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  1. #1
    jovo's Avatar
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    P67 battery life with TTL prism

    I just bought a TTL prism finder from KEH for my P67. It uses the camera's battery rather than one of its own. I've gone through four batteries with it almost immediately. The batteries were 4SR44 silver oxide. I've had them in my bag for a while, but I can't believe they're so expired that they drained almost immediately. Is the TTL prism the culprit? Do people who use this prism turn it off almost immediately after metering? Should I be using a different battery? Will the world end in December? Will I win the lottery? Any help with the camera questions would be appreciated very much...the other two....well....you probably don't know either!
    John Voss

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  2. #2

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    Silver oxide batteries are expensive. They do not have higher capacity if I remember it correctly. They are only better in having a flatter voltage curve before exhausted and they withstand cold temperature better. Because they are more expensive people tend to buy cheaper Alkaline batteries. So the Sliver oxide ones may remain on sellers's shelf longer. Then you had them in the bag for some more time. This maybe the reason they did not last.

    Try to get the cheaper Alkaline batteries and if they too drain quickly your loss will not be that much. Get those cheap ones from ebay. They may come from Hong Kong or China but they probably sell a lot of them so you will get fresh ones. If this proves that there is nothing wrong with the TTL prism you can get Lithium ones. They will last much longer.

    My P67-ii AE prism does not use much power from the two CR123s. But it is a totally different prism. The AE prism is fantastic, by the way. It is the best thing to have for P67-ii.

  3. #3
    Chrismat's Avatar
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    I've had a TTL prism for my Pentax 6X7 for a long time and it's never gone through batteries like that. I think there might be something wrong with the prism. I have been using mostly alkaline batteries myself but I just received a silver oxide battery in the mail recently so we'll see.

  4. #4
    jovo's Avatar
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    Thanks. I'm interested in finding out more about lithium 6v batteries for the prism. It does work, and seems accurate, but the battery issue has yet to be resolved. I did notice that I used two 6.2 v batteries instead of the recommended 6v one, so that's another issue to resolve.
    John Voss

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  5. #5
    Hatchetman's Avatar
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    I think something may be wrong. I've had my 6x7 with the same prism for about 9 months. Probably shot 15 rolls. Still on the same battery. Not sure how long they last. I should probably change it anyway.

  6. #6
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    The TTL prism of the Pentax 67 is powered by the 6v battery in the 67/6x7 body; the prism does not have a battery of its own, even in the absence or presence of an on/off switch (later versions of the TTL prism [1991->) have a discretionary on/off switch that also switches off by itself after 20 secs).

    The battery will last around 10-15,000 exposures with a moderate amount of bulb/MLU exposures (be it noted that the 67 or 6x7 is a poor choice for extended bulb exposures as the mechanism employed — magnetic solenoids to hold the mirror up under MLU — is a heavy drain on the battery). Examine the contacts in the battery compartment, the contacts on the base of the prism and those on the camera. The 4xSR44 silver oxide batteries you speak of do not last as long as the single 6v A544/4LR44 battery. Further, one set will last about 5 hours with MLU or bulb operation. An alkaline battery should be used; it is no crime to go from silver oxide to alkaline or even a nuclear fuel pellet e.g borrow one from Curiosity on Mars...

    I assume meter is actually reading a scene and not reading "dead" (needle persistently at bottom)? Just a check as not observing mount/dismount and remount process of lens and prism can result in the meter coupling pin not engaging and thus causing the meter to remain on indefinitely. A shorting of the shutter speed resistors that govern shutter speeds is also a possibility. If a changeover of batteries does not show an improvement, I think a bench examination of the entire camera is warranted, particularly if it is quite old, and all of the 67 and 6x7 bodies are getting on now, but still some beautiful little used specimens about.
    Last edited by Poisson Du Jour; 09-01-2012 at 01:35 AM. Click to view previous post history.
    “The photographer must determine how he wants the finished print to look before he exposes the negative.
    Before releasing the shutter, he must seek 'the flame of recognition,' a sense that the picture would reveal
    the greater mystery of things...more clearly than the eyes see."
    ~Edward Weston, 1922.

  7. #7
    jovo's Avatar
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    Thank you Poisson Du Jour. The meter works very well. The picture I've posted "Sunlight, Fog and Cross" was metered with it, and the exposure is spot on. I will check the other mechanical things you've mentioned, especially the coupling pin not engaging.

    Thank you all for the suggestions.
    John Voss

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  8. #8
    benjiboy's Avatar
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    It seems to me John the equipment has an electrical fault that's causing the excessive battery drain, if the prism was mine I'de get it checked out by a professional.
    Ben



 

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