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Sony Alpha DSLR Focus Problem a900

Sony Alpha DSLR Focus Problem a900

Posted on Feb 16, 2012 by Paul White

I recently bought a Sony a900 DSLR off ebay. The camera is in mint condition, but it had a major issue. Some of my lenses would not lock on focus, and the view finder was dark when compared to my a700. Turns out the problem is a bent aperture arm. There is a quick and cheap fix for this problem, however I opted to send my a900 in to Sony for a repair that was covered under the warranty.

What is the Aperture Arm?

All Sony DSLR cameras have a metal ring with a small aperture arm that sticks out. The aperture arm is designed to rotate the camera's aperture blades controlling the amount of light that is able to enter the lens. If your aperture arm gets bent then sometimes it doesn't line up with the matching arm located on the lens.

How do you know if your Aperture arm is bent?

The symptoms are a dark view finder. By default the aperture is held wide open while you compose your shots. Then when you press the shutter the aperture blades will close to the proper level and take the picture. If your view finder seems darker than it should be, then this means the aperture is not being held open. This typically means your aperture arm is not making contact with the matching arm located on the lens. Another symptom is your camera hunts for focus and can never get a focus lock.

Sony a900 DSLR bent Aperture Arm
In the above picture you can see the bent aperture arm of my a900. This arm is supposed to be making an 90 degree angle with the ring its mounted on.

Aperture Lever on Sigma 30mm F1.4 EX DC
In this photo you can see the Aperture lever on my lens. Notice how its straight.

Bent Aperture only issue with some lenses

Of the 6 lenses I have, 2 worked fine
  • Minolta 50mm F1.4 Prime
  • Sony 16-105mm
While these 4 lenses had problems.
  • Sony 75-300mm
  • Sigma 30mm F1.4 EX DC
  • Sigma 10-20mm EX DC
  • Sigma 20mm F1.8 EX DG
This has to do with minor gap differences in the lenses. All these lenses worked perfect on my A700, and have worked perfectly for years.

How to Fix a bent aperture on a Sony DSLR

There are 3 solutions.

Needle Nose Repair

The first one is to take a pair of needle nose pliers and carefully bend the arm back into place.

Send it to Sony for Repair

The other solution is to send the camera to Sony for repairs. If you are still under warranty (Sony DSLR come with 1 year warranty in the USA ) I highly suggest you just send it in for repair, so they can replace the aperture ring. Else the repair might be $100-$200.

Buy the part and do it yourself

If you are comfortable with taking apart your camera, and want to replace the part rather than try to bend it back into shape, then try one of the links below to buy a new ring.
Sears$22.31A900 Ring Iris #410931401


If your Sony DSLR starts having problems. Won't get a focus lock, and the viewfinder is dark or dim, then your problem could be a bent aperture arm. Hope this guide helps others.

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C.F.Klaassen | May 5, 2012 6:20 AM
Thanks very much for this info. Last week I got the aperture problem with my a900 during a walk through the Claude Monet Gardens in Giverny, France. I tried the 'Needle Nose Repair' but the hardened steel material doesn't bend easily. So now I will try option 2 and send it to a Sony Repair Center in Holland. Just one more question: the A900 Ring Iris that can be obtained from Sears is the redesigned one, isn't it. I hesitate however to do the repair job myself.... 
vbr | Apr 1, 2013 3:35 PM

I had similar problem with a500 - but it was other way around, the piece on objective has bent. But exactly same symptoms, with autofocus not working. THANK YOU FOR SAVING MY CAMERA MATE!!! THANK YOU!
mirthseeker | Mar 1, 2017 3:50 PM

It's worth noting that the aperture lever can also be displaced if the ring it is attached to slips off a roller / rollers (2 white rubber rollers).  See the posts in this thread: http://www.dyxum.com/dforum/a900-error-message-camera-locks-up_topic64253.html

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