Pentax K3-Ii First Results - Coin Community Forum

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Author	Replies: 4 / Views: 1,535
rmpsrpms Pillar of the Community United States 4038 Posts	Posted 05/22/2016 1:24 pm I became interested in Pentax's Pixel Shift Resolution mode based on srs77's favorable results with the K1. I was less interested in FF, so started looking at the K3-II, which has the same Pixel Shift mode. The K3-II has smaller pixel pitch (3.9um vs 4.9um of the K1) but otherwise are similar, except of course the K3-II is 24MP APS-C while K1 is 36MP FF. srs77's images were taken around 0.5:1 at f8, so are slightly diffraction-compromised. I wanted to test the K3-II such that the camera was the limiting factor, not the lens, so my first images were taken at M=0.7 and f3.3. My subject was the 1949-S Lincoln Cent that I'm using for my 80mm shootout. Critical focus was on Lincoln's throat near the center of the image. I did 3 shots: #1 with my Canon T2i as a reference; #2 with the K3-II in non-PS mode; and #3 with the K3-II in PS mode. See the cropped images below: T2i (reference) K3-II no Pixel Shift K3-II with Pixel Shift To me, the non-PS image looks over-sharpened , and the PS image looks even more over-sharpened and very noisy. Shadow contrast has been reduced, and the noise level is so high that it is actually losing resolution. I also tested the K3-II at 10x magnification on the same coin, zoomed-in to the date and mintmark area. I took 100% crops at the bottom left corner of the "4" of the the date. Here are the T2i and both K3-II crops: T2i (reference) K3-II no Pixel Shift K3-II with Pixel Shift The setup is stable and shows no vibration in Live View, so any movement is caused by the camera. The T2i has EFSC in Live View, but the K3-II does not and shows significant shutter shake blurring in the no Pixel Shift mode. The K3-II does have EFSC in Pixel Shift mode, so the shutter shake is gone, but it appears the Pixel Shift operation creates significant artifacts. Maybe the sensor movement causes a little vibration, as I can see both horizontal and vertical artifacts in the image. So, do I have a bad K3-II? Or is this technology just not suitable for photomacrography? Are there improvements that went into the K1 that were not present in the K3-II? Contact me for photographic equipment or visit my home page at: http://macrocoins.com Report this Post to the Staff

austrokiwi Pillar of the Community 2087 Posts	Posted 05/22/2016 1:59 pm I understand, perhaps incorrectly, that pentax's pixel shift is aimed at color resolution. It's purpose is to compensate for faults that are inherent in the Bayer sensor design we all use. You should get much better color resolution but not image resolution. The Olympus system is the one we would prefer where the sensor shift creates photographs as if they were from a much larger ( better resolving) sensor. So A 16mp Olympus camera can produce 40 mp pictures of the type we coin collectors would want. You may need to check that I am correct about my understanding of the pentax sensor shift . I will go and look again for the reviews that gave me this understanding. Edit found the DPreview of the K1 it says this: Quote: Then there's the Pixel Shift Resolution mode that increases color resolution by shooting four consecutive images with the sensor moved by one pixel - effectively canceling the Bayer color filter array and lowering noise by image averaging. The image averaging is probably what you are seeing and not liking( I guess) 2nd edit. To expand.. what the Pentax is doing is creating a dynamic range that a medium format or large format camera is capable of. I find the Sony's A7rII dynamic range is great for every day photography but with coins because I control the lighting..it isn't so important Edited by austrokiwi 05/22/2016 2:13 pm Report this Post to the Staff
rmpsrpms Pillar of the Community United States 4038 Posts	Posted 05/22/2016 2:23 pm The Pentax system samples all colors at each location. This is supposed to have the effect of improving the sharpness of the image since the color information is not being interpolated. Note that a Bayer sensor does not really have full stated resolution because all the required information is not contained in each pixel. The Pentax system was designed to give full resolution without the need to interpolate. This is a great concept, and indeed much more appealing than what Olympus does (and with better results based on internet images), but it definitely has its limitations if my K3-II results are to be believed. Contact me for photographic equipment or visit my home page at: http://macrocoins.com Report this Post to the Staff
austrokiwi Pillar of the Community 2087 Posts	Posted 05/22/2016 2:52 pm It would be interesting to see a comparison between the Olympus and Pentax systems. I had thought that the Olympus system would produce better resolution in terms of cycles per mm and so was better suited to macro. I had thought the Pentax system was a mechanical version of Sigmas Foveon sensor. There is one issue with comparing Olympus and pentax sensor shift tech... that's the sensor size the MFT sensor produces more noise than a larger sensor so might hide the potential difference between the two. I wonder if part of the problem is the actual sensor shifting is creating more vibration( with Macro work) Edited by austrokiwi 05/22/2016 2:55 pm Report this Post to the Staff
rmpsrpms Pillar of the Community United States 4038 Posts	Posted 05/22/2016 3:36 pm I think both are true...the Olympus system should produce better resolution, but from the example photos I've seen the result falls short. The Pentax is indeed a mechanical version of Foveon. The images I've seen from Foveon are superb and that gave me hopes of similar performance from the Pentax. It does look like the sensor shift movements are creating some camera vibration. In the last pic you can see vertical and horizontal artifacts that I think could only be caused by such movement. Contact me for photographic equipment or visit my home page at: http://macrocoins.com Report this Post to the Staff
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