Lens fiddling

September 19, 2007

Decided to play a little bit with the two lenses I have for my 8×10. One is the landscape singlet I made, approximately 400mm, f/10. The second is a rapid rectalinear ca. 1880 which looks to be about 13″ and f/8, but I haven’t measured properly yet.

Still using B&W RC photo paper for my “film” as it is cheap and slow. Slow is important with both these lenses as they are barrel only, no shutter. Exposure times on the order of seconds to minutes are easier to deal with.

Decided to just shoot closeups of a small Alaskan totem pole that my grandparents acquired sometime in the 50’s (I think). In both cases, the Seneca needs to be racked out quite far. For my singlet lens, out to about 660mm, for the r.r. about 17″. Because this puts the bellows out past the focal length of the lens one must apply an exposure compensation factor to account for the light drop off. The factor is (BELLOWS^2)/(FL^2). Then multiply the exposure time by this factor.

Landscape Singlet Lens result: Landscape Singlet

Rapid Rectalinear Lens result: Rapid Rectalinear Lens

The position of the camera was not changed, but because the R.R. lens is more wide angle, the apparent magnification is less. So the scans were cropped to show approximately the same portion of the image.

Definately gotta try the singlet lens for some portraits!


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