It is hard to judge our images completely when we only examine them on screen.
Especially since the arrival of digital, many of us do not print images as much as we used to. Images look different in print than they do on the screen. You can gain a different perspective.
The key to the value of prints lies in the resolution. With any camera above around 2MP, if you view the full image on screen you will not be seeing the actual pixels, but rather a scaled down version. With higher resolution cameras you may only be seeing a full image at 16 to 20% of real size. It is not possible to judge anything like detail, sharpness or focus from such a reduced size image. This means that you must zoom in to 100% and out again to assess an image, and in doing so there is a strong risk that you will lose perspective over the whole image.
An appropriate sized print can show you all the detail that is in the image. For up close viewing a 300dpi (more correctly 300ppi) image is right for printing on modern, high resolution printers (360dpi for Epsons) that have print resolutions of 2000dpi and above. The table below gives the minimum print sizes for various digital camera resolutions. If you print at least this size you will see all the detail in the picture.
5616×3744 21MP Canon 1Ds Mark III 19″ x 12.5″
4672×3104 14.6MP Pentax K20D 15.5″ x 10″
4368×2912 12MP Canon 5D 14.5″ x 9.5″
3888×2592 10MP Canon 400D 13″ x 8.5″
3456×2304 8MP Canon 350D 11.5″ x 7.5″
3008×2000 6MP Nikon D40 10″ x 6.5″
Note that these are not the maximum sizes of prints you can produce with these cameras, since you can usually increase these camera images by at least 2x in each dimension with no real loss in quality and at larger print sizes you can drop significantly below 300dpi and get a good result (since you don’t commonly view very large prints at a close distance).
In the old days in the darkroom I’d get my negs, take a loop to them on the lightbox or to a contact proof, eliminate the obvious flawed ones and then do small prints, for me usually 8×10′s, to examine the images further, get an idea of how to ‘develop’ the image with dodging and burning, etc. Now with a digital workflow we tend to look at low resolution versions that our viewing software, whether Bridge, Aperture, Lightroom or whatever has prepared. Now you can judge composition from the low res version. But you can’t judge composition in relation to sharpness from the downsampled version you see on screeen, and so things like considering sharpness contrasts across the image (sharp areas vs blurred areas), for example, aren’t possible and you need to zoom in. But when you do you loose the overall perspective.
So doing a suitably sized print allows you to judge and compare all aspects
simultaneously and thus keep the whole image in mind at all time. I find that
superior. This is a great aid for you in understanding your images and in advancing your art.