OK, the first thing I have to say is that I am not a tester; I am a photographer. My typical way of testing a camera or lens is to use it for a while and see how I feel about the pictures. That said, I do see the value in more formal testing, and sometimes even dip a toe into that area myself. But please do not expect this to be as comprehensive and exacting as a lab might do.
However, I am curious as heck about my new K-x. This was generously provided by Pentax and Pentax Forums as a prize in the competition held earlier this year. Thanks to Adam for this!
Besides being compact and well-specified, the most interesting thing about the K-x is its high ISO noise handling, reputed to be better than any previous Pentax camera, including the top-of-the-line K-7. After using it a week I wanted to explore for myself, a bit more formally, these characteristics. Since I am intimately familiar with the K20D, the comparison was made with that camera. (I have used the K-7 only slightly.)
I shoot the K20D at ISO 200 and 400 most of the time, going up to 800 in a pinch. I generally do not bother with noise reduction, since I find the noise characteristics in that domain to be pleasing. I do have a licensed copy of Noise Ninja for higher ISO situations.
To test I used the FA43 at f/4, a wide enough aperture, but one at which the lens excels. I used a tripod with 2s shutter release (hence SR off) and chose a section of my bookshelf as a suitable target. I did this at night with one overhead light bulb -- a typical dark room scenario. The distance was about 1 meter.
In Av mode I started at the lowest sensitivity, 100, and changed by one stop (eg doubled) for each shot. I found that both cameras underexposed in this situation, and so dialled in a constant +1EV compensation.
I let the camera auto-focus, which was maybe not the best decision in retrospect, though a typical one for most shooters. Strangely, the K-x refocused between each and every shot, while the K20D did not. I welcome an explanation of that phenomenon.
I used PEF files in sRGB colour space, though I have since changed my K-x to DEF for convenience. I retained auto white balance which produced some issues, as we will see. I am not one to fuss with grey cards since I have no problem correcting in post. (If I shot studio and strobes I would have a different practice.) The K-x Expanded Sensitivity custom setting (#3) was set On, so as to get a range of ISO 100 to 12800. However the Shadow Correction and Highlight Correction were left Off. The K20D sensitivity range was left unexpanded at ISO 100 to 3200.
This resulted in 8 shots from the K-x, at ISO 100, 200, 400, 800, 1600, 3200, 6400 and 12800. The recorded exposure times (in seconds) were 4, 2, 1, 1/2, 1/4, 1/8, 1/15 and 1/30. That's as close as can be to a perfect ratio of stops. The 6 shots from the K20D at ISO 100, 200, 400, 800, 1600, 3200 resulted in exposures of 4, 2, 1, 1/2, 1/4, 1/8. It's nice to see both cameras meter the same.
I processed through Adobe Camera Raw with all settings on default, no sharpening and the same brightness settings. Shots were layered and cropped in Photoshop, again with no processing. I could have obtained much "better" results following my normal procedures, but that is not the point here. Finally I cropped to 600 pixels square and produced JPGs (quality 10). Note that because of the difference in sensor size, these "100% crops" show a different amount of the subject.
The photos have been uploaded to Flickr and linked here. Since each has its own Flickr page, it makes it easier for you to compare one to another.
OK, here are the images.
K20D ISO 100 K-x ISO 100 K20D ISO 200 K-x ISO 200 K20D ISO 400 K-x ISO 400 K20D ISO 800 K-x ISO 800 K20D ISO 1600 K-x ISO 1600 K20D ISO 3200 K-x ISO 3200 K-x ISO 6400 K-x ISO 12800
Finally, just for kicks, I ran the highest ISO of each camera through Noise Ninja with my default settings (Strength, Smoothness and Contrast at 10, USM at 60/1.2, Turbo checked) just to see what would happen.
K20D ISO 3200 Noise Ninja K-x ISO 12800 Noise Ninja
Conclusions in the next post.
Last edited by rparmar; 08-24-2010 at 10:26 AM.