Gossen Lunasix F - Inaccurate

DavidClapp · Feb 28, 2025

I have tested this meter, comparing grey card and real world readings from a Sekonic L758D, a Nikon DP12 on my F2AS and a Mamiya 645 Pro TL. It’s measuring 1 stop out.

- exposure compensation on main dial is on 0
- set to reflective not incident
- needle sits in the base green line when inactive

So the meter has a calibration screw on the back and the only way if been able to get a more accurate result is to meter on the grey card and then take the meter out of calibration. This means the red needle does not align with the green base line - see below.

Am I going to get weird values in different lighting conditions now I’ve set it out of calibration?

Is there a way of properly calibrating it so everything properly aligns?

loccdor · Feb 28, 2025

That small green line is not an indicator of where the meter needle should rest.

Notice that it's the same color as the "BATT." The needle points to "BATT." when you press the battery test button and there's a good battery in. It points to the green line when there isn't good battery power.

In all other cases, it can point right or left of the green line. I tried it out on my Luna-Pro which has the same markings.

(And thanks, you reminded me to change the 9 volt in mine)

DavidClapp · Feb 28, 2025

loccdor said:
That small green line is not an indicator of where the meter needle should rest.

Notice that it's the same color as the "BATT." The needle points to "BATT." when you press the battery test button and there's a good battery in. It points to the green line when there isn't good battery power.

In all other cases, it can point right or left of the green line. I tried it out on my Luna-Pro which has the same markings.

(And thanks, you reminded me to change the 9 volt in mine)

This is from the manual - there is no picture to go with it, but (3) means the small green line on the left…

The needle is calibrated when it sits over the little green line on the left of the readout. When I put mine on the green line, by adjusting the trim put on the back, it underexposes by a stop.

Disconnekt · Feb 28, 2025

I have the Luna-Pro SBC, it says pretty much the same thing.

loccdor · Feb 28, 2025

Does it go to the green line when you take the battery out? That's what mine does.

Since you have a known good meter, couldn't you test it at various brightness levels? For instance aiming it at a monitor while varying the settings.

F4U · Feb 28, 2025

I believe I'd be suspecting a failing meter cell. In such cases you may be able to get meter accuracy at only one narrow range of light intensity, For instance if you can get accuracy a high noon in summer, but not as dusk nears, or vice versa. The cell has gone out of linearity and is failed. Depending on how bad, going into the meter and attempting to compensate by calibrating the high and low ranges may pull everything back where it needs to be. But it's been my experience that by the time it has come to that it's to late. And it wouldn't stay that way for any length of time anyway. I had a Luna Pro SBC once. Worst meter I ever had. For years it was the bane of my existence. Not implying yours is. I suppose lots of people like theirs fine.

ic-racer · Feb 28, 2025

That is not calibration. That is to zero the galvanometer. Unlike the modern digital meters, you have to send that in to service for calibraton.

reddesert · Feb 28, 2025

I agree with ic-racer, the various Luna Pro meters, including the earlier Luna Pro not-F, have a screw on the back to set the resting zero setting. This is often mistaken for a overall calibration screw, but it isn't. If you set it off its zero mark, the readings may be off in some unpredictable way. The Lunasix F / Luna Pro SBC is a nulling meter, unlike the earlier models, which should eliminate some sources of error but not all.

I would at least try to compare it against a known good meter at bright / medium / dim levels (like outside, inside, dusk) and see if it's always off the same amount.

DavidClapp · Feb 28, 2025

Appreciated replies. In the end my Mamiya 645 Pro TL, Sekonic 758D and DP12 on my F2AS all measure the same - the Gossen measures a stop under. For now I have just adjusted the screw on the back, to get the readings approximately the same.

I do like the layout and the format of the light meter - is this something that could be serviced? Could Gossen do it in Germany?

chriscrawfordphoto · Feb 28, 2025

DavidClapp said:
Appreciated replies. In the end my Mamiya 645 Pro TL, Sekonic 758D and DP12 on my F2AS all measure the same - the Gossen measures a stop under. For now I have just adjusted the screw on the back, to get the readings approximately the same.

I do like the layout and the format of the light meter - is this something that could be serviced? Could Gossen do it in Germany?

The screw on the back is NOT a calibration screw; the meter needs serviced. It may not be serviceable. Gossen will not work on it; they do not support meters that old anymore. It likely has a bad metering cell and they're no longer available unless you can find a shop that has some old ones left. I had two old Gossen Ultra-Pro meters that I tossed in the trash for that reason. You have a Sekonic L-758D, one of the best meters ever made; why bother with old junk like this?

F4U · Feb 28, 2025

Make your determination as to whether it is serviceable by doing this: Meter a brick wall in full sun with the Sekonic and the Gossen. Then step into a shadow area and measure a gray card laying on the ground in the shade. If the difference between the 2 meters is the same number of stops inaccurate, the meter might be able to be recalibrated as-is. If one of the 2 readings (light and dark) is off unequally between the 2 meters, that is a sure sign of a failed meter cell. I have no idea if compatible replacements are available from places like Digikey, Mouser, or some place on the internet. A bad meter cell will ofter let you calibrate beautifully either in the bright light or a dark area. It's either-or, but not both.

MattKing · Feb 28, 2025

Don't use the back screw to re-calibrate.
Use the other adjustments instead.
This one is particularly handy:

Check that the ASA/DIN dial is properly working and where it should be.
And make sure you are using a good quality alkaline battery.
Also - check for dirt, obstruction or damage to the window at the front that the metering cell is behind.

BrianShaw · Feb 28, 2025

That last point is a good one (not that there’s anything wrong with the other points but it meshes best with the comment Im about to make). One precaution I take with Gossen meters is to keep the incident done over the sensor at all times except when doing reflected metering to, theoretically, reduce the chance of that window getting dirty or damaged. I think it’s fairly robust but better safe than sorry.

DavidClapp · Mar 1, 2025

MattKing said:
Don't use the back screw to re-calibrate.
Use the other adjustments instead.
This one is particularly handy:
View attachment 392491

Check that the ASA/DIN dial is properly working and where it should be.
And make sure you are using a good quality alkaline battery.
Also - check for dirt, obstruction or damage to the window at the front that the metering cell is behind.

I have had issues before where modern batteries are too powerful. I had a Soligor meter that wouldn’t operate properly due modern batteries being too powerful, so I used a flatter battery and it worked fine.

It’s fine, I do what you recommend and just add a stop of compensation. It’s not much of a chore in the end.

DavidClapp · Mar 1, 2025

chriscrawfordphoto said:
You have a Sekonic L-758D, one of the best meters ever made; why bother with old junk like this?

I guess it’s because it’s a complex spot meter and feels less immediate. I really gel with the instantanous of the DP12 on my F2AS as it’s accurate and all in the camera viewfinder. I thought just pulling out this Lunasix would give me a similar experience using a rangefinder this weekend. Let’s see what the results bring home.

Hassasin · Mar 1, 2025

chriscrawfordphoto said:
The screw on the back is NOT a calibration screw; the meter needs serviced. It may not be serviceable. Gossen will not work on it; they do not support meters that old anymore. It likely has a bad metering cell and they're no longer available unless you can find a shop that has some old ones left. I had two old Gossen Ultra-Pro meters that I tossed in the trash for that reason. You have a Sekonic L-758D, one of the best meters ever made; why bother with old junk like this?

Goossens are not junk, not even the older ones, they've never been. One might argue they surpass L758D ever had to offer. Sure not as fancy, but super accurate for what they were meant to do, and arguably a lot easier to see what's going on with measurements. Calling L758D "one of the best meters ever made" is a stretch, no matter how subjective that may be.

Comparing the Gossen to readings of other listed meters is suspect approach. Not sure how it was done to ensure exact same area was read at exact same angle ... and nothing else. Cameras have centre weighted meters, not same what Gossen does. And because Gossen isn't all that old, I doubt cell is gone, but not improbable.

I would advise against throwing zero position out just to get it to match readings of some other meters. There is exposure correction on the dial, use that instead if you're sure you need to make such adjustment. The zero adjustment ought to stay on the green line, it's where meter's cell was calibrated for at the factory.

BobUK · Mar 1, 2025

MattKing said:
Don't use the back screw to re-calibrate.
Use the other adjustments instead.
This one is particularly handy:
View attachment 392491

Check that the ASA/DIN dial is properly working and where it should be.
And make sure you are using a good quality alkaline battery.
Also - check for dirt, obstruction or damage to the window at the front that the metering cell is behind.

I picked up a PROFISIX sbc in a parcel of oddments.
Lovely meter, but slightly out.
It appears to have the same dial layout.

I agree with Matt regards using the compensation dial.
Compared it with a fairly new Sekonic and a couple of cameras.
For my meter I set the compensation dial shown in Matt's picture to -1 for reflected light, and -2.6 for incident light.

There does not seem to be any information on line to readjust these meters , so I have a reminder label on the meter showing the compensations required, and happily live with it.

MattKing · Mar 1, 2025

BobUK said:
For my meter I set the compensation dial shown in Matt's picture to -1 for reflected light, and -2.6 for incident light.

That makes me wonder about your meter's incident dome - you are sliding it in place, aren't you, before taking the reading?

And in response to the OP, I just thought of another thing with the Lunasix F.
There is a button on the side that you push in to switch it from ambient light reading and flash reading. Its operation isn't entirely intuitive, and it can stick!

darkroommike · Mar 2, 2025

DavidClapp said:
Appreciated replies. In the end my Mamiya 645 Pro TL, Sekonic 758D and DP12 on my F2AS all measure the same - the Gossen measures a stop under. For now I have just adjusted the screw on the back, to get the readings approximately the same.

I do like the layout and the format of the light meter - is this something that could be serviced? Could Gossen do it in Germany?

Why not just adjust either the ASA or the exposure compensation dial so that the Lunasix "jibes" with the other meters?

chriscrawfordphoto · Mar 4, 2025

Hassasin said:
Goossens are not junk, not even the older ones, they've never been. One might argue they surpass L758D ever had to offer. Sure not as fancy, but super accurate for what they were meant to do, and arguably a lot easier to see what's going on with measurements. Calling L758D "one of the best meters ever made" is a stretch, no matter how subjective that may be.

Comparing the Gossen to readings of other listed meters is suspect approach. Not sure how it was done to ensure exact same area was read at exact same angle ... and nothing else. Cameras have centre weighted meters, not same what Gossen does. And because Gossen isn't all that old, I doubt cell is gone, but not improbable.

I would advise against throwing zero position out just to get it to match readings of some other meters. There is exposure correction on the dial, use that instead if you're sure you need to make such adjustment. The zero adjustment ought to stay on the green line, it's where meter's cell was calibrated for at the factory.

When its broken and there are no replacement parts available, it becomes junk. I drive a $50,000 Cadillac; it was a VERY nice car when it was new, and it is still a nice car, but eventually it will wear out, will start to rust, will start costing more to service than it is worth. Then it will be junk, and I will go buy a new car. Nowhere did I say that Gossen made bad meters; but old meters become junk when they cannot be fixed anymore.

wiltw · Mar 4, 2025

What are you using for batteries?! The Lunasix was made back when almost all meters relied upon 1.35V constant output from Mercury Oxide cells, and if you substitute alkaline button cells which fit the battery compartment, their varying Voltage starts at 1.5V and drops on a declining slope to under 1.3V.

Gossen actually offered a supplemental product to drop alkaline button cells down to about 1.4V held constant until the cell was depleted, to address the metering error inherent to not using Mercury Oxide button cell.

In comparing meter readings, point ALL of them at a BLANK (featureless) wall which is uniformly illuminated (no hotspots) and regardless of the reflected meter measurement angle, or bias (metering zones, centerweighted, spot) they should all measure to within about 0.3EV of each other (what the metering calibration standard assumes for meter accuracy)

Lastly, a meter in a digital camera WILL be measuring the same as a meter for a film-based camera...there is no such thing as a meter designed 'for digital'...I have several film cameras and handheld meters that are just as applicable (with matching meter readings) as my digital cameras!

Disconnekt · Mar 4, 2025

wiltw said:
What are you using for batteries?! The Lunasix was made back when almost all meters relied upon 1.35V constant output from Mercury Oxide cells, and if you substitute alkaline button cells which fit the battery compartment, their varying Voltage starts at 1.5V and drops on a declining slope to under 1.3V.

Gossen actually offered a supplemental product to drop alkaline button cells down to about 1.4V held constant until the cell was depleted, to address the metering error inherent to not using Mercury Oxide button cell.

In comparing meter readings, point ALL of them at a BLANK (featureless) wall which is uniformly illuminated (no hotspots) and regardless of the reflected meter measurement angle, or bias (metering zones, centerweighted, spot) they should all measure to within about 0.3EV of each other (what the metering calibration standard assumes for meter accuracy)

Lastly, a meter in a digital camera WILL be measuring the same as a meter for a film-based camera...there is no such thing as a meter designed 'for digital'...I have several film cameras and handheld meters that are just as applicable (with matching meter readings) as my digital cameras!

The Lunasix F, along with the Profisix & Lunalite (aka Lunapro F, Lunapro SBC & Luna-lux) all take 9V batteries (http://camera-wiki.org/wiki/Gossen_Profisix_/_Lunasix_F)

wiltw · Mar 4, 2025

Disconnekt said:
The Lunasix F, along with the Profisix & Lunalite (aka Lunapro F, Lunapro SBC & Luna-lux) all take 9V batteries (http://camera-wiki.org/wiki/Gossen_Profisix_/_Lunasix_F)

Thx for advising that the Lunasix F (and other newer meters) use 9V battery, while the older Lunasix used mercuric oxide.

Hassasin · Mar 4, 2025

chriscrawfordphoto said:
When its broken and there are no replacement parts available, it becomes junk. I drive a $50,000 Cadillac; it was a VERY nice car when it was new, and it is still a nice car, but eventually it will wear out, will start to rust, will start costing more to service than it is worth. Then it will be junk, and I will go buy a new car. Nowhere did I say that Gossen made bad meters; but old meters become junk when they cannot be fixed anymore.

The meter described has blue cell and is a mere 40 year old meter, it ain't "old junk" even if it is indeed off by one stop, which I expressed doubts is actually the case. And in all this, can be easily compensated right on the dial if that one stop change is needed. No need for any service from the given description of a "problem". And it is one of the best meters ever made. So this is what I was saying.

Gossen Lunasix F - Inaccurate

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Gossen Lunasix F - Inaccurate

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