Lens sharper wide open than stopped down?

Does anyone ever experience this? I have a minolta 35mm F2 RS which I swear is sharper at f2 than f3.2 and f4

Without explaining to me that this is optically impossible...anyone comment on this with their lenses?

Is it just the depth of field difference? Or am I mistaken?

Thanks for all replies (except ones that say "this is stupid and not possible"   :-) I'm just saying it seems like it to me

thanks

jordan

If the light is the same, every time you stop down the lens, you are reducing the shutter speed as well. Could it be that the slow shutter speed is causing blur which might be interpreted as softness?

One reason I have a problem with switching to Nikon, is that so many of their lenses shift focus position depending upon f/stop used. It's dramatic in some cases, and it occurs at closer focusing distances.

The Minoltas rarely shift focus with f/stop changes. But some, like the 20mm, will shift a little at the infinity setting. f2.8 will be spot on infinity focus, but f/5.6-f11 may not be... you'll have to back focus a bit to get perfect infinity focus.

The 35mm f/1.4 doesn't shift focus. I don't currently own a 35/2, but I don't remember it shifting either. I only had the 35/2 in the film days, so I may not have noticed it. I've never heard a report that it does, so I'd very much doubt it would. It performs similar to the 28/2 which doesn't shift at all.

Are you seeing focus shift at infinity, or closer distances? I often thought focus was shifting when I had G screen installed into a900. But installing M screen allowed for more precision on close focusing, and confirmed that I was just missing the mark with the G screen.

Your 35/2 should be giving peak performance at around f/5.6... better than wide open, except perhaps in the center. But certainly no worse.

Jordan, could you please post some sample shots (same scene from a tripod at different f-stops)? It is hard to answer your question without looking at the same pictures as you.

jordo7 wrote: Serdar A wrote: If the light is the same, every time you stop down the lens, you are reducing the shutter speed as well. Could it be that the slow shutter speed is causing blur which might be interpreted as softness? I went back and looked at all my photos from my son's birthday party. I think that this probably is the best explanation. The shutter speed went from 1/60 at F2   and was 1/30 at f3.5    Simple answer to my question and it probably is this. Thanks so much. Thanks to photosopher for the explanation of many things I never considered or knew, too. I learn stuff all the time from this board. Thanks

the reduced shutter speed will make it seem like it's not as sharp but it really is due to you not holding still enough.

sybersitizen wrote: FineArt wrote: A lens should be better wide open than stopped down. Common wisdom says, and experience has shown, that the majority of lenses are sharpest neither at their widest nor their smallest apertures. They are almost always at their best near the middle of the aperture range. The impact of diffraction increases as the lens is stopped down. Diffraction typically plays only a minor role at apertures of roughly f/8 or larger. Stopping down farther than that will invite some visible diffraction effects. When you have to stop down to sharpen the image you are making up for error tolerances. I don't know what that means.

Yes, I understand that most lenses work best at f5.6 to 8. That is usually what I shoot at unless I am looking for a specific bokeh effect.

The fact remains that wide open is part of the operating design criteria of the lens. If they dont figure the lenses to work well at f2.8 (such as cheap kit lenses) they take it out of the operating parameters. They make an f5.6 wide open lens.

The reason lenses are weaker than optimal wide open is the curvature on the lenses is highest at the edges making it the most difficult to manufacture. Every element has a manufacturing tolerance +/- x wavelengths. Add them up with tolerances of glued in place positions and you end up with a mild blur or chromatic aberrations , etc. Every lens test will show a diagram weakest at the edges.

Here is one for one of the best Alpha lenses, the Zeiss 24 T* Prime

http://www.dpreview.com/lensreviews/sony_24_2_m15/4

Most of the weakness is in the corners for the reasons stated above.

There is no discrepancy. All you have to do is look at a lens to know the rate of curvature increases to the edges. Keeping an increasing rate of curvature within the design tolerance all along that surface is the issue.