Canon 10-22 + Sea & Sea Compact Dome = picture quality problems

Having moved to digital from a Nikonos 5 + 15mm & 20mm lenses, I was shocked by the drop in picture sharpness and I'm wondering what AM I doing wrong!

I'm using a Sea & Sea DX-400D housing + Canon 10-22mm lens + Compact dome port with an extension ring 40. I find that only about the centre 20% of each picture is really sharp the rest gets progressively worse towards the corners which are VERY soft. All my test shots were taken using f8, which I found worked very well with my old system.

Am I using the wrong size dome port or extension ring or perhaps I should be using a + 2 dioptre to help sharpen the corners (sea & sea don't make any recommendations on using dioptres) or even stop the lens down to f11 or f16?

Perhaps someone else is using a similar setup and could give some advice.

On a positive note this setup together with a pair of YS110’s is giving me cracking exposures which unfortunately shows up the soft corners even more.

I also intended to try my Canon 17-40mm with the same port setup but am now having second thoughts, although I see that this lens has been used successfully in other manufacturers housings.

Any ideas? Thanks.

not sure what the diameter of the compact dome is, but I believe rectiliniear lenses perform much better with a large dome, like a 20cm/8inch. The lens will be focusing super close with a small dome, requiring a stronger diopter. I know a 20cm dome is optimized with a +3 diopter, and a small dome will need a stronger one.

You are also comparing the best prime lens ever made for underwater shooting (nikonos 15mm) with a zoom lens behind a small dome - I doubt you can get the sharpness of the amazing 15mm. Hope this helps. Cheers,

Chris

Something else to check - the nodal point of the lens should coincide with the center of curvature of the dome.

I've had similar disappointments with my 10-22 and an Athena glass dome (now sold by S&S) although I don't recall it being as bad as only 20% sharpness - maybe the other way around - 80% sharpness but very soft corners (OK for blue water shots, but if you anything of detail in the corners - mush)! I never got around to testing a quality diopter. I would suggest taking a look at the Tokina 10-17mm fisheye lens w/ a 20mm extension. I've been real happy with the results plus the closer focusing ability of the Tokina is a real treat...

Thanks for your advice and ideas, I would hate to have to go back to using my nikonos & 15mm lens to get edge to edge sharp results if only because i've spent a small fortune on this new kit.

I have checked the nodal point with the center of curvature of the dome 'jcclink' and it looks a little out but not much. Problem is Sea & sea only have 2 extension ring options a 20 and the 40 which i am using, adding a 20 to that would put the lens way too far back. Perhaps the larger fisheye dome will be the answer as thanks to 'pakman' getting the optical glass dome is not really the answer, and i would like to stick with the lenses i have.

Thanks All

Andrzej