Sunday, April 19, 2015

Two Rivers Spring Star Party: Image Planning

Sometimes planning seems like an exercise in futility, but it can be helpful when preparing to image far from home.

My first 2015 star party trip is to the Two Rivers Spring Star Party at the May new moon. This is located a little north of Barry, IL on a private farm. There's no power except for recharging batteries, so I'll be running from my big batteries all three nights.

What's to image? There's a cluster of five ALBN objects to go after. Fitting neatly into a 135mm field are LBNs 8, 10, 11, 19, and 1122. All are emission nebulae. 1122 is a brightness four, 11 a five, and the rest sixes. This is an all-night group, complete with a meridian flip around 2 A.M. if the four hours from 10 to 2 aren't adequate. This should make a nice LRGB image!

LBN 10 is located at the red "X" NE of LBN 8and is about the same size as LBN 1122
Assuming there's a second clear night, I'll go after something not possible from Minnesota. LBN 1091 transits at 12:49 at an altitude of almost 16 degrees. This has an LBN brightness of 6, so it's going to be difficult if not impossible.

The rest of the ALBN objects I have to do are better imaged later in the summer. If there's a third night of clear sky I'll do a pretty picture. Maybe an LRGB of the Antares area at 135mm. What're the chances of that?

Thursday, April 16, 2015


I changed my imaging plans (as I often do) and imaged M5 instead of M82. I'd have more time on target that way. As it ended up, I had 105m unbinned L, and 40m binned 2x2 of R, G, and B. These were about the longest I wanted to go with the C925 operating at f/10.

I'm still having issues with the image--the sensor plane is not perpendicular to the optical axis. Possibly this happened at the coupling, or potentially much worse is an issue with the secondary mirror. Coma-like stars aside the big issue was the sky brightness. Once again the limiting magnitude was awful, something like 3.5.

Another ongoing issue is the poor showing of blue and the color balance in general.(Note the pink star at left and the blue-green one to the right.) I'm going to be a bit of a purist and suggest that many imagers oversaturate M51 to make the arms a vibrant blue. Something between what they do and what you see above would be more to my taste.

This weekend I hope to return to ALBN imaging, but as the day has progressed the weather forecast has deteriorated. If it clouds out I'll have a chance to clean my optics and work on my binocular holder. Almost time to send in my registration for the Two Rivers Spring Star Party!

Sunday, April 12, 2015

Last Night Could Have Gone Better

Some nights are great. All the hardware works just like it's supposed to, the weather cooperates, and you end up with a fine image. Then there are nights like last night.

How it went:

Finder and C925 axes aligned using Venus. No problem.

Polaris was still visible through the leafless tree branches (it won't be in a couple of weeks) and I could use my polar scope to get me approximately aligned. Then I fired up PHD2 and that got me a much better alignment.

Now which to image first? Dwarf planet Orcus or dwarf galaxy Leo I? Fire up Sky Tools and figure it out. But wait, Orcus isn't in the list of Dwarf planets like it is on my desktop PC. Fix: Download the data. No: WiFi signal is too weak in the back yard. Bring Laptop inside, still won't connect. Seems it has forgotten the network password, as have I. Look up PW, get laptop on the Internet. Download dwarf planet observing list. Still no Orcus. Go through Supplemental data area for the update, still no luck.

Create a SkyTools synch backup from my desktop, which takes almost five minutes for some reason. Load the synch onto the laptop, and there's Orcus. Go back outside.

Decide that Leo I is first. Navigate to Regulus. Begin to refine focus. Whoa: Stars are way out of round and any sort of reasonable focus is impossible. Obviously the C925 needs collimation. Mine came with Bob's Knobs from its previous owner, so I tweak one of the knobs and hope for the best. This initially makes it much worse, but eventually I walk it back to as bad as it was.

I begin to wonder if this is a problem with the focal reducer. I remove that from the optical path and try focusing again. No improvement, and now I've got an even smaller field of view to work with.

More playing with Bob's Knobs to no avail. I discover that the secondary's lock ring is loose and that the secondary can be spun around. Really not good.

At this point it dawns on me that there won't be any imaging. In desperation I get Leo I composed and shoot a 300s light frame binned 2x2. All I get is an overexposed field full of really horrible looking stars. The sky is too bright?

Yes, it is. I shoot another frame unbinned and get a better background. But where the dwarf galaxy is supposed to be is only darkness, even after the usual stretching. The sky is simply too bright.

So Leo I is off because of collimation and sky brightness, and Orcus can be forgotten because of the poor alignment. Evening over.

Imaging can be fun, but not when one doesn't pay attention to details.

One other detail I let slide was on the satellite loop. During the late afternoon it was obvious that what looked like a wide layer of smoke was moving northward out of Iowa and Missouri. I've seen smoke obliterate the view at a dark site, and over the light dome of the city it lit up to make imaging difficult if not impossible. My backyard limiting magnitude is typically 4 to 4.5; last night I estimated it to be around 3.0.

Tonight I collimated my C925 using the Hubble artificial star light, a really slick little LED flashlight with a precisely drilled mask. I also read up on the process of collimation at Starizona. Interesting to me was what Starizona said about Bob's Knobs:

In our experience, the original screws on an SCT secondary mirror are much better to use for collimation purposes than the aftermarket thumbscrews that can be added.  Thumbscrews cannot be turned as precisely, making accurate alignment difficult.  Also, thumbscrews do not hold the mirror as tightly, increasing the need to collimate more often.  Thumbscrews also tend to make people "collimation happy," tending to collimate a scope far more often than necessary.  Under normal use, you should be able to go months without collimating a telescope.

I removed the Knobs, snugged the locking ring, and collimated just fine. I have nothing against the product, but I can definitely relate to the idea of them tempting someone into being "collimation happy." I think I achieved "collimation loony" last night.

The weather service AND the CSC says that tomorrow night will be gloriously clear here, so I'll try again.

Maybe things will go a little better?

Saturday, April 11, 2015

Leo I First Attempt; LBN 1089?

Last night was clear and I tried imaging LBN 1089 and 1090 from the club's dark sky site Cherry Grove. It did not go well.

LBN 1089 rises to an elevation of only about 16 degrees; LBN 1090 maxes out at 13 degrees. There's simply too much extinction and horizon glow for it to show up. A total luminance exposure of 21 x 5 m at f/4 produced not a hint of nebulosity.

This shouldn't be surprising, I suppose. Dan Crowson created this image of 1089 and had this to say about it:

Lynds Bright Nebula 1089 is a very faint cloud of dust located in southern constellation Antlia. This object at -29 declination only reaches about 20 degrees in altitude from my imaging location. Lynds’ gives this one a 5 out of 6 on the brightness scale (with 6 being the dimmest). This is by far the faintest object I’ve tried to image so far. I had to stretch the data more than normal to get this result. This is another one of the ‘bright nebula’ that are found on the Astronomy League’s Bright Nebula Program. I could not find any other images of this one.

I've added the emphasis. When Crowson says something is very dim, it's dim. In fact if you look at the image the nebula looks more like an integrated flux nebula than any sort of "bright" nebula. Yet it's on the ALBN and supposedly can be visually observed.

I think an open question is why this nebula is on the ALBN list. The same issue applies to many of the other nebulae with Lynds brightness 5 or 6.

The magnetic finder worked great. There could be a little more friction between the base of the magnet and the steel plate, or possible some sort of detent to keep the finder from moving when turning it on and off.

At the end of the evening I tried imaging dwarf galaxy Leo I. It's brighter than I thought-- it was distinct on individual 5m, f/4 light frames. Tonight I'll try it again with my C925. It should look a lot better at a focal length of 1480mm than it did at 135mm!

Leo I at 135mm FL (5x5m at f/4)

As above from SkyTools3

Also on tonight's agenda is dwarf planet Orcus. Currently at magnitude 19.1 it's quite faint but should be in reach if my experience with MakeMake is repeated. In  that image I could see down to 19.4.

Thursday, April 9, 2015

A DIY Finder for Wide-Field Imaging

Aiming a CCD when imaging through a lens: Not so easy.

Here's what the ST-8300 looks like when sporting a lens:

ST-8300 + filter wheel + 200mm lens
ST-8300 + filter wheeel, rear view. Note the lack of any useful sighting lines.
After a few nights out with 135mm and 200mm lenses it became apparent that a fair amount of time could be spent getting a target into the field of view. I thought it would be easy, but it's nothing like using a well-aligned finder scope. Perhaps with practice I can learn to sight along an edge on the mount but I plan on using the lenses so infrequently I'm almost sure to lose that skill between sessions.

To get an idea of how small a 200 mm field is, take a look at this:

200mm field of view with ST-8300
Now imagine aiming a sightless camera at this.

A finder that addresses this problem should: 
  1. Have a large field
  2. Not be permanently attached to the camera; it won't be needed when imaging with longer focal length telescopes
  3. Not require permanent modifications to the camera or filter wheel
  4. Be secure regardless of the orientation of the CCD
  5. Not interfere with the operation of the CCD
This suggests a 1X finder of some sort. A sighting tube or aligning posts would be fine, but I prefer a red dot finder for when it's really dark. Generic red dot finders are lightweight and inexpensive. I bought this one from Telescope Warehouse on eBay for $16 (including shipping):

Generic Red-Dot Finder
The nice thing about this particular finder is that the bottom of the stalk is perfectly flat. It comes with a shoe that's essentially useless for this project.

It would be nice to have some sort of quick-release attachment. Because of the way my ST-8300 is mounted the filter wheel (FW) presents a clean edge on which to mount a finder:

Top edge of filter wheel

My first thought was to use magnetic coupling but the filter wheel case is aluminum. If I could attach some steel to the FW and then use strong magnets on the stalk to hold it to the steel I'd be in business.That way after the target is composed I can remove the finder and its magnetic influence. (I don't know if a magnet can affect the FW operation, but why take a chance?)

The finder stalk glued to a bar magnet:

 A small strip of steel glued to the top of the FW. It's sized to not span the seam of the FW.

For the adhesive I prefer to use something that can eventually be removed without damaging the FW's finish. Beacon 3-in-1 Advanced Craft Glue works well

Beacon 3-in-1 Advanced Craft Glue
Here's the finished finder + CCD.

This can aim in any direction and the finder stays in place.

I should mention that an earlier prototype didn't work. Instead of a steel plate I used two washers, and the magnetic hold was too weak. Also be aware that some magnets have their strongest attraction on one face. The big bar magnet I used here is overkill; smaller yet stronger rare earth magnets would be preferable, but I used what was on hand. If I encounter any slippage I'll probably replace the bar with stronger magnets.

Odd but true. In 1979 I viewed a total solar eclipse from a point north of Williston, ND. If I live to be 91 (plus 22 days) I would be able to return to the same exact spot and see another total solar eclipse. Although a point further south will have a longer duration, so I'll have some decisions to make if I live that long!

Wednesday, April 8, 2015

Astronomical League Bright Nebula Project List Update

I've gone through the entire ALBN object list and updated the coordinates to those provided by SIMBAD*.

In general the coords provided by the AL were close to a match (given the corrections noted at the bottom of the document). For some reason most of the AL Coords differed slightly from SIMBAD by one or two tenths of minutes of RA and DEC or more. A couple were off by half a degree of DEC.

For most people these differences are of no importance--they are using software to locate the objects by name. If you're doing that, you should be aware that some software may be in error. For example, SkyTools3 (which I use) has incorrect positions for LBN 1088 and LBN 10.

The new version of the ALBN is here.

* Coordinates are J2000. The coords for Pickering's Wisp were taken from SkyTools 3.

The SkyTools LBN 1088 error has forced me to change my imaging plans a little. Instead of being at a DEC of +31° the object is at -31°! It's actually just a little west of the LBN 1088/1099 area, so there isn't much time to image it from my northern latitude. Friday night is forecast to be clear, but there won't be time to do 1089/1090 and 1088 for several of hours each. Instead I'm going to go for quick and dirty: An hour each at  f/4, binned 2x2.

Monday, April 6, 2015

M81/82/NGC 3077 under bright skies

Last week I was in another ALBN gap with nothing but large, very dim targets to image, and a nice bright gibbous moon to ruin any chance of actually doing that.

How about a nice bright Galaxy? Too windy, you say? Then use something short like an AT65. Which is what I did:

NGC 3077 (lower left), M81 and 82--you already know them
I don't think that my skills are up to battling the light. This had a terrible sky gradient that had to be removed. Shooting into sky over a city will do that, I suppose. There were also quite a few satellites that crossed the light frames, also. Do I sound like I'm making excuses?

What I learned is that I'd like to go back and image NGC 3077--it has an interesting core. Longer focal length and darker sky!

This next week is forecast to feature clouds every night. Not just clouds but dribbles of snow and rain, too! Doesn't the sky know I have things to image?

Next Time, adding a finder to an SBIG ST-8300M.