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  1. #11
    MattKing's Avatar
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    The A-1 (like the AE-1) uses a PX-28 battery. The PX-28 is a currently available battery. There are a number of versions available - alkaline, silver oxide and, I believe, lithium. As I understand it, the Canon A series cameras will function equally well with the alkaline and silver oxide variants, with the silver oxide version lasting much longer. The lithium version didn't exist when the A-1 was being manufactured, so I don't know whether they are compatible.

    When you refer to your A-1 shots being "brighter" I'm assuming that you are referring to prints or scans. The differences between the cameras may be due to your metering technique and/or the differences between the metering sensitivity patterns for the cameras (e.g. the Pentax may be metering more of the sky than the A-1). Alternatively, one or both of the cameras may be out of calibration.

    You can adjust the exposure by adjusting the ISO (ASA?) setting on the cameras. To make your prints darker on the Canon, increase the ASA setting. You will need to experiment to find the right amount, but if you wish to use the Pentax as your target, I'd suggest using both cameras to take reading off something like a blank wall illuminated by the sky on a cloudy day, and then adjust the ASA on the Canon to make those readings match. Then note how many "stops" you have adjusted the meter for.
    Matt

    “Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”

    Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2

  2. #12
    hpulley's Avatar
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    I'm glad I bought a box of Mercury cells while I still could. Still have some still in package and they still work... Must still be some more around.
    Harry Pulley - Visit the BLIND PRINT EXCHANGE FORUM

    Happiness is...

  3. #13
    ic-racer's Avatar
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    The Wein 625 is a 675 with a washer on it as mentioned. If you can't find the correct sized metal washer, you can buy a Wein 625 and take the washer off when you are done. The 675s can be found frequently for less then a dollar a piece.

  4. #14

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    Quote Originally Posted by MattKing View Post
    The A-1 (like the AE-1) uses a PX-28 battery. The PX-28 is a currently available battery. There are a number of versions available - alkaline, silver oxide and, I believe, lithium. As I understand it, the Canon A series cameras will function equally well with the alkaline and silver oxide variants, with the silver oxide version lasting much longer. The lithium version didn't exist when the A-1 was being manufactured, so I don't know whether they are compatible.

    When you refer to your A-1 shots being "brighter" I'm assuming that you are referring to prints or scans. The differences between the cameras may be due to your metering technique and/or the differences between the metering sensitivity patterns for the cameras (e.g. the Pentax may be metering more of the sky than the A-1). Alternatively, one or both of the cameras may be out of calibration.

    You can adjust the exposure by adjusting the ISO (ASA?) setting on the cameras. To make your prints darker on the Canon, increase the ASA setting. You will need to experiment to find the right amount, but if you wish to use the Pentax as your target, I'd suggest using both cameras to take reading off something like a blank wall illuminated by the sky on a cloudy day, and then adjust the ASA on the Canon to make those readings match. Then note how many "stops" you have adjusted the meter for.
    Thank you for your kind reply. That tells me *exactly* what I need to know-- it's not an issue of mercury vs silver oxide cells. I will do just that and try to figure out the compensation necessary now that I understand it is not a set factor related to voltage output of the battery. My apologies to any and all for the momentary derailment of the thread.

    John

  5. #15
    DWThomas's Avatar
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    The A-1 also has an exposure compensation dial that can be used to temporarily increase or decrease exposure without changing the ISO setting. In fact, that should be on the highlighted "1" arrow for normal use -- is it?

  6. #16

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    Quote Originally Posted by DWThomas View Post
    The A-1 also has an exposure compensation dial that can be used to temporarily increase or decrease exposure without changing the ISO setting. In fact, that should be on the highlighted "1" arrow for normal use -- is it?
    It is indeed. I think it's overexposing slightly. Ektachromes shot in both the Pentax and the Canon show a difference-- Pentax is more pleasing to the eye at the same settings as the Canon. Underexposing with the Canon by 1/3 to 1 stop produces similar results, but I haven't done a more exact test to determine the difference between the two. My friend suggested using an external light meter and testing comparing the readings between the two cameras to the reading of the light meter. I will try that with the knowledge that the results from the Pentax are what I'm shooting for. Maybe I can devise a mathematical equation to equate the exposures and if necessary have the Canon calibrated to match the readings of the Pentax. Thank you as well for your reply. I really appreciate the help!

    John

  7. #17

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    Interesting that the extra .5v of the 675 batteries doesn't make a difference in meter accuracy but one more volt does! I found 675s at the local supermarket at $10.99 for an 8 pack. Definitely more economical than the Wein cells!

    Am I correct in believing that unlike the old mercury batteries, which maintained a steady voltage till death, that the 675s would gradually fail, and thus start giving meter inaccuracy with the dropping charge? I'd probably just replace them at a set interval anyway but my geek side is interested.

    Thanks for all the info!

  8. #18
    Ralph Javins's Avatar
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    Good morning, Mtngael;

    There is one characteristic about the Silver-Oxide battery that makes it the best choice generally as a replacement for the old Mercury battery -- the voltage discharge curve as it goes from new to fully depleted or used up. The old Mercury battery had a very flat discharge curve; it stayed at the same voltage as it was used up, right until the very end, where it had a sharp "knee" and the voltage suddenly dropped from its standard 1.35 VDC to going down to the bottom at zero. The Silver-Oxide battery has a very similar flat discharge characteristic, but a slightly higher voltage of about 1.50 to 1.55 VDC. This 0.15 VDC difference can induce an error in many of the older light meter circuits which expect to see a constant 1.35 VDC power source at a very low current draw. The MR-9 Battery Adapter adds a Schottky Barrier diode in series with the Silver-Oxide battery. The normal V(sub f) or Forward Voltage Drop rating of the Schottky Barrier Diode at this current level will be around 0.15 VDC, so it provides almost a perfect compensation for the higher nominal voltage of the Silver-Oxide battery for the light metering circuit.

    The only real criticism I have about the MR-9 Battery Adapter is the $40 price. When you have a lot of old cameras, this can add up. One cost effective way to work around this is to just get some small Schottky Barrier Diodes of almost any voltage rating -- we are going to be using it in its forward biased mode in a very low voltage circuit -- and putting the diode in series with the terminal on the battery holder in the camera and the wire that was going to that battery holder terminal. If you can do this yourself, it will save you a lot of money by then just putting in the Silver-Oxide (Ag-O) battery in the camera battery socket with any required additional mechanical positioning ring to hold it where it should be. The anode end of the Schottky Barrier Diode should go toward the Positive or Plus Terminal of the battery, or the cathode end of the Schottky Barrier Diode should go toward the Negative or Minus Terminal of the battery. The opposite end of the diode not connected to the battery terminal should go toward the light metering circuit wiring.
    Enjoy;

    Ralph Javins, Latte Land, Washington

    When they ask you; "How many Mega Pixels you got in your camera?"
    just tell them; "I use activated silver bromide crystals tor my image storage media."

  9. #19
    Tony-S's Avatar
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    I have the MR-9 for my F-1n and the silver oxide battery and it works very well for me.

  10. #20
    MattKing's Avatar
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    Quote Originally Posted by mtngael View Post
    Interesting that the extra .5v of the 675 batteries doesn't make a difference in meter accuracy but one more volt does! I found 675s at the local supermarket at $10.99 for an 8 pack. Definitely more economical than the Wein cells!

    Am I correct in believing that unlike the old mercury batteries, which maintained a steady voltage till death, that the 675s would gradually fail, and thus start giving meter inaccuracy with the dropping charge? I'd probably just replace them at a set interval anyway but my geek side is interested.

    Thanks for all the info!
    The 675 hearing aid batteries are zinc-air technology, so they too maintain a steady voltage until discharge.

    The difference is that they don't nearly as much capacity as the mercury batteries, and they have a tendency to lose capacity even when not under load. So they don't last as long.
    Matt

    “Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”

    Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2

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