Here is the picture I promised. Just one f-stop scale. No 12.5
How can I use this one scale for three different lenses?
The fstops on the shutter are for the using the lens with both elements attached. You can calibrate ftops for using the single element lenses from the chart I attached by matching the iris opening dimension you would get for the combined lens to that which you need for the single elements.
For the combined lens, f7.7 has a 17mm iris opening. f45 has a 3mm iris opening. You can get the iris opening size for stops between f45 and f7.7 from the chart. Then go to the section that says "Protar Lens". This gives the iris openings for the single elements. For the 22cm element, f12.5 has an 18mm iris opening. Therefore, you can set the fstop scale on the shutter to f7.7 to shoot at f12.5 with the 22cm element. To shoot the 22cm element at f45, set the iris between f22 and f32 (closer to f32). This will give an iris opening of 5mm. You can use the 35cm element in a similar fashion. For the 35cm lens, you will be limited to stops between f22 and f45 within the scale limits, but this is no problem since you have to stop down the single elements to get decent performance anyway. You can make a chart to help you remember the correct positions. Just remember to put the single element at the back of the shutter, behind the iris.
Thanks Pete. I was thinking about making a small chart too.
This must be a real early Protar since it does not have anything Zeiss on it. Or it was after WWI when they no longer used the Zeiss name. But not having the three scales on the shutter is odd.
It was not made by Zeiss. B&L licensed the Zeiss patent and manufactured the lens in the US. B&L used english units (inches) for focal lengths. Zeiss used mm or cm for their lenses. For practical purposes, they are the same. There is a thread on the LF forum regarding B&L serial numbers and date of manufacture.
Protar VII had different focal lengths front and back; the Protar VIIa had the same focal lengths front and back. You could get them either way...
Actually, as I understand it the Protar VIIa is any convertible made up of two Protar VIIs. If they are the same focal length, it's an F6.3 Protar VIIA. If they are two different VIIs, it's still a VIIa, but will be F7 or F7.7. I just figured this out when I bought my first VIIa....