The Canon EF 70-300mm f/4-5.6L IS USM and Teleconverters
By: Gary Gray
I love to play with the new stuff from time to time, it's an obsession I've had all my life. I've tested the Kenko 300 Pro 1.4x teleconverter on the new canon 70-300 L and the 7D body. It works perfectly from what I tell. Amazing considering this isn't a f/2.8 lens and the 7D is a good 4-5 years old too. This equates to a hand-holdable, lightweight, image stabilized, 157-672mm effective focal length that shoots at f/5.6 at 672mm. With autofocus and image stabilization no less.
Canon have really dinked with this lens. It should kick doobie on a 7D mkII.
I did a little testing to see if using the Kenko Pro 300 1.4x teleconverter on the Canon EF 70-300mm L was a viable setup. Normally, teleconverters will degrade image quality. Some more than others. A simple test is to take the same photo, with and without the teleconverter attached to the lens. Crop both shots to the same size scene and compare the results.
Shot with the Canon 7D, which has a 1.6x crop factor.
The math is simple.
300mm x 1.4 x 1.6 = 672mm effective with teleconverter.
300mm x 1.6 = 480mm effective without teleconverter
The Kenko 1.4x image is on the left, with an effective focal length of 672mm. The Lens only image is on the right with an effective focal length of 480mm.
In this situation, the teleconverter isn't helping and is slightly less sharp than an image that is cropped straight from the lens. But, it's really close and totally usable. The teleconverter gives a little more reach but with slightly less resolution.
In this situation, the teleconverter isn't providing more resolution and is slightly less sharp than an image that is cropped straight from the lens. But, it's really close and totally usable. The teleconverter gives a little more reach but with slightly less resolution.