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I have a camera adapter for my 1200mm reflector that I can put eyepieces in and I've tried it a few times but the area I'm photographing is too narrow, even at prime focus. (no eyepiece) I only get a small fraction of the Orion nebula, for instance.

How can I increase the field of view when shooting through my scope? Piggyback instead? Some sort of extra adapter that would reduce the magnification?

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3 Answers 3

up vote 2 down vote accepted

When you use a camera with a small sensor (APS-C) the equivalent focal length is increased by a 1.6 factor, with that type of camera your 1200mm telescope would be behaving as a 1920mm lens, for a single exposure of all the nebula using a 1200mm FL telescope without a focal reducer, you need a full frame or bigger sensor, but that brings other considerations, as vignetting.

There are a number of possibilities:

a) Use composite images. There are a number of programs that make easy to do this, the easiest to use IMHO is Deep Sky Stacker, other options are IRIS or Nebulosity

b) Use your camera in a wide field image, piggybacking on your telescope. Please note that this will reduce the detail in the image, as a Canon 300D with APS-C sensor in prime focus with a 1200mm telescope would have a resolution of 1.272 arcseconds per pixel, against 5.088 arcseconds per pixel using a 75-300 lens at maximum zoom. (Orion Nebula would cover about 780x720 pixels in that specific configuration)

3) Use a focal reducer, if your reflector is a newtonian is possible than the focal reducer helps to reduce the coma in your optics, just be sure to make the calculations for the FOV of your specific equipment to get the appropiate reducer for your target. Most FOV calculators can help you with that, i.e. FOV Calculator

Good luck, and clear skies.

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You could always take multiple pictures and stitch them together afterwards. This would let you get an arbitrarily large field, and you would have to do some post work anyways if you're stacking together lots of exposures.

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Yeah, that would do it but I was hoping to avoid that if I could manage it. –  Jeff Snider Jun 2 '11 at 15:47

There is such a thing as a focal reducer (see some interesting articles and products) designed to widen the field of view.

Most of these are designed for specific telescopes, though, and I don't know if there is one that would work for your reflector.

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