CT
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This is a direct comparison between identical shots taken with the Canon 20D (1.6 crop sensor) and the Canon 1DMK2n (1.3 crop sensor). We have a lot of bird photographers on the forum now and this article is aimed primarily at them in the hope that it's some help to them in choosing the best sensor format for their needs. Photography of small birds brings it's own peculiar problems as it almost always involves cropping of the original image and problems in maintaining image quality in the process. I might add that I'm still coming to terms with which is the best sensor size myself.
The following two shots were both taken tripod mounted from the same position and both with the 500mm F4L IS and 2X converter. The range was about 25 feet. The minimum focusing distance for this lens is around 15 feet, so it doesn't really get much better than this for filling the frame with small birds as much as possible. Remember that both cameras put out identical sized uncompressed TIFF images - 3519 X 2345 pixels and 23.6 megabyte file size.
At first glance the difference in the field of view from each camera doesn't appear too significant, but it's very deceptive. The following shot is the full frame shot from the 1DMK2n cropped by eye, but fairly accurately, to the same FOV as the 20D shot.
The significant thing here is that the image size has now fallen to 2736 X 1872 pixels and only 14 megabytes - nearly 10 megabytes of 'wasted ' pixels. The situation would obviously be much worse with the same shot taken on a full frame sensor. The thing to note here is that despite the fact that both mages were recorded at the same size on the sensor, the uncropped 20D shot is now showing that branch (where a small bird could be perched) quite significantly larger than the cropped 1DMK2n version.
This next shot shows the cropped shot from the 1DMK2n superimposed over the uncropped 20D shot to graphically illustrate the difference.
If I were to submit either of these two shots to Alamy, in truth, a small Blue Tit or Sparrow sized bird still wouldn't be filling the fame that well in this shot and further aesthetic cropping would probably be required, impacting on the quality of both images, but more so on the image from the 1DMK2n which is already losing the battle, but the 20D image would require a 143% increase in file size to reach 48b, whereas the image from the 1DMK2n would need a 182% increase. The impact on the fine feather detail in a bird shot would be fairly obvious from the smaller 1DMK2n image.
These last two images are just 1:1 crops from shots of a bird bath detail taken with the 500mm F4L on both the 20D and the 1DMK2n to show the difference in the size of the actual subject when viewing the full size (1:1 )file from each camera.
20D
1DMK2n
I think the results speak for themselves!
It's not all about birds of course and I wont be getting rid of my 1DMK2n any time soon. The build quality is far superior and there are occasions when the faster AF and drive speed is going to be better for larger flying bird shots. The larger sensor also comes into it's own with wider lenses, and any shot in fact where you can fill the frame reasonably. If you're primarily a bird photographer though, and hankering after a 1 Series body, I think you'd do far better to spend the money on top end long glass if you want to see the best results. Even if you really can't avoid the temptation to buy that 1 Series body, make sure there's a 1.6x crop sensor camera in your bag for the best of both worlds.
The following two shots were both taken tripod mounted from the same position and both with the 500mm F4L IS and 2X converter. The range was about 25 feet. The minimum focusing distance for this lens is around 15 feet, so it doesn't really get much better than this for filling the frame with small birds as much as possible. Remember that both cameras put out identical sized uncompressed TIFF images - 3519 X 2345 pixels and 23.6 megabyte file size.
At first glance the difference in the field of view from each camera doesn't appear too significant, but it's very deceptive. The following shot is the full frame shot from the 1DMK2n cropped by eye, but fairly accurately, to the same FOV as the 20D shot.
The significant thing here is that the image size has now fallen to 2736 X 1872 pixels and only 14 megabytes - nearly 10 megabytes of 'wasted ' pixels. The situation would obviously be much worse with the same shot taken on a full frame sensor. The thing to note here is that despite the fact that both mages were recorded at the same size on the sensor, the uncropped 20D shot is now showing that branch (where a small bird could be perched) quite significantly larger than the cropped 1DMK2n version.
This next shot shows the cropped shot from the 1DMK2n superimposed over the uncropped 20D shot to graphically illustrate the difference.
If I were to submit either of these two shots to Alamy, in truth, a small Blue Tit or Sparrow sized bird still wouldn't be filling the fame that well in this shot and further aesthetic cropping would probably be required, impacting on the quality of both images, but more so on the image from the 1DMK2n which is already losing the battle, but the 20D image would require a 143% increase in file size to reach 48b, whereas the image from the 1DMK2n would need a 182% increase. The impact on the fine feather detail in a bird shot would be fairly obvious from the smaller 1DMK2n image.
These last two images are just 1:1 crops from shots of a bird bath detail taken with the 500mm F4L on both the 20D and the 1DMK2n to show the difference in the size of the actual subject when viewing the full size (1:1 )file from each camera.
20D
1DMK2n
I think the results speak for themselves!
It's not all about birds of course and I wont be getting rid of my 1DMK2n any time soon. The build quality is far superior and there are occasions when the faster AF and drive speed is going to be better for larger flying bird shots. The larger sensor also comes into it's own with wider lenses, and any shot in fact where you can fill the frame reasonably. If you're primarily a bird photographer though, and hankering after a 1 Series body, I think you'd do far better to spend the money on top end long glass if you want to see the best results. Even if you really can't avoid the temptation to buy that 1 Series body, make sure there's a 1.6x crop sensor camera in your bag for the best of both worlds.
Oh and BTW the birds seems to have buggered off too 
CT 
