light meter batteries

[dr.sanchez]

I have a Nizo 561 Super 8. I got it a few months ago and it had some old mercury batteries for the light meter. After a few over-exposed rolls, I'm replacing the batteries. According to the fella at the photo shop, mercury batteries are illegal in the U.S. so he sold me some alkalines.

The problem is, he told me that the mercury batteries kept a constant charge of 1.35 volts while the alkalines will start at 1.5 volts, then gradually lose their power. So, while the batteries are new, I'll be underexposing my film (if in auto mode). The batteries will eventually hit 1.35 volts, exposures will be fine, then they'll keep decaying and overexposing my film.

So why even have a light meter if it's dependent on an ever-changing battery voltage? Or is this all bunk? Do I need to worry about it? Should I only take external light meter readings with brand new batteries? Has anyone encountered problems with battery voltages?

Thanks for your help.
David.

[BolexPlusx]

I was kind of lucky on this score. I managed to grab up a few remaining mercury cells for my Bolex 150 Super before the well ran dry. I have the two in the camera and the two in the fridge, after that I'm thinking of trying this:

http://www.criscam.com/mr9.htm

If the cell that's giving you trouble is PX-13, this is a viable solution. It is a mechanical adapter with an internal voltage regulator which will allow commonly available silver photo cells to act like the PX-13 1.35V Mercury cell.

Another solution is the Zinc Air cell:

http://www.photobattery.com/zincair.html

The real problem I have is with a GAF (Chinon) ST/602 which I grabbed mainly because this is the same type as my first camera when I was a teenager. It takes the PX-14 cell which is two PX-13s in series inside an outer shell for 2.7V total. Here I was stuck to go with the 3V Alkaline replacement because no exact voltage replacement is easily available.

I intend to do an experiment with this camera. I am going to tripod it with a roll of K-40 and jumper in a variable power supply in place of the battery. Then I am going to vary the voltage from 2.7V to 3.0V and see if I can get the light meter to move. If I can't that means the meter voltage is regulated after the cell and I have nothing to worry about. If I can change the meter reading by fooling with the voltage I will use the camera's exposure adjustment to give me identical meter readings at 3 Volts that they would have been at 2.7V with 40 ASA film in normal daylight (which is how I want to use this camera anyway). If it is very sensitive to cell voltage, I am going to have to watch the battery closely and replace it more often than usual.

<font color="#a62a2a" size="1">[ July 07, 2002 04:53 PM: Message edited by: BolexPlusx ]</font>

[prophet67]

It is interesting to read this post.

I recently acquired my first camera, and installed a PX-13 equivalent for the light meter, but am unsure if it is doing anything, or as was suggested if the battery is giving bad information to the camera. I didn't know some of the technical voltage issues described here.

I have a very simple Bell and Howell 308, but it does have an Auto/Manual meter adjustment.

[I'm presently having a test roll developed before I splurge on a manual, for which I have found a source]

In general, if the meter was not working properly, what sort of situation have I been in/will I be in?

Thanks for being patient with a new camera user.

[BolexPlusx]

Well,
Your exposure may be slightly off (Probably a little on the underexposed side)
If the camera has a voltage regulator between the battery and the meter circuit the exposure will be OK regardless of whether the battery is 1.35V or 1.5V. However, most people would not design a camera to specify an expensive mercury battery, and then back it up with a voltage regulator (may I be wrong!)The whole point of the mercury battery is how well it regulates itself, if you're going to add a regulator you might as well stick with an alkaline cell.

If when you were in Auto-exposure more the meter was reacting to ambient light, it can't be all bad.