old school: dome recommendation for D850 & 8-15mm lens

All,

1. I've searched the forums for this (and found a lot but nothing specific...)
2. I'm late to the game on DSLR FF fisheye solutions
3. Yes, everyone will eventually go mirrorless, but not me, not yet

I'm looking at the Nikon 8-15mm fisheye lens to shoot mostly reef scenes with a couple of clear (warm) water destinations coming up over the next few months.

I've read a bunch on the appropriate dome to get (and checked Nauticam's port chart). I thought I would ask for the collective wisdom here...

I already own the WACP-1 for other w/a scenarios, so this is mainly for wide reef scenes...

Smaller domes are obviously easier to handle, however will consider larger if it makes that much difference in image quality.

If you are looking at Nauticam domes they do a 140mm which is the one marked "*" .  Fisheyes are less sensitive to dome size than rectilinear lenses, however there is some impact particularly on full frame.  I know Adam recommends a 6-7"dome but Nauticam don't make one. 

To me it comes down to a process of elimination  - You probably don't want an 8.5"acrylic as it is quite buoyant, so are you prepared to travel with a 230mm dome?  If not then it's the 140mm which will also allow some close focus wide angle work.  Nauticam recommend it as most optimised so if there is anything to be gained in the corners by going larger it is probably minimal.

You could look at converting other manufacturer's domes, notably Isotta or S&S which in theory are convertible to Nauticam by changing the lug ring, however their 6- 6.5"domes do not appear to be full 180°  hemispheres so you won't be able to place the entrance pupil at the centre of curvature of the dome and also avoid vignetting.

I don't shoot full frame underwater, so this is not advice or personal knowledge, but Underwater Zen does list their 170mm dome with a 20mm extension ring as compatible with the 8-15.  In their port charts, Zen makes no distinction between DX and FX.  I will have to let someone else with personal knowledge speak to whether that offers meaningful improvement over the 140, but I could see where it may give a stop or two improvement in the corners.  Maybe?.  it is at least smaller and lighter than the WACP, if that is worth anything.

3 hours ago, Draq said:

I don't shoot full frame underwater, so this is not advice or personal knowledge, but Underwater Zen does list their 170mm dome with a 20mm extension ring as compatible with the 8-15.  In their port charts, Zen makes no distinction between DX and FX.  I will have to let someone else with personal knowledge speak to whether that offers meaningful improvement over the 140, but I could see where it may give a stop or two improvement in the corners.  Maybe?.  it is at least smaller and lighter than the WACP, if that is worth anything.

 

The problem with the 170 dome is it is about a 120° segment of a sphere, while the 140mm is 180° segment.  This means the centre of curvature is down inside any extension used.   Fisheyes generally have the entrance pupil right up close to the front of the lens, so the lens must be placed so that the entrance pupil is maybe 30-40 mm in front of the centre of curvature of the dome to avoid vignetting.    It is reported to work fine with an adapted 8-15 in m43 but would be a roll of the dice as to how much the corners might be impacted on full frame.  This is the same problem I alluded to with the 6"domes in my previous post

7 hours ago, ChrisRoss said:

The problem with the 170 dome is it is about a 120° segment of a sphere, while the 140mm is 180° segment.  This means the centre of curvature is down inside any extension used.   Fisheyes generally have the entrance pupil right up close to the front of the lens, so the lens must be placed so that the entrance pupil is maybe 30-40 mm in front of the centre of curvature of the dome to avoid vignetting.    It is reported to work fine with an adapted 8-15 in m43 but would be a roll of the dice as to how much the corners might be impacted on full frame.  This is the same problem I alluded to with the 6"domes in my previous post

Hi Chris,

How do you calculate this out of curiosity? Keen to understand how I can replicate this for different dome sizes ! thanks

1 hour ago, waterpixel said:

Hi Chris,

How do you calculate this out of curiosity? Keen to understand how I can replicate this for different dome sizes ! thanks

See this reference:

https://www.mathopenref.com/sagitta.html

If you know the radius of curvature and you measure the Sagitta from the dome then calculate L with formula 2 then you can draw a right angle triangle below the chord with Apex at the centre of curvature and calculate the included angle of that triangle using trigonometry, then 2x that angle is included angle of the segment of a sphere.  This link shows the angle theta  you are trying to calculate:

https://www.ck12.org/c/trigonometry/length-of-a-chord/lesson/Length-of-a-Chord-TRIG/

A fisheye lens entrance pupil needs to sit at or above the chord line to have a 180° field of view.  Rectilinear lenses can sit further back dictated by their field of view.  In general the entrance pupil of a rectilnear lens needs to sit a bit forward of a triangle with an included angle equal to the file dof view to not vignettte.  This is not a precise calc as it assumes the sensor is a point when in fact it it has a finite size.

I was just providing information about the Zen option.  I would hope the folks at Zen would not recommend a dome/extension/lens combination that gave poor results, but I have no personal experience shooting a fisheye in the 170, in DX or FX.

The folks at Reef Photo / Zen should be able to address those questions if someone wanted to call them. 

5 hours ago, Draq said:

I was just providing information about the Zen option.  I would hope the folks at Zen would not recommend a dome/extension/lens combination that gave poor results, but I have no personal experience shooting a fisheye in the 170, in DX or FX.

The folks at Reef Photo / Zen should be able to address those questions if someone wanted to call them. 

Don't get me wrong, it will certainly work but the basics of dome port optics suggest it may not be an improvement over the 140mm dome where you place the lens correctly.