by ʇolɐǝz ǝɥʇ qoq

Submit your Photo
Hall of Fame

Please participate in Meta
and help us grow.

Photography Stack Exchange is a question and answer site for professional, enthusiast and amateur photographers. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I saw that in Why do some people prefer 50mm to 35mm prime lenses? , in @MattGrum's answer:

The 50mm is a simpler design compared to the retrofocus 35mm

What's retrofocus?

share|improve this question
See also Why are wide angle lenses so much more expensive? – mattdm Aug 23 '12 at 10:57
up vote 21 down vote accepted

Fundamentally a telephoto design is used to make a lens body shorter than it's focal length, for practical reasons [what if your 18-300 ultrazoom was actually 30cm long?], a retrofocus design is the opposite, and makes a lens longer  than it's focal length in order to leave space for the mirror on an SLR.

You can tell if your lens is a retrofocus or telephoto by removing both caps and holding it in front of a bright background so you can see the aperture (the hole in through which light passes). For a retrofocus lens this aperture will look bigger from the back than from the front. For a telephoto lens it will look smaller from the back than from the front (the extreme telephotos you see have lens barrels which are much narrower toward the rear so this would have to be the case).

If it's about the same size front and back, then you have a symmetric  lens, such as the 50mm I was referring to. This is a simpler design as it is neither retrofocus or telephoto and this allows them to be made cheaply despite having a large aperture such as f/1.8.

share|improve this answer
Perfect explanation, thanks :) – Kiril Kirov Aug 23 '12 at 10:54

Retrofocus lens is a reversed telephoto lens in which the front element is negative, moving the rear nodal plane (from which the focal length is measured) behind the rear of the lens. It is the standard design for wide-angle and fisheye lenses in SLR and cine cameras where a conventional lens would foul the shutter mechanism.

See here for a simple explanation. Also see here for more info.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.