2+ diopter for Megadome?

I have a new Aquatica AD800 housing with a 9.25 megadome. I am shooting a Nikkor 16-35mm f/4 behind it. The Aquatica website does not indicate a need for any close-up diopter with this set-up. One of the vendors I purchased the rig from told me that my corner sharpness will be much better if I uses a 2+ diopter. Pros & cons or opinions on this?

Thanks, Doug

I have an aquatica d40x housing with the 6 inch domeport. I use the 16-85mm lens from nikon. I use the +4 diopter to recreate the focus point on land. My buddy has a nikon d90 in aquatica housing with the 8 inch domeport also using the 16-85mm lens and he uses the +3 diopter to recreate the focus point on land. On your system if you use the +2 diopter your focus point under the domeport would be closer. I checked the nikon site and your lens spec is below. Right now your closest focus point is 1 foot. With a +2 diopter your closest focus point would be around 10 inches. With the size of your domeport and sunshade on the domeport i think getting strobe position might be difficult and create shadows trying to light subjects starting at 10 inches.

I think the 10" focus distance is focusing on the apparent image of the dome, and not the distance from the exterior of the dome, so I don't think strobe position should be a problem. Correct?

No the specs i gave you is from nikon site which is 12 inches from the sensor plane. And if you look at it 1foot when set to 16mm and .9 foot when set to 20mm to 28mm. And the distance from the sensor plane to the exterior of the dome is about 6 inches. You could shoot pictures from about 3 inches from the exterior of the port which would be hard for strobe position. It would be real close focus wide angle. On my system i use the +4 diopter as per aquatica chart. For macro i do add a second +4 diopter to get 1:1 macro but even with 2 - +4 diopter i have about 6 inches from the port to subject so lighting is not difficult.

Saga , I don't think you are understanding the optics of the apparent image we are dealing with when using dome ports. The distance from sensor to the subject is not the focal distance to the virtual image we are taking a picture of. Also, strobes are aimed to illuminate the subject, NOT at the focus point of the virtual image! (it might help if you read this http://scubageek.com/articles/dome_field.pdf ) , but thanks for trying to help me anyway. Does anyone have experience with the Aquatica 9.25" megadome and the 16-35mm? If so, please let me know if you are using a diopter. Thanks.

Bump

have you emailed Jean@aquatica.ca?

Sorry, 'been kind of all over the place lately :-), while the +2 diopter is not obligatory, it does help with the close focusing capability of the lens. You can use it both way, if you consider close focusing on your subject, then a resounding yes is my answer, if on the other hand, the subject is rather far (wrecks, whale...) then I don't feel it is a must, it does reduce the field of view of a lens BTW.

It's one of those situations where both side are rights, whether you see a benefit in using one will be up to you and the type of context you are likely to use it in.

Cheers

Thanks Jean!

I use the 16-35mm as a wide-angle behind a 9" dome without a diopter:

Blue-striped snappers, Ari Atoll, Maldives. Nikon 16-35mm, Nauticam 9" dome with a 70mm extension ring.

Thanks, I am thinking I will go with the 2+ for starters to improve the corner sharpness!