CANON A-1 Over-Exposes now -- help needed !

pentaxpete

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HELP ! My 'Gift' A-1 has developed an exposure fault when used in AV or TV auto modes -- it OVER-EXPOSES by 1.5 Stops ! I had Kodak Ultramax 400 outdated loaded and rated it at 250 ASA as it was outdated but the negs were so DENSE -- I found to get the same reading as a Hand Held meter I had to set ASA to 800 !! Any IDEAS ? I can take off base-plate with correct JIS Screwdriver OK -- do you think the magnet surfaces may need clean ?
 

Nitroplait

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Just verify the readings from the A1 next to a reference meter you trust, and adjust iSO accordingly on the A1 to match. If the readings are corresponding in linearity everything is fine, if not - use a handheld meter instead or send the A1 out for repair, as simple as that.
 

koraks

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pentaxpete said:
the negs were so DENSE -- I found to get the same reading as a Hand Held meter I had to set ASA to 800
Click to expand...

Eh? Your camera overexposes, but it gives the same reading as a meter set to 800, which would result in underexposure. Or am I missing something crucial?

Anyway, replace the battery in the camera and see what happens.
 

Andreas Thaler

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pentaxpete said:
I can take off base-plate with correct JIS Screwdriver OK -- do you think the magnet surfaces may need clean ?
Click to expand...

No, please don't do that, the magnets have nothing to do with exposure problems, they only release the shutter, mirror or even the aperture. They either trigger or they don't. It's best to wait and see what solutions come up here. The A-1 is highly complex, so every step should be thought about three times.
 

Chan Tran

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First to verify if the meter is correct. The OP said he had overexposed, dense negative but the meter set at ISO 250 gives the same reading as a handheld meter set at ISO 800 so it doesn't make sense. We need to verify this first and the possibly the shutter speeds.
 

cmacd123

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the A-1 was about the first camea that uses an all digital exposure set up. the photocells drive an A2D converter, and the microprocessor figures out the exposure. needless to say, any adjustments have to be by the book, and probably require accurate test gear, if you don't want to make things worse.

splurge on the Manual from "Learn Camera repair" (I think he still only wants a dollar) and read the part about calibration. I think you will be Glad to send it off to a A-1 Expert.
 

BrianShaw

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Great advise in this and many other situations!
 

Laurent

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Some time ago my AE1P developped an erratic behaviour when metering. The culprit was the ASA setting dial, which was oxidized. Before the CLA I was able to get it to work better by turning it fast across all the range
 

Andreas Thaler

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The Canon A-1 is technically fully covered in the Sep./Oct. 1981 issue of SPT Journal, just published on Learn Camera Repair:

SPT Journal: September-October 1981

Society of Photo-Technologists Journal
learncamerarepair.com


Finally, in addition to Canon's service manual, we have now a complete technical description of the A-1, which gives us further insights and repair options, especially on the electronics
 

wiltw

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Not quite clear which of these applies to OP issue....
  1. difference of METER reading
  2. differency of EXPOSING (even per handheld meter of know accuracy)
If #1, it could be use of wrong battery type, or need for meter re-calibration, or defect in electronic circuit part
When comparing two meter readings, one needs to NULLIFY any difference of angle of view of the ,meters...aim both meters at a uniformly colored and uniformly illyuminated area (blank wall)

If #2, it could be mechanical timer movement or sticky shutter movement issue, or lens diaphram closing issue... all of which could be need for cleaning + fresh lubrication.
 
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koraks

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wiltw said:
Not quite clear which of these applies to OP issue....
Click to expand...

Good call; it's important to distinguish between these two issues. I've read it as issue #1, resulting in overexposure.

wiltw said:
or lens diaphram closing issue
Click to expand...

That in particular is a good one, too; I've had it happen on some older Mamiya equipment with sticky aperture blades.
 

Chan Tran

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According to the OP if it's #1 then it would be underexposure not overexposure because the meter read the same at ISO 250 compared to a handheld meter at ISO 800. But the OP negative was overexposed so the OP needs to correctly determine what.
 

mshchem

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Do you have any reason to suspect over development? Fresh batch of developer without starter, maybe something like that?
 
OP
OP

pentaxpete

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NO -- I put it away for a time as over Christmas I have been giving my CONTAX RTS II Quartz an outing .
 

Dustin McAmera

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At the risk of stating the obvious, the A-1 has an exposure-compensation dial alongside the film-speed dial. Check that you haven't left that with an offset. If not, it could be the film-speed or the compensation dial that's misbehaving.
There's also the exposure-memory button beside the lens-mount. If that was stuck down, I guess it would affect all subsequent exposures.
 
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