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View Full Version : J. Lancaster & Son meniscus lens questions

benrains
2-Jul-2010, 16:11
I recently picked up a J. Lancaster & Son meniscus lens from Eddie here. Its aperture scales are unlike any other I've encountered before. There are two scales on the lens. One is marked 10, 20, 30. A second is labeled "TIME" and is marked in the increment 1, 2, 4, 8--with the number 1 corresponding to "10" on the other scale, 4 corresponding to "20", and 8 corresponding to "30". The TIME scale is different from similarly numberd US aperture scale though (where 1 = f/4, 2 = f/5.6, 4 = f/8, etc.) Based on my own calculations, it looks like the lens is somewhere in the area of f/11-f/16 at its widest aperture and f/22-f/32 at its smallest opening. I was wondering if there's some sort of published conversion table for what looks to be J. Lancaster & Son's proprietary scales.

Oh, and unrelated to that, does anyone with a copy of the Vade Mecum know in what range of focal lengths the J. Lancaster & Son meniscus lenses were sold?

CCHarrison
2-Jul-2010, 16:34
Here is an 1888 ad that may help

Dan

Stephane
2-Jul-2010, 16:51
10 = f/10
20 = f/20...
no conversion needed.
the numbers 1, 2, are time equivalent for smaller apertures if you measure your base exposure from f/10. Thats at least how I saw it.

benrains
2-Jul-2010, 18:33
10 = f/10
20 = f/20...
no conversion needed.
the numbers 1, 2, are time equivalent for smaller apertures if you measure your base exposure from f/10. Thats at least how I saw it.

Ah, clever! That makes sense.

Steven Tribe
3-Jul-2010, 00:34
On larger objectives the 1,2,3 etc. scale is actually labeled "time". This very common for Lancaster lenses of all types.

Ole Tjugen
3-Jul-2010, 02:12
The "10 - 20 - 30" and so on scale is usually marked in AU on older J. Lancaster lenses.

"AU" is an abbreviation for "Arbitrary Units". They bear little or no resemblance to "real" f-stops. At least that's what I've found by looking hard at my own!