Now, I still want to see the same comparison with the 5dMkII, 50D and 30D. Does anyone have that series of cameras to work with. Unfortunately all the online resolution samples that are done with these cameras are not applicable. They always fill the frame with the target. In this scenario, the 5DMkII needs to be moved farther away so that only the portion of the frame that is equivalent to the 1.6x crop factor will be visible. This eliminates the step of resizing in photoshop or some other tool.
It so happens that a 1.4x extender on a 5D2 produces very closely a pixel for pixel comparison with a 50D used without extender. Since the 20D pixel pitch is the same as that of the 5D2, and since the noise characteristics of the 5D2 pixel are very similar to those of the 20D, bearing in mind that at both cameras' nominated ISO values the 20D has an actual ISO which is higher, it becomes possible to simulate the performance of the 5D2 using the 20D.
Since there's a likelihood that I will eventually buy a 5D2 after the initial mad rush is over, I decided to do my own comparisons out of curiosity.
The following shots compare the 20D using a 400mm lens and 1.4x extender, with the 50D using the same 400mm lens without extender. I've used the same aperture of F11 for both shots since I didn't want to give a shutter speed advantage to either of the cameras. As it so happens, the 20D shot is at 1/800 sec as opposed to 1/640th for the 50D, despite the fact that ISO 800 was used for both shots and despite the fact that both shots are equally well exposed.
This confirms other results which indicate that the 20D is more sensitive than later Canon models, including the 5D2. However, that's all right for the purposes of these tests because a 560mm lens needs a faster shutter speed than a 400mm lens.
For those who don't want to bother looking at the following images, the deductions and conclusions are:
(1) When maximum telephoto reach is required, the 5D2 with 1.4x extender will produce detail and sharpness on a par with the 50D without extender, when images are viewd at 100%.
At an extreme pixel-peeping level, at 200% and 300% magnification, the 50D still has the edge, though, and this edge would have been slightly greater if I had used the 50D at F8.
(2) Despite the greater exposure given to the 50D shot at the same ISO, it appears to be noisier that the 20D shot, once again confirming that the smaller 50D pixel really is noisier than the 20D pixel and that total image noise is only equalled when the 50D image is downsampled to the 20D image size (or the 20D image is upsampled).
(3) At the lower edge of the 20D image, nearest the camera, it can be seen that the 20D shot is beginning to lose sharpness due to its shallower DoF. This is more apparent in the corners where the shallower DoF is combined with (I suspect) a fall-off in resolution due to the presence of the converter. In other words, the 560mm lens has poorer edge and corner resolution than the 400mm lens.
It should be noted that introducing an extender always reduces DoF, even when the main lens is at the same aperture. For example, a 400mm lens at F8 becomes a 560mm lens at F11 when a 1.4x extender is used. The DoF of a 560mm lens at F11 is still slightly shallower than a 400mm lens at F8.
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