Need help identifying lens mount

[Stephen]

Jul 19, 2014 6:56:03 GMT -5 philbirch said:

Telephoto is the opposite of retrofocus more or less, ie making the lens physically shorter than the focal length. We are more familiar with the word telephoto than retrofocus.

A 28-200 such as I have would definitely be a retrofocus design, but an 80-200 wouldnt necessarily be.

I think there are no hard and fast rules for lensmakers but I suspect that a long focus lens would have better image quality then a telephoto and a short focus lens would be better then a retrofocus wide. simply due to the number of elements needed. All things being equal.

The break point on the 35mm reflex is 40mm approx, plus an allowance for practical design of the zoom and focus movement, so zooms above about 60 mm min are possible without a retro design, anything less will have to be. Zooms that are "universal fit", and involve an adaptor, like Tamron, favoured an all retro design up to about 120 mm minimum, just to ease the space problems.

It is true the feeling is that simple lens give sharper results, but careful design work and the need for corrections mean a design like the Biogon wide angle is better than a plainer lens with fewer elements.

But with longer lenses true length designs work well, although in practice, corrections are needed, so Telephoto designs (more compact), are used in the real world.

Stephen.

[philbirch]

My comments were guesses based upon the scant knowlege I have on these things. It would seem that I'm not far from the mark. Long lenses are more prone to colour fringing, that I DO know so extra elements are necessary.

Interestingly, once I dismantled a broken Hanimex 135mm lens out of curiosity and discovered the front element had a focal length of nearly 300mm. but bags of distortion.