Metering on Olympus OM-1.....Way off!!

Discussion in 'Camera Building, Repairs & Modification' started by Mike Kennedy, Jul 28, 2010.

  1. Mike Kennedy

    Mike Kennedy Member

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    (Kindly let me premise this post with a special thank you to our own Jon Goodman (Interslice light seals).Without his assistance I would not have been able to figure out the method of resealing this particular camera.It was prompt and it was free.)

    Newly resealed,mint cosmetics but my recently acquired OM-1 meters terribly.It is totally out of whack when compared to my Nikon FE2.
    What should I look for?

    Mike
     
  2. E76

    E76 Member

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    Is the battery fresh? The OM-1 was designed to use mercury cells, which do not exhibit the voltage fluctuations that the alkaline batteries do. The OM-1's metering system is very sensitive to these fluctuations. In order to ensure accurate metering at all times, you can either have your camera converted to use alkaline cells, or use a zinc air battery such as a Wein cell. Zinc air batteries have a discharge curve very similar to the old mercury cells.
     
  3. lxdude

    lxdude Member

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    It can be adjusted to use silver oxide cells too, right? More stable voltage curve than alkalines.
     
  4. Steve Smith

    Steve Smith Subscriber

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    To use silver oxide cells it will need either an adptor with a schottky diode to reduce the voltage or the camera can be modified to have the diode fitted internally in series with the cell connection.


    Steve.
     
  5. lxdude

    lxdude Member

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    I thought there was a potentiometer to adjust the meter. Guess not.
     
  6. Ulrich Drolshagen

    Ulrich Drolshagen Subscriber

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    Sorry, no help with the metering. But you should know that you'll find the same goo to which the lightseals degraded inside the camera around the prism. It will eventually destroy the prism so this should be changed too. May be you could talk to John Hermanson from zuiko.com about a CLA. The camera is worth it.

    Ulrich

    PS haven't seen that you are located in England. So you might consider Frank Timmann at om-doctor.de. There may be someone knowledgeable in UK too of cause.
     
  7. John Hermanson

    John Hermanson Member

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    Alkaline battery creates non-linear readings. Camera can be converted to use silver oxide battery (ms76 type). There is no potentiometer inside for adjustment. Fine adjustment is done with eccentric. Use open cell foam for resealing. John
     
  8. lxdude

    lxdude Member

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    So the galvanometer has its own adjustment, right? Heck, IMO that's even better. If that's the case, then adjustment could easily be done along with other service.

    Or does eccentric refer to the repairman?:D
     
  9. MPandolfo

    MPandolfo Member

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    Time ago, for little money, I bought a used OM-1 in excellent cosmetic condition excepting the leatherette and seals (I thought). Interslice (Jon Goodman), CameraLeather (Morgan Sparks) and a C.R.I.S. adapter took care of the easiest part of the overhaul/update.

    But I had a similar problem with a grossly misaligned (but working) light meter. After fumbling for a while, I realized that someone (not me) had mounted incorrectly the ASA indicator disc on the ASA dial. So, when I set a film speed of ASA 400, the camera calculated an exposure for a, let's say, ASA 25 film.

    Check if meter readings are self-consistent (speed vs aperture) and repeatable, if so, there is a possibility that you are having the same problem. Its very easy to mount this disc, just glued to the dial, in any position you want, but only one is correct.
     
    Last edited by a moderator: Jul 28, 2010
  10. CGW

    CGW Restricted Access

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    I'd check at photo.net(search "PX-625" or "mercury cells")for a trove of info on how to cope without merc cells. Given the dearth of capable repair guys in 2010, I'd try using zinc-air cells rather than risk totally botching the meter with "recalibration" surgery. As long as you stick to C41 films their huge exposure latitude will cover your Oly's meter being off a stop+/-. Few cameras that age escape age-related metering issues, so as long as it's off but linear you'll be OK.
     
  11. Rick A

    Rick A Subscriber

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    I use a Wein cell in my OM-1n and have no problems with the meter. It shows spot on with E-6 films and B&W, so I will recommend using them.
     
  12. Mike Kennedy

    Mike Kennedy Member

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    Thanks folks.
    Made a rookie mistake.The battery was almost dead.Checked out everything else but forgot to see how much juice left in the cell.Dah.......
     
  13. lxdude

    lxdude Member

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    Read and heed all ye rookies and not so much rookies and forgetful old farts. :D

    It's always great when the solution is so simple. I'll always take embarrassment over hassle or expense.

    I've Homer Simpson'ed enough times it's a wonder my forehead isn't flat from smacking it.
     
  14. wiltw

    wiltw Subscriber

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  15. wiltw

    wiltw Subscriber

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    The problem with the OM-1 is that how much the meter is inaccurate is dependent upon at least these two factors: A) actual battery voltage being output at the time of reading, and B) HOW MUCH LIGHT the reading is being made in.

    As a result it is impossible to simply compensate. Use of Wein air cells, or use of MR-9, or permanent installation of an electronic modification are the only available solutions for the OM-1
     
  16. CGW

    CGW Restricted Access

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    It's an old camera and the sensors fade. My old Nikon metered finders are all out by a stop, same goes for a couple of Minolta SRT 101s and Nikkormats. All show this with fresh batteries and in all light levels. It's the price you pay when shooting with a relic--live with it or get something newer.
     
  17. lxdude

    lxdude Member

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    He said it turned out the battery was almost dead.
     
  18. Mike Kennedy

    Mike Kennedy Member

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    Since I've touted the great service from Jon Goodman and his light seal kits I'm going with his Tri-Dot Battery Adapter.Uses cheap & readily accessible #675 zinc air hearing aid batteries.Correspondence sent to Jon,money to follow.
     
  19. John Hermanson

    John Hermanson Member

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    I'd say cds failure or weakening in OM-1/1N is less the 0.5%. EXTREMELY rare to have to replace the cds cells. Eccentric screw on meter maybe gives you a one stop adjustment arc. I solder a schotkey diode into the meter circuit to replace the MR9. Some repair shops "adjust" the meter by regluing the asa plate in the wrong position. This works in some ways but you lose some of the high or low asa settings (because plate is wrong position). John