Nikon F Photomic finder - replacement for mercury cells?

[GRHazelton]

Almost on impulse I bought a Photomic F finder for my Nikon F; the finder is in excellent condition. It takes 2 Px 13 or equivalent mercury cells. While zinc air cells with an adapter would do the job, the ideal is the installation of a diode within the meter. The diode allows using silver oxide cells. I've seen a YouTube of this procedure; it looks like more than I care to attempt.
Do any of you out there know of any "drop in" replacements for mercury cells? I am aware of using zinc air cells, but I'd rather have a way to use silver oxide cells, since they have a long life. Anyone know of a good repair person to install the diode or diodes within the finder?

 

[John Koehrer]

Easiest would be using the s76 with a #9* O ring slipped on it.

* As I recall(?) Ace Hardware

 

[Pieter12]

email Frans at battery.adapter@online.nl

 

[GRHazelton]

Easiest would be using the s76 with a #9* O ring slipped on it.

* As I recall(?) Ace Hardware

Sadly, its not that simple. The s76 is a silver oxide cell with a voltage of 1.55 more or less. The Photomic used 2 mercury cells, combined voltage of 2.7v. If the Photomic used a bridge circuit it would be quite tolerant of 2 s76 cells with a combined voltage of a bit over 3 volts. My Pentax Spotmatic F originally used a mercury cell, 1.35 volts, its happy with a silver oxide cell, 1.55v, since it has a bridge metering circuit. Same with my ancient Praktica LTL, also a bridge circuit. (My understanding is that a typical bridge meter circuit requires aligning the meter needle with a fixed, central marker, which indicates that both halves of the circuit are "balanced.")
So zinc air cells with a voltage approximating that of a mercury cell will work. But zinc air cells have a comparatively short life span. Since my Nikon F is not in continual use the zinc air solution would be a crap shoot - are the bloody cells still good? Not to mention needing to carry replacements to be installed in the field.
Then there's the case of my vintage Bulova Accutron SpaceView. The original Bulova Accutron with the tuning fork, not the current quartz "impostor." It came with a mercury cell, some can be adjusted to run on a silver oxide cell.....but not mine! So I need to have the diode installed to bring it back to life.

 

[wiltw]

Many years ago, I bought the CRIS MR-9 adapter from the manufacturer in USA, that is sized like a PX13, but holds a 386 Silver Oxide battery and which converts voltage to 1.35V. I use this with Olympus OM-1n
About 6 years ago, someone conducted tests and concluded:

"My conclusion:
Wein Cell = CRIS adapter = Pratedthai adapter.

The Pratedthai adapters are not a fraud. They work, and work great. I no longer need to purchase Wein cells with their corrosion risk as a result."​

Looking now, I find there are some 'alternative' MR-9, and I have doubts as to the legitmacy of some of these (Chinese manufacture?)
This particular one seems legit, converting 1.55V to 1.35V in its description.

https://www.ebay.com/itm/MR9-MR-9-P...m-Camera-Exposure-Meter-Mercury-/130646083632

but this one listed on Amazon https://www.amazon.com/Battery-Adapter-Camera-Exposure-Mercury/dp/B07XT7KVV6 says in its description, "Use Zinc Air 675A 675 A675(1.45V) battery with this adapter, the actual voltage is approximately 1.4V, so as to replace MR-9 PX625 PX13 Mercury battery (1.35V)." That makes me doubt the legitimacy of this specific offering!

 

[GRHazelton]

Many years ago, I bought the MR-9 adapter from the manufacturer in USA, that is sized like a PX13, but holds a 386 Silver Oxide battery and which converts voltage to 1.35V. I use this with Olympus OM-1n

Looking now, I find there are some 'alternative' MR-9, and I have doubts as to the legitmacy of some of these (Chinese manufacture?)
This particular one seem legits, converting 1.55V to 1.35V in its description.

https://www.ebay.com/itm/MR9-MR-9-P...m-Camera-Exposure-Meter-Mercury-/130646083632

but this one listed on Amazon https://www.amazon.com/Battery-Adapter-Camera-Exposure-Mercury/dp/B07XT7KVV6 says in its description, "Use Zinc Air 675A 675 A675(1.45V) battery with this adapter, the actual voltage is approximately 1.4V, so as to replace MR-9 PX625 PX13 Mercury battery (1.35V)." That makes me doubt the legitimacy of this specific offering!

Thanks! I agree, the first one looks legit, the second one....No way!

 

[btaylor]

I bought several CRIS adapters. And I bought the Chinese knockoff. They all work fine, silver battery regulated to 1.35v. There are a number of sellers with an adapter that uses the hearing aid battery- not the same.

 

[reddesert]

I used one for years with two PX625A (alkaline) cells when those were available everywhere (now I think you can still get them online), and battery adapters were not yet a common item. I compensated the film speed by a small amount, certainly less than a stop. You need to test / calibrate a Nikon F meter now anyway because the resistive track might have degraded.

Alkaline cells gradually decline in voltage (unlike silver oxide), so I just replaced them when they started to get a bit dodgy. Silver oxide would have been ok, but then you need at least an O-ring to adapt the size. Not sure which prism you actually have, I know the common FTn prism has an actual battery check needle, so it is pretty easy to tell when your batteries are dying.

There are people who will swear up and down that using the slightly higher voltage cells will cause your meter to be uncalibratable and send all your negatives to China where they will be developed in expired Xtol, but IME for at least some cameras those concerns are overrated.

 

[guangong]

Excuse me for taking a different tangent, but from my experience decades ago, the Nikon’s meter prism makes F camera bulky, unbalanced and unwieldy. I quickly changed to plain unmetered prism.
I use MR-9, which adjusts voltage, for some cameras. Some cameras allow use of alkaline 625. For others I use Wien cells.
No matter which, a good habit to follow is to remove battery from camera when not in use. I tape mine on camera using painters tape. Keep in mind that repair parts for our cameras are becoming harder to find, and harder still for parts that were most often replaced.

 

[Donald Qualls]

I recently bought a PX640 adapter from this web site. No, that won't fit, but the seller also has made (and doesn't offer on the site, for some reason) a 2xPX625 adapter that runs on a lithium button cell. Regulated voltage (3V down to 2.7), one-piece unit with a screw cap, drop in fit for cameras that use two PX625. Should outlast even a silver oxide cell, and the adapter will protect the camera from cell leaks, in the unlikely event that happens with the lithium cell.

 

[John Koehrer]

RE: voltages & adapters I only mentioned The #9 ring because I ASSUMED you were having the diode conversion
done. Because of that the only thing you needed was the O ring.