Gossen meters

[David Lingham]

I have a problem with two Gossen meters. A Lunasix F that I’ve had for a number of years, and a recently acquired Profix SBC. I’ve zeroed both meters and put in new batteries. In reflection mode both give the same readings. However with the diffuser in place for incident readings, the SBC gives two stops more than the Lunasix F.

 

[grain elevator]

Maybe the incident dome of the SBC has yellowed/become more opaque?

 

[Kino]

Are you using the proper battery?

If not the original spec battery, make sure it is the right voltage or use the appropriate voltage dropping adapter with a substitute battery.

 

[Arvee]

On a bright sunny day, which one indicates an incident reading close to Sunny 16? Also, yellowing of the dome wouldn't account for two stops. Yellowing typically accounts for 1/3 to 1/2 stop at the most.

 

[RalphLambrecht]

On a bright sunny day, which one indicates an incident reading close to Sunny 16? Also, yellowing of the dome wouldn't account for two stops. Yellowing typically accounts for 1/3 to 1/2 stop at the most.

I agree; sunny16 is an excellent way to check a meter; the sun is a very stable light source!

 

[David Lingham]

Thanks for the replies.

Kino: These meters are both version of what in the US were called Luna-Pro F and Luna-Pro SBC. These take a standard 9v battery. I’m using a new Duracell battery in each.

Grain elevator: both the domes look the same, no discolouring, but I will clean them both.

Arvee/Ralph: I’ve had the Lunasix F for a while and it gives consistent results, accurate to sunny 16. The Profix SBC was bought recently as a backup. I can’t understand why they match readings in one mode but not the other. Perhaps it is the discolouration of the dome thats creating the discrepancy. As long as I know how each meter responds, I can work with it.

 

[BradS]

It has to be the diffuser domes. They do discolor with age and exposure to UV (direct sunlight). Still, two stops seems extraordinary. Swapping the domes will be enough to isolate the issue to the dome and not the meter itself. If by doing this experiment, you find that the two stops follows the dome then I'd replace both of them with new domes and possibly send them (the whole meter) in for calibration. The domes used to be available as a replacement part for not a lot of money - perhaps, they still are.

Let us know what you find.

 

[Arvee]

Hi Dave, judging from your response, if both meters read the same with the dome to the side, then the likely suspect is the dome. Perhaps a small insect managed to get inside the dome and create an obstruction.

If you wish to inspect, you can remove the single screw on the back plate and remove the plate. Take a small piece of scotch tape and tape the meter zero plastic slotted screw in place so it doesn't fall out. Once inside you will find four brass slotted screws at the corners of the PC board. Loosen these screws a couple of turns or so and you can possibly create enough slack to remove the dome for inspection/cleaning.

The meter's clamshell is held together by these four screws AND three wires coming from the nulling pot/dial and to completely separate the two halves you must un-solder these wires. If you decide to try and remove the dome and not un-solder the three wires, do not exert much force in trying to create enough slack to separate the two halves enough to extract the dome as the wires to the nulling pot will break. Usually you can can gently create enough of a gap at the dome to remove it. The dome is flat on the 'bottom' side and has a 'spring loaded' plastic bump on the top side. Push the dome down into the slot in the bottom half and tip the dome out for cleaning. Once cleaned, re-insert the dome by re-inserting the flat side in the bottom slot, slightly compress the spring loaded bump and tip back into its slot. Re-tighten the four brass screws gently, remove the scotch tape and re-install the back plate with its screw. When re-installing the back plate, don't let the slotted plastic meter zeroing screw fall out of its hole. It's tricky to get it back into the slot on the meter movement's adjustment arm. That's it!

 

[waynecrider]

My Gossen came with 2 domes with different values.

 

[Arvee]

My Gossen came with 2 domes with different values.

That's interesting; what was the purpose of the two domes? Or was it a case of the meter just came with a 'back up' dome of sorts?

 

[Chan Tran]

Not familiar with the Gossen but I believe when you switch the dome in and out it has to activate a switch to switch the mode. I believe when the dome is in, the switch causes the meter to read lower for correct reading. If the dome is in and the meter still thinks it's in reflective mode the reading would be high. I don't remember correctly but my Minolta meter would read 2.3 stops too high if the switch doesn't work.

 

[DWThomas]

My Gossen came with 2 domes with different values.

Were they different shapes? I seem to recall some incident metering is done with a flat diffuser for copy work (but I've been wrong a few times! )

 

[Arvee]

Not familiar with the Gossen but I believe when you switch the dome in and out it has to activate a switch to switch the mode. I believe when the dome is in, the switch causes the meter to read lower for correct reading. If the dome is in and the meter still thinks it's in reflective mode the reading would be high. I don't remember correctly but my Minolta meter would read 2.3 stops too high if the switch doesn't work.

True with Minolta meters, a dial change is required for Sekonic meters; no switch activation with the Gossens.

 

[Arvee]

Were they different shapes? I seem to recall some incident metering is done with a flat diffuser for copy work (but I've been wrong a few times! )

Yep, I'm anxious to hear what this is about! I have never heard of a Gossen coming with two domes and I've been collecting Gossens for many years! I suspect you are correct and the meter is not a Gossen but perhaps a Sekonic that came with the flat diffuser and the hemispherical dome and the reflective attachment/aperture.

 

[AgX]

Are you using the proper battery?

If not the original spec battery, make sure it is the right voltage or use the appropriate voltage dropping adapter with a substitute battery.

In "switching" to incident mode all that one does is sliding a plastic dome in front of the sensor. No electrical circuit, or other optical devices are involved.

The battery might only come into play if one already in reflected mode is at the verge of sensitivity of the meter.



The best guess I can give is that the OP erroneaously reset the dial when changing the metering mode and explains to himself the error in result by switching the mode as such. Though it is just a coincide.

Another guess is some dirt having come under the dome and this is slided over the sensor opening too.

 

[David Lingham]

Arvee: Many thanks for your comprehensive reply. Possible a bit to involved for me to attempt.

waynecrider: I’ve not heard of a Gossen with two domes. Maybe a Sekonic.

Thank you all for your replies.

 

[runswithsizzers]

On my LunaLux SBC I can position the plastic incident dome so the photocell well is only half covered. In this position, it may be possible to direct a jet of air under the dome. Might blow out any trapped debris?

 

[waynecrider]

Arvee: Many thanks for your comprehensive reply. Possible a bit to involved for me to attempt.

waynecrider: I’ve not heard of a Gossen with two domes. Maybe a Sekonic.

Thank you all for your replies.

I have the manual and will check.

 

[Arvee]

On my LunaLux SBC I can position the plastic incident dome so the photocell well is only half covered. In this position, it may be possible to direct a jet of air under the dome. Might blow out any trapped debris?

Excellent suggestion!!

 

[Sirius Glass]

The two readings are aimed in different directions for starters. It is not unusual for them to not match, however they should be close.

 

[runswithsizzers]

The two readings are aimed in different directions for starters. It is not unusual for them to not match, however they should be close.

Define "close"

 

[chriscrawfordphoto]

There were a couple of Gossen models that had interchangeable domes. The Luna Star F and Luna Star F2. They came with the standard dome, and you could buy a flat diffuser and another dome made for work in very bright light which had a nuetral-density filter built in. You had to compensate the exposure readings with it.

 

[Sirius Glass]

The two readings are aimed in different directions for starters. It is not unusual for them to not match, however they should be close.

Half an f/stop.

 

[waynecrider]

There were a couple of Gossen models that had interchangeable domes. The Luna Star F and Luna Star F2. They came with the standard dome, and you could buy a flat diffuser and another dome made for work in very bright light which had a nuetral-density filter built in. You had to compensate the exposure readings with it.

Chris is corect, the two domes were standard and +5 for bright work.

 

[Deleted member 88956]

Chris is corect, the two domes were standard and +5 for bright work.

So OP has Lunasix F and Profisix SBC, how is this correctness relevant to his problem? Beacuse it isn't even remotely so.

A friend of mine had a problem with his BMW and I kept telling him why my Fiat was misbehaving, he still couldn't get his head around the problem he was dealing with.