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Is there a forum or information somewhere about constructing large lenses with rather large image circles.
In Photo 1 I often turn the classroom into a camera obscura to help excite students about photography. I think showing them how a lens affects the exposure and the sharpness would help. It doesn't need to be super complex or sharp. just needs to get the basic ideas across.
If the lens doesn't need to be sharp enough for photography then you don't really need to construct anything - surely a simple lens from Surplus Shed would show the principle well enough? there is a 6 inch, 2600mm meniscus on there which would have a huge image circle at infinity.
in the "primitive photography" book, there is a section on making lenses.
some lenses are very simple, and others are a bit more complicated.
what sort of coverage + image circle are you looking for ?
i have gotten some very small meniscus lenses from "the shed" and
used them on 11x14 cameras ...
The bigger the image circle, the better. I think something in the 14" range would be minimum size I'd want . . . just so that the students don't "strain" themselves too much (I wish I was joking but I've had to explain what a ratio is more than once this semester to college level students).
a rr lens is just a pair of groups with a big airspace between them ...
maybe the good folks at the surplus shed could suggest which plano concave + plano convex lenses to use
i have made barrels out of cardboard.
you can also remove one of the groups, to increase the focal length, and coverage since it is convertible
sounds like a fun project !
I'd just get the biggest cheap magnifying glass you can find. Put it in a piece of pipe made of cardboard or plastic. Make waterhouse stops if you'd like an aperture. Put it a few inches ahead of the lens.
E. von Hoegh
A pair of surplus telescope achromats mounted in a barrel will give you a Rapid-Rectilinear lens of about half the focal length of the single achromat, with a decent image circle. Waterhouse stops could be used, placing them midway between the cells. A R-R is a pretty good lens, too. Very sharp in the central zone, not bad in the corners.
Yeah my photo 1 class starts with the very basics of converting a room into a C.O. Then I get them to make their own pinhole cameras. While they're drying, etc. Introduce them to photograms. Then I make them go out and "properly expose" their paper.
It works decently but there's a jump b/n pinhole and actual camera.
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