FE 8-15 F/4 with RF 1.4x TC?

Hi all, I'm considering different lens/port routes I might take for Sony or Canon gear. One of the options I'm considering is adapting the 8-15 F/4 to the R6 or R5. I was wondering if anyone has tried to adapt the RF 1.4 TC to the 8-15 fisheye using the Commlite RF-EF or similar port adapter as shown in the video below. This adapter is quite inexpensive and gets decent reviews, and can also be modded to accept the TC per the video. My guess is the RF optics are better than the Kenko Teleplus TC but I'm wondering if there are any obvious reasons why this wouldn't work, or other factors that would make the Kenko TC a better option. For me, this would save a small amount of money as I already have the RF TC. 

There was a post here recently where a WP member used a Sony 1.4TC with a SONY - EF adapter with the Canon 8-15 and that was reported to work well.  Optically there's probably no real issues it's whether the adapter can be modified to fit the 1.4x TC and if the adapter works well. 

The issue with the RF 1.4x is that it may be a different flange thickness compare to the Kenko 1.4x and this might require a custom zoom gear.  Nauticam offer a zoom gear for the kenko plus 8-15 combination.  If the RF 1.4x is thicker this will move the lens forward into the dome compared to the kenko setup which is less optimal, but fisheyes normally handle this well.

The front element of most teleconverters sticks out beyond the front of the tc. This is not the case on the cheaper designed kenko, which is why this is the go to solution for use with fisheyes. 
However using an adaptor for the lens (between tc and lens) would provide appropriate space for the sticking out part, however, I fear the unknown optical problems this might introduce.. 
Also what we don’t know is how well a TCs optimised for specifically for telephoto lenses (a Canon or Sony one) will work with a fisheye - it may help or hinder the optics with a fisheye compared with a Keiko.

First I would not conclude that the rf teleconverter will work better than the kenko and there may be a challenge with the zoom gear
Can you not use the canon rf to ef?
Some adapters seem to work but may end up locking up and requiring removal that you can’t do when in a housing
The kenko new model cost me £149 and the performance and speed are excellent is it worth the risk?


Sent from my iPhone using Tapatalk

I am concerned about the idea of using the teleconverter not next to the lens - as designed - but with the adaptor between the TC and the lens - which surely will impact on performance. Although again, not sure for the good or bad, I fear the latter. 

7 minutes ago, Alex_Mustard said:

I am concerned about the idea of using the teleconverter not next to the lens - as designed - but with the adaptor between the TC and the lens - which surely will impact on performance. Although again, not sure for the good or bad, I fear the latter. 

A long telephoto lens (I have both the Sony 100-400 GM and the 200-600 G as you saw yesterday). Has a cavity in the lens where the rear element moves when the lens zooms

The native teleconverter is designed to fill this gap and the front element of the tc protrudes accordingly

The adapter between RF and EF mount is 26mm thick but the teleconverter will not protrude that much

This means that, if the front element of the teleconverter is not long enough it will be further away from the rear of the master lens when passing through the adapter.

This will result in an extension tube effect. The lens may potentially loose infinity focus on land, but underwater this is not an issue as behind a dome there is no infinity. However the reported f/stop is incorrect and the teleconverter lens combination will vignette more

this means that instead of 10.7mm for 15mm you are looking perhaps at 11-11.5 mm to get 15mm and ultimately the range will not be 15-21 but something like 15-20mm

It is not possible to comment on the image quality and it is not necessary a better or worse solution but it is not a recommended solution

From my analysis I see no major deterioration of the lens in terms of chromatic aberration especially because we use lenses stopped down to f/8 or smaller anyway

Off topic, but @Interceptor121 do you know if the Sony 1.4x TC fits on the 90mm? I often use the Nikon 1.4x and 2x on the Nikon 105mm. 

6 minutes ago, Alex_Mustard said:

Off topic, but @Interceptor121 do you know if the Sony 1.4x TC fits on the 90mm? I often use the Nikon 1.4x and 2x on the Nikon 105mm. 

It doesn't. If you want to use a teleconverter with a macro lens on a Sony system, you have to use adapted lenses.

12 minutes ago, Alex_Mustard said:

Off topic, but @Interceptor121 do you know if the Sony 1.4x TC fits on the 90mm? I often use the Nikon 1.4x and 2x on the Nikon 105mm. 

I have created another thread with the situation in case someone wants to find a solution