12-24mm Nikon lens with Aquatica housing - help!

Hello,

I have an Aquatica housing with an 8 inch dome port in which I use my 12-24mm Nikon lens. The center of my pictures are super sharp but the edges are always out of focus. I tried two different extension rings between the lens dome port and the housing and neither one has fixed this problem; the edges are always out of focus. Aquatica suggested that I use an extension ring (I don't have the model number at hand right now), which I did, but the problem is still there. Can anyone please tell me what I need to do in order to have a completely sharp picture with this setup?

Thanks for your help.

Check this to determine the proper extension ring. The distance from the body flange (where the lens mounts) to the nodal point of the lens is approximately 65mm. This is where the center of curvature of the dome should also be located. So calc the distance between the housing flange & nodal point of lens. This is the width of ext ring you need (+/-). Make sure the dome is a full 180 deg. If not the width of the ext ring needs to be increased to make up the difference. Also try a diopter on the lens, like +3 or +4. Need to test this to see which is best for your system. For ref I use a 40mm ext ring & +4 with a FP170 (6.75" dia) port on my Nexus. Hope this makes sense.

The problem will not fully go away with any extension ring. It is just the way it is with that lens. The 9.25" dome does a better job, but it is not perfect either.

This problem has been discussed time and time again: basically, you need the biggest dome that you can find. This is a useful lens, but never performs as well underwater as it does on the surface.

If you search back in wetpixel, there's more advice than you really want to read....

Tim

like the others have said, there are tons of threads about getting sharp corners with a wide rectilinear. as mentioned, the larger the dome the better, and getting the riht extension ring and diopter are key.

but the other question is, what apertures are you shooting at? no matter how perfect your diopter/dome/extension ring is, if you shoot at f/4 you will always have horrid corners. you need to stop down as much as possible, preferably f/8 or smaller aperture. i have had acceptable results with the 12-24mm, 8" aquatica dome and recommended ext ring (though i think they recommend a longer one now than when i got mine). i have since moved to the beautiful 9.25" glass megadome and love it.

beyond that, if you want really sharp corners, get a fisheye lens, as the curvature more closely matches the curvature of the virtual image created by the dome. the nikon 10.5mm FE, sigma 15mm FE or tokina 10-17mm FE are all good choices on a DX camera and are very sharp UW. cheers,

chris