Port for Sigma 30mm F1.4 AND Sigma 10-20mm wide angle

[TheDeuce]

Hey all,

Just picked up a housing for my Rebel XTi and now need a suitable port. I want to be able to use both my Sigma 30mm F1.4 prime lens and my Sigma 10-20 mm wide angle. Is there a single port that will do both?

The Ikelite website notes that the 10-20 mm will work with the 5503.50 standard 6" dome, and that the 5503.50 works with lenses 'less than 4 inches long'. At 2.5' (including UV filter) my 30 mm is certainly less than 4 inches, but is it too much less than 4 inches to work without vignetting?

It would be nice if the website noted the range that a given port services (ie both minimum and maximum lengths) since there are two limiting factors in port selection. Since all my lenses are less than 6 inches long, the 5503.85 should work with all of them, right???

Also - diopter query. Anyone shooting the 30 mm without the diopter? I measure the focusing distance at under 12 inches but the spec sheet calls for 15 inches. That said, I'm measuring from the front of the camera body - I don't know if that's the right way to do it.


Thanks in advance for good advice. Everyone have a good weekend!



m.

 

[BrettF]

TheDeuce,

The Sigma 30mm F1.4 lens is 2.3" long, so the better 6" dome port option would be the #5503 port, which is 1" shorter than the #5503.50 port. The lens would need to be physically tested for vignetting if used with the longer #5503.50 port.

Another consideration is that by using the #5503.50 port, you are moving the dome farther away from the lens nodal point which could adversely affect your image quality.

Sigma specifications rate the minimum focusing distance at 15.7" from the "sensor", not the front of the camera. You should remove the UV filter and attach a +4 diopter when using the 30mm lens behind any dome underwater, regardless if it is a 6" or the preferred 8" dome. The diopter is "necessary" to allow the lens to focus underwater on the apparent image which is created on the dome.

Regards,