Saturday, September 26, 2015

Test of Canon Extender

Trying the Canon Extender EF 1.4x III today on the EF 100-400mm f/4.5-5.6 IS II USM and Canon 7DII.  My earlier tests with the Kenko 1.4 and the Mark-I version of the lens showed that I was better off never using the extender.  My test with the Canon extender is much more promising.

In the following test, I set the camera up on a tripod, used mirror lock-up, and fired with a cable release. I used AF to focus on the bark of a tree. Camera was set to ISO-100 and all shots taken at the "tele" end of the lens where I normally shoot. I shot one raw frame fully open and one frame stopped down by -1.0.

I imported the images into Photoshop with default corrections. sharpening 50%, radius 1.0, no smoothing. On the images taken with the extender, I cropped to a 2:3 region at the center of the frame with width 1400. On the images taken without the extender, I repeated the cropping with a width of 1000. I then stretched these two frames to a width of 1400. All four frames were saved in highest resolution JPG.

Canon EF 100-400mm II - 400mm, f/5.6, ISO-100
Canon EF 100-400mm II - 400mm, f/8, ISO-100
Canon EF 100-400mm II with Extender 1.4x III - 560mm, f/8, ISO-100
Canon EF 100-400mm II with Extender 1.4x III - 560mm, f/11, ISO-100
All four images except the last are virtually identical. The improvement in the last image maybe due either to the additional reduction in aperture or simply due to a moment of better seeing. I did not due further comparisons.  All of these tests are center-of-frame. I did not carefully test the peripheral image quality as my subjects are rarely framed there. However, my cursory inspection of the full frames did not show any significant differences either. I am initially satisfied that the addition of the Canon extender does not adversely affect the sharpness of the images, the same conclusion that can be drawn from Canon's published MTF diagrams.

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