Placement of cells - 5x7 triple convertible lens

[rrunnertexas]

OK, this should be an easy question to find an old thread about, however, I have not, so I'm asking...

I just finished cleaning a Wollensak Seneca Autic shutter that now works great - with a Seneca triple convertible lens.

The lens aperture scale is marked as follows:

8"
14"
18"

Each with their respective aperture scales.

Both front and rear lenses together are 8", but what is the configuration for the 14" and 18" focal lengths?

Thanks!

[mdarnton]

There are various ideas on this, but for the authoritative opinion, page 45, here: http://www.piercevaubel.com/cam/cata...enecalp262.htm

The reason to move components to the rear is improved optical quality; the loss is a slight loss of effective lens speed. Some lenses work quite differently with different placements, and some are designed for the front to go on the front, regardless. Not this one, apparently.

[rrunnertexas]

mdarnton - that is the information I needed. Thank your for sending the link.

I made one exposure using the rear element only and the negative looks nice. I'll scan it and know for sure soon.

Having a "zoom" was really nice for the shot I made. I was at fence line composing a shot of an old house and was too far away to get what I really wanted in the shot. So, I removed the front element, leaving just the rear. With only that element the scene was brought closer to me and I made the exposure at f/32 for 1/8th second.