Recalibrating Gossen Profisix & Lunasix F lightmeters - misreading a couple of stops

[Keith Graham]

Hi,

I have a Gossen Profisix, and a Lunasix F light meter. The second hand Lunasix was bought on E bay as a replacement for the profisix which was consistently misreading by a couple of stops. However, the Lunasix appears to suffer from the same problem. Both have been out of use for an extended period.

I fould that one trimmer pot on the Profisix (bottom right viewed with the back plate removed) appeared to provide adjustment. This was the first pot I tried turning and as it provided adjustment, I didn't touch any of the others. I have yet to carefully compare the readings from the Profisix with another meter/cameras for different light levels, but on the face of it, it looks like the Profisix is now reading correctly.

The board is different in the Lunasix - there is one trimmer pot visible, but it appeared to have no effect on the needle position. Perhaps this is for Flash calibration. There's a row of pots at the bottom of both the Profisix and Lunasix boards. Interestingly, the Lunasix has holes in the casing to allow adjustment when assembled, which are taped over.

Does anyone have experience of fixing/recalibrating these meters, are there service manuals and circuit diagrams available? I feel compelled to master this thing rather than send it/them back to Gossen.

Thanks and best regards,

Keith Graham

 

[Diapositivo]

Two stops is not a little mistake, and two light meters erring by two stops is diabolic a coincidence.

Maybe this is a daring question, but are you sure you use correctly the light meters?

For incident light metering you normally have to put the translucent dome in front of the cell, walk to the subject, and point the light meter toward the camera.

For reflected light metering you normally have to set a translucent dome aside (or take it out etc.) and you meter from the camera toward the subject.

When comparing two incident light meters have both instruments either in shade or directly facing the sun. The weighting of "peripheral" light might be different and when the sun is 45° or so the two instruments can give a different reading.

Maybe this is all already very clear to you.

Fabrizio

 

[Keith Graham]

Hi,
Thanks for the reply. I can confirm that I am using the meters correctly.

I have a cheap Jessops meter which reads correctly for incident and reflected light.

Best regards

 

[MattKing]

Is there any chance that your meters have two EV's of adjustment dialled in on the dials - the meters are set up to permit this?

Quality Light Metric is a good repair source: http://losangeles.citysearch.com/profile/55388/los_angeles_ca/quality_light_metric_co.html