cameron12x
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Like everything else in life, "it just depends..." Diffraction is a very interesting discussion topic.
The 18mp sensor on the 7D opens up a number of IQ tradeoffs. Whether you notice diffraction depends on your final print size or whether you do 100% pixel-peeping of your files.
Will you notice it sooner on 4x6" prints? Probably not. What about on A3 and larger sized prints? Or on a large, high-resolution monitor? Well, that all depends... There are two things to consider: image-level diffraction, and pixel-level diffraction.
Image-level diffraction is based on the sensor form-factor (the 7D is a crop camera with a smaller sensor than a FF camera). Pixel-level diffraction is based on the resolving power (pixel density) of the sensor itself. Given the same lens focal length and apertures, diffraction will visually appear sooner with a crop camera than with a full-frame camera, and will also manifest itself visually sooner (at the pixel-level) with a more densely packed sensor (such as the 7D).
DOF is a focusing characterstic which has an arbitrary CoC (Circle of Confusion) resolution metric underlying it. It basically says that, for a given focusing range, the image will be "resolved" at this basic CoC detail level. So, for small prints, the CoC is usually sufficiently large enough such that absolute pixel-level sharpness (and any diffraction effects at that level) will not be visually meaningful for a small print. The larger the print that you make, however, the more important CoC becomes, and the sooner that you'll likely start to see diffraction effects.
These concepts apply not only to the 7D, but also to all cameras. But since the 7D currently offers more pixel-level resolution than any other DSLR crop sensor, its effects are often-times seen sooner when pixel-peeping at 100% magnification.
Diffraction, as it manifests itself at the "pixel-level," may very well be a major reason why so many people have commented subjectively that "7D images appear soft."
Consider the tradeoffs when you are shooting. What is the target output medium? Is it a large print, or a small web image? Or something in between? How much DOF do you need?
The 7D can certainly do landscape photography, and do it well.
However, IF for a given landscape you require maximum sharpness throughout the entire intended DOF, then that does open up a discussion of whether the 7D would be the right tool for the job. Depending on your shooting requirements and the landscape subject matter, a full-frame camera with a smaller pixel-pitch could give you better results. Keep in mind, however, that the full-frame form factor also provides less DOF at a given aperture and focal length than a crop sensor.
Diffraction effects also vary from lens-to-lens, dependent upon their design limitations and compromises. So, also keep in mind the lens selections available for each vendor, and for each sensor form-factor (FF or crop).
In short, there are many things to consider, and it's not a simple answer. I will be keeping my 7D, but I am also looking forward to the full-frame successor to the 5D2, when it arrives perhaps a year from now.
Buyer beware. Your results may vary.
Edited on Nov 20, 2009 at 10:50 AM · View previous versions
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