Which battery works best in the Nikon F?

The original photomic meter just uses one battery but all of the others use two batteries.

There are 4 options to power the Nikon F meter.

This battery is perhaps the best battery replacement for the Nikon F. It is 1.5 volts and has a good voltage time curve. The battery can be purchased at online battery surplus stores like:

http://www.wholesaleadvantage.com/batteries_photo.html PX625s $1.92 each

and

http://www.photobattery.com/index.html#S625 $6 each

2. Alkaline battery, PX625A

This is the battery that I use in my own meters and recommend to most people. Although, the silver-oxide battery has a better voltage curve, the alkaline battery works very well in the Nikon F meters. The batteries last about a year, during which time they slowly decrease from 1.5 to 1.4 volts. The corresponding change in the meter reading is only about 1/3 of a stop. This is not a large change in exposure. After a year or so, I replace the alkalines with new ones. The alkaline batteries are inexpensive, $2.77 at Wal-Mart, and are available at most drug stores.

3.Wein cell battery

I have not had good luck with these batteries. I purchased a set from a photo store for $16 and put them in my photomic Tn meter. Within two months, the meter was reading at least 4 stops off. At first, I thought that the meter was broken, but then I put in some alkaline batteries and the meter worked fine. Since then, I have never gone back to the Wein cell.

4. Voltage regulated power sources

Some people like the thought of a voltage regulated power supply but I have found them unnecessary in the Nikon F meters. The C.R.I.S. MR9 voltage regulator will even cause a 3 stop error when used in the Nikon F Ftn meter in daylight. So I do not recommend using a MR9 adapter. The following study shows why I do not recommend the CRIS MR9 adapter in the Nikon F meters.

C.R.I.S. is a company that makes voltage regulators that you place a 1.5 volt silver battery into which then fits into the Nikon F battery compartment. The device drops the voltage down to the correct voltage of 1.35 volts, but only over a limited load range of 10K - 30 K ohms. When the load of the meter moves outside of this range, the battery output of the voltage regulator also changes. The load is the electrical resistance of the meter that the batteries are subject to. The load range of the Nikon F meter is much greater than 10K - 30 K ohms. I measured it at 650 ohms through 156 K ohms.

The internal resistance of the meter changes depending on the f-stop/shutter speed setting as well as the light intensity. Using 100 ASA film in sun light, you would have the shutter speed and f-stop around 1/125sec at f-16. Under these conditions, the electrical resistance of the meter is very low, around 650 ohms. At the other end of the spectrum, a dark room, the electrical resistance of the meter would be very high, in the 150 K ohm range. The CRIS adapter will not provide a constant voltage output when the meter load is outside the 10 - 30 K ohms. Therefore, the CRIS adapter will cause the Nikon F meter to be inaccurate. To find out how much error was introduced when two CRIS adapters were used in a Nikon Ftn meter, I measured the voltage output of two CRIS adapters and corresponding exposure error as a function of load.

The load column is the averaged load measurements from 2 Nikon F Ftn meters. Both of these meters work properly and are accurate using two 1.35 volt mercury batteries. I used my Sekonic L-408 digital light meter and a 18% gray card to measure the light levels from 15 EV to 3 EV at 100 ASA. 15EV corresponds to a sunny day and 3 EV corresponds to a dim room.

The following table shows the data that I collected:

EV	Load of Ftn	Voltage of 2 MR9's	Error of Ftn meter (stops)
15	650 ohms	1.823 volts	3 stops over
14	776 ohms	1.848 volts	3 stops over
13	1160 ohms	1.974 volts	2 stops over
12	1659 ohms	2.137 volts	1.5 stops over
11	2650 ohms	2.288 volts	1 stops over
10	3.87 K ohms	2.504 volts	0.5stops over
9	5.6 K ohms	2.556 volts	0.3 stops over
8	11 K ohms	2.665 volts	0.2 stops over
7	16.7 K ohms	2.702 volts	On
6	30 K ohms	2.761 volts	0.1 stops under
5	56 K ohms	2.805 volts	0.3 stops under
4	90 K ohms	2.841 volts	0.5 stops under
3	156 K ohms	2.872 volts	0.8 stops under

The voltage at no load, (batteries and MR9 adapters themselves) was 3.091 volts.

The above table shows that the CRIS adapter only provides the correct voltage of 2.7 volts when the load is between 11 K and 30 K ohms. Within this range, the meter was accurate. In sunlight, 15 EV, the meter would be 3 stops overexposed since only 1.823 volts was getting to the meter when it should have been 2.7 volts. The adverse effect of the adapter is not as bad in the low light situation as it is in day light levels.

This data shows that the CRIS MR9 battery voltage regulator does not work very well in the Nikon F meters since the load range of the Nikon F meter is larger than the working load range of the MR9.

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