Quantity of sensor pixels is just not as important a measure as people seem to think. In reality as long as you have a camera that’s 8mb+ you’re good to at least 8″X12″print sizes (roughly A4) at serious resolution! I can count on one hand the number of times I’ve needed to print larger than that for a client…a commercial photographer working on campaigns has vastly different imaging needs, and for them enlargements may be the rule rather than the exception…which is why we have medium format digitals!
The calculations work as follows, assuming a 300dpi (dots per inch) print, which is pretty normal for glossy / matt images printed for ‘normal’ viewing use at close range.

8″ X 300dpi = 2400 pixels
12″ X 300 = 3600 pixels

That gives us the pixels required along the edges…now we need the area (or total number of pixels required):
2400 X 3600 pixels = 8,640,000 pixels required to give us an 8″X12″ at 300dpi.
In other words, an 8mb sensor is right on the money.

Print Quality:

Newspapers print at about 150-200dpi as far as I remember, magazine covers at 300-400dpi, magazine internals at 300dpi, and high end commercial prints sometimes up to 600dpi…so the question as to which sensor you need actually becomes a product of:

• Your intended target audience (web or print?)
• Viewing distance *
• The resolution that target audience needs to produce an acceptable print.

*Keep in mind that as prints get bigger, the viewer tends to be further away…roadside billboards for example might be printed as low as 10dpi! So the extra image information doesn’t actually contribute to creating a better print which is one of the reasons that some newspaper photographers still use the 4mb Canon EOS 1D (still allows them an 8″X12″ @ 200dpi) – they don’t need the extra resolution, and the smaller files are quicker to send via (sometimes dodgy) 3G connections…

Finally, Pixels are not created equal:

To my mind what’s far more important than the number of pixels is the closeness of the pixel sites on the sensor and the size of each pixel site.
To put it simply bigger pixel sites mean better light gathering ability, and more space between them means less cross-talk, less noise.

The classic example of this is cellphone cameras – some sporting 8mb sensors in their onboard cameras – which have uniformly dismal quality. The images may look good on Facebook (at 72dpi) but I have yet to see a print from a cellphone camera that I would be proud of, much less frame. Even the iPhone 4 which has one of the best looking cameras I’ve seen on a cellphone at 5mb is pushing the limits of what’s possible on that tiny sensor with our current technologies. The fact is a lot of camera sensors are just too small for the number of pixels they have crammed in.

Canon realised that the law of diminishing returns came into play with the Powershot G10 – at 14.7mb the image quality suffered, no surprise then to see that the G11 and G12 have been dropped back to 10mp with the upgrade emphasis placed on useability improvements rather than extra megapixels.

It boils down to what’s most important to you.

• If absolute image quality is your thing, then you might well be better off looking at a second hand EOS 5D, or a 1Ds MKII
• If it’s image size: Go for the most pixels you can get…but beware that at some point your image quality may suffer.
• If it’s shot to shot speed for sports etc then more modern processors give you faster burst rates and more flexibiity regarding picture styles and recalleable user settings.

Personally it’s a tough call as whether to sell my 5D or 50D – the 12mb 5D takes noteably superior images to the 15mb 50D, colors are better, transitions are smoother, noise is far better controlled. But the bigger 50D pictures will leave me more ability to crop for shots that I might take of surfing etc. The higher burst rate will probably prove advantageous as well. So while my heart says keep the camera with the highest image quality, my head says that the 50D will probably stay – but only because I have replaced full frame sensor of the 5D with another full frame sensor in the MKII.

The photo below shows us the relative sizes of various sensors, I grabbed it from:http://www.cambridgeincolour.com/

Following Richard Avedon’s death in 2004, the New York Times said that “…his fashion and portrait photographs helped define America’s image of style, beauty and culture for the last half-century.” The difference between a Richard Avedon and the average portrait photographer can be summed up in the thoughtfulness of his approach to portraiture.

Henry Kissinger’s Portrait
by Richard Avedon

I once went to Washington for what they call a “photo opportunity” with Henry Kissinger. As I led him to the camera, he said a puzzling thing. He said, “Be kind to me.” I wish there had been time to ask him exactly what he meant, although it’s probably clear. Now, Kissinger knows a lot about manipulation, so to hear his concern about being manipulated really made me think. What did he mean? What does it really mean to “be kind” in a photograph? Did Kissinger want to look wiser, warmer, more sincere than he suspected he was?

Do photographic portraits have different responsibilities to the sitter than portraits in paint or prose? Isn’t it trivializing and demeaning to make someone look wise, noble (which is easy to do), or even conventionally beautiful when the thing itself is so much more complicated, contradictory, and therefore fascinating? Was he hoping that the photograph would reveal a perfect surface? Or is it just possible that he could have wished – as I would have if I were being photographed – that “being kind” would involve allowing something more complicated about me to burn through: my anger, ineptitude, strength, vanity, my isolation. If all these things are aspects of character, would I not, as an artist, be unkind to treat Kissinger as a merely noble face? Does the perfect surface have anything to do with the artistic integrity of a portrait?

A photographic portrait is a picture of someone who knows he’s being photographed, and what he does with this knowledge is as much a part of the photograph as what he’s wearing or how he looks. He’s implicated in what’s happening, and he has a certain real power over the result. The way someone who’s being photographed presents himself to the camera and the effect of the photographer’s response on that presence is what the making of a portrait is about. The philosopher Roland Barthes once said a very wise thing about photography. He said, “Photography is a captive of two intolerable alibis. On the one hand, ‘ennobled art pictures.’ On the other hand, ‘reportage’ which derives its prestige from the object. Neither conception is entirely correct.” He said, “Photography is a Text, a complex meditation on meaning.”

What Barthes recognized is that we need a new vocabulary to talk about photography. Not “art” versus “reality,” “artifice” versus “candor,” “subjective” versus “objective” – photography falls in between these classifications, and that’s why it’s so impossible to answer questions like “Is photography really art?” and “Is this an accurate picture of your friend?” As I have said on other occasions, “All photographs are accurate. None is the truth.”

I don’t think pictures have to justify their existence by calling themselves works of art or photographic portraits. They are memories of a man; they are contradictory facets of an instant of his life as a subject – and of our lives as viewers. They are, as Barthes said, texts, and as such they exist to be read, interpreted, and argued over – not categorized and judged.

So who is Henry Kissinger? And what, or who, is this photograph? Is it just a shadow representation of a man? Or is it closer to a doppelgänger, a likeness with its own life, an inexact twin whose afterlife may overcome and replace the original?

When I see my pictures in a museum and watch the way people look at my pictures, and then turn to the pictures myself and see how alive the images are, they seem to have little to do with me. They have a life of their own. Like the actors in Pirandello, or in Woody Allen’s movie The Purple Rose of Cairo, when the actors leave the screen and join the audience. They have confrontations with the viewers Photography is completely different from every other form of art. I don’t really remember the day when I stood behind my camera with Henry Kissinger on the other side. I’m sure he doesn’t remember it either. But this photograph is here now to prove that no amount of kindness on my part could make this photograph mean exactly what he – or even I – wanted it to mean. It’s a reminder of the wonder and terror that is a photograph.