I use the R.D. Gray Periscope No. 6 on my 8x10. I'm curious if the lens design being described in this thread is of the same family as the R. D. Gray by the same name? I'm curious as I've traveled these forums for a number of years and have never heard mention of the Periscope lens. Now it's the talk of the town. ;-)
Basic sales info for the R.D. Grays No. 1 through No. 10 (ef 2-3/8" thru 36") can be found here . . .