Does anyone know why a +4 diopter lens is needed to use a zoom lens with a dome port, but a diopter is not needed for a prime lens?
Jeff
Jeff
Ikelite Dome Port...
- Thread starter Jeff Toorish
- Start date
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jtoorish:
Thats not true..
whether or not you need a diopter (not necessarily a +4) depends on how close the lens is capable of focusing.. A vitrual image is created in front of the port and thats what it needs to foucs on.. how close depends on the size and thickness of the domed port.. The virtual images usually fall in the range of about 5 inches to about 9 inches infront of the dome..
There's a whole boatload of explanations on dome ports and when to use a dioptre and which dioptre to use etc if you seach on www.wetpixel.com! Beware - some is pretty heavy slogging!
MarkH
Contributor
In general, zoom lenses don't focus as close as prime lenses.
OP
swankenstein:
Okay, that makes sense.
On the Ikelite website, on their port specs page, they specify which lens/port combinations require a diopter...and they always specify a +4.
JT
kdietz
Contributor
Typically, if the lens will focus in less than 12", it will not require a diopter
Karl
Karl
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