Friday, March 15, 2002, 2:34:02 PM, Steve wrote: SL> Hi, SL> The compensation needed for the difference in voltage (1.35 vs. 1.5) SL> is about 1/8 of a stop. In my opinion it is not a factor. I made a plate out SL> of aluminum with a hole in it and put a rubber grommet in it to shield the SL> negative and positive inputs, screwed it to the baseplate of a Spotmatic II SL> and applied 1.35V, then 1.5V. The difference on the match needle was SL> negligible. SL> Voltage came from a linear 1.1-30VDC 5A linear power supply (home made), SL> with a transformer you can arc weld with, yes that`s bragging.
Hi Steve, unfortunately that's a wrong prepared experiment ;-) with your laboratory DC source, you have neglected one difference between Mercury and Zinc-Chloride batteries: the old Mercury batteries had much more stable voltage over time, so it did remain at 1.35V almost to the end of the battery. The newer, ZC batteries, have 1.5 at the start but much less at the end. That's what produces the meter problems. Although the difference might not be big between 1.35 and 1.5, it certainly is between 1.1 and 1.5 or what's the voltage of full and nearly empty ZC battery. Also, when you tested at one EV only, you didn't test for meter linearity affected by the voltage, which might or not might be (dunno). It's Pentax's (and many other Japan camera makers at that time) "fault" that they didn't invest slightly more in bridge circuitry which would make the whole point of different battery voltage moot (I am led to believe there is such circuit in the SP. F, so they did change to it at some time). Of course, I may be wrong too :) Good light, Frantisek Vlcek - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
