Author Topic: Evaluating Legacy Tele Lenses on my E-P2 (Read 1243 times)

ratobuhler · « **on:** December 10, 2011, 02:01:00 PM »

I just took a few pictures (a piece of news paper far enough away to make the small print barely legible) with a Zeiss Jena Sonnar 4/135 and a Leica (Leitz Wetzlar) Elmar 4/135. For both lenses I get the best (sharpest) results at 4. After 5.6 the resolution falls of drastically. I did not realize that these lenses are at their best wide open. I understand that for a perfect optical system the resolution is determine by the aperture only but photographic legacy lenses are usually at their best when stopped down a bit. Am I doing something wrong? Any comments?

voyager · « **Reply #1 on:** December 10, 2011, 02:34:37 PM »

Probably has to do with the design of the lenses in conjunction with your adapter. That is strange though, never heard of lenses being sharpest wide open.

tamoio · « **Reply #2 on:** December 11, 2011, 09:52:47 PM »

One word: diffraction

ratobuhler · « **Reply #3 on:** December 12, 2011, 09:07:11 AM »

Wide open, the resolution of a photographic lens is usually not approaching the theoretical diffraction limit.

This was done on a solid tripod. I just realized that image stabilization was on. I will do the tests again w/o IS.

overflow · « **Reply #4 on:** December 12, 2011, 11:26:40 AM »

Depends on the quality of the lens wide-open... diffraction starts setting in on the average u4/3 sensor (12MP) at about f/4.5, though I don't think becomes very noticeable until a fair amount smaller. But if all other aberrations are insignificant, than quality should be best at f/4

Not that I've played around with it much, that's all theoretical.

tamoio · « **Reply #5 on:** December 12, 2011, 11:41:13 AM »

Quote from: ratobuhler on December 12, 2011, 09:07:11 AM

Wide open, the resolution of a photographic lens is usually not approaching the theoretical diffraction limit.

This was done on a solid tripod. I just realized that image stabilization was on. I will do the tests again w/o IS.

My suggestion regarding diffraction was a response to this: "After 5.6 the resolution falls of drastically"

I think there is even a diffraction calculator somewhere in this little app from panasonic:

http://www.geocities.jp/dvcpro24/lens_calculator.html

voyager · « **Reply #6 on:** December 12, 2011, 12:40:55 PM »

The IS has been known to destroy my photos before when I'm using a tripod. Strange how it doesn't always do it though.

ratobuhler · « **Reply #7 on:** December 12, 2011, 03:51:47 PM »

Mystery solved. I just re-did the test w/o IS and the results are as expected. Only gradual degradation after 5.6 with 22 the worst.

Evaluating Legacy Tele Lenses on my E-P2