Subject:	Yikes.
Author:	drdread
Date:	2/6/2002 10:15:35 AM
Message:

Extension tubes are not a good plan in a housing, because they basically cost you the ability to focus the lens. You'll be stuck with a lens at a single focal length. The traditional way to get extra magnfication from a macro lens is to use diopter elements. Even then, you lose some focal range; the lens will only focus over a very short range of distances. For instance, with a +2 diopter on my 105mm macro lens, I seem to recall a focus range of ~3 inches to ~1 foot.

I don't think you'll have any trouble using the macro lens behind the dome port, with or without a diopter, but be advised that the dome will cost you some magnification. The dome essentially acts like concave lens, widening the field of view. So if high magnfication is what you want, you're much better off with a flat port, which actually acts like a weak convex lens. The flat port will actually increase your magnification, while the dome will decrease it.

So my advice is: go ahead and try the macro lens in the dome port, with or without the diopter element, but plan to buy a flat port if macro is your game. FWIW, flat ports are pretty cheap, especially for Ikelite housings.

Good luck,
D

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