Canon A-1 Maximum Aperture Question

[john_zwick]

Several years ago, my Canon A-1 was stolen. I recently located my

old FD 35-105mm 3.5 lens and decided to purchase a used Canon A-1

camera on eBay so that I could try it out.

 

It has been a while since I used this equipment (I liked the camera a

lot when I owned it), but I have noticed something that seems odd

with the lens maximum aperture and thought that someone could help me

to confirm the problem.

 

The used camera I purchased came with a 50mm 1.8 lens. The maximum

aperture sensed by the camera seems to work fine. When I try to set

an aperture of 1.4, the camera still reads 1.8 (works as the manual

says). However, when I attach the 35-105 3.5 lens, the camera thinks

that the maximum aperture is 2.0 (this seems contrary to the expected

operation in the manual). I don't recall seeing things work this way

on my original camera, and my lens hasn't been used since my original

camera was stolen.

 

It seems that there is some type of adjustment problem with the max

aperture linkage pin. I don't really understand how the problem can

appear with one lens and not the other. Could the problem be with

the 35-105 lens? The used camera I purchased was serviced by a

camera technician prior to sale and is still under a 30 day warranty.

If the issue can be isolated to the camera, I might have a chance of

arranging a repair or refund.

 

Would certainly appreciate any advice.

[aki_dick]

I don't have a A1 but a F1N and some of them seem to suffer from a related problem, the aperture indicator being off for half a stop.<br>I notice this only with some of my lenses, while others work perfect. And all the lenses work perfect on another body.<br>But as mentioned the abberation is only 1/2 f-stop, and not 1 1/2 like you described. I was told by a camera technician, that this is not easy to fix.<p>"The used camera I purchased came with a 50mm 1.8 lens. When I try to set an aperture of 1.4, the camera still reads 1.8"<p>Is there a typo somewhere? How else can you set a 1.8 lens to 1.4?<br>Anyway, while I can't speak for the A1, I would take the camera back and try with some other lenses. And take your 35-105 with you and try that one with another body.

[awahlster]

This is a known problem with the LENS what has happened is the Max aperture signal pin (It is approx 3mm in diameter and located at the 7:00 position with the red dot at 12:00 looking at the lens from behind). This pin is to short and as a result signals the camera body an inaccurate Max available aperture. (A note here I have as yet never heard of this problem going the other way the pin signaling to small of Max aperture but it is possible if the pin is to long)The problem has been corrected by many simply by placing a single layer of black electrical tape on the end of the pin there by lenghtening it. (I would use a pc. of black paper and a tiny drop of glue for a more secure fix)The problem is not with the Camera body as long as one or more of your lenses work properly.One thing about this temp type of repair is it can be done by anyone who can handle tape and is totally undoable if it should turn out that some other problem (not known to me) has caused the problem.

 

As to the second posters question HOW DO YOU SET A F1.8 lens to F1.4 the Canon A-1 having aperture priority as one of it's 6 metering exposure modes allows the aperture to be selected with the control wheel (when in shutter priority this wheel is the shutter speed dial) So John is just selecting an aperture with the wheel not the lens as you would have to on an F-1.

 

Hope this helps,

 

Mark W.

[alan_swartz]

John,

 

There is an adjustment for the maximum aperture sensor in the body, but it will of course affect any lens you mount. (It is locked with a thread-locking compound that must be dissolved before readjustment.) If your error was small, the camera might be on the borderline between two max aperture readings. I have a T90 that suffers from this. I doubt that's what's happening here, though.

 

The T90's maximum aperture sensor is composed of multiple switches that close in a certain pattern as the plunger is depressed further and further. The camera looks at the switch closures and decides which lens is mounted, similar to the way the DX sensor in the film chamber "reads" the DX code from the film canister. If the A-1 is the same, and I suspect it is, one or more of the switches may be oxidized from disuse, sending the camera false information. The offending switch may be needed for the 35-105, but not the 50.

 

Just this week, I dug out one of my old A-1's to find that it wouldn't enter stopped-down metering mode. Exercising the stop-down slide eventually brought it back to life.

 

It may be worth your while to exercise the max aperture plunger. It's easy to depress with a pencil eraser. Give it a good workout and see what happens. I've also heard that the manual/automatic switch will oxidize, and can be treated with the same method.

 

It stands to reason that these switches would become unreliable with disuse. It's the same as volume controls and switches in older audio equipment becoming noisy. Most switches are "self-wiping" designs that polish their contacts when operated, so disuse is more likely to cause problems than constant use.

 

You're right, the camera should not set a maximum aperture larger than the maximum on the lens in use. The camera knows that the lens' maximum aperture lies between f/5.6 and f/1.2, based upon the distance the plunger is depressed. The only way your 35-105 could indicate f/2.0 is if the pin is somehow far longer than it should be. I measure the f/3.5 pin at about 0.043" and the f/2.0 pin at 0.080"--twice as long.

 

Good luck!

[alan_swartz]

John,

 

I just looked this up in the A-1 service guide. The camera does use a brush-type switch with four poles to determine maximum aperture. Comparing the switch closures for apertures of 3.5 and 2.0 yields what is probably our answer: three of the four poles are the same for the two apertures; only one of the four is switched opposite, and it is open for f/2.0, closed for 3.5. That would seem to prove the theory. One of the four brushes is not making contact. Exercise that sensor and let us know if it starts working again!

[john_zwick]

I want to thank all of you who provided some ideas to try to help with my situation.

 

As suggested, I have tried to exercise the max aperture plunger without success. I suppose that it is possible that the identified pole of the brush switch has failed to the point that exercising won't help. I studied an online version of the service manual and realized that this particular pole also remains open for an aperture of 1.8, so the problem won't show up with my 50mm 1.8 lens.

 

My last step is to try swap lenses and cameras and see if I can pinpoint the problem to a specific piece of equipment. I will see if I can locate a camera shop to help with this. I am certainly not a camera technician, but I think that everything is pointing to the camera body. Considering that there is still a warranty, I should probably contact the seller and see what can be arranged.

 

Thanks again for the advice. I am more savvy now and at least can eliminate some possible causes. If anyone has more suggestions, then please let me know.

[pensacolaphoto]

Hi,

I would take camera and lens to a camera repairman for a quick look at the problem. Most likley, there will be at most a $20 fee or less for correcting this error. Good luck.

[vesa_perala]

John, you could try the following. I had an A-1 perhaps 20 years ago so my memories of operating it are not that accurate anymore:

 

Adjust aperture 1.0. While looking through the viewfinder push the max aperture sensing pin in the camera body (don't touch the mirror!). My understanding is that the aperture value should change from min to max (or vice versa) nicely (1.0 - 1.2 - 1.4 - etc) if everything is working well. At least you should be able to see if it behaves oddly.

 

Vesa

[john_zwick]

Thanks again to all who responded to my question.

I did set the aperture to 1.2 and depressed the max aperture adjustment pin.

 

The aperture reading in the viewfinder changed from 1.2 to 2.5 smoothly and then 2.5 back to 1.2. Out of the four switches that determine the maximum aperture, one switch must be closed for any reading above 2.5. This is the switch that I think is not closing. I think this confirms the symptom and theories presented for this issue and isolates the fault to the camera body. A technician would have to confirm the exact switch failure.

 

I think it is time to explore the warranty still on the camera.

[nic_olas]

Hi, did you ever resolve this?

I have picked up an A1 and have a similar situation. The body readys EVERY attached lens a stop smaller than the max aperture; an f1.4 lens is reading as an f1.8 max, and f4 reads as a f5.6 max etc.

I feel like the pin isnt being engaged properly by any attached lens. Any help would be great!

Thanks

 

Edited March 22, 2023 by Grim Nicholas