Published 2013/02 

An important companion article "Perception of Detail" is found HERE. It explains some things about how much detail the eye can actually resolve and how this relates to common image display technologies.

The System

This is a new page (February 2013) and existing equipment reviews will be gradually updated for consistency with what's documented here. Expect revisions in the weeks to come.

I leave most formal testing to the pros, relying primarily on many years experience in photography as a guide to rating photo equipment. It is my observation that the attentive, experienced observer working with ordinary photographs can come to conclusions agreeing well with purely objective tests and that results obtained in the field will sometimes expose both flaws and virtues in equipment that elude formal methods of examination. This is not to dismiss lab based reviews but, rather, to suggest reasonably useful evaluations can be made in other ways. 

The foundation of my system is the concept of "presentation", that is, how do we plan sharing our images in terms of size and medium? Will the presentation be in the form of an 11 x 14 print, a monitor or a snapshot in a photo album? The answer to that question determines all the rest. Fine prints reveal by far the most detail whereas even high resolution computer monitors can render only a modest amount of detail but ... monitors have other advantages. We are apt to overlook the weak detail capabilities of monitors because of those advantages. You can read more about monitors here.

Camera body, lens and display technology (e.g., printer) comprise a photographic presentation system.  Weakness in one of these components determines the best that can be achieved. An "Excellent" lens cannot provide an excellent image if it is mounted on a merely "Good" body in which case only "Good" images can be produced, etc.

In this rating system a camera, lens or lens/camera combination meets all the criteria for photographic presentation excellence if the following condition (1) is met and criteria (2, 3) are satisfied:

1. Viewing Distance: The finished image, in presentation form as chosen and prepared by the photographer, is viewed at a comfortable viewing distance. There's an element of personal preference involved here but many people find 1 1/2 to 2 ft a comfortable minimum viewing distance for small images or text. If you like to get much closer than that or use a magnifier that's up to you, of course, but IMO this gets us into "pixel peeping" more properly belonging in the lab. Here I am not interested in forensic image evaluation and the conclusions that might inspire. Larger prints and monitors (see later definitions) will prove comfortable only at greater distances, at about the point where you don't have to turn your head or move your eyes too much to see the entire image. At that distance the image quality in terms of close-up sharpness (for example) is less critical. You will often see 1 1/2 to 2 times the image diagonal cited as a good viewing distance.
2. Freedom From Distracting Flaws: At the comfortable viewing distance there are no significantly distracting defects such as chromatic aberration, distortion, noise or other evidence of flaws in the imaging system. These might very well be present at some closer level of examination but they must not prove distracting (if visible at all) at the comfortable viewing distance. In other words, you are able to enjoy the photograph as intended without having to forgive its technical shortcomings.
3. Retention of Detail: The image, when enlarged to the dimensions of the desired presentation, will have sufficient underlying detail remaining that the display technology will not be able to render all of it or will just barely be able to render all of it. That sounds odd. Put another way, the presentation will not suffer from visible softness owing to insufficient detail in the original image. In the case of monitors there will almost always be loss of detail attributable to the monitor itself.

The above leads to a ratings scale with some relevance to the way in which an image is intended to be viewed. IMO this is more useful than purely subjective observations or, conversely, those based entirely upon laboratory findings.

Definitions

The following terms describe various presentation formats/methods. Again, there are approximations and there will be some slight overlap of categories:

Prints:

• Small - 4 X 6, 5 X 7 and smaller
• Medium - 8 X 10, 8 1/2 X 11
• Large - 11 X 14
• Very Large - 19 or 20 inches on longest size (Super A3)
• Huge - 24 - 32 inches on a side
• Poster - Sizes larger than huge.
  

Monitors and TVs:

• Small  - Phone displays, iPods
• Medium - Tablets such as iPads, notebooks
• Large - 15 to 17 inch monitors and the largest notebooks
• Very Large - 19 to 23 inch
• Huge - 24 to 32 inches
• Projection - Projected images, large plasmas etc - not discussed here.

Practically all monitors have the same dot density or "pitch" which is near 100 dots/inch (dpi). That means we can usually estimate the dimensions of a monitor by dividing the total maximum dots on each axis by 100. Display software can combine dots in various ways to provide a reduced resolution (lower effective dpi), which increases image size at the expense of apparent detail.

The visual properties of monitors and prints differ considerably. At comfortable viewing distances and even beyond the individual dots comprising a monitor image are usually visible but monitors have advantages of their own. Accordingly, a relaxed standard for resolution applies to these devices, especially when viewing video as subject motion is apt to conceal shortcomings in resolution and other presentation characteristics. Extreme sharpness isn't always the most important characteristic of a fine image. Note that it is rare for any image to fail criterion (3) on a monitor. Monitors are discussed in more detail HERE.

Ratings Scale for Components of a Photographic Presentation System: 

I use a 1 - 10 scale or an equivalent wordy rating such as "good/excellent" etc. At each level, the image satisfies the criteria specified in points (2, 3) above in order to qualify as visually excellent. At the next larger size the image is visibly compromised, most likely in terms of detail:

IMPORTANT: This scale is relevant primarily to print presentation. The much lower resolution of monitors means that criterion (3) for an excellent image is more easily satisfied because of the relaxation of our standard for absolute sharpness. A "Good" imaging product would create images we'd possibly rate "excellent" even on a Very Large monitor because we accept some degradation of detail owing to the lower dot distribution density. This assumes other properties of an excellent presentation such as low chromatic aberration remain controlled at the larger size.

To illustrate use of the scale, consider a photographic product rated "Excellent" or "8". That would mean in conjunction with other "Excellent" components needed to create a finished image, the criteria in points (2, 3) could be satisfied at Super A3 print size and for monitors at at least the next size up. 

Suppose, furthermore, we use a "Good" lens/camera combo but try printing on Large paper. The perceived image would then probably qualify only as Fair and if we went up another size, then possibly Poor.

We could get silly and go into yet more superlatives such as "Astounding" and "Flabbergasting" (thinking of truly exotic imaging systems such as the Hubbel Space Telescope) but that sort of thing is outside the realm of conventional photography.