Re: What kind of camera or telescope would u need to get a good view of the site from Tikaboo?

Message posted by gary on November 12, 2002 at 17:52:12 PST:

This is a good question. It depends on the final product, i.e. will you be scanning prints or having your slides or negatives scanned. If you are going to scan prints, you should have about 4000mm equivalent focal length. If you are going to scan the film, 2000mm equivalent focal length will do. [You lose a great deal of resolution in most prints.] If you print 8x10's like Steve Hauser does, probably 2000mm will work. I scan kodak black and white film (TMX) pushed 1 stop to increase the contrast.

Now doing things backwards, lets define equivalent focal length. The assumption here is that you will be using some sort of telecoverter (or maybe several in series) with a telescope or lens. The lens or telescope should have at least 90mm aperture. As you add teleconverters, the image will get dimmer. A 2x teleconverter means you have 1/4th the light, i.e. a square law relationship. So if your telescope has a focal length of 2000mm, you need a 2x teleconverter to get to 4000mm equivalent. In practice, you will always need a teleconverter if your telescope is a relatively small reflector (i.e. folded mirror optics). This is because the secondary mirror of most telescopes is not large enough to fully illuminate a 35mm frame when used "prime" (no teleconverter). [The big SCT that Steve Hauser uses should have this problem.] The teleconverter could be one made for your camera, or it could be a barlow designed for a telescope. [If you use a telescope, you need a t-ring for your camera.] If the telescope is a refractor, you will still need a teleconverter as the focal length of most refractors is around 700mm, which is not enough to see what you are photographing from Tikaboo. An alternative to the teleconverter (and a bit to complicated to discuss in a post) would be eyepiece projection.

I've done photos with a large Pentax screw mount lens (500mmf4.5) I got off ebay and 4x worth of teleconvter (though only at the TTR, not Tikaboo, thus far). This is an alternative to getting a telescope. A camera lens (and refractor telescope) has much more uniform lighting across the film plane than does a reflector telescope, and most camera lenses are sharper at the sides of the image that a telescope, though the reflector telescope tends to be sharper in the center of the image. The biggest source of blur in the image will be the atmosphere, much more than the lens, though there will be days when good optics will be worth the money.

The last thing required in of course a camera. The camera will need mirror lock-up, a cable release, and the ability to meter with any kind of lens. [Some cameras can't meter on the back of a telescope.] The best choice is the Nikon F3 with the DW4 magnifying viewfinder. These can be rented if you don't want to buy one, but I wouldn't mention where you plan on taking it. ;-) Obviously a tripod will be needed if you expect the image to be sharp.

In Reply to: What kind of camera or telescope would u need to get a good view of the site from Tikaboo? posted by Will on November 12, 2002 at 12:52:19 PST:


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