OM-2n overexposing

Discussion in 'Camera Building, Repairs & Modification' started by DutchShooter, Aug 19, 2009.

  1. DutchShooter

    DutchShooter Member

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    My OM-2n (which has been very happy for the last six months or so after CLA) just developed a new problem: it overexposes every shot with about 1.5 stops. I checked all the obvious and have the feeling I'm missing something very easy/stupid....

    -Batteries are 4 months old and give 3.1V, battery terminals OK
    -Lightmeter of om-2n is completely the same as my handheld calibrated meter (in both auto-mode and manual-mode).
    -Overexposure happens both with open and closed aperture (same density for zone V exposure @ f/1.4-1/1000 or f/22-1/4). it happens with all my 3 zuiko lenses.
    -Happened on 3 different brands of film in 2 different types of developer
    -Developed a roll of APX-100 from my om-2n together with a roll of APX-100 from my canonet-28 in 1 tank: roll from canonet was perfect, from om-2n overexposed by about 1.5 stops.
    -No exposure compensations set.
    -No difference between auto-mode and manual-mode. In auto-mode a long exposure (5 seconds or so) gives exactly the same overexposure.

    What am I missing???
     
  2. BetterSense

    BetterSense Member

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    You say the lightmeter of the OM2n is the same as a handheld meter. If it's overexposing even in manual mode, the only conclusion I can come to is the shutter is sticking or staying open too long. Do you have a shutter speed tester?
     
  3. Steve Smith

    Steve Smith Member

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    Or it's a bit slow stopping down the aperture blades.

    EDIT:
    Possibly not then!


    Steve.
     
  4. John Hermanson

    John Hermanson Member

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    Are these B&W films? I'll guess that as you mention using different developers. Overexposure would have to be determined by running all the films through a densitometer to read dmax and dmin. A "perfect" exposure may be off but one that you are used to printing with. Your other cameras may be underexposing. Usually viewfinder indication is adjusted independently of actual exposure. They should match but in this case who knows. I seriously doubt manual speeds are off 1.5 stops consistently. Oily magnet will cause over-exposure but it is usually very erratic and unpredictable. Oily magnet would affect auto too, but would be just as erratic. Alkaline batteries (A76 and LR44) are the wrong type for the 2/2N and can cause meter needle errors of 2 stops or more. In this case, auto can be correct, but shutter lockup may result. Alkaline and lithium batteries (also wrong) came out after the camera was designed. 2/2N was designed around silver oxide 1.55v batteries (357, SR44W, G-13, MS76, KS76, 303) and are the only ones that should be used. John, www.zuiko.com
     
  5. DutchShooter

    DutchShooter Member

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    Hi BetterSense. I tried testing the shutter with the TV-method. I found it hard to diagnose, they looked more-or-less ok, but it's hard to see precisely...

    John, thanks for the informative reply! During the last CLA, oily magnets were cleaned (I had a problem with a way too long shutter time on the first exposure of the day back then).
    I use APX-100 in rodinal 1+50 for all my cameras since a month or 2. At first all cameras were giving OK exposure (my notes of 6 weeks ago when I did some testing say: Zone I = 0.25 (base+fog=0.15), zone V = 0.75, zone VIII = 1.35, zone X = 2.05), but since 2 weeks only the OM-2n gives overexposure (all zones give a higher density), even though I kept using the same film/dev-combination...I just tried two other types of film and another developer to be sure that that was not the problem.
    I just bought some fresh silver oxide cells today (v76px, same as the old cells). Even though the old cells are relatively new (4-5 months), their expiry date was sep/2009 and I used the camera quite intensely (about 3 rolls/week). New cells have expiry date nov/2011. I will test the camera tomorrow (I won't look at the exposure needle for now, just put in the aperture/shutter speed I read from my light meter).
     
  6. verney

    verney Member

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    It should be simple to spot 1.5 stop over exposure by ear if it's a shutter problem. Just take a shot where metering needle indicates 1s. Difference between 1s and 3s is easy hear.
     
  7. DutchShooter

    DutchShooter Member

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    I just tried with the new batteries a test shot on an indoor wall which needed an 1 second exposure wide open (zone V). It really sounded like 1 second, so time seems ok. As the shot was wide open, if the negative is still overexposed, it must be my development...I guess.
     
  8. Poisson Du Jour

    Poisson Du Jour Member

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    My first choice for checking exposure would be through the use of reversal film where any gross over- or under-exposure will be patently obvious and immediately negates post-exposure (processing) errors. Negative film has a lot more latitude than reversal and this is where judgement of over- under-exposure can be prejudiced.

    As you have repeated tests using all the Zuiko lenses you have, a good idea would be to run a test on a lens you do not have (loan one, if possible) i.e. a Sigma or another, different Zuiko. If the tests return the same fault, the shutter curtain (already a suspect given the age of the camera) and the TTL meter need to be examined. I wouldn't leave it to guesswork especially if at some stage you have an unexpected, important assignment, but to nail the problem run a roll of reversal film through it and beside normal exposure, key in N (normal exposure), +0.5 and +1.0 stop, then N, -0.5, -1.0. Errors from these settings will be quite alarming on reversal film (given its characteristic narrow latitude).
     
  9. DutchShooter

    DutchShooter Member

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    Checked my negs and they are perfect again. Zone I density 0.12 above fog, Zone V 0.74, zone VIII at 1.36, and zone X at 2.03.
    After my regular rest-wall, I also made some photo's of some real-life scene again (the kids): they also look normal again :smile:
    So the batteries were at fault probably!

    Thanks all for your help!
     
  10. DutchShooter

    DutchShooter Member

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    PS, out of curiosity, I shot until zone XV. Up till zone XII, there were measurable density changes, from zone XII-XV the density change is about 0.1 (for APX-100 in rodinal 1+50)
     
  11. John Hermanson

    John Hermanson Member

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    Wrong batteries in the 2N will affect meter needle position but have little effect on auto otf exposure. If magnet was not cleaned with the proper solvent it is still oily and may cause overexposure which increases with how long the camera has been sitting unused (with the shutter cocked). John
     
  12. DutchShooter

    DutchShooter Member

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    Hi John, thanks for the info.

    I may have an alternative explanation. The last 2 weeks in which I had overexposed shots, the room temperature was around 35 deg C in the room I use for developing. And it may be that developing temperature may have been a few degrees higher than normal...which may have caused the problems. I will have another look at the "problem negatives" to look whether the problem is overexposure or overdevelopment. During these two "hot weeks", I developed 3 rolls of the om-2n and just one of the canonet and none of my other cameras...

    Anyway, I'm now in China for work for a a few days. I've shot quite a few rolls here. I will develop them when I get back home and hopefully see whether they are OK or not...
     
  13. John Hermanson

    John Hermanson Member

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    So you're saying you develop B&W film assuming the developer is the correct temperature and don't check it with a thermometer? ahem.....John
     
  14. DutchShooter

    DutchShooter Member

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    I use a thermometer to mix tapwater at exactly 20 degrees for rodinal. However, tank and film are at room temp and during my 17 min development, I leave the tank at room temp. Normally, this works ok, but maybe at these high room temperatures, the tank with the developing film increases enough in temperature to cause overexposure.