Lens optimised for ... what does it mean?

[justinlht]

Hi all,

Hope the seasoned veterans in here can enlighten me...

I've read somewhere that lenses are optimised at a particular f-stop. Am I right to say that at that particular aperture the lens is sharpest? Or is there more to it?

Also, I've got a really clean copy of a Jupiter-8 that i'd like to use more. How do I check to what aperture is this lens optimised to? And if I'd like to change the 'optimisation' how should I do that?

Thanks in advance!

 

[Yoricko]

Hello,

Lens optimised for, and optimal aperture are 2 different things.

All lenses have one particular optimal aperture where they will get the most center and corner resolution before the limits of diffraction kicks in. Most often, it would be around f5.6 or f8 for an average good lens. But, there also other lenses which have their optimal aperture at f4 or f11. Just a rule of thumb, f5.6-f8 for 35mm cameras. In some cases for really good lenses (usually) by Leica or Zeiss, you get amazing center resolution at f4, and if you stop down any further, there will be slight loss of resolution in the center (corner resolution would definitely improve substantially).

Lens optimised for a particular aperture is a whole different story. Some lenses have some focus shift issue. It not back or front focus problems, but, a change in focus when you stop-down the aperture. So, some people decide to customise their lens by sending it to a technician to get it 'optimized' for a certain aperture. So the focus would be spot on for that particular aperture. If I recall it right, the 50 f1.5 Sonnar is one example.

If you want to change the 'optimization' of the lens, you need to be a skilled lens technician first.
Additionally, it doesn't work on most lenses. Since most lenses do not have very severe focus-shift issues.

Hope this helps,

 

[justinlht]

Thanks yoricko! kinda cleared things up a bit

I think what i've had in mind was your second point. Yeah I do recall reading about focus shift issues on the Sonnar. What's a good way to check for focus shift / optimised for a particular aperture on my lens then, assuming I only have film bodies...?

Thanks again

 

[Yoricko]

Impossible.

A simple M4/3 camera with an adapter would do the job.