Does anyone else have experience with Imperial Duo-Flex?

DOF is funny -- because you're enlarging twice as much for the same final viewing size, you have half the allowable circle of confusion. That said, I recall getting very good focus with my Kievs (20 mm lens, as I recall) even near minimum distance of 0.5 m (around 20 inches), at f/11 or so in daylight, and never had complaints with my fixed-focus MG (which I bought in 1981, when you could still buy Minolta 16 film in 2-3 different emulsions at most camera stores and some drug stores). Never tried printing bigger than 4x6, though.

Edit: You can check it here -- use LMF 2.0 (this is effectively your frame's multiplier to get to 35mm full frame).

RLangham said:

Yeah, I was corrected on the name above. Does yours perhaps have the lens in backwards? It is supposed to have the curved surface forward, much the contrary to what someone experienced with simple cameras would expect-- it is not a meniscus like on a Brownie.

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Well you made me check! I took the thing apart and it turns out that the taking lens is actually a simple plastic meniscus (the viewing lens is bi-convex for whatever it's worth). The lens was installed with the convex surface facing outward, which should be the correct way, as far as I know. My suspicion is that the "duo-" or "dua-" in the name of many cameras of this class was meant to indicate a twin lens camera, rather than a dual-element lens. Anyway, if I get ambitious one of these days I think I'll run a roll of film through it to see what kind of results I get. That should provide a good indication of whether the blurry frames from the original photographer were the result of camera design, camera defect, or some kind of film loading error.

I've seen single-element meniscus lenses in two common orientations: convex forward, in front of the shutter/aperture, and convex toward the film behind the shutter/aperture. The latter, in my experience, tends to give "better" images -- a flatter focus field, less aberrations. Some cameras with the latter setup have a simple flat cover glass in front of the shutter (Brownie Hawkeye), others don't (Ansco Jr. and many other cardboard box cameras).

My belief is that those with the lens mounted convex forward, in front of the shutter/aperture, were made so in order to sell better, because consumers were comforted by being able to see the lens -- and at f/11 to f/16 it doesn't make a huge difference in image quality, just more focus falloff at the corners.

I've also got a camera that was close to this class, the Speedex Jr., a 6x6 folder with 2-3 aperture settings, one shutter speed plus B, and fixed focus -- that has two meniscus lenses, one in each of the classic positions. This would have raised the price a bit compared to the common box camera lens, as would the folding configuration -- but the combination takes the camera up the ladder a rung or two. The images are very good: count the bricks in a wall at a block away, identify the species of climbing plant from leaf shape at the same distance.



Speedex Jr., Portra 400.