When you look at the TDP site, it seems that all TCs degrade the image. But, Bryan moves the camera further away from the chart to produce the same size image when a TC is attached. What I want to know is what the images are like from the same distance and does the gain in focal length more than compensate for the degradation of image with the lenses and TCs I use. Inspired by my recent purchase of a Kenco Teleplus 300 Pro DG 3xTC and a bright sunny day (the clouds having cleared after the eclipse), I compared the 100-400mm II and 300mm f/2.8 II bare and with Canon 1.4 and 2xTCs and the Kenco on the 7DII. The target was an iso12233 chart 24m away. Focussing was done automatically in liveview. Here is a collage of the centre ring, which is only 12.3 mm across. The unsharpened images are on the left.
At 400mm, only the two broadest of the fine semicircular lines can be resolved. Resolution gradually increases until a focal length of 1800mm is reached by stacking the Canon 2xTC III with the Kenco 3x on the 300/2.8. The stacked TCs at f/17 just about resolve all the lines.
I resized all images to the size produced by the 300/2.8 x 2 combo, on the right. The downsampled image from stacked TCs is the best.
At 400mm, only the two broadest of the fine semicircular lines can be resolved. Resolution gradually increases until a focal length of 1800mm is reached by stacking the Canon 2xTC III with the Kenco 3x on the 300/2.8. The stacked TCs at f/17 just about resolve all the lines.
I resized all images to the size produced by the 300/2.8 x 2 combo, on the right. The downsampled image from stacked TCs is the best.
