Since many years Canon and Nikon full frame users are able to use their respective 8-15mm with a teleconverter underwater, however this is not a very popular configuration.
In this article I will look at the Canon 8-15mm with the Kenko Teleconverter 1.4x for Sony full frame cameras.
First and foremost a teleconverter is not cropping the image it has optical elements. Cropping means reducing the resolution at sensor level while a teleconverter induces a deterioration of the image and possible defect but does not affect the sensor resolution. Generally 1.4x TC is much better than 1.4 crop. If you find yourself cropping a lot your fisheye shots or even using the 8-15mm in APSC mode the teleconverter may add some real value to you so read along.
In addition to the set up required to use the Canon 8-15mm you need 3 additional items:
- Kenko 1.4 Teleconverter
- Canon 8-15+TC zoom gear
- Extension ring N120 20mm
The benefits of this set up are clear:
- Unique field of view
- Smaller additional bulk
- Relatively low cost
Some readers have emailed asking if the Kenko is compatible with the Sigma MC-11. I do not recommend using the Sigma MC-11 with the Canon 8-15mm because it only supports single AF and it is unclear if the Kenko will work or not and how well. I have tested with the Metabones smart adapter and this is the one I recommend.
Field of view
The 8-15mm lens with teleconverter will give you access to a zoom fisheye 15-21mm with field of view between 175 and 124 degrees. This is a range not available with any other lens of water contact optic that stop normally at 130 or 140 degrees.
The additional items add circa 370 grams to the rig without teleconverter and make is 20mm longer due to the additional extension. The additional fresh water weight is circa 110 grams.
The latest version of the Kenko Teleplus 1.4X HD DGX can be found in UK for £149.
The 20mm extension ring II is £297 and the C815-Z+1.4 Zoom gear is £218. Note this is in addition to the 30mm extension required for the 8-15.
With a total cost of £664 you are able to obtain the entire set up.
The rig looks identical to the fisheye except is a bit longer. You have a choice of 140mm glass dome or 4.33″ acrylic dome see previous article.
With the rig assembled I made my way to the pool with the local diving club.
The 8-15mm with teleconverter was my first pool session with the A1 on the 3rd of February I was very much looking forward to this but at the same time I had not practiced with the A1 underwater previously and did not have my new test props. I think the images that follow will give a good idea anyway.
At 15mm (zoom position somewhere between 10 and 11 mm on the lens) the image is excellent quality in the centre and I find very difficult to tell this apart from the lens without TC except for the color rendering. I believe the Kenko takes a bit away from the Canon original color rendering.
At close range you get the usual depth of field issues depending on where you focus but this is not a teleconverter issue.
For comparison a 15mm image without TC.
Obviously what is interesting it that you can zoom in here a set of shots at 16, 18, 21 mm.
Finishing up with the required selfie.
I enjoyed the teleconverter with the Canon 8-15mm and in my opinion in the overlapping focal length this set up provides better image quality of the WWL-1. I shot for most at f/8 as I was not very close and this actually shows the TC does not really degrade the image much.
You need to ask yourself when you will need 124 to 175 degrees diagonal and the answer is close up shots of mantas and whalesharks where a fisheye may be too much and 130 degrees may be too little. The set up also works if you want to do close up work and zoom in however I reserve the right to assess more in detail using my new in water props when I have some time.