Normal for a-mount aperture asymmetry stop-down?

Hey guys,

I swear I wasn't after alitteration!

I'm trying to find out, is normal for Minolta A-mount lenses to have an apereture that appears asymmetrical when it's stopped down to the maximum / not attached to camera?

I recently acquired a "mint" Minolta 135mm f/2.8 STF and without the lens attached the aperture looks like this:

https://postimg.cc/gallery/3HZbrbn

And I'm trying to find out if that's normal for this lens and/or Minolta a-mount in general.

I am new to Minolta A-mount but have owned lenses in almost every other mount (OM, Canon FD, Leica R-mount, Hexanons, Nikkor F-mount, Canon EF, Pentax K-mount) I can't recall ever seeing anything like this before

This is an image of the 80-200 taken from Ken Rockwell's site ( https://www.kenrockwell.com/minolta/maxxum/80-200mm-f28/D3S_9736-front.jpg) and it also looks non-circular when stopped down. Given I'm seeing the same thing on a totally different lens design, it makes me think maybe this is normal A-mount.

The seller of the 135mm f/2.8 STF is being kind and is offering a return but before jumping the gun and claiming it's defective, I wanted confirmation.

Edited by slrl0ver - 09 December 2022 at 09:03

Hi,

Thanks for the quick reply.

It always returns to that position when not mounted or when the lever is not pushed by a tooth pick, etc. When it's near wide-open or open it does "looks" normal.

Not trying to drive clicks to KR, here's his review of the 80-200 f/2.8 APO and the image I linked was below the word Diaphragm (

https://www.kenrockwell.com/minolta/maxxum/80-200mm-f28.htm )

Looking on eBay at other 80-200's, they show a similar "non-circular" shape.

I looked at the Ken Rockwell photo and indeed that looks "non-round" as well.

I've now checked all my A-mount lenses and also found one with the same behaviour, i.e. my Minolta DT 18-70 kit that came with my KM5D that I bought in 2006. All my other A-mount lenses show a perfect round aperture when fully closed down/disconnected from the camera.

Obviously the STF is a much more special and valuable lens compared to my cheap kit so if you feel uncomfortable about it developing more serious aperture problems in the future I would return it. But if you got a real good deal and the rest looks fine it may be worth the risk, you don't buy an STF for use at very small apertures anyway.

I think the Sony version I had was like that too. It seems mostly irrelevant to me. The lens loses its character the more it is stopped down.

Hey all,

Thanks very much for the feedback.

To answer a question I did NOT get "bargain" pricing on the lens, I paid market value for a mint lens, so I'm likely going to return it.

In the mean time, I spent a few minutes to try and take better photos of the aperture from close to wide-open all the way to stopped down. I had use to an A-mount lens adapter (without any optics) so it's possible the "detents" on this adapter don't quite correspond to typical 1/2 stop (i.e. f/2.8, f/4, f/5.6, etc).

https://postimg.cc/gallery/ShHBZpC

I didn't have a jig or a rig to hold the lens perfectly still so if you play these images back the lens moves slightly but hopefully there's not enough parallax error here to draw false conclusions.



Edited by slrl0ver - 12 December 2022 at 09:56