Do you remember the previous “Beyond Autofocus” post here? It was about one year before and it was when I first tried to focus using the “Liveview focus” option of the Canon 7D. I was satisfied with the results and I started using the 2x extender again on my 500 f/4L IS lens when extreme reach is required on static subjects.
Last weekend I came across a similar situation and with the same subject! On my way to mount Parnassos I came across a female Merlin again! After taking many pictures using the 2x extender (teleconverter) and I was satisfied with the results, another thought came into my mind: What if I use both 2x and 1.4x teleconverters stacked together? (This is possible only with the second generation of Canon extenders. The feature was removed in the third generation that Canon released recently. Fortunately I haven’t yet upgraded my set of extenders so it was easy for me to do the test). There was enough light and since the Merlin wasn’t going anywhere, I stacked my Canon 1.4x II extender at the rear of the Canon 2x II extender for a focal length of 1400mm. Given the crop factor of the 7D this is the equivalent of 2240mm in Full Frame. Liveview focusing with the 7D was without problems beside the fact that it was even slower than before. Nevertheless the focus was quite accurate. I managed to make about 10 images before the bird finally left and almost all of them were in focus. Image quality was decent and so was sharpness given the use of 800 ISO on the 7D and the fact that we are talking about lots of glass between the image sensor and the subject. The biggest problem was some chromatic aberration but even this was not so much of a problem. The image shown here is the full frame capture without any crop. You can view the Exif data by clicking on the picture as always.
Of course it is not possible to judge image quality from an image 800 pixels wide. For this reason I am also showing a 100% crop from a spot with some detail in order to judge image quality yourself. This crop is unsharpened. This means sharpness at the RAW file was set to 0 during conversion and no sharpening was done later during image processing. After that, I am seriously thinking of using two 2x extenders for my next Merlin :-)…
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