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Forum: Pentax SLR Lens Discussion
02-27-2015, 04:37 PM
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Thanks! That's a great article (also part 1). The calculators let you easily check if you should expect any resolution gain going from 16mipx -> 24mpix if you know how the lens perfom on the lower resolution sensor at certain f-stop.
Another good one that I've stumbled upon recently is this one:
Do Sensors ā??Outresolveā? Lenses? - Luminous Landscape
which might be little more "scientific" but basically describes the same thing (how diffraction,aberations and sensor resoliton are related to final image resolution)
---------- Post added 02-27-15 at 06:28 PM ----------
OK, that's true, it only will work close to that on a "perfect" sensor - with no AA filter, demosaicing, etc. Both K-5 IIs and K-3 lack AA filter so for my naked eye results there will be very close to a "perfect" sensor.
When there's AA filter, its purpose is to blur the image - so no matter how sharp are the lens, the resolution is somewhat lower than the sensor resolution before the image is sampled by the photosites - to avoid moire. The sharper parts of the image are still sharper as result but the difference is minimized by the blurring. Also the less megapixels on the sensor - the stronger the AA filter needs to be, lowering the resolution even more. That can easily be seen on the photozone.de charts say for DA70 since it is tested on both 10 and 16 mpx. You can see on 10pix all the results are proportionally lower than the upper limit (which is the sensor resolution) comparted to the results on the 16 mpix sensor (both models have AA filter so they should never reach the limit). And at the optimal f/5.6 and f/8 on 10 mpix resolution is is almost even across the frame (so to me that is - the lens totally outresolves the sensor there) while on 16 mpix central resolution is noticably higher, almost hitting the maximum (so for me that reads: center certainly outresolves the sensor, k-5 AA filter is weak and rest of the frame may not really outresolve the sensor).
On a side note one some other lenses on photozone.de they have the central resolution hit or even exceed (i think the 43 ltd on k10d was one :) ) the maximum possible resolution which ... should not be possible unless some sharpening was applied to the image before analyzing (like in the raw conversion/demosaic process).
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Forum: Pentax SLR Lens Discussion
02-24-2015, 11:03 PM
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To put it in a different way - I know they are not going to be any worse, but is the resolution noticably better on k-3? Like if I take the same image with k-5 iis and k-3 and up-size the 16 mpix image to 24 - will I be able to really tell the difference?
I've seen some really impressive sapmples from the longer lenses and with the teleconverter where the ability to crop more is also very handy but I rarely use telephotos and I'm trying to figure if it is worth upgrading to K-3 some time in the future considering these are the lenses I have.
Anyway, seems everybody is happy with their limiteds on the K-3 so I take it as good sign :)
Well, if a lens outresolve a sensor across the frame, you won't be able to see any difference in sharpness between the center and edges of the image.
Of the 3 lenses in question (my copies of course) on K-5 IIs I can only say this for the 35 ltd. I guess if measured there is difference, but to my eyes it is as good as it gets.
That's why I was so surprised with the results on the a5100. Maybe it's just that it has an AA filter...
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Forum: Pentax SLR Lens Discussion
02-24-2015, 02:44 PM
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I have a K-5 IIs and I am definately ok with the performance of my 15/21/35 limiteds on it. But the 21 is not the sharpest lens ever and the 15 is known for its corner issues.
The 35 is fine on K-5 IIs but recently i saw some pictures taken with it mounted on sony a5100 via adapter and I was somewhat dissapointed with the results (the sony has a 24mpix sensor but I'm not sure if it has AA filter or not) ...
So I was wondering - what is your experience with these lenses on K-3 ? Are they up to the 24 mpix sensor?
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