Sea & Sea Dome Port Extension Ring Confusion

I'm Confused!

With a canon EF-S 10-22mm lens, Sea & Sea now recommend an extension ring 40 with both the NX Fisheye a NX Compact dome ports. (incidentally last year the Compact dome only required an SX Extension ring!!). What I find really confusing is that both the Canon EF 16-35mm & EF 17-40mm lenses require no extension ring at all when used with the NX Fisheye Dome Port, this seems totally wrong?! Both these lenses are taller than the 10-22 and extend a long way into the Fisheye dome port so you would expect that the Extension ring 40 would HAVE to be used. Having checked a block diagram for all 3 lenses they are all fairly similar in design so the lens entrance pupil should in theory be in a similar location as well, with the lenses set to the widest setting. To add to the confusion Sea & Sea DO recommend an Extension Ring 40 with the EF16-35mm but only with the NX Compact Dome Port! sad.gif sad.gif sad.gif

My intention to use a Canon 400D + EF 17-40 + NX Fisheye Dome Port + Extension Ring 40, am I correct or am I missing something? Would this setup also benefit from the use of a +2 diopter to bring the picture edges more into focus.

I have had limited success with the EF-S 10-22mm lens + NX Compact Dome Port + Extension ring 40, resulting in pictures with sharp centers but very soft edges so am hoping that switching to the Fisheye Dome Port will improve the situation with this lens. Would a +2 diopter also help?

Sorry for such a long question but any advice would be much appreciated.

Andrzej

Hi Andrzej,

The Sea and Sea port charts have horrible recommendations for the wide lens setups.

For the 10-22, 17-40, and 16-35, I recommend extension ring 40 and a +2 diopter. I always recommend the larger Fisheye dome port over the smaller compact dome. All 3 of the those lenses will benefit from the diopter. The combination of the large dome, extension ring, and diotper will allow for better corner sharpness, especially at the wider settings.

Best regards,

Jim

Hey Jim, glad you jumped in. What's your recommendation for the Tokina 10-17 with the NX Fisheye dome? (MDX -40D) I'm trying it in the pool with no extension and it looks OK so far, (actually it looks great) but I haven't had it in the Ocean yet. I'd really appreciate any guidance.

Steve

Hi Andrzej,

 

The Sea and Sea port charts have horrible recommendations for the wide lens setups.

 

For the 10-22, 17-40, and 16-35, I recommend extension ring 40 and a +2 diopter. I always recommend the larger Fisheye dome port over the smaller compact dome. All 3 of the those lenses will benefit from the diopter. The combination of the large dome, extension ring, and diotper will allow for better corner sharpness, especially at the wider settings.

 

Best regards,

 

Jim

Hi Jim,

Thanks so much for your advice, its good to know that I'm not going mad and that its Sea & Sea who have there port chart so wrong (surely not a good marketing move!). After the poor results I had with the 10-22 + compact dome + extension ring 40 last year I was all for going back to my trusty old film Nik' 5 with 15mm Lens!

Andrzej

Hey Jim, glad you jumped in. What's your recommendation for the Tokina 10-17 with the NX Fisheye dome? (MDX -40D) I'm trying it in the pool with no extension and it looks OK so far, (actually it looks great) but I haven't had it in the Ocean yet. I'd really appreciate any guidance.

 

Steve

Hi Steve,

The 10-17 will work with no extension ring, but it will actually benefit from a very short extension, the SX extension ring. This will allow the dome to be out as far as possible from the lens without vignetting. Also, this helps with access to the front command dial on the new MDX housings.

Best regards,

Jim

Thanks Jim, great to know. I haven't noticed an issue with the command dial clearance but with no extension ring the o-ring joint is hard to see and the port is a little hard to install if you have the neoprene port cover on. It can get in the way and hold off the port. Not a big deal but something to watch. I like the idea of moving the lens aft a little, it just looks like it's too far into the dome.

Cheers,

Steve

Another thing I forgot to mention is that you should shoot at around F8 for better corner sharpness. Shooting the lens wide open at f2.8 or f4 can cause the corners to not be sharp, especially at the wider settings on the zoom lenses.

This is because of the virtual image with the dome. The virtual image is a lot closer than actual distance, and it is curved in the same shape of the dome. However the film (or sensor) plane is flat. This makes the corners closer to the film plane than the center. By closing down on the aperture, it will increase the depth of field, helping with corner sharpness.

The other thing to do is to make sure you focus on the closest distance subject in the photo. About 1/3 of the depth of field is in front of the focus point of the lens and about 2/3 behind that point.

Hope this will help with de-mystifying the magic of the dome port...

Best regards,

Jim

So, Sea&Sea makes a "Dome port" for wide angle ($649 B&H), and an "Optical Dome Port" ($1,249 at B&H), neither of which are the compact or the fisheye dx port. I've seen the $1,249 dome on sale for "only" $849. seems a bargain. Trouble is, I can't really get a feel for whether I need it.

So far, I am told I should "start" with 60mm aAF-S Micro Nicor f/2.8g ED. Obviously, no dome port required for that one. Though I don't know which of the many ports is best.

My next lens will be either the Tokina 10-17FE, OR the 12-24 Nikkor. I don't know which to choose as I assume I can't "house" both under the same port. It looks like the 12-24 won't work on an 8" dome but only the DX , compact or fisheye ports.

Which seems to suggest going for a Dx or Fisheye port since I can use the fisheye lens and the 12-24 in the event I feel that works better for me.

I hate the confusion. Can't wait for my camera coming in the mail monday.

hey dave, I used to be confused too... but here's what I (think) know now...

I never heard of the "fisheye dx port"..

here's the 3 ports.. I own the fisheye dome port and the compact dome port.

fisheye dome port (9 inch) - works well with 10.5,10-17mm, 12-24 - but you'll need an extension ring with the 12-24mm, probably the 40mm (more money), and a diopter; 20mm extension ring with the 10-17mm is optional.

compact dome port (6 inch) works well with 10.5,10-17mm; smaller, lighter than the fisheye; but you need an extension ring (20mm) with the 10-17mm

optical dome port (6 inch), same info/requirements as the compact dome port above, but its made of glass, for improved sharpness.

as you can see, I believe you get better performance with larger dome ports with wide rectilinear lenses.. but for fisheye lenses, the results seem similar to me. the proper extension is important for optimal corner sharpness.

hope this helps,

scott