Lunasix 3 meter
There's one for sale in town and the price is right $5.00).I realize it takes the ole' Mercury cell and a person can buy the adapter for lowing voltage of LR44's but can I use the 1.5v battery and calibrate the meter (ie.set the iso)by comparing the reading from my N90s or F3hp?
I'd be sure to zero the meter before you load the batteries. Switch the meter into the "on" position, without batteries, and hold the switch down. The needle should land exactly on the upper left line, the "zero" mark; if it doesn't, there is a small screw, which you access from the underside of the meter body. Tweak that until the needle lines up. Release the switch, battery up, and off you go.
It would be a good idea to do a linearity check. You will need a selection of neutral density (ND) filters to make this test. For example, if you take a reflected reading from a light source, like a light box, or a white lampshade, you place an ND filter of known density in the meter cell's path, and the reading should change by the amount of the ND filter. With a 1.0ND filter in the path, the needle should deflect by exactly 3-1/3 stops.
My method is to use a lamp and diffuser, and to adjust the voltage of the lamp to get a reading on the meter scale of 19-2/3, which is equivalent to "sunny 16" conditions, roughly 6400 footcandles (fc). I then use a series of neutral density filters, until I reach 7 on the meter scale, equivqlent to about 1 fc (for those of you who wish to photograph in Ottawa anytime soon, that is about the intensity of the light given off by the Centennial Flame on Parliament Hill).
If the linearity check fails, if adding that 1.0ND filter doesn't produce the desired change, them the meter will have to be serviced. There are probably adjustment potentiometers for a linearity adjustment, but I don't know for sure; I've never open the case on my vintage 1976 Lunasix 3 meter.
I am still using the last of my 1.35V mercury cells; I have two of the air-activated type I bought from Freestyle two years ago, and still haven't used. When the current batteries die, and I install the air-activated ones, I am going to order the adaptor from B&H and fly with the 1.5V batteries.
