I was reminded about photographic sharpness from a question I got from a student who wanted to know if a full frame DSLR camera would give sharper results than a smaller format. This is an interesting question and relates to a lot of misperceptions about sensor size, too.
Full-35mm-frame (I like to use that term because “full-frame” is very misleading - if the 35mm size cameras are full-frame, then what are larger format cameras?) has no effect on sharpness. I shoot mostly with Olympus gear which is a four-thirds size sensor, smaller than most digital SLRs, plus some with Canon APS-C cameras, and even a small, compact digital camera often called a “point-and-shoot”, and I have no problems with sharpness due to sensor size from any of those cameras. That said, it is important to note that megapixels will affect ultimate image size, and that small sensors with high-megapixel counts can have “mushy” looking small details because of the processing the camera does to handle noise from the sensor.
From many years of classes and also from judging a lot of photo contests over the years, I can definitely say that the biggest impact on sharpness is from camera movement during exposure. This can be a big issue with less-expensive lenses, not because they are bad lenses, but because they are “slow” lenses (referring to aperture) and often mean shooting at slower shutter speeds that increase the possibility of unsharpness due to camera movement.
The only way to see how much this affects your work with your camera and lenses is to do some tests. Shoot a scene handheld at a variety of shutter speeds, then shoot that same scene with the camera on a tripod. Compare the shots. Most photographers are surprised at how quickly sharpness degrades with slower shutter speeds that aren’t necessarily that slow. Telephotos and close-ups increase the problem with camera movement during exposure.
Some photographers are capable of shooting at very slow shutter speeds - and I am jealous of them because I am not. It is really good to know what shutter speeds start causing you problems with sharpness.
A solid tripod can make more of a difference in sharpness than anything else. I will take on anyone who shoots with the most expensive lenses and camera possible, with me taking the least expensive camera with its kit lenses, but I will shoot on a solid tripod and they will shoot handheld. I will guarantee most of my photos will be as sharp or sharper than theirs.
There is one other thing to consider about sharpness and sensor size that affects how you deal with what is sharp or not sharp in the image. Full-35mm-frame does affect how a sensor sees what a lens sees. I have a new Internet class at BetterPhoto.com about aperture - The Magic of F-stops - that looks a bit at how selective focus affects images.
Selective focus is definitely affected by sensor size as it relates to focal length. Larger sensors will show less apparent depth of field with a given angle of view because they require a longer focal length to get it compared to a smaller sensor (e.g., a 100mm lens on a Four Thirds camera acts like a 200mm lens on a full-35mm-frame camera in angle of view, but gives more apparent depth of field than the 200mm).
Note: For interactive online courses on photography basics, creative photography and Photoshop, as well as DSLR camera tutorials, check out the online digital photography school at BetterPhoto.com.