'll probably reprocess this and adjust the color balance a little. It looks a tad too yellow-green to me.

Still awaiting processing are the Cat's Paw nebula, Sh 2-183, and NGC 1333 (vdB 17). For those I binned the color channels 2x2, and I need to shoot some dark frames to match.

More about NSP 2014 in a subsequent post.

Sh 2-137

The list rolls on with another faint nebula: Sh 2-137 in Cepheus. This object its also known as LBN 498 and has a brightness value of 5

This images represents 3.5 hours of integration on a night with a bright waning gibbous moon.

Sh 2-137

The bright star at left is GSC 04271-2621 with magnitude 4.57.

No Luck With the State Fair; Weather Update

Just a quick update--my entry into the Fine Arts competition was not accepted. That means I get to keep my nicely framed picture, although I'll probably make it a gift to someone.

Unfortunately the judges don't give explanations for their decisions. I'm going to speculate that it was seen as lacking a sufficient element of artistic merit. If that's their reasoning, I can certainly understand it.

---

The long-term forecast for conditions during the Jeffers star party suggests that the very cool weather we've been experiencing will come to an end just before the party begins. Temperatures will climb into the low 90s with dew points in the low 70s. Typical steamy Jeffers weather, and if it persists into the following week and the Nebraska Star Party, there may be some big bad thunderstorms to deal with.

Imaging Targets for This Summer's Star Parties

I'm probably going to four star parties this summer: The Jeffers Starry Nights (JSN), the Nebraska Star Party (NSP), the South Dakota Star Party (SDSP) and Iowa Star Party (ISP). I'm hoping to do quite a bit of imaging at these, taking advantage of the dark skies and slightly more southern locations. It's not much, but every degree of elevation helps!

I'd like to bump along my Bright Nebula list work, and take a couple of pretty pictures, too.  The dark locations let me image reflection nebulae that I can't get from my light-polluted back yard. Another constraint is that whatever scope I bring to Jeffers will also be the one I use at NSP. So what should I image?

(1) I'd like to go really deep on the Iris (NGC 7023). It's a reflection nebula on the list, and it's pretty. Near by are some barely luminous clouds. A wide field shot with my AT65 will take them all in. The Iris a better target during the JSN/NSP time period than in late August. This would be a multi-hour object, to say the least.

(2) I've always wanted a good image of the Helix nebula (NGC7293). This is better imaged around labor day, so it should be during either the SDSP or ISP. ISP has darker southern sky, so that's where it will be imaged. The C925 produces a nice image scale for it.

The Helix from 2009 JSN.

The above is my only Helix image, taken using my TV102, an unmodded Canon DSLR, 16 x 180s @ ISO 1600. Not at all adequate. A few hours (or longer) of LRGB could be much better.

(2a) Other objects I would like to go really deep on are the Ring--see a previous post about the outer shell-- and the Dumbbell. Those would be best in the C925.

(3) I have only one so-so image of the eagle nebula (M16) from a couple of years ago. Unfortunately it doesn't include the portion of the nebula that's considered LBN 68, a list item. So that should be reimaged from a dark site. This would probably look better in the C925 but the wide field of the AT65 would be adequate. Best during JSN/NSP.

(4) There are a good number of large list items in Scorpius and Sagittarius that would image well in the AT 72. These should be imaged at JSN/NSP. These include Sh 2-13, 2-16, NGC 6334, IC 4628, IC 4701 and LBN 52. An hour each should produce images that could satisfy list requirements.

So there you are:

• JSN and NSP get the Iris and the large list items. This means that I can travel to them with the smaller, lighter AT65. One pretty picture (Iris) and a flock of list items.

• SDSP and ISP get the Helix, Ring, Dumbbell, and whatever else comes along. For those it's the C925. Pretty pictures all, and perhaps list items left over from July.

Now it's all up to the weather!

Another Obscure "Bright" Nebula: LBN 185, and IC 1470

The AL Bright Nebula list has quite a few not-very-bright nebulae on it. Here's one that's bright enough to image from a red zone + a nearly full moon: LBN 185 in Cygnus, a 5 on the LBN brightness scale.

LBN 185

I believe LBN 185 is the bright area near the center of the image. There's another bright area at the left edge of the image, but so far as I know that has no designation. This took 3.8 hours of H alpha imaging, and even at that the background is still rather rough. A couple of nights before I also got this image of IC 1470:

IC 1470

On the other hand, IC 1470 is bright, and small. This was taken with a C925 at a focal length of 1480mm, while the LBN 185 image is wide field with a 422mm AT65EDQ.

Going a Little Deeper with M 57

When the first really deep images of M 57 started showing up, I was amazed at the wealth of structure that surrounded the familiar oval that gave the Ring it's name. As it turns out, many planetary nebulae show this kind of layered structure. The explosive events that drive the star's outer atmosphere into space aren't just a one-time event; instead, they can happen repeatedly, producing a set of expanding nested shells. The outer shells are older, farther from the central star, subjected to less intense radiation, more diffuse, and have had more time to cool, all of which means they are less luminous at visible wavelengths.

M 57 is quite bright and easy to image. Even the central star, elusive visually thanks to the diminished contrast in the Ring's interior, is easily imaged. But what about those outer shells? Can they be imaged by folks with modest gear?

Last night I made my first try at finding out. While waiting for another object to climb out of the trees, I had some time to spend on M 57. I used a C 925 SCT with a 0.63X focal reducer, an SBIG ST-8300M CCD camera shooting through a Baader Ha narrowband filter, and accumulated 39 minutes of 3-minute light frames. That's not very much, compared to some projects where one have a total exposure time of over five hours. But it was all I had time for last night.

The result was surprising, at least to me:

My image is on the left; at right is a deep image from the U of Oregon for comparison.

In both images the Ring is wildly overexposed, but you can see the second ring clearly in my 39-minute shot. Also visible are a couple of the brighter knots in the next outward ring.

The image scale here isn't the greatest, and only 39 minutes through an Ha filter leaves a lot of noise, but I think it's going to be worth going back to this and shooting for hours. 

If you haven't tried going deep on M 57, you might give it a try. The result may surprise you, too.

Finally!

This is the first image of the year! Let's just say it's been a bad year. Amazingly everything worked smoothly, including me. This is yet another AL Bright nebular object, LBN 331.

A so-so picture, but I'll take it--LBN 331 is a brightness 4 object, so given my skies I don't expect much from 1.6 hours total exposure.

LBN 331

Details are here.

Tonight's supposed to be clear again (we'll see), so with luck I can bag another object, or go back to this one and shoot some RGB so that the stars have color.

Framed and Registered

The print of M31 I talked about last time has now been framed, and I've registered it for the Fine Arts competition at the State Fair.  Here's what it looks like framed:

This is a snap using an inexpensive digital camera, and I think it went blue-heavy, but you get the idea. The matte and frame are blacker than this shows. I chose anti-reflection glass, too, which lends a very slight blue tinge, much like it can do when viewed on a lens.

In a fit of optimism I decided to put a for-sale price on it. My cost, disregarding time and travel is $14 for the print and $261 for the framing, for a total of $275. The fair takes 20% of the sale price, so that becomes  $330. I set the price at $350, which means I'll have a "profit" of $20. 

Two things about that. It would be nice to have the costs taken care of, and it would be a great pleasure to know someone was willing to pay for one of my images. Seeing it hanging in the Fine Arts building with a "sold" sticker would be a blast. 

One thing at a time, though, and I won't find out what its status is until July 14-15. If it's accepted, I'll take all the mounting hardware off, and my wife will deliver it to the Judges (I'll be at the Nebraska Star Party).

This week I should really finish my Binocular mount project. The Jeffers Stargaze and NSP are going to arrive quicker than I know.

Getting an Image Ready for the Fair

I'm a fan of our state fair, which I've attended almost every year since I was a child. In recent years I've been entering baked bread in the baking competitions with some success. My wife usually enters some of her craft work, too. And my mother, now 91 years of age, enters both stitched and baked goods.

The first day of the fair is usually dedicated to visiting the buildings where our entries are on display and seeing what ribbons we've won (most years at least one of us gets a ribbon, some years, all three). After that it's on to the Education building, the 4H building, Fine Arts Building, and then to wherever time permits. It's not unusual to attend on a couple of days, as there's a great deal to see.

One of my uncles was a painter (as I hope to be some day) and managed to get his work displayed in the Fine Arts building on a couple of occasions. He never won a prize or mention, though, which I think irritated him a little. To carry on with his tradition I'm going to submit an astrophoto this year.

In the past there's been some astronomy presence in the building. A local painter has entered her impressions of astronomical objects, and there's usually at least one picture of the Moon. Last year was a particularly fruitful year, with these on display:

At top are two star trail images, lower left is an aurora, and bottom right is art with a fairly realistic depiction of the northern sky (note the big and little dippers). Obviously my pictures don't do justice to the works!

Seeing these got me thinking that the judges might be receptive to other examples of astrophotography. So I'm submitting my M31 image from the South Dakota Star Party:

While I'm not suggesting that it's great astrophotography, it's one of my best to date, and I like it. I've had a test print made using the services of National Camera Exchange in Burnsville. It looked good and faithfully reproduced the image I submitted, but for the full-sized print (11x14 inches) I changed the yellow-blue balance a little, which nicely brought up the blue. I'm also going to print it on metallic paper, which is said to enhance the vibrancy of the color. The print will be ready next week, and then it's off to the framing shop.

The Fair requires that the image be framed with a glass or plastic cover, and I'll go with glass. Registration requires submitting an image of the art that is about 1,000 pixels on the short side. 

Judging takes place in several phases; Phase 1 is where they cull the entries based on the submitted image and is completed by July 13. Phase 2 is where the jurors do the hard work and decide what will be displayed and how awards will be allocated.

Between now and the end of registration on July 7 I need to decide if I will offer the print for sale. The price would be set by the cost of printing (a modest $14) and framing (probably not as modest) plus 20% to cover the Fair's cut and a few bucks so I can say I came out ahead on the whole thing. 

There are cash prizes awarded, and the dream would be to land one of those, sell the print, and do this over again next year with a better image. At this point reality says: Let's just see if I can get past Phase 1.

I'll post more about this as the process rolls on.

A DIY Binocular Mount

Thanks to a change in plans--a wedding I want to attend is on the same Saturday as the Wisconsin Observers Weekend--I am going to go to this year's Nebraska Star Party. No offense intended to WOW, but NSP is a bit of a bigger show with more people and darker skies. NSP begins as the annual Jeffers Petroglyphs party ends, so I'll be able to save a couple of hours of drive time by going straight from Jeffers to NSP.

But what to do at NSP? I'll have my imaging gear from Jeffers with me, but maybe I should just make my first NSP a strictly visual affair. All that really dark sky, you know!

I've come into possession of an old pair of Celestron binoculars, their 11x80 Giant model from the 1990s:

This is not the model that was labeled "Comet Hunter" or "Comet King" apparently to cash in on Halley's Comet in 1986. What reviews I can find for this later model are mixed.

Good features from my standpoint:

• It was free
• It has a wide FOV (4.5 degrees)
• It comes with a mounting bracket. 

Cons:

• Probably not the greatest optical quality
• Heavy (6.7 pounds) 
• Exit pupil (~7mm) that is too large for my old eyes. I'm 60, and although I haven't measured, I would guess my pupils don't open past 5mm. This means that some of the objective size is being wasted, but some people suggest this has a small silver lining in that one's eyes can move a little laterally and stay in the light.

My past experience with large binoculars suggests that a mount is a very good thing to use for steadiness and comfort. A little googling turned up this plan, which I am adapting to the top of my CGEM tripod. The CGEM tripod has two threaded holes for mounting the azimuth post. These are perfect for attaching a base plate. In my case I'm changing the plan to substitute a 3/4" piece of hardwood for the 3/8" aluminum plate. The rest will be pretty much as the design suggests.

I was unable to find the nice round counterweights seen in the explanatory pictures, so I'm using lead scuba weights from the appropriately named Lead-co USA. Construction begins next week.

An update on May 20: Lead-co uses fixed-cost USPS mailing boxes, and I had paid for a medium sized-one. It turns out that the weights I bought fit in the small box, so Lead-co refunded the difference. Nice!

Definitely Rusty

First the unpleasant winter, and then too much work. I'm barely able to keep up with the lectures I need to prepare, so maybe it's been a blessing in disguise that the winter has made it difficult to get out and observe. I really don't have the energy or, sad to say, the will.

That said, last week it was finally nice enough for me to get out and try to resume imaging. Amazingly, I remembered how to get everything put back together and working. The fist night by the time my polar alignment was done my target (Thor's helmet) had moved behind a tree. I thought I'd swing up to Regulus and take a stab at trying to image Leo I dwarf galaxy. I screwed up and instead centered on Gamma. Nice shot of it, but not what I wanted.

The next night I was ready for the Helmet and started shooting as twilight ended. The tree won the battle, though. All I got was 9 frames for a grand total of 27 minutes of H-alpha. Not nearly enough to get the fainter outer regions.

As expected, the Bright Nebula list has a gaping hole in the sky during spring, so I'll be imaging other targets until the summer milky way starts rising.

I'm going to go back and get Leo I, I think, only I'll use my TV 102 or C9.25 for it. And maybe I'll do some planetary imaging. Classes end the first week of May, and after that I'll be free to do as I please!

Snow.

We had our biggest snowfall of the season last week, and while it wasn't all that much (maybe 12 inches) it brought our snow depth up to a level we haven't seen since 1982. This winter has been unlike others in that the temperature has stayed low enough to prevent the usual gradual melts that keep the snow cover in check. Each snowfall has added to the last and now we're up around two feet of the stuff.

I know for other parts of the country that's not so much, but winter is somewhat subjective. Thirty two years between mounds of snow like this are almost enough to erase it from the collective memory. Almost.

Anyway, with the forecast for continued cold (and I mean sub-zero lows cold) cabin fever is pounding at the door. To do something--anything--constructive is to hold the madness off for a while. So I decided to go dig out my observing platform.

BEFORE

The Pristine Winter Wonderland/Wasteland

AFTER

80 cubic feet of snow and ice later

THE SNOW

The yard stick does not lie.

The depth was 26" on one side and 24 on another, with the average as you see it above.

This was completely futile, of course. March, only days away, is our snowiest month on average. But it was nice to see the wood planking again, and maybe--just maybe--the Sun will do some work and melt it clear before the next snowfall.

---

I did manage to do some astronomy evangelizing the week before last. I volunteered to make an astrophotography presentation to three photography classes at Richfield High School. It was fun, and doing some show-and-tell gave me an excuse to get out my neglected cameras, now three months into their winter exile.

Nebraska Star Party Weather

(Continued cold and clouds have curtailed all my imaging activity, so thoughts continue to turn to the summer)

I'm still toying with the idea of attending the Nebraska Star Party, which in 2014 is from July 27 through August 1. I have some concerns.

A minor concern is electrical power. I run off two deep-cycle batteries, and it's unlikely that I can get more than a few nights off my gear. I'll be coming from the Prairie Grass Star Gaze. It's likely my batteries will need to be topped off before getting to NSP or I might have less than two night's capacity.

The bigger concern is the weather, both the heat and the potential for damaging storms. This has led me to investigate the weather that's typical for late July. Here's what I've found for nearby Valentine:

TEMPERATURES (all in degrees F) (source 1)
---------------------------------------------
July 27- Average, 89/61, records 106/43
July 28- Average, 89/61, records 108/44
July 29- Average, 89/61, records 110/42
July 30- Average, 89/61, records 105/38
July 31- Average, 89/61, records 110/44
August 1- Average, 89/61, records 106/44

WEATHER PROBABILITIES (source 2)
---------------------------------------------
Entire period, daily chance of thunderstorm is about 39%; daily chance of rain is about 50%.
An average five day interval will see two days with thunderstorms and two or three days with rain.

CLOUD COVER PROBABILITIES (source 2)
---------------------------------------------
In late July and early August the skies are clear or mostly clear about 66% of the time. This probably understates the likelihood of favorable conditions at night, when clouds are less common.

Sources:
(1) http://www.weather.com/weather/wxclimatology/daily/USNE0494?climoMonth=7
(2) http://weatherspark.com/averages/31908/Valentine-Nebraska-United-States

Numerous attendees have reported that the thunderstorms can be strong. I usually take down my scopes at night but leave the mount up so that my polar alignment is retained. I might consider looking into how to stake down the mount so that really strong gusts don't topple it.

As for the heat, it could easily top what I experienced at the Iowa star party last year. The Solution is a lot of water, and either bring or borrow shade.