I recently came in the possession of a Minolta/Sony 50mm F1.4 camera lens with stuck aperture blades. The iris/diaphragm blades were stuck fully open and because of that I was only able to use the lens with an aperture of f/1.4.
This is a problem that can occur when excess oil or liquefied grease ends up on the aperture blades. This can happen, for example, when the lens gets left in a hot car. The heat causes the grease from the inner helicoid barrel to separate. After that the lighter oils from the grease make their way to other parts of the lens, such as the aperture blades.
Aside from the stuck aperture blades the lens was completely functional. I was hoping to be able to clean the oily blades and use the lens again. Luckily I was able to do so, with the help of the service manual and some other resources I found online.
The only way to clean the oil from the aperture blades is to open the lens up to get access to the iris mechanism. After that the oil can be removed using a solvent like alcohol, or with the use of an ultrasonic cleaner. Because the iris mechanism is rather fragile I opted to go for the ultrasonic cleaner method. That way I did not have to wipe down the individual delicate aperture blades by hand.
To help you clean your lens’ oily aperture blades, I have described the entire process below. I have also listed the materials and tools that I used.
Please note that the lens I repaired is a Minolta AF 50mm f/1.4. After Sony purchased Minolta, the Minolta AF 50mm f/1.4 was re-branded as the Sony SAL50F14. The Sony version has different lens coatings and does not have a built-in lens hood, but is otherwise near identical to the Minolta version. Therefore these exact instructions can be used for both lenses. The instructions can also be used to repair the Minolta/Sony 50mm f/1.7, 35mm f/2.8 and 28mm f/2.8 lenses. Their construction is very similar to the Minolta/Sony SAL50F14.
It is possible that these instructions can also be roughly followed for different lenses. But you may need to keep the service manual for your specific lens at hand. This applies to prime lenses only. The internal construction of zoom lenses is a lot more complicated.
After cleaning the oily aperture blades the lens works like new. Just like with repairing the Sony A77, repairing it yourself is not as hard as it seems, and is definitely worth a shot. Especially when the alternative is paying a lot of money for a repair service or for buying a replacement lens.
If you liked reading this article or have any questions about this project then feel free to leave a comment or check out some of my other projects linked on the all projects page.