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Photography Question 
KJ Callaway

Mirror Lens vs. Telephoto Lens

I would like to buy a 500mm lens for wildlife/nature photography. I've got a Canon Rebel 2000 and will soon be getting either a Rebel Ti of a Rebel K2. What is the difference between a mirror lens and a telephoto? Which one would be the best to use for what I want to do? Thank you!

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8/29/2004 10:20:14 AM

Gregory LaGrange
BetterPhoto Member Since: 11/11/2003
  A mirror is still a telephoto but it's made with internal mirrors to achieve a long focal length in a smaller physical sized lens. Incoming light is reflected forward by the first mirror, then a second mirror reflects it back towards the film.
They don't have a way to change apertures. I don't know how much has been put into developing them over the years, because they aren't the lenses the companies push as having the latest aberration-correcting glass. So I can't say that a mirror lens would be just as good as a recently released zoom that may be in the same focal length and maximum aperture range.
Mirror lenses are usually around the f/8 range.
So I don't know if something like Sigma's mirror lens would be better than their zoom around the same focal length. But mirrors are lighter, and cost less.

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8/29/2004 11:17:31 AM

Jon Close
BetterPhoto Member Since: 5/18/2000
  Telephoto generally refers to any lens with longer than "normal" focal length (around 50mm), so a 500 mirror lens is a telephoto.
A mirror or reflex lens tends to be very compact, lighter weight, and much less expensive than traditional lenses of the same focal length. While quality varies, they potentially can be very sharp because the mirror elements don't have the spherical aberrations (light through the outer portion of a lens does not focus to the same point as light through the center) and chromatic aberrations (different color wavelengths refract focus to different distances) that conventional lens elements have.

On the other hand, the reflex design makes an adjustable aperture impractical, and so they have a fixed aperture, usually a relatively slow f/8. Thus, you are limited to either manual or aperture priority exposure mode only. With the exception of Minolta's 500 f/8 Reflex for their Maxxum SLRs, mirror lenses are manual focus only. And because of the "folded" light path, out of focus highlights appear as doughnut shapes instead of flat disks. Like lens flare ghosting, these doughnuts can be a distracting annoyance or an additional "artistic" element.

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8/29/2004 11:30:15 AM

KJ Callaway   Thank you both for your answers! I appreciate the help.

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8/29/2004 12:53:04 PM

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