This lens appears to be a convertable; the shutter has three aperature scales (7, 12, and 18") and the rear cell is marked 12". What combination achieves the other focal lengths? the front cell is not marked as to what its focal length is.

It looks like a neat old lens; any comments on its reputation?

If original it will be the 18", combined you get the 7". You'll get less distortion if you use the single cells behind the iris, but it takes a bit more bellows draw that way.
Use a strong yellow filter. They usually came with them new.

Thanks, Les. Closer examination of the front cell disclsed a very small marking of "18", so your are right.

I have heard about the use of a yellow filter with this type of lens, but have never heard an explanation as to why the filters are expected. I take it that the optical design needs the filter to correct for some inherent flaw?

I am guessing that my lens predates the first world war or thereabouts. Any idea as to when these were made?

These were popular from the trun of the century until WWII,

Most of these lenses, particularly when using a single cell exhibit various amount of color fringing. By using a strong yellow filter, you cut the blue light, which film is always excessively sensitive to anyway and moderate the fringing. A #8 wratten at least, better to use a #11.

Les