The Problem:

All Nikon F metered finders used one or two PX625 1.35v mercury batteries that were banned in the US several years ago. They provided a constant output voltage for much of the life of the battery similar to the newer Silver 76 1.5v batteries, but the Silver 76 batteries are smaller and run at a higher voltage producing erroneous meter readings.

A constant output voltage is desired so that the meter's sensitivity does not change as the battery wears. In contrast, as an Alkaline or Carbon-Zinc battery wears, near the later stages of the battery's life the voltage drops from its initial value prior to dying rather than running at full voltage and dying quickly.

The effect in a flashlight is the dimming of the light, so you would know when to change the batteries. The effect in a light meter is noticed only by getting back poorly exposed pictures!

One 1.35v PX625
Photomic finders with external meter cell:

• 1962 - Photomic S Model 1 "flag switch"
• 1963 - Photomic S Model 2 with "on-off switch"

Two 1.35v PX625s (2.7v)
Photomic finders with TTL (Through-The-Lens) internal metering cells:

• 1965 - Photomic T "Averaging type w/manual indexing of maximum aperture"
• 1967 - Photomic Tn "Center-Weighted type w/manual indexing of maximum aperture"
• 1968 - Photomic FTn "Center-Weighted type w/semi-auto indexing of maximum aperture"

Solution 1:

Wein Corporation manufactures a 1.35v Zinc-Air battery with the same dimensions and voltage as the PX625 called the MRB675. It's around $7 each, but once the seal is broken and the battery exposed to air it lasts at most 4 to 6 months whether used or not.

My Opinion: Good if you use the camera regularly.

Solution 2:

Check http://www.criscam.com. They sell an adapter for each PX625 replacement. It consists of a hollowed out case that is the same outer dimensions as the PX625. You drop a $3.00 Silver 76 1.5v battery into each adapter. Inside the adapter is an $0.79 Schottkey Diode (just showing off my electronics engineering background) to drop the battery replacement voltage down to 1.35v. The part no. is MR-9. It is $30.00 each and you need two for the finders that use two batteries. (Note: This is a one-time investment). When the battery (or batteries) wear out you simply replace the battery (or batteries).

My Opinion: Best long-term technical solution but requires initial investment.

Solution 3:

Use 1.5v Alkaline PX625 replacements ($3 each) and have the meter compensated for permanently by a camera repair shop. ($125 - $175). You must change the batteries more often than Silver 76 due to the voltage drop problem discussed above.

My Opinion: Least desired of all due to initial cost and alkaline battery voltage drop.

Solution 4: My personal (cheapo) solution.

Use 1.5v Alkaline PX625 replacements ($3 each) and calibrate your existing meter. This method is not as accurate as meter modifications, but the difference in my opinion is negligible.

Take a light meter reading of a scene using another camera (or handheld meter) set at the same ASA as your camera's meter. Set the proper exposure. Jot down the shutter speed and aperture.

Position your camera looking at the same scene. With the same ASA value, set your shutter speed, and aperture the same as the other camera. Your match needle will not be centered yet. Adjust the exposure compensation dial until the needle is centered.

Presto...you now have a calibrated meter using Alkaline 1.5v batteries. Again, you must change the batteries more often than Silver 76 due to the voltage drop problem discussed above.

My Opinion: It's a cheap compromise. Just remember to replace batteries more often or recalibrate the meter a few times during the battery's life

Solution 5:

I've seen ads on the internet for Mercury 1.35v PX625 batteries at $5.00 each.

My Opinion: Surf at your own risk.