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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://imgur.com/a/tSCWHAy

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.

crop

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    @xiota I disagree with you saying the body is at fault. OP states that no problems arise with other lenses, and that this lens has a particularly stiff aperture lever (for a lack of a better word). It would seem the body struggles to close the aperture, and the shutter is only fired after this happens. This is backed up by the hard-to-press DOF preview button; it indicated that aperture lever is putting up a fight.
    – timvrhn
    Jul 8 at 8:02
  • @aswine if what I wrote above it true, there should be no problem when you set the aperture to wide open (in this case f/1.4). Can you confirm or deny this?
    – timvrhn
    Jul 8 at 8:02
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    I diasgree with @xiota. OP is correct to assume this is an issue with the lens. Actuating the lens aperture happens in the camera's release cycle before the mirror is lifted and the shutter is released. A sluggish automatic aperture lever can delay shutter release. The DoF preview button is mechanically linked to the automatic aperture lever and can be hard to push if there is an issue with the lens. The video shows that the automatic aperture lever returns slower than normal.
    – cmuseum
    Jul 8 at 8:21
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    @timvrhn The automatic aperture lever is actuated with the same force and by the same distance no matter what aperture value is set. The force for closing the aperture is provided by a spring inside the lens, not the camera. Hence I would expect that the problem occurs at any aperture value.
    – cmuseum
    Jul 8 at 8:35
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    @timvrhn I tested shooting with the aperture wide open (f/1.4), then at as closed as possible (f/22). I got the same results for both. The shutter doesn't release until I push the DOF button. I'm not a force meter machine, but it felt to me like I needed equal force to push the DOF button both at f/1.4 and f/22.
    – aswine
    Jul 8 at 14:37
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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.

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    Thanks for the advice. Maybe this doesn't sound convincing, but when I move the bayonet, it feels like there's just nasty old gunk in there, not like something's bent or incorrectly assembled. I think if there were dirt in there, it would feel gritty, but it feels very smooth, just slow. I might look into doing a little disassembly to get a better look at what's in there. I'm tempted to put a drop of WD-40 or something in there to break up any "dried" oil. See the photo I added to the question.
    – aswine
    Jul 8 at 15:07
  • @aswine I recommend you do not apply WD-40, or any other water-displacement fluid, nor any lubricant for that matter. The proper way to get "gunk" out of the mechanism is partially disassembly and cleaning. Products such as WD-40 might provide short term relief by unsticking some accumulated debris, but it has low viscosity and low surface tension, so it tends to creep to lots of places, and leaves a residue behind that can attract and stick to dust.
    – scottbb
    Jul 8 at 17:30
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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.

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