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John Bantin

Sea & Sea Glass Dome Port

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So I got all excited and ordered myself a glass dome port for the Sea & Sea DX housing but now it has arrived I was surprised to find it is only 7 inch in diameter instead of the 9 inch plus of my acrylic dome.

 

So... can I use it with my 10.5mm fish-eye lens? Will it focus? Will it suffer cut-off?

 

Do I need stronger dioptres to use it with the 12-24 zoom?

 

I know, RTFM, but I made an assumption and was wrong. Anyone who has experience of using the 7 inch port (probably the same rules apply with a 7 inch acrylic) might give me a steer in the right direction before I flog off somewhere distant with both ports in order to find out for myself.

 

Thanks.

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Hi John,

 

Is the Athena OPD-F170 glass port what you have? If so, no worries. It works great with both the Nikkor 10.5mm and 12-24mm DX lenses as is, no diopters needed, but the Extension Ring 40 will be needed for the 12-24mm lens. I bought the same from Reef Photo and have been shooting the 12-24mm with a +2 diopter, per Ryan's suggestion that he thinks the diopter sharpens the images at the edges, but the diopter isn't required. I've shot both with and without the diopter and can't say I've noticed any signficant differences, but my subjects were quite different in each case. The only thing I learned about why I'd not want the diopter is that is cuts off your distant focusing and thus if you should find you're trying to take a photo while out of the water, you will be limited on your focusing range. While in Roatan a couple weeks ago, we came upon a large pod of pilot whales that I was unable to get good photos of using my housed D200 because I had the diopter on the 12-24mm lens. Only those whales nearest the boat were within my focusing range. I could've removed the port and diopter but didn't really want to since another dive was coming up.

 

Regards,

 

Daryl

Edited by Ambress

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Hi John,

 

Is the Athena OPD-F170 glass port what you have? If so, no worries. It works great with both the Nikkor 10.5mm and 12-24mm DX lenses as is, no diopters needed, but the Extension Ring 40 will be needed for the 12-24mm lens. I bought the same from Reef Photo and have been shooting the 12-24mm with a +2 diopter, per Ryan's suggestion that he thinks the diopter sharpens the images at the edges, but the diopter isn't required. I've shot both with and without the diopter and can't say I've noticed any signficant differences, but my subjects were quite different in each case. The only thing I learned about why I'd not want the diopter is that is cuts off your distant focusing and thus if you should find you're trying to take a photo while out of the water, you will be limited on your focusing range. While in Roatan a couple weeks ago, we came upon a large pod of pilot whales that I was unable to get good photos of using my housed D200 because I had the diopter on the 12-24mm lens. Only those whales nearest the boat were within my focusing range. I could've removed the port and diopter but didn't really want to since another dive was coming up.

 

Regards,

 

 

Daryl

 

Thanks Daryl,

 

What great service!

 

I am simply substituting for the larger acrylic port I already use, so I have the extension of course.

 

I know what you mean about the plus 2 dioptre on the 12-24. Frustrating isn't it? However I found that plus-2 just gave me the closer range I needed underwater. I have had some lovely Double-Page-Spreads from the bigger port and am anticipating better!

 

All the best

 

JB

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John,

Just out of interest where did you order your glass dome port from? - I'm guessing these are not available in the UK yet?

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John,

Just out of interest where did you order your glass dome port from? - I'm guessing these are not available in the UK yet?

 

I do not think that Sea & Sea (UK) intends to import it so I went to a very nice man called Yuzo, in Japan...http://www.naturephoto.co.jp or www.uwdigitalcamera.com

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I do not think that Sea & Sea (UK) intends to import it so I went to a very nice man called Yuzo, in Japan...http://www.naturephoto.co.jp or www.uwdigitalcamera.com

 

We got ours the day before yesterday.

 

These are the same piece of glass as the Athena OPD-170 that we've been selling for nearly 3 years at $899 w/ shade. Sea & Sea's retail price is $1199 for the same thing...

 

But it does come with a neoprene cover, rear port cover, and a nice hat box. :)

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This is also the same dome glass used with the Olympus PT-E01,2,3 housings. Works great with my 8 mm fisheye and 7 to 14 mm zoom with extension ring. Also with a nice dome cover and rear cover. I´ll let Ryan tell you the price on the Olympus dome.

 

Phil

Edited by tropical1

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The out side diameter is only of concern if you are vignetting in the cornors.

 

The radius of curvature is what you should be watching and it will effect the location of the projected virtual image.

 

Depending on where the dome is cut, a 8 or 9 inch hemispherical dome may only be 7" on the out side if it was cut about 1-2 " off center!

 

Most zooms have floating nodal points.

Extension rings are used to match the dome center of curvature to lens nodal point for optimum sharpness.

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I use a 7 inch dome (acrylic) with the 10.5 and 17-70 sigma with no problems. For some reason I keep always hearing problems with the 12-24 setup not being really wired for many people and a 7 inch dome may not work as you expect (best opinions I have heard come from seacam´s superdome)

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Most zooms have floating nodal points.

Extension rings are used to match the dome center of curvature to lens nodal point for optimum sharpness.

 

Very true, but most decent W/A zooms only move the entrance pupil by tiny amounts. My Canon 16-35mm L only shifts by 1-2mm over the zoom range.

 

 

It should be a very straightforward test to see if John B's rig is going to work before winging off to far flung places. Once you've got the entry pupil in the right place, which you could easily test with an empty toilet roll tube*, just put the rig in the bath and see if you can focus on the plug chain from the kind of distance you'd want to for CFWA shots.

 

HTH,

 

Martyn

 

 

* OK, so the toilet roll trick goes like this. Any cylindrical tube, when pressed up against a spherical port with sit with its axis along the local normal to the surface. If you look down the tube, you should be able to see the entry pupil of the lens. This is the point at which you can see light coming through from the viewfinder. I'm guessing some knew that, others hadn't thought of it like that. Hope it helps someone somewhere. :)

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, just put the rig in the bath and see if you can focus on the plug chain from the kind of distance you'd want to for CFWA shots.

 

HTH,

 

 

Crikey! He thinks I have a house with a bath! Actually, I was about to set off to the exotic outer regions of Putney.

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Oooh, look at that! John the Journo off on one of his swanky jollies :)

 

Enjoy your dip John and good luck with the optics. My educated guess says you should be fine.

 

If your dome is about 7" diameter, then the radius of curvature (given the design of the port) is about 9cm. That puts the virtual image for infinity at about 27cm. If you reckon your closest subject might get rendered about half that distance, so 14cm from the dome to the virtual image.

 

The 10.5mm fisheye has a min close focus of 14cm and is 6cm long, so it should focus easily for CFWA.

 

The 12-24mm has a min CF of 30cm, but is 9cm long. This cuts it a little finer, but if you take the 30cm, and take off 9cm for the length of the lens, then say 7cm for the air gap, then 14cm for the dome to virtual image, you're in business for most scenrios.

 

I'll be interested to hear if your trip to the pool proves my back-of-the-packet calculations and theoretical hand waving.

 

Martyn

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