grunzster:
Is there any real benifit to using a real lens post instead of plexi?
Will the image quality be much better?
I'd imagine that if I don't mount the port (at least with a dome port) centered perfectly in front of the lens that it would actually cause distortion, correct?
Grunzster, I'm not sure what you're refering to. Do you mean actually having the wide angle adapter lens sealed to the front of the housing, so the lens element contacts the water?
If so, the optics are designed for contact with air; it will work terrribly (if at all). The refraction index of air-to-glass is part of the design. Just look at the the Nikonos 15mm, 20mm and 28mm, both of which are built to work with water contact (not air) so they are underwater-only* lenses.
I've never had a lens grossly misaligned from the center of a dome, so I can't say what the results would be, but it just
sounds like it would look all whacked.
If you're using wide angle, a dome port is really the only way to go. If not, a flat port would sure be easier to align, as there isn't really an "optical axis" beyond having the port surface perpindicular. I've noticed that few consumer video housings have dome ports, though. It's possible the problems of flat are covered by the limited video resolution.
Check here for a good reference between the merits of both.
If you were asking about the difference between domes that are mineral glass or acrylic, you will have opinions split about the advantages (or weaknesses) of each. I suspect you will find that those with the glass ports passonate about their quality, and those with acrylic think that glass is overpriced for little gain. Personally, I've found the greatest correlation between dome size and end quality. All my still housings have 8" domes and I'd have a 14" one if Aquatica still made them.
All the best, James
*The 28mm can be "cheated" into shooting above water, by setting the focus at a tad over 3'. This becomes infinity. Stopping down, for depth of field, will cover for not having exact focus.
