As there is some interest in this combination I am reposting a link I put on wetpixel some time ago.

 

For me it is clear that the Kenko 1.4x in the newer version is a very strong proposition with the Canon 8-15mm and it is my default set up for fisheye. I am not even mounting the bare lens anymore.

In this link I have added a studio comparison to the open water shot

https://interceptor121.com/2023/08/13/open-water-canon-8-15mm-with-kenko-1-4-teleconverter/

 

This is the original post 

https://interceptor121.com/2023/03/18/canon-8-15mm-with-kenko-1-4-teleconverter/

 

I cannot comment on experiences with the Nikon 8-15 and teleconverter I do not own this lens however it is quite clear to me that the Canon 8-15mm works identically with and without the Kenko in the newer version. I never owned the old version so no comment there either.

 

As reported elsewhere the Kenko 2x instead has a visible drop of image quality and in addition does not have a zoom gear to make it work (though there is a workaround)

Thankyou Massimo. Your tests were a big help in me choosing the Canon 8-15 and newer Kenko 1.4 on Sony A7Rv. On this camera there is also the versatility of using APS-C mode and getting a good zoom range with the same image quality as the A6700, but having both options works well. 

 

 

With this set up in an Isotta housing I am trying to find out what (if any) the sharpness compromises are on a smaller (4.5 inch fisheye dome) versus a 6 inch dome, and if small apertures and no need for circular fisheye, or absolute 180 degree coverage, mean the 4.5 inch is fine. 

 

I notice Zen have a 100mm fisheye port for the Canon 8-15..... a European company gives diameter in inches and an American company in mm   ¯\_(ツ)_/¯

3 hours ago, John E said:

With this set up in an Isotta housing I am trying to find out what (if any) the sharpness compromises are on a smaller (4.5 inch fisheye dome) versus a 6 inch dome, and if small apertures and no need for circular fisheye, or absolute 180 degree coverage, mean the 4.5 inch is fine. 

 

I notice Zen have a 100mm fisheye port for the Canon 8-15..... a European company gives diameter in inches and an American company in mm   ¯\_(ツ)_/¯

Hey John,

 

Alex Mustard did a test of small domes with the 8-15.  He found the Zen 100, which I owned with my APS-C, worked well with that format.  For FF, however, he found the 140 dome was the smallest dome with acceptable corner sharpness.  This would especially be true with the 61MP detail of the a7rV in FF.

 

Hope this helps,

Chip

 

Edited March 10, 20241 yr by ChipBPhoto

I would add that Isotta list 3 6"domes, the polycarbonate one is a partial hemisphere while one of the glass models is a part hemisphere and the other a full hemisphere.  To get the best out of the fisheye you would want the full hemisphere, to allow you to get the entrance pupil somewhere near the dome centre of curvature.  . 

 

It of course will still produce quiet OK images with the part hemisphere domes, you just have to have a look at the Ikelite compact travel dome they sell for CFWA work with full frame fisheyes.

 

https://www.ikelite.com/blogs/buying-guides/when-to-use-a-compact-8-dome-port-underwater

 

The pics they post look OK at that scale and many people would be happy with them , even though the dome centre of curvature is well down inside the dome extension and possibly 100mm behind the dome surface.  Fisheyes seem to be less sensitive to this issue at least for edge sharpness.  However if you want the very best the camera can deliver you would want to get the centre of curvature better positioned. 

 

On the issue of a 61MP image being more demanding yes it's true the greater resolution will show up lens errors more readily, but only if you view them in a manner that allows you to see that.  If for example you thought the corners were OK on a 30 MP image, you still have 30 MP grade resolution (as set by 30MP chip pixel size) in the corners on a 61 MP image.  I'd also question if you achieve 61 MP resolution shooting at f11-13 range, shooting through water and also contending with the air-water interface and all the issues that brings with it.

Thanks. I hadn't noticed the two different 6.5 inch ports. 

6 hours ago, ChipBPhoto said:

Hey John,

 

Alex Mustard did a test of small domes with the 8-15.  He found the Zen 100, which I owned with my APS-C, worked well with that format.  For FF, however, he found the 140 dome was the smallest dome with acceptable corner sharpness.  This would especially be true with the 61MP detail of the a7rV in FF.

 

Hope this helps,

Chip

 

As you can see from the topside tripod shots fisheye have distorted and blurry corners 

this is normal as there is nothing interesting in the corners of a fisheye lens

There are two considerations when it comes to dome size for a fisheye lens

1. how close to your subject you need to get

2. The minimum size of the dome so that it is no so small that the lens doesn’t focus on the dome

 

for close focus wide angle you want a small dome to shoot large subjects you want a large dome

 

nauticam has 3 fisheye domes

4.33 acrylic

140mm glass

8.5” acrylic 

all work with the canon 8-15mm And I own the first two

my experience and looking at photographers that stress the dome concept is that for very close shots of fish rhe mini dome is actually the best see the works of Mimmo Roscigno and Marco Gargiulo in the Mediterranean those guys shoot minidomes

the 140mm dome is an excellent compromise when getting super close is not essential according to Nauticam tests there is no benefit going larger hence that is their recommended port

for split shots or shots far away where depth of field is important the 8.5” may be a better choice but nobody I know uses it 

as the radius goes up your infinity point increases 

The 4.33” wont reach hyperfocal even at f/22 so if there is something far away in the background it may look blurry.

The 140mm will hit it at f/20

the 8.5” at f/16

Larger domes with 12 cm radius at f/14

this is why you hear mustard talking about f/14

however when your focus point is really really close and your dome is really huge you don’t even get that close 

corner sharpness is not a consideration fisheye lenses dont usually have anything interesting in the corners and they are dark and super distorted most times

going back to isotta something around 6” should work well as compromise solution