My current set up is a Canon 300mm F4 L and a 1.4x Extender II, it's a great combo but I am tempted by the convenience of the zoom. I was also interested in the possibility of combining the lens with 1.4x extender to get a 560mm f8 manual focus lens as my budget definitely won't stretch to a 500mm prime lens.
I am by no means an expert at testing lenses and just wanted to try a few simple tests. Most of these have been done before and can be found on the 'net but there is nothing like personal experience.
The first test I put together was just to shoot a static high contrast target and try and compare the results. The set up was pretty basic, the card was attached to a door and illuminated with a standard lamp. The camera was mounted on a tripod and fired by remote release with mirror lock-up. The distance between camera (a Canon EOS 40D) and target was approximately 4m. Unless other wise stated auto-focus was used with only the centre spot active.
Images were captured in RAW and converted to jpg in Lightroom no sharpening was applied. The images are 100% crops from the centre of the frame.
Full size jpg files have been loaded onto Flickr.
Canon 300mm f4 L with 1.4x Extender II
420mm 1/100 @ f5.6
420mm, 1/50 @ f8
Canon 100-400 f4.5-5.6 L
400mm, 1/60 @ f5.6
400mm, 1/30 @ f8
Well to my untrained eye it looks like I won't be losing anything in quality at the long end, if anything the 100-400 is a little better than the 300 + 1.4x combo.
The next test I tried was to attach a 1.4x extender II to the 100-400 and tried some shots at 560mm. On my 40D autofocus is lost as the minimum aperture exceeds f5.6, so the camera was focused manually using live view with 10x magnification.
I did try taping the pins and while this did mean the camera tried to auto-focus it was erratic and not only that it ruined focusing when the extender was put onto the 300mm F4, so this isn't something I will be doing in 'real life'.
Canon 100-400 f4.5-5.6 L + 1.4x Extender II
560mm, 1/50 @ f8
560mm, 1/25 @ f11
I was pleasantly surprised, whilst a little soft wide open stopping down really does improve things. time will tell if this combination is practical (I am not the best at using manual focus on moving objects).
If the weather holds out I will hopefully be able to take the lens out into the field for some real life examples.
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