either way, here they are. Today I was just messin with an EF35mm f/2 lens, and stuck 31mm extension tube behind it too see how close I could get. The lens is basically resting on the plate here. No idea what the effective aperture of this set up is, though this is shot at f/8 on the lens. I think it is close to f/16 as far as light transmission goes. The extension tubes have no glass in them, just a tube, but they add a lot of length to the lens. Their purpose is to drastically reduce the minimum focal distance of the lens.
From memory the theory goes the longer the lens, the less effect extension tubes will have. I think there is a ratio going on, ie ratio of lens focal length to lens plus extension tube length. I think 31mm on a 35mm lens is a lot, but the same tube on a 135mm lens may make only a small difference in minimum focal distance. I will try it out one day, because really, 35mm is too close for macro - the lens is almost touching the subject here.
This was shot at iso160, f/8, 1/250s with a 60x90cm softbox held over camera. The shadow yo can see in the refeletion of the softbox on the orange m&m in pic is the camera :)
Just playin' today.
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