'A' lens won't go below f4 (even though it can go to f2.8)

Hi All,

I have a 100m 'A' f2.8 lens which I've attached to my K7 and all is working fine.

However, I noticed that when I use the 'A' setting on the lens, I'm unable to set the aperture to anything below f4.0. I can go above (so f8, f11, etc.) without any problems, but I can't go down to f2.8.

I'm not quite sure how to troubleshoot this problem, but any advice would be great.

Thanks,

Steven

Check the contacts are all nice and clean.

I'll try my A100/2.8 on a K5iis later just to confirm it's not an oddity

Correction, I meant to say 50mm not 100mm.

I'll give that another try this evening.

Thanks,

What exposure mode does this happen in ?

Have u tried seeing the aperture manually on the lens to F2.8 ?

You may need to make an adjustment in the menu so the camera will fire on a manually set aperture.

Ok, I managed to do some testing which actually makes me more confused, but perhaps someone else will know what's going on.

I'm able to figure the lens in both 'A' mode and using a particular aperture on the lens. Therefore I did a little test where I set the lens to f2.8 manually, took an image, and then took the same image, but setting the lens to 'A' and setting the aperture to f4 (as I can't make the lens go to f2.. I set the camera to 'M' mode and set the shutter speed to the same in each test.

The exposure was exactly the same. Therefore my camera is saying f4, but it is setting the lens to f2.8.

I then tried this throughout the aperture range up to its max at f22, and the same happens. In fact, it meant I was unable to set the lens to f22 using the camera, but I could using the lens.

So it seems like my camera is showing close to 2 stops above what I'm actually setting the aperture to.

I tried checking the contacts and they seem fine (not many being a MF 'A' lens).

Unfortunately I don't have another 'A' MF lens to test, so I'm now unsure if it's the lens or the camera (or just me setting things up badly) that's not working correctly.

Steven

Just tried a couple of 'A' lenses on my K5 - with the lens set to 'A' and the exposure mode dial set to "AV" (Aperture Priority Automatic) I can set any aperture from maximum to minimum. :

Just checked and I'm seeing that in the viewfinder. It shows the incorrect aperture (I.e. f4 instead of f2.8 ) when set to 'A' and 'F--' when on set any aperture on the lens.

That's an interesting read. I'll get my multimeter out tonight and check the contacts on the lens to see if they are correct.

If I understand correct, a '1' should be a short between the pin and the 'A' pin. Is that correct? Or is it a short between the pin and the bayonet (or are they the same...). Either way, I should be able to test it tonight.

Thanks, Steven

Okay another test this evening seems to have found the problem. As some suggested it was the contacts on the lens. It seems that one of the pins (the one that makes the camera think the lens is f2.8 instead of f4) isn't electrically connected to the bayonet. Easy enough to check with the multimeter.

I then used a bit of tin foil to short the connection to the bayonet, attached the lens and now it shows f2.8.

Now I just need to summon the courage to open the back of the lens to fix the connection internally.

Thanks for the advice and help. Steven