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.

HOASP, CCD Returns

It's back, and it works. SBIG contacted me after about three weeks that the problem had been diagnosed. The news was not good: both circuit boards were fried and would have to be replaced. The cost would be $695.

Ouch!

I told them to go ahead and do the repairs. My options were limited. The filter wheel and 36mm filters I use are tied to the ST-8300 and can't be easily adapted to another camera. While $700 could probably buy a used CCD, but it wouldn't be as good a camera as the 8300--and I would have to add the cost of a new filter wheel and filters to that.

A week later the 8300 came back, and it works like new so far as I can tell. The fan runs and the filter wheel aligns itself when powered up, the shutter clatters when initialized, and the cooling system cools. It's been cloudy here since the camera was returned, so all I've been able to do so far is shoot dark frames.

Two questions I asked SBIG that you may be interested in if you are an ST-8300 owner:

Q. How did the breakdown happen, and how can it be prevented in the future?

A. The camera apparently much prefers to be powered up first; always connect the 12V power before plugging the USB connection into your laptop.


Q. Even though the sensor was not replaced, do the new boards mean that I need to shoot new dark frames?

A. Probably not, but it would be a good idea to shoot some test dark frames that match the exposure time and temperature of old dark frames. If they compare well, then my flat library doesn't need to be rebuilt.

So I'm back in business, once the skies finally clear. While I'm waiting, I'm going to make myself a poor man's camera case using a Plano #761 toolbox, some foam from a craft store, a twin-blade electric carving knife and a hot glue gun. It won't be a Pelican, but it will cost about 1/4 as much. I'll post more about this micro-project when I'm finished.

The Heart of America Star Party was a viewing and imaging bust, but I had a good time, as did most of the attendees. All three nights were cloudy, and it rained pretty much from the second night through all of the third day, with a lot of lightning the second night. Severe weather was forecast for the third night so I folded my tent and stayed at the Days Inn in Butler. Fortunately the severe weather bypassed the observing area.

HOASP featured an abundance of knowledgeable and friendly people, excellent talks, great food (assembled if not made on the premises) and nightly movies to help people cope with the clouds. One vendor (Bushnell) was on site, the daily door prizes were decent (I won none). One word of advice: If you decide to play bingo, take several cards. It's a cutthroat game, bingo.

I'll definitely want to return.