I came across this the other day - I had heard about it over a year ago but the camera store finally got some fresh stock.

It is quite simply, a resistor housed in a PX13 battery shell and allows you to use the readily available 76PX (SR44) battery in your older camera. Say goodbye to obsolesence!

This wonderful piece of gear drops the voltage from 1.5 volts down to the required 1.35 volts! Now, if you happen to have a Bolex 155, you simply need two of these to drop the voltage to 2.7. You could even stack two and with a metal shim use it in place of the PX14 battery!

Personally, I was a little concerned using my Bolex RX2 Vario-Switar lens with the wrong voltage battery. The standard PX625 (1.5volts) battery worked fine but I was worried the exposure may be a bit off. So, now I can rest assured I am getting the correct exposure and not risking any undue underexposure.

Okay, so the $39.99 (US) is a bit pricey. But let's face it - it is a highly specialized adapter that only people like me (and you) require.

So, if you have an older camera like the Bolex 150/155/160 or the Canon 518SV, you may want to seriously consider investing in this little gem of a contraption. Personally, I am glad they didn't charge $50 for it.

Now, some of you may argue that there is little harm in using the 1.5 volt battery. All I say is, you are right: film latitude (especially with B&W) should be okay and if anything, your images will be a little more saturated due to the slight decrease in exposure. But, personally, usually I have enough going on that the last thing I want to think about is whether the light meter is responding correctly. Plus, if you are using a hand-held Weston Master II or similar, things get confusing always having to adjust what the camera says to what the meter reads. So, I think it is really a small price to pay and encourages more companies to make unique items like this that support our hobby.

Here's a picture of my H8 with the ASA dial unscrewed to show where the PX13 battery goes. The big "Kern Paillard" cover is for the lens (of course) and the smaller silver plate with the inscribed circles is where the light meter dial is located. This part does not come off! Notice the two small circles at the shutter release. The circle with more black in the middle allows for bright viewing prior to releasing the shutter (basically the exact opposite of what a depth of field button does on a 35mm camera). The white circle is for no bright-preview and shows exactly what the lens sees through the proper f-stop. I like the first setting the best! Very advanced for its day (circa 1950's).

Before I go, I should provide a little discussion on the different types of batteries out there. Specifically, there are "zinc air" batteries, silver oxide batteries, alkaline batteries, and mercury batteries. Mercury batteries were perfect for light meter applications since their voltage held constant up until the bitter end of their life cycle. However, after it became clear there were serious environmental side effects from using mercury in batteries, they were, for all intents and purposes, banned.

Zinc air batteries are often referred to as hearing aid batteries. They offer the correct 1.35 volts (or 1.4 initially, 1.35 volts after the first 5% of life has passed) but begin breaking down as soon as the air seal is broken. They can last as little as two months. Not to convenient for the average super 8 hobbyist.The only good part is they tend to maintain their 1.35 volt rating through most of their very short life.

What about the easy-to-find alkaline batteries? The 625? Well, the first problem is they start at 1.5 volts. All alkaline batteries then drop pretty quickly down to 1.3 volts and then with about 30% life left eventually taper off to even lower voltages. Again, the real problem is that alkaline batteries never stay in their zone of 1.35 volts for very long at all.

The last type of battery you will come across is the silver oxide battery. The bad news is that they are rated for 1.6 volts; just like alkaline batteries, the voltage is a bit too high at first. However, unlike alkaline batteries, the voltage drops to about 1.5 volts and remains there for about 95% of their life. This is exacly what we need. From this, any kind of recalibration or circuit you can come up with would reduce that voltage to 1.35 and we would then have a mercury-like battery! That's where the MR-9 adapter comes in!

If you need more information on this issue of mercury batteries vs alkaline and zinc air batteries, here are some links for you to check out (cut and paste these links in your browser):

http://www.rolleicamera.com/sales-batt-adapt.htm

http://www.nikonhs.org/tech_articles/battery.html

http://www.nemeng.com/leica/012e.shtml

http://www.nemeng.com/leica/binz/px625.txt

http://home.pcisys.net/~rlsnpjs/minolta/mercury.html

Happy Metering!