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Canon EF lens mount repair

ctowle
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p.1 #1 · p.1 #1 · Canon EF lens mount repair

Hello All,
I have a version 1 of the 400mm f/2.8 lens that continues to serve me well despite its age and weight! Just recently while shooting a football game the lens began to have movement or play when mounted to the body. This was about 1/4" back and forth which was significantly different than normal. I took the body off the lens and a piece fell out and onto the ground never to be found again.

When I got home and was able to examine the mount on the 400 to other lenses it seems that the piece highlighted below is missing. I thought this was something CPS could assist with since it is an EF mount lens. Come to find out my version of the lens is no longer serviceable but they will gladly sell me a new one.

Has anyone experienced this on an EF lens and is there a DIY fix or other 3rd party that could possibly service the lens? CPS wouldn't service it even though my problem seems to be mechanical and is attributable to the EF mount.

I would love to get a new lighter one but out of the current budget and this one is still sharp and works well.

The first pic is my lens, the second pic is just one for reference I found online.

Thanks in advance

My current situation

Reference photo of 400.

Oct 12, 2023 at 08:49 AM

deepbluejh
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p.1 #2 · p.1 #2 · Canon EF lens mount repair

The mount is standard and should be able to be replaced by most any repair shop that repairs lenses. EF mounts are abundant and easy to find. Swapping one out is likely no difficult task either.

Oct 12, 2023 at 08:55 AM

Peter Figen
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p.1 #3 · p.1 #3 · Canon EF lens mount repair

deepbluejh wrote:
The mount is standard and should be able to be replaced by most any repair shop that repairs lenses. EF mounts are abundant and easy to find. Swapping one out is likely no difficult task either.

While the mount and the locking pin hole may be standard, There are many variations in the EF mount with different numbers and placements of the mounting screws. Finding one that matches those and where the rear baffle aligns and fits properly is another thing altogether. I would contact Midwest Camera Repair and see what they have to say.

Oct 12, 2023 at 09:03 AM

rscheffler
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p.1 #4 · p.1 #4 · Canon EF lens mount repair

I'm not sure the part you highlighted on the mount of your lens is the sole reason for the additional looseness.

The EF mounts on super-tele lenses have a reinforced locking pin hole and it appears the small reinforcement 'ring' inside the locking pin hole of your lens is still present, though it appears larger and slightly elongated compared to the 'found' photo you posted of a different lens.

The elongation of the locking pin hole is to be expected given the age of your lens (23 years based on the date code) and would result in some play between the camera and lens. But there is also a small 'post' (or stopper) that should be present under the lip of the mount flange just below the locking pin hole (but wouldn't be visible in your photo). Please see the photo of my 200-400 below. The small post is just under the mount flange diagonally up and to the right of the locking pin hole. Is this present on your lens?

I believe this post acts as a stopper to block the camera's mount flanges from further movement and preventing over rotation when mounting the lens on the camera. If it's not present, the elongation of the locking pin hole combined with the slight flex of the locking pin and the amount of mass involved, could be the reason for the additional amount of play.

I initially thought this post was a screw that could be easily user-replaceable so that you might be able to order it from Canon's part department, rather than have to replace the entire mount. But I had a closer look at it with a 15x magnifier and it does not have any kind of slots in it that would fit a screwdriver head. It's possibly attached from the inside of the mount. And I'm not sure if it's a separate part that could be ordered from Canon's parts department.

Assuming this is the problem and it's a serviceable part, and if you're willing to do some disassembly, you might be able to buy a cheap beater or 'for parts' EF lens as a donor for that post and transfer it to your 400/2.8. A place like Midwest should be able to better advise you of available solutions.

Oct 12, 2023 at 10:07 AM

ctowle
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p.1 #5 · p.1 #5 · Canon EF lens mount repair

Guys,
Thanks for the replies. I will need to look when I am home to answer the question. Good insight.

Oct 12, 2023 at 10:18 AM

AmbientMike
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p.1 #6 · p.1 #6 · Canon EF lens mount repair

If you spent half an hour calling different repair places I'd bet you'd have a much better idea, it does look easily replaceable. My guess is , this part is made to be replaced once the lens develops play over time in pro use vs having to replace the entire mount. It doesn't look like you could just buy an old 28 90 or something, take the mount off, and have the exact same thing, though imo

Have an old 3rd party lens that developed a bit of play in the mount, so I rotate it if it gives an error, probably makes the connection then. I could probably use the 400mm lens, carefully, realizing it's probably more prone to damaging the camera pin or something. Are you getting any errors?

I'd try keh repair, one in Rhode Island looked good, and any local repair places, in addition to Midwest. Doubt it's a difficult repair but hopefully you can get more info. hopefully it's the same as mounts on other lenses as opposed to some esoteric focusing motor or something specific to that lens

Oct 12, 2023 at 11:37 AM

Photonadave
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p.1 #7 · p.1 #7 · Canon EF lens mount repair

The little stop pin is not shown in the parts list for your age lens, an EF400mm f/2.8L IS USM, so I conclude that it is an inseparable part of the Lens Mount.

The Lens Mount part number is YF2-0128-000 that is also shared on the EF600mm f/4L IS USM, EF300mm f/2.8L IS USM and EF400mm f/4 DO IS USM. I took a quick look and do not see it used on any other large lenses from that era.

Oct 12, 2023 at 11:43 AM

justashooter
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p.1 #8 · p.1 #8 · Canon EF lens mount repair

You can purchase a replacement mount at Canon Parts. The part # is YF2-2049, that part # has replaced the original part # YF2-0128. They are $80 plus shipping and handling, they are sometime out of stock but get them in regularly. That mount fits at least the 300, 400, 600mm IS lenses. I would also replace the 4 screws that hold the mount. It looks like someone has used a Phillips screwdriver to tighten them and buggered them up, instead of the correct Japanese Industrial Standard screwdriver (or crosspoint), that seats into the screws correctly. You need to get a set of JIS screwdrivers. I can give you a step-by-step on the replacement process. I have replaced a number of these over the years on my lenses and friends lenses, especially since Canon (and independents) have quit repairing them. It is not that difficult to do. Canon Parts Dept. # is (866) 481-2569‬‬‬ Option 3. You can confirm the part # and get the correct screws, with the advisor on the phone. The pin mentioned in previous posts is press fit into the mount and can come out.

Oct 12, 2023 at 12:49 PM

ctowle
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p.1 #9 · p.1 #9 · Canon EF lens mount repair

Hey Everyone, I greatly appreciate all of the replies and details. I have ordered the lens mount kit and screws today and I will have it next week.

@justashooter - If you don't mind sharing the step by step instructions I would appreciate it greatly.

I will pickup a JIS screwdriver set on amazon. I bought this lens a few years ago and don't have the history on the lens to know who buggered the screws.

Thanks!

Oct 13, 2023 at 02:25 PM

goalerjones
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p.1 #10 · p.1 #10 · Canon EF lens mount repair

Didn't even know about JIS tools. Just ordered regular and micro tool sets for our PC needs and other issues that now make sense. I had a feeling something wasn't right when I was tightening down my 100-400 and kept feeling the philips slipping.

Oct 19, 2023 at 03:57 AM

ctowle
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p.1 #11 · p.1 #11 · Canon EF lens mount repair

Hey everyone,
Just a huge shoutout @justashooter on the guidance and phone consult. I was able get the parts ordered and mount assembly fixed and all is good. Had to do a small amount of additional sanding to get things to fit and all is good. I am shooting a football game tonight and am excited to have this thing back in action!

Oct 19, 2023 at 02:18 PM


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