150mm Computar Question

[Michael Kadillak]

In the process of assisting the wife of a fellow large format photographer who recently passed go through his camera and lens inventory in anticipation of selling it for her, I came across a unique lens that I wanted to see if anyone can help me with it. The lens is a 150mm f9 Computar and it is mounted in a Copal #1 shutter with a dual aperture scale the lower one being F9-F64 and the top one being f18-F90 (a near doubling). Curious about if this is in fact a correct aperture for this lens I am able to singularly use the front as well as the rear lens elements to form an image which seems to make sense. With both elements the lens appears to cover 8x10 as do each individual element individually. So my question is is this in fact a designed convertible lens and does the second aperture scale work with either individual element? Any additional details would be welcomed. I have the 305mm Computar and the 240mm Computar lens and never considered them as convertible lenses.

Many Thanks!

[xkaes]

These convertible lenses appeared at first under the Computar label, and later under the APO Kyvyx label, and one stop faster -- same manufacturer & same formula.

The front element is unscrewed and the second scale (higher f-stops) is used. The focal length is basically doubled -- hence the f-stop change. The rear element alone is slightly softer.

They came in 150/210/240/270/305/360/480mm. The Computars were f9, and the APO-Kyvyx f6.8 -- except for the 360 & 480.

These are all process lenses with flat fields.

[Dan Fromm]

http://www.largeformatphotography.in...overage/page10 See post # 97. Read it carefully. Coverages claimed in
text are much larger than coverages claimed in the tables.

[Oren Grad]

I have the 150 Computar, in a late-model Copal with just a single aperture scale. Re coverage, I've used it well stopped down as a wide for whole plate with satisfactory results, but I can't vouch for 8x10. Afraid I haven't tried the rear cell alone.