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blueline

S&S NX Compact dome port

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Hello,

 

I seem to have enough clearance on a zoom/wide angle lens that I already have, and have been thinking if it is necessary to buy an extension ring with an NX compact dome port? Do you absolutely have to have the extension (i.e. SX extension ring) because of image distortion without it, or is it useful in case someone needs to mount longer length lenses down the road? After looking at the S&S website, I can see you can mount the NX compact dome port directly to an MDX-40d housing without the extension ring. I favor this since it would mean one less o-ring to worry about.

 

Thanks,

Blueline

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In my experrience the need for an extention depends on the lens. Which one are you thinking about?

 

Steve

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In my experrience the need for an extention depends on the lens. Which one are you thinking about?

 

Steve

 

Hi Steve,

 

I got a Sigma 17-70mm that I'd like to give a shot at an upcoming trip(also planning to get a magic filter and shoot with ambient light at shallow depths). I was told that being a rectilinear lens it would not be a good idea to place behind a flat port (i.e. compact wide port L), even though a similar lens, the Sigma 18-50mm Macro, is listed with the Compact Wide port L on the S&S system Zoom lens chart.

 

I tried contacting S&S on Friday, however, no one was available to talk to.

 

If I can do away with one O-ring, I'd prefer the NX Fisheye dome, instead of the NX Compact Dome port(which has less clearance). I also have a Kenko 1.4x TC that I can use to boost macro ( Sigma 17-70mm not a 1:1 macro).

 

I read Alex Mustard has used that lens with a TC.

 

Thanks.

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This question seem to solicit some ambiguous answers.

 

One need to calculate the extensions required. The dome diameter at the base is 145mm with a rise of 47.5mm.

The calculated radius of curvature of the dome is thus 79mm. (sorry all calcs were done in metric units Imperial has gone out of fashion in the 60's in SA)

 

You have to use the lens field of view and front element diameter to calculate the nodal point of the lens.

 

at 17mm the Canon 17-85 IS EFS lens have a nodal point at 62mm from base (If the Sigma is of the same dimensions the values should be similar)

 

The calculated extension length for my Housing (S&S DX30/60), Camera (D60 or 30D) and lens combinations ( Canon 17-85 and Sigma 10-20) is 49mm. In our conditions the 10-20 will probably see little use.

 

In my opinion the nodal point is more important in limiting aberrations at the short end of the zoom but less so at the long end.

 

I hope you have some better idea.

 

Reef said to me I wood need the 40 for the 10-20 and the 40+SX extension for the 17-70. I did not get round to get the 17-70 we will see what the outcome will be.

 

Regards

 

Dirk

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I use the 17-70mm with both the 40mm and the SX extension together with the Compact Dome port.

 

I think both are required to prevent the lens hitting the port.

 

I have had some success with achieving good quality at all focal lengths.

 

Regards,

 

Mark

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I use the 17-70mm with both the 40mm and the SX extension together with the Compact Dome port.

 

I think both are required to prevent the lens hitting the port.

 

I have had some success with achieving good quality at all focal lengths.

 

Regards,

 

Mark

 

Thanks both.

 

I think I'll wait a bit longer to get a dome port. I ordered the compact wide port L with a Sigma 18-50mm (I'm returning the 17-70) since it was not listed on the Sea & Sea port chart. I also ordered the manual gear, so flat port but when I called Sea & Sea I was told the only tested lens was the 18-50mm. At any rate, I'd rather go with a glass/optical port down the road (I have an acrylic aquarium and have to worry about scratches all the time. Given I'm going to Komodo in a couple months, I figured an acrylic dome port would be prone to scratches/possible disaster with raging currents.) Plus I also read the 18-50 has a better low light performance than the 17-70, so ...

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