Subject: Wow. (+) Author: drdread Date: 1/17/2002 10:45:38 AM Message:    That's a much different lens than the one I have. Mine is 5 years old, so I'm guessing they redesigned it. My lens has a minimum length of around 5 inches (~13 cm) and a maximum of around 8 inches (~20 cm). That's why I say you'd have a tough time using the lens. If yours is really only 7-12 cm, that's a different story. About the dome port: dome ports are used for wide angle lenses. For a 28mm lens, you probably don't need a dome port. For a 200mm lens, you *definitely* don't need a dome. When you can get away with flat ports, you're generally better off doing so. However, be advised that a 28mm lens behind a flat port will have a field of view more like a 32mm lens would -- the flat port magnifies things! If wide angle operation is what you want, the flat port will not help. OK, about diopters: you only need a diopter if you plan to use a dome port. Dome ports create a virtual image that is positioned at 2x the dome radius. For 6-inch (15 cm) ports, that image would be ~12 inches / 30 cm from the nodal point of the lens, which would mean the lens would have to be able to focus *at least* that close. Hence the need for a diopter. If you're going to use a flat port, I'd leave off the diopter, especially if your lens can focus down to 50cm. The diopter will cost you the ability to focus far away, limiting your focus range severely. So my advice is: leave off the diopter, use a flat port, and go for it! Do be wary of vignetting, however. Flat ports can indeed handle a 28mm lens, but 'regula' prime 28mm lenses are very short compared to the Tamron lens at full extension. The port has to be long enough to accomodate the extension. Thus you need a flat port long enough to handle the extension but wide enough to avoid vignetting the 28mm setting... Good luck, Dave

Subject

Author

Date

Lenses for SLR in UW housing (3)

peter van der voort

1/14/2002 5:59:36 AM

Great lens, but probably no good under water. (+) (2)

drdread

1/14/2002 10:43:52 AM

I still think I am going for it (1)

peter van der voort

1/17/2002 5:27:06 AM

Wow. (+) (0)

drdread

1/17/2002 10:45:38 AM

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