Older Pentax honeywell 1/21 10-21 range

[Mark Miksis]

I have recently purchased an older Pentax honeywell 1/21 spot meter. In taking a reading it seems to reference the lower scale 3-9 on the meter. By using this I get accurate readings. There is a upper scale through the viewfinder reads 1 0-21 and corresponds to the dial on the handle but I cannot find anything on the meter that will switch the meter to this scale. There is the trigger reading " L", a grey button reading "B" - I assume this is the battery check. There is a small set screw above the battery with an arrow pointing in both directions. Th at is it. Anyone have any answers.

Why does this meter have both a 9V and smaller battery?

[David Richhart]

Mark... you can probably get a manual for the meter at www.craigcamera.com

[Richard Stum / Kinesis]

I have this very meter. Mine is also for sell -- so send that one back and buy m ine WITH the manual! The L is for low light and provides a reading on the 3-9 sc ale (don't press this outdoors as it will peg the needle causing potential damage). B is for battery check -- the needle should reach the black horizontal line in t he viewfinder. I believe one battery controls the L scale (9v?) and the other for t he High scale. The white button on the side illuminates the viewfinder. I believ e the set screw is for calibrating.

[Wenbiao Liang]

Mark, I have the same meter.

The high scale does not need a switch to turn on. You simply aim the meter at the target, if the target's EV is higher than EV 10, you should see the reading in the 10-16 scale.

Hope this helps. Wenbiao

[karl payne]

I, too, have the Pentax 1/21 spotmeter. The 9v supplies power to the 3-10 lower range while the single, 1.35v KX640 (a fat mercury cell) powers the 10-18 upper range (no switch, always on) as well as low- level viewfinder illumination activated by the white button on the side of the handle. The 1/21 provides a closer view of the subject than the Pentax Spotmeter V (which has one continuous scale active only when the trigger button is engaged.) I like both these meters. I would like to know about alternative power sources for the kx640 mercury cell. Also, what is the effect of alternative batteries on the operation of the meter. Thanks. karl payne.

[John Adams]

I also have the "Honeywell Pentax 1/21 Meter" and on the back of the handle it says "Ashi Opt. Co.. Japan No. 21417". It is not like the other 1/21 pentax meters in one way... it does not have the button on the side of the handle to turn on the display light. As far as I can see it has no display light. The case is dark brown with black front. The rest seems to be the same as the other meters.

My question is... what mercury battery does it take? Is it the same as the one in the newer 1/21 meters? I may just have to hope that they didn't make a battery change with the button addition. There is a pretty big empty hole in the handle to fill, and it was empty when I got it. the 9volt battery seems to be no problem and operates the low light scale. The manual for the newer version calls for 1.3v mercury RM640R or E640N or equiv. If this is correct for my version is there a Wein Cell replacement?

I hope someone can help me with this... please.

thanks, john

[Duane Becker]

Hi. I have designed for a photography buff buddy of mine, a very good replacement for the mercury 640 style cells. It looks like a double tipped coin, and plugs down inside the battery well first, then you drop a cr1632 3 volt lithium cell in on top of it, and screw down the cover. The device has a regulator circuit inside one of the brass tips that regulates the lithium cell voltage down to 1.35 volts, steady as a rock for the life of the cell. He's using it in an old Pentax spotmeter, and he has given me very good reports of its use. I'm considering making a small batch of them and trying to sell them. If you guys need a regulated replacement for your 640 mercury cells, fire me an email, and I'll put you on the list. I'm guessing I'd have to charge maybe $30 apiece, given that there are two machined brass tips, a circuit board, a regulator, and two tiny resistors, and four springs around the circumference. The springs were designed to contact the "+" edges of the metal battery well. The design is only for those battery wells that are metal on the sides, and a minus tip spring tab in the bottom. The beauty is, you buy one adapter, you never have to remove it, and I custom calibrate each one for somewhere between 1.35 and 1.36 Volts.

[Duane Becker]

I've built a supply of these PX640 regulator adapters, and you may learn more or order one or two at the website:

http://www.sover.net/~snowleop/merc