A new tool for battery compartment caps

Steve Goldstein · Dec 21, 2019

For many years I've used Japanese 1-yen coins on the battery compartment caps of my mixed collection of cameras and light meters. It's slightly smaller than a US nickel and is made of aluminum so it won't mar the slot. However, both the nickel and the 1-yen coin are small and it's hard to generate much torque. Maybe that's a good thing, maybe not.

Today I stumbled onto a new tool - a Chinese 1-yuan coin. It's slightly thicker than the 1-yen coin and is actually a better fit to every cap I tried (over half a dozen cameras and light meters from Nikon, Olympus, Voigtlander, Mamiya, Pentax, Zeiss, and Gossen). Aside from the improved fit, it's a bit easier for me to handle.

The downside is that the 1-yuan coin is steel (or some magnetic alloy), so it'll damage the slot if you're not careful and it slips. But it's a good fit, and its increased size reduces the chance of that happening.

Left to right: Japanese 1-yen coin, US nickel, Chinese 1-yuan coin.

BrianShaw · Dec 21, 2019

Great news! How much does this tool cost?

Steve Goldstein · Dec 21, 2019

Sadly, good things aren't free. It costs about 14x as much as the tool it replaced. Airfare not included...

mike c · Dec 21, 2019

There could be a run on the market for 1-yuan coins soon, better stock up.

BobD · Dec 21, 2019

Once upon a time Ed Romney sold a tool for this. I think I still have one somewhere. It's a disk made of some sort of tough plastic with a handle a couple inches long. It works quite well on stubborn battery covers.

macfred · Dec 22, 2019

Bah ! Made in China ? Here's the Leica version ...

A Carthaginian shekel, dated 237-227 BC

AgX · Dec 22, 2019

I mill my respective tools to size (radius, thickness).

mrosenlof · Dec 22, 2019

Most Japanese cameras from The 70s and 80s at least are a perfect fit to a 100 yen coin.

Steve Goldstein · Dec 23, 2019

I was wondering about that, but unfortunately don't have any 100-yen coins in the after-travel small currency stash. As I recall there's a Korean coin of virtually identical dimensions, maybe 100 won, which at the time was the equivalent of about 10 yen. I believe I once inadvertently used one in a Japanese vending machine with success.

That Carthaginian shekel is lovely, but I'd only use it on my Leica (if I had one).

MattKing · Dec 23, 2019

The Canadian $1.00 and $2.00 coins ("Loonie" and "Toonie") seem to work well.

Trask · Dec 23, 2019

macfred said:
Bah ! Made in China ? Here's the Leica version ...
View attachment 236711
A Carthaginian shekel, dated 237-227 BC

Last evening I was watching the first season of sci-fi show “The Expanse” where I heard a character refer to the space ship “The Scipio Africanus.” That rang a bell, in part because I’ve live in both Algeria and Tunisia, so off to Wikipedia, where I re-learned that Scipio had defeated Hannibal near Carthage o/a 202 BC. And had defeated Hannibal’s brothers in Carthaginian Iberia. Cool that you have a coin from all those centuries ago; I’m sure Hannibal et al would be pleased to know they are remembered

benjiboy · Dec 23, 2019

I use a British 20 pence piece, it works fine on my Canon F1n's

Ian C · Dec 24, 2019

Per the Japan Mint website, a 100-yen coin is 22.6 mm diameter, thickness 1.69 mm. This is often touted as “fitting the Nikon coin slot perfectly.” I don’t think so.

https://www.mint.go.jp/eng/operations-eng/eng_operations_coin_index.html

A U.S. quarter is both larger in diameter and thicker than the 100-yen coin and should provide a better fit. The quarter is 24.26 mm diameter x 1.75 mm thick. It fits the Nikon coin slot rather loosely, because it bottoms in the center of the slot and is 0.23 mm thinner than the slot width.

https://www.usmint.gov/learn/coin-and-medal-programs/coin-specifications

The cross section of a coin-drive slot has the shape of a segment of a circle.

https://en.wikipedia.org/wiki/Circular_segment

The length of the slot, c, is the chord of the segment. The length of the slot, c, the depth of the slot, h, and its width, w, can be measured.

The diameter of the ideal coin is

d = (c^2)/4h + h

The Nikon FE, FE2, FM, FM2, FM2n, and F3 use the same battery cover whose slot has length c = 10.5 mm, depth h = 1.02 mm, and width w = 1.98 mm.

The diameter of the ideal coin or tool for this Nikon cover is d = 28.0 mm and its width should be about 1.96 mm. The edges should be slightly chamfered or radiused in case the corners of the slot are not quite “sharp”.

The coin slots of other cameras or devices with coin-drive slots in the battery cover can be measured and the ideal diameter calculated.

guangong · Dec 24, 2019

Coincidence! Last night just watched Patrone’s 1914 Italian blockbuster film Cabiria, which takes place during the days of Hannibal and Scipio. However, my Leicas are less picky. I use pennies, quarters, whatever fits. What I don’t do is use excessive force to tighten cover, but just enough to hold securely so that removal doesn’t require super torque.
The battery covers that are a real pain are the non-screw in type that are held in place by two little plastic prongs...they are never secure

AgX · Dec 24, 2019

In Europe you may grind a 20€cent coin just a little bit thinner and you got a tool that quite often will fit.

A serious proble are those caps made from PE and already are worn out.

BrianShaw · Dec 24, 2019

Ian C said:
Per the Japan Mint website, a 100-yen coin is 22.6 mm diameter, thickness 1.69 mm. This is often touted as “fitting the Nikon coin slot perfectly.” I don’t think so.

https://www.mint.go.jp/eng/operations-eng/eng_operations_coin_index.html

A U.S. quarter is both larger in diameter and thicker than the 100-yen coin and should provide a better fit. The quarter is 24.26 mm diameter x 1.75 mm thick. It fits the Nikon coin slot rather loosely, because it bottoms in the center of the slot and is 0.23 mm thinner than the slot width.

https://www.usmint.gov/learn/coin-and-medal-programs/coin-specifications

The cross section of a coin-drive slot has the shape of a segment of a circle.

https://en.wikipedia.org/wiki/Circular_segment

The length of the slot, c, is the chord of the segment. The length of the slot, c, the depth of the slot, h, and its width, w, can be measured.

The diameter of the ideal coin is

d = (c^2)/4h + h

The Nikon FE, FE2, FM, FM2, FM2n, and F3 use the same battery cover whose slot has length c = 10.5 mm, depth h = 1.02 mm, and width w = 1.98 mm.

The diameter of the ideal coin or tool for this Nikon cover is d = 28.0 mm and its width should be about 1.96 mm. The edges should be slightly chamfered or radiused in case the corners of the slot are not quite “sharp”.

The coin slots of other cameras or devices with coin-drive slots in the battery cover can be measured and the ideal diameter calculated.

Seems like we need to mint a new coin. Denomination = 35 cents, perhaps. On the obverse there could be a camera... a different Nikon every 3 months. On the reverse I’d propose these calculations!

But could we add a handle to this “ideal coin” to accommodate those of us with arthritic fingers... please.

AgX · Dec 24, 2019

BrianShaw said:
But could we add a handle to this “ideal coin” to accommodate those of us with arthritic fingers... please.

Actually a necessity in some cases.
At the Mnox 35 for instance the coin of ideal radius already is too big to pass the lens barrel !

benjiboy · Dec 24, 2019

Changing the batteries. is the least of a photographers worries it needs to be done so infrequently

bdial · Dec 24, 2019

Instead of actual coins, there is this;

coin driver

Steve Goldstein · Dec 24, 2019

Brilliant! But I can't find dimensions anywhere, even on the manufacturer's web site.

A new tool for battery compartment caps

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