Nikon F Photomic Meter way off (i think?) with 1.5v batteries

Discussion in '35mm Cameras and Accessories' started by shootfilmto, Oct 8, 2017.

  1. jim10219

    jim10219 Member

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    This would be my first thing to check. The difference in battery voltage wouldn’t make the readings that your experiencing. You’ve got another electrical issue. It could be a loose wire or corrosion somewhere, but potentiometers (or electrolytic capacitors if there are any) are the most likely culprits on old circuits. They combine exposed elements subject to oxidation and moving parts that create wear and tear.
     
  2. cooltouch

    cooltouch Member

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    I neglected to mention in my above comments about the 1.4v 675 hearing aid battery that it needs an adapter to work in an F meter.The 675 has a smaller diameter than the old 1.35v mercury battery. The F meter picks up the + voltage from the side of the battery, not the top. There are people who sell adapter rings to make the 675 as wide as the original, Jon Whatshisname of "Interslice" fame being one. For my F's meter, I took a piece of 14 ga copper wire that I stripped out of a piece of household wiring and then wrapped it around the battery. It's kinda clunky but it works.

    More recently, I bought a camera outfit and the camera had a dead Wein cell in it. I was able to determine that all that Wein cell is is a 675 battery with an adapter set in place. I was able to knock the 675 out of the adapter ring with a few well-chosen whacks. So now I have a best way of getting my F's meter to work reliably. It was kinda hit-or-miss with the copper wire.
     
    Last edited: Nov 23, 2017
  3. wiltw

    wiltw Subscriber

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    No, a Wein cell is a zinc-air cell, like hearing aid batteries!
    You probably have a Criscam MR9 adapter https://shop.criscam.com/products/mr-9-mercury-battery-adapter
     
  4. cooltouch

    cooltouch Member

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    The 675 is a hearing aid battery. I buy cards of 48 of them at Costco for less than $10. I'm too big of a cheapskate to buy a CRIS adapter.
     
  5. OlyMan

    OlyMan Member

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    There is no such thing as a 'one fits all' compensation setting, because different light levels require different amounts of compensation. The best solution is 1.4V zinc-air hearing-aid batteries.

    I had a huge row about this once with an online 'specialist' who offered Olympus OM prism-foam replacement and 'meter recalibration for 1.5V': I only wanted him to replace the prism foam and leave the meter settings alone but he refused to split the jobs and quote me for just the prism foam. Said I was a moron for not wanting the meter changed. You can probably guess he didn't get the job.
     
  6. Exopix

    Exopix Member

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    I am not sure I follow you here. The 1.55V silver oxide battery, like the mercury battery, has a constant, albeit higher, voltage. So the meter deviation ratio must also be constant, regardless of the light level, and thus it would be possible to compensate with the ASA-setting, right? That's my theory.
     
  7. OlyMan

    OlyMan Member

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    No, sadly not. The only sure-fire solution would be a voltage regulator that drops the voltage, and the voltage regulator would also need to compensate for the fact that the voltage from the battery trails off as it depletes, hence the battery-check function in cameras that don't use mercury batteries.

    It all seems a bit moot and over-thinking the problem when zinc-air ZA675 hearing aid batteries have been so readily available, for at least as long as mercury batteries have been banned, if not longer. If your camera or device takes the +ve from the rim of the battery instead of from the face, you possibly will need an adapter that expands the diameter of the ZA675 cell. They are easily available and are of course completely re-usable when your battery is exhausted.
     
    Last edited: Nov 24, 2017
  8. Exopix

    Exopix Member

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    But the problem with the ZA675 is that they don't last very long, 2-3 months depending on temperature, and they are 1.4V or 1.45V (depending on what brand). Maybe you meant the Wein Cell MRB675, produced especially for camera use, that is 1.35V and lasts about 9-11 months?
     
  9. OlyMan

    OlyMan Member

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    Wein cell is over priced. I once wasted a staggering £7 on one only to find it lasted the same 3-4 months as the 1.4V ZA675's I buy online for £2.99 for six. Pack of six ZA765's can last me 18 months to two years.
     
    Last edited: Nov 24, 2017
  10. wiltw

    wiltw Subscriber

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    I did testing about 20 years ago, using a PX-13 (mercury) and a PX-625A (alkaline) So I was able to use it to compare 1.35v HgO vs. 1.5v alkaline. And I did find variability in the amount of error related to the brightness of the scene being metered.

    I still have one usable mercuric oxide battery! Following measurements were less than a year ago, done in EV10 ambient light, as measured with Minolta Autometer Vf (I mention this because I know the amount of error is dependent both upon battery voltage and level of light being measured.)
    • OM-1 with PX625 mercuric oxide with 1.34V output (yes, I still have one of those!) reading 18% gray card = baseline reading (0EV)
    • OM-1 with PX625A (alkaline) with 1.48V output reading 18% gray card = -0.5EV
      (camera thinks more light is present than when measured with genuine PX625
    Since the amount of error is dependent both upon battery voltage and level of light being measured, it is not possible to use a simple offset via an ISO value faster/slower by a fixed amount. In bright light I measured a 1.5EV error
     
  11. cooltouch

    cooltouch Member

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    Wilt, might your results have been different if you would have compared the 1.35v mercury cell against the 1.5v silver-oxide cell? The latter is reported to have discharge characteristics more similar to the mercury cell.

    One thing I really like about the 675 zinc-air hearing aid battery is its discharge profile is almost exactly the same as that of the original 1.35v mercury battery. The alkaline discharge profile is subpar.

    I've been using 675s ever since the 1.35v mercury cells were banned. True, they don't last very long, but so what? They're so cheap it scarcely matters. As I mentioned above, I buy cards of 48 at Costco for less than $10. If you don't have a Costco card, you can still buy them cheap enough at your local grocery store or drug store, like Walgreens or CVS. Their prices are a lot higher than Costco, but still, for the price of one Wein battery, you can buy six or more 675s at the drug store. What I do with the ones I buy at Costco is I cut off a portion of the card of batteries -- let's say the part I cut off has six or eight batteries in their bubble packs. I just put this card fragment in my camera bag so I always have spares. If it's been a while since I've used a camera that takes these batteries, as a matter of course, I just pop in a new one so I don't have to worry about loss of battery power during the middle of my shoot.

    The cameras I use most that take the old mercury batteries are my old Canons -- original F-1, FTb, and EF. The original F-1 has a meter that is very accurate. With a fresh 675 loaded in my old F-1, it agrees exactly with my Luna Pro F handheld meter. That's plenty good enough for me.
     
  12. wiltw

    wiltw Subscriber

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    The voltage decline characteristic might be a bit less variable on Silver Oxide, but that merely changes the point on the slope (and for how long) the battery is at 1.5v vs. at 1.41v...IOW the error will be different, but the error will be there nevertheless. The difference would be that the Silver Oxide is more constant and unchanging because its voltage is fairly flat for most of its life, whereas the variability of the alkaline mades that error variable as well. But since the error is also dependent upon the brightness of the scene a contsant error induced by 1.5v is nevertheless variable with BRIGHTNESS.

    [​IMG]
    image from http://www.rokkorfiles.com/minolta/pix/batterychart.gif
     
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  15. cooltouch

    cooltouch Member

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    Yeah, you can't ask for a much flatter discharge curve than what zinc-air provides. And alkaline's s-shaped curve is precisely why I don't like using the 1.5v alkaline cells in my Nikons and Pentaxes.
     
  16. Exopix

    Exopix Member

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    Tested the Nikon F now (that I mentioned above). The Photomic Ftn meter acts really strange. Apart from that the needle is a bit jumpy sometimes (there are some traces of battery leakage in the battery compartment so that could be the reason) it also shows totally wrong values. Compared to another reliable camera it is about 5+ stops wrong(!). Like if the other camera shows 1/125 and f 2.8 this says f16(+).
    I installed ZA675 hearing aid batteries in adapter rings and they are 1.45V so a bit to high, but I don't think this misreading could be explained in all by that. What do you think, could cleaning the resistor ring inside help?
     
  17. wiltw

    wiltw Subscriber

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    The Photomic linkage to the lens index pin swipes across a linear potentiometer, and after five decades it is not surprising that there may be some built-up oxidation along the potentiometer. It might be useful to slide it back and forth a number of times to burnish the surface of the pot to decrease the amount of resistance which is being presented
     
  18. Exopix

    Exopix Member

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    Thanks, I will try that and also some deoxit cleaning.
     
  19. E. von Hoegh

    E. von Hoegh Member

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    The resistor is actually a ring. You meter is behaving oddly, reading way too high. That and the jumpiness makes me suspect the ring is worn out, but one can be sure only by measuring the resistance.
    Cleaning it can do no harm, but please remove the ring from the finder - spraying Deoxit into the finder will only lead to a mess.
     
  20. Exopix

    Exopix Member

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    Damn, can't unscrew one of the 4 screws to get access to the ring resistor. The screw of the head got damaged (soft metal it seems) when i tried to unscrew it...
     
  21. E. von Hoegh

    E. von Hoegh Member

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    Not soft metal, your screwdriver doesn't fit. The blade must fill the slot, both width and thickness, and go all the way to the bottom of the slot. Otherwise it will twist out of the slot and damage the screw. Sometimes these screws are cemented, a tiny dab of acetone and a 20 minute wait will loosen this
    I'm also wondering if your finder could have been reassembled incorrectly, the error is in the wrong direction for bad Cds cells. The slight jumpiness is typical of a dirty ring, Deoxit will loosen some of the crud, what it doesn't remove can be removed with an eraser either the white Staedtler-Mars type or the tan Artgum that is cube shaped.
     
  22. Exopix

    Exopix Member

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    Yes, I was in a hurry trying to get that screw out... there was some cement/laquer that secured the screw, and I guess the slot was filled so the blade didn't go all the way down. Now it's impossible to get it out I'm afraid.. What to do?
     
  23. E. von Hoegh

    E. von Hoegh Member

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    Clean the lacquer out of the slot and try a screwdriver that fits. IF the screwdriver fits correctly, you need only a very shallow slot. Use a loupe, and if you're in a hurry save yourself a lot of bother and throw it in the trash right now. Acetone will loosen the lacquer.
     
  24. Exopix

    Exopix Member

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    The head of the screw is totally damaged so I can't get a grip at all.
     
  25. E. von Hoegh

    E. von Hoegh Member

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    Unless you have the tools, skills, and experience to drill the head off and remove the stump from the cover of the prism, then find or make another screw, you have option a) get another finder, or option b) find a watchmaker to remove the screw.
     
  26. Exopix

    Exopix Member

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    I guess alternative a) then :wink: