FD lens aperture is slow

Question

I bought a Canon AE-1 Program on eBay along with a 50mm f/1.4. The camera works well with other lenses, but the 50mm's aperture seems slow. Moving the bayonet (I think that's what it's called) takes much more force than on my other FD lenses.

As a result, the time between pushing the shutter button and the shutter releasing is sometimes hours. However, if I push the shutter button while holding the depth of field preview button, the shutter releases immediately. Similarly, if I push the shutter button and then push the depth of field preview button, the shutter releases. The depth of field preview button is very hard to push. Sometimes the shutter works as it should.

Do I need to lubricate it? How can I fix my lens?

https://i.stack.imgur.com/FGZEU.jpg

Here's a photo of the lens. Notice the gunk by the bayonet. I'm not sure if this is a pure observation or if I'm imagining it, but it feels like the gunk is what's making the bayonet hard to push in both directions; for both my finger and the spring. It's like there's old oil or molasses in there. Obviously, I haven't cleaned the lens at all.

Answer 1

Based on the information you provide, the suspected cause for this issue is higher than ususal friction in the lens' bayonet mount and in its aperture actuation mechanics. Possible reasons are:

• Damage, e.g. bent parts or corrosion
• Incorrect assembly
• Dirt has accumulated

Whether repair is required or cleaning and lubricating will solve the issue is impossible to say at this point. Further inspection which involves disassembly will be required.

Just “lubricating it”, in the sense of applying a drop of oil here or there, is not a proper repair procedure. It may cause other issue in the long run. Low friction between the fast moving parts of the aperture actuation mechanics is achieved by choice of materials and play in bearings, not by lubricants. Lubricants are only used for slow moving parts, e.g. the aperture control ring.

Given that good copies of this lens can be had for EUR 50 to EUR 100, professional repair is unlikely to be economic. If you want to give it a try yourself, plenty of video tutorials can be found online that show how the mount part is disassembled and what tools and skills are required.

EDIT

The picture that has been added shows some stains and residue. This may hint to some sort of liquid having entered the lens. Its residues may have made the mechanics “sticky”. Cleaning will very likely be required.

Whether cleaning can be successful depends on how far the contamination reaches into the lens and on your repair skills. Cleaning the mount assembly can be a delicate job because there are literally hundreds of small stell balls in the bearings. These are a nightmare to reinstall and opening the bearings is one of the last things you will want to try.

Overall, it may be easier to replace the entire mount assembly with a good one salvaged from a donor lens of the same type.

Answer 2

I removed the mount and soaked it in isopropyl alcohol. When I put the first few drops of alcohol on the bayonet, the gunk was already gone or dissolved. There was a lot of gunk in the stainless steel ring that holds the mount on. The lens now works perfectly on the camera.