Re: 'A Sensitive Issue'

Mike Levy asked:

I got a question re pixels and sensor size.

I might be buying a 6.1 mp Pentax, 'cause i don't see the new 10 MP
versions coming before Xmas. My wife currently has a Sony P&S with 6
mp, but the sensor size is tiny-- it might be half the C-sized (or
APS-sized) sensor in the SLr, so would this make any difference in
picture quality?



Yes, in many ways.

Lets assume two sensors, one APS-C sized, the other a much smaller one. Both have 6 million pixels. Obviously, the pixels in the smaller sensor are smaller, in order to fit all 6 million in a space 1/4 the area or less. Thus, fewer photons land on any given pixel during a given exposure. Thus, to gain an equivalent ISO sensitivity, the signal from the smaller sensor must be amplified much more... and more amplification means more noise. That is why most P&S digi-cameras limit their upper ISO to 400 or so. Conversely, your 6.1mp Pentax (APS-C sized sensor) should do much better than your wife's P&S.


Or put another way: I am s told that a 6 mp SLR will easily print to
A4 size -- I assume  without radical cropping -- so the smaller P&S
sensor should do the same?

6 millions pixels may print to A4 size, but with what quality... no matter what the source. These days, all photo prints are digital. At least, those from the 1 hour labs. Film is developed and then scanned. It is printed by "painting" the picture on real photo paper using coloured lasers, at 300dpi, which makes a "photo quality" print that 99% of the population cannot tell from the real thing. So, using 300dpi as a guide, the 10.2 megapixels from a Leica DMR (2590x3882) will enlarge to 8.63x12.94 ...or a 8x12" (roughly A4 sized) print. For top quality, your 6.1mp cameras should enlarge well to A5 (a bit bigger than 5x7). With interpolation, larger prints can look great (I have some 12x18" prints from an 8mp Canon 20 D on my wall) but they lack the fine detail, when examined closely.

 Or does the pixel SIZE on the sensor make
a serious difference.


Yes. And the size of the sensor makes a big difference, too!

Besides noise, smaller sensors use smaller diameter lenses of shorter focal length... so although their f stop may be the same, their physical size is much smaller and they allow less light through (light transmission value) for a given f-stop (lens speed). For instance, if we compare a 35mm Leica with Leica's D-lux-2 and the lens on the D-lux 2 set to f2.8, you'd have to stop down the 35mm camera to f11 to get the same *amount* of light on the film as on the sensor. This means that the DOF at f2.8 on the D-Lux 2 will be the same as at f11 on the 35mm camera.

This is great for having everything in focus and makes life easier for AF systems. But it's tough to get a small sensor camera to throw a background out of focus to bring attention to your subject. If you want to do creative photography rather than all-sharp snaps, size matters.

For more on this, see "Form follows Format" in the April 05 issue of LFI, which is based on a talk (which I've heard) by Peter Karbe, head of Optical Design an Leica, Solms.


The second query is this: If the sensor is the same size in both the
Pentax 100 and the new K 10D but one has 6 mp and the other 10 mp,
what is that going to do for quality, noise issues, sharpness etc.?

See first answer. In theory, more pixels in a given area means smaller pixels and thus more noise. That being said, newer models, employing lower noise sensors and circuits may well improve the situation. Only a little real life testing of the two will tell you for sure.

I hope this helps.
---

David Young,
Logan Lake, CANADA

Wildlife Photographs: http://www.telyt.com/
Personal Web-pages: http://www3.telus.net/~telyt





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