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.
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.
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
- 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.
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.