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 |
For reference, here is the frame center:
Center 400x400 area |
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.
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