Canon AE-1 aperture linkage stops down too much

[Guy S]

I’m helping a friend sell their AE-1 and I noticed it wasnt stopping down under any circumstances. Using a short guide I removed the aperture from the front and cleaned it up. It was jammed open from oil.

Upon reinstalling it Ive noticed it stops down too much. About 1.5-2 stops too small.

Does anyone have any guides about getting the linkage working right?

 

[Guy S]

Should say that its a 50mm f1.8 with the new FD mount

 

[Guy S]

Okay so for anyone following up on this it turns out the aperture assembly has some range of motion to rotate when screwing it in that determines how much the blades move for each setting. It will be difficult to calibrate this unless I can calculate the virtual aperture from the physical aperture and check at each point.

If the relation is proportional then I could take the wide open width and f stop and use that to calculate it for the others. hmm....

 

[monopix]

Which is why you should mark everything as you dismantle it so it can be put back as it was.
If you have another lens to compare with, take a meter reading with it then adjust this to get the same reading.

 

[Guy S]

yes, unfortunately the guide didn't mention there was slop in between the screw holes and the threading underneath that would affect it so much. The slop is only a mm or two. The metering trick won't work, I don't think, as the camera meters wide open.

Thanks though as you gave me an idea, and I didn't even need another lens.

The meter in the camera is affected by the DOF preview. So I took a reading wide open, then I did a DOF preview with the aperture closed by one stop, then two, then three, four, five, and six. On each of those the meter suggested to open the aperture one stop, then two, then three etc... until the meter ran out of range.

So I'm happy that this lens is working at least okay. Certainly better than when it was gummed open.

 

[monopix]

yes, unfortunately the guide didn't mention there was slop in between the screw holes and the threading underneath that would affect it so much. The slop is only a mm or two. The metering trick won't work, I don't think, as the camera meters wide open.

Thanks though as you gave me an idea, and I didn't even need another lens.

The meter in the camera is affected by the DOF preview. So I took a reading wide open, then I did a DOF preview with the aperture closed by one stop, then two, then three, four, five, and six. On each of those the meter suggested to open the aperture one stop, then two, then three etc... until the meter ran out of range.

So I'm happy that this lens is working at least okay. Certainly better than when it was gummed open.

Yes, you're correct. I was having a mad moment.