Re: How many pixels is enough ?


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Posted by GES on 2013-03-12 13:35:33 in reply to Pentax K5 w/ 18-55 and 50-200mm WR = dust + weather resistant posted by Serge on 2013-03-09 21:03:55

When I mentioned Nikon's yet to be seen D7100 DX camera below, it raised the issue of how many pixels is enough.

Some magazine publishers wouldn't accept digital camera pictures at all; apparently too low in quality (images).

I remember when you had a choice (with Kodak) of Tri-X, Plus-X, and Panatomic-X, for B&W , and Kodachrome 25, and 64 or Ektachrome for color.

So if you wanted grainy pictures of a black cat in a cellar at midnight, you went with Tri-X, and If you wanted to take pictures of sunspots with your Questar, you went with Panatomic-X.

So digitals now have better resolution (than they used to) and better color rendition (than they used to). How they stack up against film, is a matter of choice.

Ben-L said he's through with DX format, and plans to go with the Canon 5D Mk III, with its 22.3 Mpx. He added that Nikon's D-800 36 Mpx, does nothing for him.

So is Mpx a sales gimmic? Ken Rockwell, a well read reviewer, says in his D-7100 review, that you don't need the 24.1 Mpx; you'll never see the result. He ordered one anyway.

Back in the film days, I actually used test charts to take Panatomic-X pictures, with my Nikon-F film lenses to see where they performed best. Some of the better lenses, like the 105 mm F/2.5, and the 55 mm F/3.5 macro nikkors easily resolved 56 line pairs per mm at useful apertures, like f/5.6. Zoom lenses like the 43-86 nikkor, were disasters.

Today, Nikon publishes graphs at 10 and 30 LP/mm on their modern lenses, typically wide open (such as wide open is these days) and at the short and long end of the zoom range.

And some of those lenses look pretty sick; and when you consider you have to stop them down from their wide open f/5.6 to maybe f/11 or more, it makes you wonder what you are paying for.

An ideal perfect F/1 lens can "resolve" two spots that are about 0.5 wavelength apart. Well actually, you can tell their are two spots, but they aren't exactly apart, that's astronomers counting stars.

More realistically you should get two spots if they are one micron apart. So that would say if you had alternating black white lines, as dense as 500 pairs per mm, you could see the separate lines.

Well perfect F/1 lenses are as scarce as hen's teeth.

A perfect F/4 lens would be able to see 4 micron lines, which is about the pixel size of the D-7100 sensor (3.9 microns).

Most color sensors have a BGGR square Bayer pattern of pixels, although other possibilities are also used.

So it would not be unreasonable to consider such a 2x2 set, as being one "real" picture element, with color and detail information, so now we are up to about 8 microns per picture element, or 16 microns for an adjacent pair of black and whie lines which comes out to about 62.5 line pairs per mm.

So we now are in the range of older B&W films; but we don't have any perfect F/4 lenses either, specially zooms.

So Nikon (and others I'm sure) now have digital "film" that is as good or better at resolving detail, as old films were, and apparently better than most of their lenses can do by a long way.

Well that is the way it is supposed to be. The camera sensor is a digital sampling system, and if the areal images formed by the lenses, contain finer detail than the sensor resolution, then you get aliassing noise, and Moire color fringes, in your pictures.
When pixel numbers were smaller and pixels were bigger, you had to have a fuzzy filter in the camera, to remove any image detail finer than the sensor resolution.

Nikon found with their D-800E at 36 Mpx, that they could remove the fuzzy filter, and get sharper pictures, so long as the user could use software to remove color fringes if they occurred.
Now with the D-7100 and its smaller pixels, they find they don't need the fuzzy filter at all; well unless they finally make some sharp DX lenses.

Ken Rockwell, said the 24 Mpx was overkill (or words to that effect) and he also panned the D-7100 "Crop mode", where that camera can crop the sensor down by 1.3 X which makes it more like a total 2x crop of the full size FX sensor. He says it's silly.

Well I don't agree on either point. For a start, P&S cameras have been able to shoot in cropped modes for ages, going down from full pixel count, to a half or a third of that, while shooting.

The advantage of these cropped modes, is that you do the cropping in the camera, so you only use the central part of the lens field of view, where the aberrations are considerable lower so you get sharper detail to the corners of the cropped frame, and it also allows you to home in on that way too distant subject that you can't get any closer to.
So If you are trying to capture that bald eagle, way up in a distant tree, eating his catch, you can effectively zoom in closer, and still end up with a picture worth having.

The built in image stabilizing that keeps getting better all the time with modern SLRs, enables you to get photographs you couldn't get before. Yes you can crop your shots on the computer, but you can frame them better in the camera.

As for pixel noise at low light; don't take pictures at low light. Well digitals do better than old films anyhow, and modern cameras with their anti-shake, can take longer exposures, which integrate out pixel noise.

And nobody, looking at a dim subject in a low lit room, can even see the level of detail that even noisy digital cameras can see.

I believe you will see more digital cameras with smaller formats, using enough pixels to be ahead of any lens.

Somehow, I suspect Nikon's DX will stop at 24 Mpx, but their FX might eventually go up to say 48 or 50 and be done with fuzzy filters for ever.

You don't have to keep all the detail that Mpx reveals; but you can't even make that choice if it isn't there to begin with.

But if 4x6 prints is what you want, then your iphone will do just fine.

George


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