Monday, February 27, 2012

Wide-Field Imaging with EOS Lenses

I would like to do some very wide field imaging, in which I can capture entire constellations or significant parts of them. This means imaging with focal lengths less than 200 mm, which can be done with camera lenses. I have a few Canon EOS lenses, and lenses that can be adapted to work as if an EOS lens, but the problem is mating the lenses to my SBIG CCD.

A search of internet forums suggests that there's only one way to do this: With an SBIG EOS to ST-8300 adapter ring. The problem is that this adapter is pricey: $295 + shipping. A Wanted ad on Cloudy Nights failed to produce someone willing to sell a used one, so yesterday I faced reality and ordered one from Oceanside. I should say, back-ordered it. With luck it will be here for the warmer weather expected to arrive in April.

Update 2/27: OPT wrote that the adapter would be delivered no earlier than late April! Tomorrow I'll call around to see if any other dealers have it in stock.

Update 2/28: Oh, well. It seems that SBIG items are usually special order most places and are fulfilled in 30 to 60 days. I'll stick with OPT.

Thursday, February 23, 2012

Alternative views of M31 and M104

I created the following images while doing class prep for my astro class and thought they might be of interest. I wanted to show how M31 would look from a view above one of its poles, so I tried to compensate for the foreshortening we see because of its inclination to us. The goal was to show the central bar more clearly for those who have trouble seeing it.
M31: Visible light (left) and Infrared (right, Spitzer NASA/JPL/CalTech)

the left image is one of mine, and the second is a Spitzer image from NASA/JPL and CalTech. My image of M31 is not so hot; if you want to try this yourself, you would do better to start with this amazing image. I think I've got the two images reasonably aligned and scaled to match. The brightest portions of the Spitzer image coincide with the dark dust lanes in the visible-light image.

You might find this fun to do with other inclined galaxies. It won't work with very nearly edge-on galaxies. Here's the Sombrero, for example:
M104 (Sombrero Galaxy, NASA Hubble)

Notice how the central bulge obscures the more distant portion of the dust/gas ring.

To remove foreshortening first rotate an image so that the long axis of the galaxy is either horizontal or vertical. Then resize the image, stretching it greater in the direction of its thinnest axis. (Make sure to turn off your graphics program's preservation of the aspect ratio.) Adjust the stretch amount until you have the galaxy looking round and you're done. We assume the galaxy is round, but that's not always the case. It's a decent first guess.

Thursday, February 16, 2012

PEC at last, maybe.

Finally a clear night, maybe. And the end of my head cold, maybe. And an understanding of how to use PEC, maybe. Results to be posted here, maybe.

The results: PEC seemed to work fine, although I have no way at present to objectively confirm that. My setup (AT72ED and autoguiding ST80 side-by-side on the mount) was far out of balance, and I had to up the PHD signal length to 1000 ms. That allowed PHD to correct for the problem, but the results were less than desirable. My target was M44--high cirrus precluded looking at nebular targets--and it was more an exercise in LRGB imaging and processing. Here's the result:

Messier 44

This is a fairly unimpressive cluster, with quite a few blue stars. Normally I don't like diffraction spikes, but they might add some visual interest to the image. (L=20x3min, R=10x3min, G=5x3min, B=10x3min). I spent a lot of time trying to get the color right. I'll probably redo this using the color balance workflow suggested by Ron Wodaski.

Just to give you an idea of what the PEC was trying to deal with, here is the PE for my CGEM:

8-minute cycle of PE, average of 10 runs
That's about 18 arcseconds peak-to-peak.

I've now jury-rigged a couple of dovetails together to get my setup balance, so next time I'll see if I can get things tracking better. Next time promises to be some time off as the weather has moved into a period of instability. *sigh*

Saturday, February 11, 2012

A Cautionary Tale

Wellll, it's been both head cold and weather cold time for me. Clear and cold nights have coincided with my lingering head cold, so I have no news to report.

The Tale? Earlier today I spotted a for-sale ad on Cloudy nights from the person who sold me my used AT72ED. He sold that scope because he wanted to move to something larger, an AT111EDT. He bought the AT111 and sold his AT72 thinking he no longer needed it, and that the smaller scope would help pay for the bigger scope. Sensible plan, really; how many scopes can a person use at one time?

The AT111 weighs 11.2 pounds compared to the AT72's 5 pounds, and perhaps more important is larger and a little more difficult to handle. I know my TV-102 surprised me at how large it was and how careful I had to be when moving it around. Not the the 102 is fragile, but I think that refractors in general are deceptively small in appearance.Once you start carting them around you find out otherwise. Just ask anyone who owns a 6-inch refractor--it doesn't have the same portability as a 6-inch Dob!

Sadly, the AT72 seller developed back problems that needed surgery to correct, and his new AT111 is now too much for him to handle. He's put it up for sale. It's unknown if the larger scope caused his back problems. I sort of doubt it, as back problems can reassert themselves for no clear reason at all.

The caution to this tale? It's tempting to suggest that one should never sell one's telescope, but that's utterly illogical and makes little economic sense. And besides, if everyone did that, where would I get my telescopes? 

I think the lesson here, if there is one, is that a factor in deciding when to sell a telescope should be the "niche" it fills in your hobby. The AT111 and AT72 are different enough that they can serve different purposes; the former is a serious scope good for almost any purpose, while the latter is a great grab-and-go scope.

Sorry for this. I know it's not as if you wanted another reason to anticipate "seller's remorse." But it can and does happen.

Tuesday, February 7, 2012


I've been under the weather a couple of ways lately. It's been very cloudy and I've got a headcold. Having the little viral critters inside me made me think about the kind of critters that share the outside world with me.

I live on the upper portion of the Minnesota River valley, a wide expanse with gentle slopes and a broad flood plain. The area has been settled for almost 50 years and the woodlands have long ago been lost to agriculture and urban development. We've seen deer only twice in our back yard in almost 30 years. One time we saw a very bedragled fox. Other than that it's mostly bats, rabbits, woodchucks, raccoons, squirrels and mice. Pretty tame, all in all. The really big mammals like bear and moose stay well north of here.

I've never seen any mammal larger than a rabbit or stray cat while observing. I've no desire to see a raccoon (or even hear one!) and the coyotes that are starting to return to the area have yet to show up.

Insect life has also been relatively benign. It's a draw between June bugs and mosquitoes for the worst of the lot. The folks who handle mosquito control do a good job here. June bugs are harmless but clumsy flyers that tend to scare me when they blindly crash into me.

I know that in other parts of the country you have to contend with nasty critters like spiders and snakes, but there's really none of that around here.

There are Owls, though. One night one swooped over me on the way to a tree it frequents. It was a huge Great Horned Owl, amazingly impressive as it flew past me. That it was perfectly silent as it did so was almost eerie.