Originally when I did this test, I photographed a feather outdoors from a 40-foot distance using the Canon 600mm f/4 L lens with a 1.4x teleconverter. Adding a 1.4x teleconverter slightly degrades the resolution of the lens. Based on comments I received, I have revised the test and have removed the teleconverter. I have also moved the test indoors to keep lighting constant as well as reduce any atmospheric distortion caused by temperature variation.
I could have also done the test with a different lens other than the 600mm, but I prefer to use this lens for my tests because I really love the bokeh that it produces and it's the lens I use the most often in the field. The bokeh, AKA blurred background is also a good area in which to see background noise.
Based on requests, I also decided to show comparisons at various ISO settings: 100, 400, 800 and 1600. I will let the test results speak for themselves as to whether there is any discernable comparison variations in image quality as the ISO value is increased.
All images were taken with mirror lockup and a remote control with IS turned off on the lens. The lens was mounted on a sturdy tripod which was positioned on a concrete floor. As far as I can see, there is no degradation in any of the samples due to camera/lens vibration.
All images were taken as RAW images and processed using Adobe Photoshop CS5. As you will see there are some minor variations in color balance between all three cameras, but I do not believe that this had any meaningful impact upon the final comparisons.
The only processing done to these images were to crop them identically at 400 dpi (See Target Crop Area below). As stated in part I, by cropping at 400 dpi, all images were upsized and therefore there was no image data discarded. The image below depicts how the images were cropped based upon their sensor size:
As shown above, the 5D Mark II required the heaviest cropping while the 7D required the least.
Here's a screen shot of how all three appear side-by-side at ISO 100. (Please click on all of the following images to view a larger size showing greater detail.):
Can you tell which camera is which? (I'll give you the answer at the end.) No doubt there are some differences between all three camera bodies when cropped identically from a fixed distance, but the differences are minimal when compared in this manner.
From a bird photographer's perspective, all three of these cameras produce similar image quality. In my opinion, the differences are so small that one should look elsewhere when attempting to decide which camera is best. I have used all three of these cameras at one point or another to photograph birds-in-flight as well as perched/standing birds. If my main objective is to do bird photography I would choose either the 7D or the 1D Mark IV. The Mark IV offers 10 fps vs the 7D which is 8 fps. Is 2 fps a meaningful difference? Occasionally you might miss that perfect shot without 10 fps. You may also occasionally miss a shot due to the autofocus not reacting fast enough, or not finding focus with the 7D. Don't get me wrong, the 7D has a very good autofocus system, but the Mark IV is slightly better. If money was no object, the Mark IV would get my vote, but on the other hand if money is an issue, the 7D is much less expensive than a Mark IV. How much less expensive? Currently you can buy three, almost four 7D's for the price of one Mark IV. That's an incredible difference in price. Canon's professional line of cameras have always been expensive, but if you want THE BEST, you pay the price.
Now what about the 5D Mark II? That camera would be my primary bird camera if it had a better autofocus system (accuracy and responsiveness) and a faster fps. I love the fact that it has a full-frame sensor. For photographing birds-in-flight, the chances of clipping a wing out of frame is much less than that of the 7D's 1.6x sensor. Being that it is a 21MP camera, you can do some pretty heavy cropping and still get incredible images. Think of all the extra room you have to crop an image and still not degrade the image to a great extent.
This leads me to my final point. In probably just a few weeks, we should start seeing full-resolution sample images from the 1DX. Although a number of wildlife/bird photographers have been turned off by the fact it will not autofocus at f/8 when combining telephoto lenses with teleconverters, it still very well may be the best camera for all worlds: wildlife, landscape and portrait photography. We should know the answer shortly.
And then there's the rumored 5D Mark III. If they keep the resolution close to that of the Mark II but increase the fps and enhance the autofocus, I will buy it in a heartbeat. This should be an exciting year!
So which camera is which in the above samples? From left to right: 5D Mark II, 1D Mark IV, 7D.