Sensor sweet spot

Does anybody know if there is a sweet spot ISO for the K10. which ISO is the best for highest quality image.
Derek

There's a theory that the "native ISO" gives optimum results and in the case of Pentax I understand that it's ISO200.

In practice, newer models give very similar performance at ISO400 and are very usable at much higher values. Noise always increses to some degree as we increase the ISO value. The K-5 is especially good in this respect.

I would say ISO 100 but it does depend on what you’re shooting and what light is available? so it can vary, for normal I use ISO 200 and for tripod use ISO 100 for that track sharp shot.

I would have thought the lenses sweet spot was the most important thing.

And isn't that usually mid aperture around f8 to f11

Thought the k5 had a higher dynamic range at ISO 80.

All of them ( K10D, K20D, K5 )have higher dynamic range at their lowest ISO setting.

http://www.dxomark.com/index.php/Cameras/Compare-Camera-Sensors/Compare-cameras-side-by-side/%28appareil1%29/676|0/%28brand%29/Pentax/%28appareil2%29/213|0/%28brand2%29/Pentax/%28appareil3%29/212|0/%28brand3%29/Pentax

Therefore the lowest ISO will give optimum results.

I have confirm this in practise by taking and editing many many thousand images with those three cams.

if you're talkign about sharpness then not on my lenses. Most of them have had sharpness fall off below F8. I would say on average f4 to F5.6 is the range of best sharpness.

However in terms of 'sweet spot' that can be a different thing altogether. The sweet spot for my 50/1.2 is F/1.2, and similar with my Sigma 30/1.4 the sweet spot is F1/.4

I don't think you can generalise with lenses. My SMC Takumar 135mm F3.5 is fantastic wide open, my 55-300 needs to be stopped down to 6.3 or 7.1, DA 16-45 is great at all apertures, Chinon 50mm F1.9 is great at 2.8 etc.

For ISO I always use the absolute lowest setting I can get away with without risk of shake.

Regards
David

Same here

When highlight correction turned on on the K-5 the lowest ISO available becomes 160. So if I can use that I do.

To get the "absolute lowest setting you can get away with without risk of shake" the TAv setting is pretty handy but one has to watch it doesn't need to go down below the lowest setting available and overexpose.

John

I often use 'P-mtf' mode and was surprised to find, as smeggypants says, that f4/f5.6 is where Pentax reckon that DA lenses perform best.

Always the lowest ISO you can get away with, for me in the studio its 100 but generally outdoors I prefer 400

f4 to 5.6 gives the highest resolution in my experience with my glass as well.

Is it possible that those that experience the best sharpness with the lens only slightly stopped down are misinterpreting their results?

Clearly, diffraction isn't going to be contributing significantly to any erosion in image quality from F5.6, say, to F11 or more.

Depth of field, and indeed lack of aberrations, are both going to be improved with a smaller hole in the middle, and both these effects would lead one to expect that IQ would improve, not deteriorate, down to moderate apertures.

Therefore, it seems likely to me that those reporting the best sharpness with lenses only slightly stopped down, are probably getting the benefit of the first stop or so of improvement that you get when the lens is no longer wide open, coupled with the least amount of camera shake, that you get with wide apertures and hence short exposures.

Feel free to shoot me down in flames with actual evidence, such as MTF charts, or where the images concerned have had shake rigorously eliminated as a contribution to lack of sharpness, but till then, my money would be on just a little camera shake being the main contributory factor as the lens gets stopped down.

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Edit: note to self: read earlier posts more thoroughly. Ken's comment is the sort of evidence I mean. What about non-DA glass? Do the charts suggest the same sort of thing?

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Further edit: Ok, supposing it's true, even for DA lenses, why is it true?

Hi Chris, I'm not sure you are correct in your post above about sharpness at wider apertures being down to shorter exposures / less shake. I am basing my experiences when images are taken on a tripod with 2 second delay or on remote control with delay, so shake is not a factor.

I can't send you definitive proof with charts etc as I can't be bothered to test the theory to this degree, but in real world usage, a lot of my lenses seem to perform best at or near to wide open.

Regards
David