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Gossen Luna Pro light meter

Mario Henriquez , Nov 06, 2008; 10:52 p.m.

I just got a Gossen Luna Pro used from KEH. I went to buy batteries, which are not easy to find. I put the batteries in but the meter gives no readings. It doesn't appear to be working. In the manuals I've seen, they say to get "Mallory" PX 625 batteries. Mine didn't say "Mallory" and, now that I remember, they had a Z at the beginning, as in Z 625 PX, or something like that. The guy at the store saw my meter and said that it took a little while for the batteries to kind of "warm up." Did I get the wrong batteries? Can someone help? Does the "+" sign go down or on top? Thanks.


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Michael Axel , Nov 06, 2008; 11:06 p.m.

Get the manual for your meter here: http://www.butkus.org/chinon/flashes_meters/gossen_luna-pro/gossen_luna-pro.htm.

Be sure to leave a few bucks via PayPal.

Mario Henriquez , Nov 07, 2008; 12:22 a.m.

Yes, got that. It's not the manual that I need. It doesn't really say anything in specific about the batteries. Thanks anyway.

Dave S , Nov 07, 2008; 01:40 a.m.

Mario, hi. Google 'PX625' or '625PX' and you'll find a lot has been written about this. The PX625 was a mercury battery widely used in photo equipment up to the early 1980s or so. They have been banned worldwide and are no longer manufactured.

You can get a silver version of the 625, called something like a S625PX. They have the same physical dimensions, but are slightly higher voltage than the mercury cells (1.5V instead of 1.35V). You would probably need to get your meter recalibrated for the different voltage.

There are other workarounds-- the Cris adapter, 675 Zn-air hearing aid batteries, and the Wein cell (an expensive modified hearing aid battery). You can read about these elsewhere.

Brian S. , Nov 07, 2008; 09:44 a.m.

I forgot to look at my meter last night, but I'm 99% sure the + faces up. You can try it both ways, though... if you haven't already. The comment from the photoshop about the bateries needing to "warm up" sounds like the babbling of a well-intentioned but somewhat ignorant crackpot.

If your meter works you still have the voltage issue to deal with, as Dave Sims mentioned. I use the adapter made/marketed by Gossen. Bought it from B&H. Not cheap, but it works flawlessly.

Mario Henriquez , Nov 07, 2008; 10:25 a.m.

Ho do I recalibrate? I nee to use it now. Thanks.

Brian S. , Nov 07, 2008; 11:32 a.m.

I don't think it's a D-I-Y job. If you need it NOW, perhaps your best bet would be to guestimate the adjustment using Sunny-16 as a standard.

Brian S. , Nov 07, 2008; 11:34 a.m.

But for a "need it now" solution... the 675 Zn-air hearing aid batteries, and the Wein cell suggestions is what you should be looking at. Depending on where you live you can get these at a local photo shop or even a local drug/variety store.

Mario Henriquez , Nov 07, 2008; 11:45 a.m.

So, Brian, I'm out the $20 I spent for the batteries I have now? Damn, KEH really screwed me on this one. They were really helpful, the guy who took my order was really helpful, but he shouldn't have sold me, a beginner (and he knew it), such a "cumbersome" light meter. Or if he was going to sell it to me, he definitely should've said that these batteries are hard to find, they were discontinued a long time ago and you have to make sure you use XXXX kind of battery, or something. He said absolutely nothing. I never could have gussed how difficult/cumbersome this little process would turn out to be. Now I'm p1ssed.

James Ollinger , Nov 07, 2008; 12:42 p.m.

The salesman may not have realized it. If you went on the internet and looked up the batteries for your meter, the battery companies will tell you that modern equivalents will work properly, even though it may not be the case.

Gossen sells an adapter that supposedly allows you to use modern batteries in the Luna Pro. It's expensive. I haven't tried it so I don't know if it works.

The best way to deal with your meter, if you don't want to spend more money (and I can't blame you) is to test it against another meter on a variety of different light levels and see how far off it is. Make notes, and then make the corrections as you meter your subjects.

Example, and I'll just make up numbers to illustrate it: let's say you have a camera meter and your Luna Pro and a gray card (or any object that can be flatly and evenly illuminated across the field of view). You set the camera and meter for ISO 100.

First subject is a low light level. Camera says f/2 @ 1/15th. Meter says f/2 @ 1/60th. You write down that your meter reads 2 stops high.

Next subject is a medium light level. Camera says f/8 @ 1/60th. Meter says f/8 @ 1/125th. You write down that your meter is 1 stop high.

Next subject is bright. Camera says f/22 @ 1/500th. Meter says f/22 @ 1/750th. You write down that the meter is 1/2-stop high.

Now you can meter unknown subjects. If you're at a low light level, open up 2 stops. At a medium light level, open 1 stop. At bright light levels, 1/2 or 1/3rd stop, or leave it alone.

(As I said, I just made that up. You need to do your own tests to get real world results).

You can do that with any meter, even old seleniums that you wouldn't otherwise trust. You see how they read vs. a known good meter and note how far off it is. If the results are consistant, then you can use the meter (provided you correct). If the results are erratic, then you need another meter.

BTW: if you end up buying another meter, try to get one that takes a modern battery. The Luna Pro SBC, for example, uses a 9v battery. It's not exactly compact, but you can go almost anywhere and get the proper battery for it (at least you can in the US).

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