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12-21-2010, 11:12 PM   #31
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QuoteOriginally posted by dosdan Quote
I'd ignore the DR stuff in DPR as it's really showing the Tone Response Curve (TRC) as applied to the JPEG. Look at the raw performance as this has had no TRC applied yet. This gives you a better idea when performing PP in a raw converter of how much you can boost EV, pull up tone curves, dodge or use "fill light" before noise will become a problem.

First off, read this article discussing the 3 regions of noise: Shadow, Mid-Tone, Highlight:

DxOMark - Noise characterization

Now compare the K7 & K-5:

DxOMark - Compare sensors

DR is the ratio of the lowest usable signal (just about the noise floor) to saturation. The difference between the K-7 & K-5 is enormous (about 3 stops between ISO200-1600), 3.75 stops at ISO 100 and the K-5 can still go to ISO80 for another 0.4 stop improvement. For example, at ISO100 the K-7 at ISO100 is 10.6 EV, while the K-5 at IS1600 is 10.36 EV, a 3.75 stops difference. So the ability to dredge signal up out of for the abysmal deeps is much better with the K-5.

"The mean reflectance of a natural scene is known to be about 18%. [See] If the camera sets its exposure parameter to reach saturation on an object with a reflectance close to 100% (a “white” object), then the SNR 18% value is representative of the level of noise in the scene". So the SNR 18% chart shows us how noisy the mid-grey/mid-tones are. The difference between the two cameras in favour of the K-5 is about 1 stop between ISO100-1600.

The Colour Sensitivity is supposed to include highlight noise performance: "Colour sensitivity is an integral value over the whole curve characteristic. In particular it depends on the noise in highlights. However, it also depends on the sensor’s spectral sensitivities which determines how the sensor can see the colours of the scene." The difference is about 0.8 stops between ISO100-1600.

So summing up, typically there is about a stop difference in performance, except when you boost the shadows. For the low-ISO shooter, this ability is enormous: 3.75-4.15 stops.

Dan, that pretty much sums things up.

Or put another way, the K-5 has better DR @ ISO800 than the K-7/K20D @ ISO100.

As a K20D owner, I'm very much looking forward to this upgrade. The K20D can deliver wonderful results when you get everything right, but it's quite unforgiving of exposure mistakes (blown highlights or noisy shadows/midtones). The K-5 will allow more latitude in exposure.

12-24-2010, 05:54 AM   #32
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Just a sample to show K-5 can take sharp pictures. I was testing the tamron 1.4 TC on my first SDM lens (DA* 60-250).

So, this is a shot taken with a TC and thus is softer than what can be acheived. DNG file opened in LR3, cropped and saved as jpeg. I used the built-in flash.

100% crop

If I have time to actually do a sharpness test without a TC, I will post those. But, the K-5 never left me thinking the images were in any shape or form to be soft, so most likely will not bother with the test.
12-24-2010, 11:25 AM   #33
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To my eye, all of these images are at least one stop underexposed, probably more, and yes I am using a calibrated and good quality monitor. It would be interesting to see the histogram to confirm this.

They look to be exposed about as I would expect from Pentax metering with the amount of white/light areas in the scene, but the white bar code label should be white and it is not (at least on my screen), which means the scene is underexposed.

This is not to say that the metering is incorrect, as metering on white should produce something close to mid-grey, so this is consistent with most all Pentax cameras I have owned, and is technically correct, IMO.

So, if the scene is actually one stop underexposed it is as if you had shot the entire test at one step higher ISO than indicated (at least).

Since you equalized the exposure between the cameras, the comparison is still valid, but it is a bit mis-leading if one wants to try and decide how either camera performs at a given ISO setting.


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