Advice on aperture repair on camera lens - Page 1
Forum section: electronics / repair

author: lukashts
author_rank: Newbie
timestamp: April 30, 2024, 08:04:39 am
content: I bought a used Sigma 20mm f/1.4 DG Canon EF-mount lens which had its aperture and autofocus broken.I fixed the autofocus simply by cleaning the switch but the aperture remains stiff. The aperture works in video mode if it goes from f/1.4 to f/16, but doesn't work in photo mode above f/3.5 because it gets stuck because of too much resistance. I tried cleaning the aperture with isopropyl alcohol but that didn't fix the problem.What could I try to fix the aperture? Should I disassemble the mechanism and clean it comprehensively? I don't want to send it away for repair since that would cost more than what I paid for the lens. The rubber also reeks of cigarette smoke but that'll probably go away with time.

author: ApertureScience
author_rank: Contributor
timestamp: April 30, 2024, 05:34:25 pm
content: I have no experience with repairing modern lenses. With old manual lenses I sometimes cleaned the whole aperture assembly with an ultrasonic cleaner, using alcohol as a solvent. That usually removed all oil and dirt.

author: lukashts
author_rank: Newbie
timestamp: April 30, 2024, 07:15:35 pm
content: That seems like a great idea, but I don't have an ultrasonic cleaner. Maybe I can justify getting one for other uses as well.

author: Koray
author_rank: Regular Contributor
timestamp: April 30, 2024, 10:39:08 pm
content: It is odd that the aperture behaves normally in video mode but not in photo mode. Could it be software related?K.

author: lukashts
author_rank: Newbie
timestamp: April 30, 2024, 11:25:40 pm
content: It isn't software related. The aperture motor doesn't have the oomph to close the aperture for a split second in photo mode but in video mode the aperture increases in small steps so there's less resistance.

author: AndrewEp17
author_rank: Contributor
timestamp: May 01, 2024, 06:40:01 am
content: If you are able the get the aperture diaphragm out i would recommend completely disassembling and cleaning the blades with isopropyl alcohol but be careful not to dent or bend the blades. and take it apart slowly and pay attention to how it is assembled so it will be easier to remember how to put it back together

author: jchw4
author_rank: Regular Contributor
timestamp: May 01, 2024, 09:45:22 am
content: Quote from: lukashts on April 30, 2024, 07:15:35 pmGiven that the smallest and simplest one costs $20 deliveredhttps://www.amazon.com/Vpcok-Direct-SU-745-Ultrasonic-Jewelry/dp/B0BJJS9RPPI see no reason not to buy one.These are sold under zillion "brands" and they are all the same.I have one that looks approximately the same and it works well for home use.In my case the timer is fixed at 1 minute and I have to run it several cycles to really clean stuff, hopefully now you can buy one with a flexible timer for 1..10 minutes.Not very powerful but I use it once or twice per year and it just works.

author: ApertureScience
author_rank: Contributor
timestamp: May 02, 2024, 07:22:26 am
content: You could start by submerging the assembly and working it a few times. Reassembly can be quite tedious. If the material permits you can also try acetone, be very careful.

author: lukashts
author_rank: Newbie
timestamp: May 02, 2024, 02:24:05 pm
content: I will try repairing it after a trip.