Dome vs flat port on 28mm lens
- Thread starter ericpitar
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tuner fish
Contributor
Greetings, I've learned and forgotten this twice now, ARG.
I'll be lurking here awaiting a wiser persons answer.
I'll be lurking here awaiting a wiser persons answer.
Eric,
Generally, lenses at 28mm and wider will benefit from a dome port as underwater the dome acts as a lens so the 75 degree FOV (field of view) your 28mm has above water will be just that underwater.
A flat port will do what typical diving masks do. make think appear a bit closer which kind of defeats the purpose of having a wide angle lens, eh?
Finally, the dome port UNDERWATER creates an"apparent image" the lens thinks is maybe 12" or so in front it. So your lens needs to be able to focus that close or autofocus won't be able to lock in this apparent image. this is a common problem with mid-range zoom lenses popular for surface shooting but having a minimum focus of like 16".
For using any lens like that you'd need to add a diopter (close up lens) and for Ikelite ports at least usually a +4 power.
Hope this helps.
dhaas
David Haas Underwater Photography
Generally, lenses at 28mm and wider will benefit from a dome port as underwater the dome acts as a lens so the 75 degree FOV (field of view) your 28mm has above water will be just that underwater.
A flat port will do what typical diving masks do. make think appear a bit closer which kind of defeats the purpose of having a wide angle lens, eh?
Finally, the dome port UNDERWATER creates an"apparent image" the lens thinks is maybe 12" or so in front it. So your lens needs to be able to focus that close or autofocus won't be able to lock in this apparent image. this is a common problem with mid-range zoom lenses popular for surface shooting but having a minimum focus of like 16".
For using any lens like that you'd need to add a diopter (close up lens) and for Ikelite ports at least usually a +4 power.
Hope this helps.
dhaas
David Haas Underwater Photography
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