[dmdctusa]

I just got a 90mm manual focus C-V APO Lanthar 90mm-f/3.5 which is in the K mount allowing auto aperture. The lens is outstanding and focuses to 16 inches for a 1:3.5 image ratio....perfect for flower and still life shots.

Exposure in full manual mode (both aperture and focus) is spot on...no problems. When I switch the lens to the "A" setting and use Av mode and set the lens wide open using the Aperture dial, the setting is registered as f2.4 instead of f3.5. This is also the setting that is recorded in the EXIF information and preview data.

In spite of this erroneous reading the image exposure is correct and is identical to the a manually set f/3.5 image.

I thought I saw a recent reference somewhere that firmware 1.30 is causing some aperture indication problems.

Apparently the lens works perfectly on all Pentax film slr's. The last production run of the lens was in 2001 so maybe something changed in digital K mounts.

All thoughts and comments appreciated.

[thePiRaTE!!]

Have you solved this issue per chance? I have the 125/2.5 and 180/4 enroute, I'll pop back in once they arrive and report.

[Serge]

...
Exposure in full manual mode (both aperture and focus) is spot on...no problems. When I switch the lens to the "A" setting and use Av mode and set the lens wide open using the Aperture dial, the setting is registered as f2.4 instead of f3.5. This is also the setting that is recorded in the EXIF information and preview data.
...

I had the same issue with my (PKA Adaptall-2) Tamron SP 90/2.5. The aperture range shown by my ist*DS body was from f/4 to f/32 (instead of f/2.5-f/22). Nonetheless, the metering was functioning properly in all modes. So I stopped bothering about it. Maybe that's property of 90mm focal length? (I also own a CV 180mm APO, it operates correctly both on film and digital).

[thePiRaTE!!]

Received the CV 125 yesterday. It registers at 2.4 instead of 2.5, and the K10D doesn't offer 125 as a selectable focal range for manual input. Had to go either 120 or 135, so, 120/2.4 is how my .exif data is going to look on this one.

While slightly annoying, its WAY better than how my straight K and M42 mounts register, lol.

Seems like something we'll have to live with, although that won't be too hard

[dmdctusa]

I have learned to live with it since the exposure is ok and as the 90 CV is my all time favorite portrait lens!!

My exif data is just blank as to aperture but I do get a focal length setting of 85, the nearest to the 90mm of the lens.

I was very lucky, the next week after I bought it the 90KA mount was sold out. I find the mechanical and optical quality equal to similar Leica and Zeiss lenses I used in my film days.