Sticky blades?

audiobomber · 11-20-2008, 03:46 PM

I have an Image A 28mm 2.8 that's acting up. I just took a series of photos in my snowcovered yard. All the photos taken with the 28mm were heavily overexposed, so I popped the 16-45mm on and took a couple more. All photos were taken in Av mode, F8, auto ISO. Here's the relevant exif data from the series:

A 28:
1/100s, ISO 100
1/100s, ISO 800
1/100s, ISO 1000
1/100s, ISO 1250

DA 16-45:
1/50s, ISO 400
1/50s, ISO 500

The evening light was fading slightly as the photos progressed. The 28mm photos were taken with the aperture ring in A mode, and this was confirmed in Photo Browser. Is this a sticky blade problem or an electronic issue? I've had overexposures with the A 28 a few times in the past. I took a couple of shots later that were fine.

JonPB · 11-20-2008, 04:35 PM

The best way to tell if the aperture blades are sticking is to take the lens off the camera, set it to its smallest aperture (probably 22), and manually flick the lever to see if the blades are stopping down quickly and reliably.

If you'd rather test with the lens on the camera, set the camera to manual, set the aperture to is smallest setting, and adjust shutter and ISO to make an appropriate exposure. Set the camera to continuous and take ~20 shots. If the images vary in brightness, the aperture probably isn't stopping down reliably.

Note too that if the aperture blades are sticking, they may do so more or less depending on whether the lens is pointed up or down or the camera is oriented vertically or horizontally.

audiobomber · 11-20-2008, 04:47 PM

Originally Posted by JonPB

The best way to tell if the aperture blades are sticking is to take the lens off the camera, set it to its smallest aperture (probably 22), and manually flick the lever to see if the blades are stopping down quickly and reliably.

Thanks Jon, I should have known to try this myself. The aperture appears to be mechanically jammed. It won't stop down at all. I can't flick the lever, it just moves a tiny bit.

**Marc Sabatella** · 11-20-2008, 08:12 PM

I don't understand why you'd get four wildly different ISO settings for the exact same shot at the same aperture and shutter speed. Sticky blades couldn't possibly have anything to do with that, but that would seem to be an issue right there...

JonPB · 11-20-2008, 08:13 PM

I don't know much about lens repair, but the one lens that I have taken apart made it pretty easy to get to the aperture lever. If it were my lens, I'd remove the mounting ring and take a look to see if there's an easy fix.

audiobomber · 11-21-2008, 07:42 AM

Originally Posted by JonPB

I don't know much about lens repair, but the one lens that I have taken apart made it pretty easy to get to the aperture lever. If it were my lens, I'd remove the mounting ring and take a look to see if there's an easy fix.

I've had this lens apart when I first got it and I had trouble reassembling such that the aperture lever moved freely. The problem comes and goes. My solution is to replace it. I made Hapo an offer on his similar Kalimar 28mm. Thanks for your help.