I like to try and stay fit, and do a number of different sports with this goal in mind. One is sea-kayaking, and it is also the only one that combines well with bird watching and -photography.

In the kayak I can easily carry my camera between my legs – as long as I’m happy to leave the big 500mm behind (or stowed in a sealed compartment). This means I use the 300mm f4 lens, and since I am shooting full-frame I also generally have the 1.4TC mkii mounted. Still, that gives just 420mm effective focal length, and that is often too short. So on this trip I tried a new approach, mounting a Kenko Pro teleconverter behind the Canon-combo described above. This gives a 588mm f8 lens, and in the following we’ll be looking at how this setup performs, image-quality wise.

I ran into a very accommodating reed warbler. Here’s an entirely unprocessed shot of the bird – click on it to enlarge:

One more of the same bird, and the same lens combo. In both instances the depth-of-field is crazy shallow; this is due to the very short distance between the focal plane and the bird, as both shots are just about straight off the sensor with no cropping applied.

This one is shot with the same lens combo as above, f8 this time.

What I encourage you to look at is the sharpness of the image in those parts that are in fact in focus; I must admit I am more than a little pleased with the image quality of these, something that is particularly interesting for a number of reasons:

• The 300mm f4 costs around 1/8 of the 500mm f4 lens
• The former is fully hand-holdable and can be carried around for days (on a normal-sized camera housing) without becoming a nuisance
• The 500mm is not suitable for use in, say, a kayak, or any other small vessel/vehicle
• Travelling on commercial flights with the 500mm lens is a pain in the arse – the 300mm fits in my normal camera backpack (Lowepro 300)

Note that there is still a place in a nature-photographers kit bag for the big lens, if you can afford it and find that the low-light benefits justify the investment, but the other option is great to have in a pinch, and can leave you with absolutely acceptable results as long as there’s plenty of light available.

Regarding autofocus, on my 1Ds mkiii and 5D mkii it worked great – best on the latter, which is slightly newer. As far as I have been able to learn, the Kenko converter doesn’t tell the camera that there is a Canon tc in front of it, so even if your camera normally won’t autofocus with anything darker than f5.6 it may still work.

The images above are unprocessed in Photoshop – only RAW-converted in Canon DPP and reduced in size in Photoshop – no sharpening applied. Here below is the first image, with one click on the USM function – again, click on the image to see the full size, and hopefully you’ll agree that this is better than one would expect from two tc’s stacked:

One dollop of USM applied, Amount: 80%, Radius 0.3 pixels, Threshold 1.