Does battery pack changes exposure of Minox ?greenspun.com : LUSENET : Minox Photography : One Thread
I am thinking of using battery pack to replace PX27 in my C, Since the battery pack is 6v instead of 5.6v, there is a change in voltage of nearly 10%, does the expsoure time changes by 10% ?
-- Linda Jackson (email@example.com), February 24, 1999
Linda, I have not notice any change of exposure in my C when I use the battery replacemet pack instead of PX27 mercury battery. in auto mode (A). I once compare the meter of two ECs, one with PX27, one with power pack; I stacked two EC together and scanned them across window and check the red LED light in the window, when two cameras scanned from dark to bright, the two red lights turned on at the same time, when they scanned from bright to darkness, the two lights turned on at the same time. This indicates that exposure meter react to light or darkness exactly the same regardless of 5.6V battery or 6v battery; otherwise the two lights should turn on or off at different time.
-- martin tai (firstname.lastname@example.org), February 24, 1999.
Linda, I am the guy who may have been responsible for the Minox battery pack being developed. In the early 1990's when the discontinuation of Mercury batteries was announced, I looked at my collection and realized I would soon have a lot of very expensive things that no longer worked. The PX-27 is very unique, and nobody was going to make replacements just for C, EC and LX Minoxes, the only things that use them as far I as I could find. I began researching batteries extensively, buying all sorts of battery data and testing equipment at Radio Shack, while I still had fresh PX-27s to compare to. The main problem was the voltage. A PX 27 is, internally, 4 stacked mercury button cells of 1.4 volts each. This gives the 5.6 volt figure in the PX-27. Now, here is the problem. Mercury batteries have a flat discharge curve. That is, voltage discharge is almost constant until the battery goes dead suddenly. This is unlike alkalines, which start higher than posted voltage, and decrease gradually until dead. This is NO GOOD for a light meter: the meter will not give consistant performance as the voltage gradually changes. Silver oxide button batteries have a flat discharge curve similar to mercuries, but they were all 1.5 volts. Too high, as I reasoned that 4 of these would be 6 volts, as you did. Then, fiddling around one day, I took 4 S-76 silver buttons I use in my 35mm cameras and stacked them, and put a volt meter on the stack. VIOLA! The stack read not 6 volts, as expected, but 5.6 volts!! (Some brand new fresh S-76s might go to 5.7v. No big deal.) I reasoned that the metal casings, when stacked in four cells, was causing a voltage drop due to resistance of the metal casings themselves. I tried four S-76 buttons in one of my LX cameras. They fit, but barely, and only if I put two end ones in first and squeezed the middle ones in next. Very tight, but the LX worked perfectly. I compared to other LX's. No discernable difference in exposure at identical subjects in the same light. I was very concerned as to fit, as the 4 S-76s would only fit in the LX, they wouldn't fit in C models at all, and the set was clearly smashing the battery contacts flat in the LX. A search in the Radio Shack battery manual revealed that the 386 silver button had the same performance, discharge curves and discharge rates as the S-76. Its main difference being less storage capacity, as it was thinner, so it would not last as long. (Not a factor in a power- stingy little Minox!) I bought four 386 buttons. Stacked, they too tested 5.6 volts. Problem was, they now weren't thick enough to fit across the battery chamber when stacked. I tried a metal spacer. Bingo. This did it. I phoned Minox Labs the next day. We had been discussing this and the lady at Minox confessed the factory didn't have an answer yet and was very worried about the situation. I told her of my experiments and what batteries I tried. I suggested that four 386's and a spacer would work perfectly. She wrote it all down and faxed it to the Minox factory in Germany to test out further. About a year or so later, the Minox Battery Pack was introduced. It is basically a metal spacer and a plastic sleeve to hold the four 386 buttons together. As far as anybody can tell, the battery packs function identically. On a similar note, I have found that a single 1.5v silver oxide S-76 will power the Minox BL's meter very well, with no difference in meter performance from the last mercury PX675 buttons I had. (External dimensions of the PX675 and S-76 are the same.) The BL does not seem to notice the difference between 1.4v and 1.5v, at least to any degree that would make an observable change. I recommend using these in BLs and not the alkaline PX675A substitute that Minox Labs has been selling. That one will not deliver a flat constant voltage discharge curve necessary for consistent metering. Go ahead and use that pack in your C. I have them in my C models and my LX's and they are all functioning perfectly, and identically to the PX-27s. Don Thayer, owner of Minox Labs (whose father was the person who imported the original Minoxes to the the USA in its infancy) also told me there are no reports of any C, EC or LX not functioning identically with the Packs as with PX-27s. Mike
-- Michael J. Vorrasi (MVorr99@aol.com), April 10, 1999.