Gossen Luna Pro: readings way off

jeffreyg · Jan 24, 2015

While I generally use a Pentax spot meter I also have an old LunaPro and an UltraPro. I have always removed the batteries after use and kept them closed in the original leather cases. I wonder if that has helped to preserve the cells. After reading this post I decided to check one against the other in both the reflected and incident modes and they were less than 1/2 a stop different. Lucky?

http://www.jeffreyglasser.com/

E. von Hoegh · Jan 24, 2015

jeffreyg said:
While I generally use a Pentax spot meter I also have an old LunaPro and an UltraPro. I have always removed the batteries after use and kept them closed in the original leather cases. I wonder if that has helped to preserve the cells. After reading this post I decided to check one against the other in both the reflected and incident modes and they were less than 1/2 a stop different. Lucky?

http://www.jeffreyglasser.com/

I don't have the established science to prove this, but I think that keeping the cells dark when not in actual use is a very good plan. I have the two Gossens, as well as two Weston Master III meters (ca. 1955) that are very accurate - one of each are NIB. I've always been very careful to keep the cells as dark as possible with the meters in use. I recently got a 1969 Kiev 4 that looks new inside and out, I doubt it's had 20 rolls of film through it. The meter is active and accurate after 46 years ( I wish I could say that for the shutter).

Sirius Glass · Jan 25, 2015

The silver oxide batteries are not the right batteries. You need an adapter for them to work correctly.

MattKing · Jan 25, 2015

Sirius Glass said:
The silver oxide batteries are not the right batteries. You need an adapter for them to work correctly.

As I understand it, the OP's silver oxide batteries were supplied with the Gossen adapter that he purchased for the express purpose of allowing the use of modern silver oxide batteries in his meter.

This one: http://www.bhphotovideo.com/c/search?N=10089868&InitialSearch=yes&sts=pi

Ken Nadvornick · Jan 25, 2015

You guys needed to look ahead...

Years and years ago I purchased, sealed, and froze two dozen PX625 mercury cells for future use. I use them in my Yashica MAT-124G TLR meter. And a Canonet QL17 GIII rangefinder. They will routinely last 5+ years each, often longer. Two dozen is way more than a lifetime supply.

And no adapters needed.

Ken

BrianShaw · Jan 25, 2015

The Gossen adapter has "looked promising" for more than a decade.

chip j · Jan 25, 2015

Wein cells seem to work well in my Luna Pro.

John Koehrer · Jan 25, 2015

BrianShaw said:
The Gossen adapter has "looked promising" for more than a decade.

As has the CRIS adapter, single cell or double.

Alex Muir · Jan 25, 2015

BrianShaw said:
The Gossen adapter has "looked promising" for more than a decade.

That's what I was thinking. Gossen was doing the conversion for these meters in the mid-90's.

Alex.

wiltw · Jan 25, 2015

John Koehrer said:
As has the CRIS adapter, single cell or double.

Have the CRIS MR-9 with my Olympus OM-1, with it I can use Silver Oxide 386

DWThomas · Jan 25, 2015

My only vintage Gossen meter, an early 60s Luna Six, has an open circuit in the meter movement, so I had been ignoring this thread. But I wonder, did Gossen or any third party ever operate on the older meters to take silver oxide cells without an adapter? If so, using an adapter in one might throw the reading off considerably -- if that made it read low, one might over expose to compensate. (Just a thought)

Patrick Robert James · Jan 25, 2015

A few years ago I bought a bunch of darkroom stuff and there was a Luna Pro included. I already had a bunch of meters including a Luna Pro SBC but there is something great about the old manual dials. I threw a couple of batteries in it and of course it was way off so I decided to convert it for fun. I put whatever diodes I needed in it and then calibrated it. It works perfectly now. It does need a bit of "ramp up" time, a second or two, before it settles. Great old meter.

OP, I didn't find it all that difficult to do. Somewhere out there among the interwebs there are instructions. Give it a go.

BrianShaw · Jan 26, 2015

Unfortunately history has long ago disproven your clever engineering research.

p.s. Regarding discharge curves, you may want to check your facts. It is not true (and never has been) that the curve only holds flat for 1/2 of silver oxide battery life. Here is an example: http://data.energizer.com/PDFs/silveroxide_appman.pdf

BrianShaw · Jan 26, 2015

Interesting. That contradicts many other generic data. Isn't this, though, the battery used in the MR-9 adapter? Note the vastly different discharge curve from your example.

http://www.houseofbatteries.com/documents/386-301.pdf

http://www.ruedespiles.com/images/PDFmedia/Fiche_technique_Maxell_Oxyde_Argent_SR43W.pdf

BrianShaw · Jan 26, 2015

APUGuser19 said:
I don't know. ...

I think I can tell, Tom/Henry.

E. von Hoegh · Jan 26, 2015

APUGuser19 said:
After day's thought, old ideas have reoccurred to me on this subject. Back when I was working on these meters I knew about these little inserts for the silver batteries and had deemed them unacceptable to me. The reason being that while diodes may drop voltage to more proper levels, they did nothing about the poor discharge curve of silver batteries. The curve only holds flat for 1/2 of battery life. I decided that while they were better than no alternatives, they simply could not compare with the discharge curve of the mercs. Doing research, I came upon some posts from another member named van Hoegh on this site and his Wein cell successes. I still think that his idea is better than the diode or resistor ideas. A meter's purpose is accuracy at all times. The Luna-Pro has no voltage regulation in its design. And silver batteries cannot deliver a flat discharge curve. Outside of fabricating an on-board voltage regulator, his Wein idea still is the best option for long-term meter accuracy.

I don't use Wien cells, I use hearing aid cells with all but one airhole blocked.

BrianShaw · Jan 26, 2015

E. von Hoegh said:
I don't use Wien cells, I use hearing aid cells with all but one airhole blocked.

Left or right nostril?

Gossen Luna Pro: readings way off

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