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09-14-2013, 05:29 PM   #1
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K-x vs. K-r image quality comparison

First, some background info. My first DSLR was a K2000/K-m. Last Spring (2012) I decided it was time to upgrade, so I bought a used K-r, which I, for the most part, loved. This Spring (2013), I discovered the flash no longer worked, so I sent it for repair. When it seemed that was going to be quite a while, I bought a used K-x as a temporary stand-in. Not having the focus point visible in the finder took some re-getting-used-to, but the K-x reminds me a whole lot of the K2000, handling-wise, so I adjusted pretty quick.

This past week, I got the K-r back after having the entire top cover & e-dial replaced, plus a standard CLA. I took some sample shots with it and noticed that they all seemed a bit "off". I couldn't quite say how, they just didn't seem right. So, I decided to do an semi-scientific comparison by taking the same picture with the same lens on each of the two bodies. What I found kind of surprised me. Of the tests I did, I uploaded the most noticeable example shots to this album. They were taken in RAW, and if you want to view the full DNGs, here you go: K-x Sample DNG, K-r Sample DNG

Both were taken hand-held from approximately the same position and with (as nearly as possible) the same settings on each camera (more on that in a moment) and using the same Tamron 28-75/F2.8 lens. The only discrepancy between the settings on the two cameras was that the K-r's shutter speed was 1/25, while the K-x's was 1/30. Interestingly, the shot from the K-r seems significantly softer or less-focused, especially in looking at the text on the plaque and the glass vase. I considered motion blur, but, if that were a factor, then the K-r shot would be sharper since it's using a faster speed.

I took dozens of other shots using other lenses (DA35/2.4 and A50/1.7) and the results are fairly consistent. Given that I was seeing this with a MF lens would seem to rule out any kind of focus accuracy issue, as well, although I was relying on the focus confirmation (beep& indicator) on each camera. My typical MF procedure is to go counter-clockwise with the focus ring until it just leaves focus, then, very slowly, turn clockwise until I reach the "middle" (as near as I can tell) of the "in focus" zone.

So, based on these photos, I'm inclined to stick with using the K-x as my primary, but I'd like to know what's causing the K-r's photos to be inferior. I believe both use the same sensor, and with the same lens, the optics are pretty much equal. Could I just have a lemon of a K-r?

09-14-2013, 05:43 PM   #2
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Focus accuracy with that method isn't guaranteed. It might be sufficient enough for most shots, but if you plan to compare images, you should really use liveview to focus.
09-14-2013, 06:11 PM   #3
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I would suggest if you wish to test/compare a camera or lens the first thing you need to do is get a solid shooting platform, be it a tripod or another flat stable surface like a bench. Hand held doesn't cut it particularly at low shutterspeeds.
Second switch to manual exposure mode and use the same settings for everyshot.
Focus should be done through live view with max magnification on a sharply contrasting object like text or similar, slowly adjusting manual focus to get the sharpest image possible.
Finally i would use mirror lockup with 3 second delay to remove any shake due to mirror movement (preferably with a remote release).
09-14-2013, 09:34 PM   #4
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Looking at the pictures, it looks like these are not focused at the same spot. The K-r appears to be focused on the glass bowl in front, while the K-x appears to be focused on the two vases and plaque in the back. Also, your plane of focus appears to be very narrow. It's hard to tell the difference in actual sharpness given these differences. But maybe what you are seeing is nothing more than front/back focusing, in which case the solution could be as simple as re-calibrating your lenses to the K-r. It might have been shifted a tiny bit while undergoing service.

Also, 1/25 is slower than 1/30, so you would actually expect the K-r to be more prone to blur (the difference is so small, anyways, that camera shake is a more likely cause). Maybe you have the shutter speeds backwards; but in any case, these are too slow to make any conclusions based on handheld shots, even with shake reduction on.

It's possible that you've confirmed the issue with the other lenses. But I would second the advice from the previous posters to confirm what you are seeing, especially using faster shutter speeds. There are too many variables in the shots you've posted.

Disclaimer: I only viewed the album you posted; I did not download the DNGs.

09-14-2013, 10:01 PM   #5
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K-x magic at work.

But really, it looks to me like simply different focus between the two shots. This sort of tests need to be done on a flat test target.

BTW, the K-x and K-r sensor's are similar but not identical. Their different DxOMark scores reflect this.
09-18-2013, 10:25 AM   #6
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OK, I did some additional tests last night (didn't have time to upload pictures, though) and it seems like it's (as someone alluded) a focus accuracy issue. In other words, the K-r seems to be focusing nearer that the indicator, uh, indicates it should. So, in the old sample pictures, the K-r image shows the glass bowl is more in focus than the plaque, but I was using the center focus point only and focusing on the plaque.

Now, is this "front focusing" or "back focusing"? To correct it, which direction do I need to go in the AF Fine Adjustment option (+ or -)?
09-18-2013, 12:41 PM   #7
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QuoteOriginally posted by wedge Quote
Now, is this "front focusing" or "back focusing"? To correct it, which direction do I need to go in the AF Fine Adjustment option (+ or -)?
Just do both and try it out

I personally find that the + and - sometimes makes little logic and the sharpest adjustment isnt where I thought it should be. So now I just adjust and compare the results before and after.
09-18-2013, 01:00 PM   #8
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Even though you focus manually, you're still relying on the AF system to get the focus confirmation point so if the AF works differently on the two cameras, that's what you get (different results). If you have the patience, try what other suggested (a tripod and full manual focus using live view... does the K-x have Live View by the way?

09-18-2013, 04:34 PM   #9
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QuoteOriginally posted by Luc More Quote
Even though you focus manually, you're still relying on the AF system to get the focus confirmation point so if the AF works differently on the two cameras, that's what you get (different results). If you have the patience, try what other suggested (a tripod and full manual focus using live view... does the K-x have Live View by the way?
Yes, the K-x has Live View. In last night's round of testing, I was doing exactly that: tripod, live view, manual focus. In those tests, I also focused on a flat subject (a book) and the image quality seemed comparable.

So, I guess I'll need to fiddle with the AF adjustment to get the focus indicator to indicate more correctly...
09-18-2013, 06:56 PM   #10
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QuoteOriginally posted by wedge Quote
Yes, the K-x has Live View. In last night's round of testing, I was doing exactly that: tripod, live view, manual focus. In those tests, I also focused on a flat subject (a book) and the image quality seemed comparable.

So, I guess I'll need to fiddle with the AF adjustment to get the focus indicator to indicate more correctly...
Yes. And also keep in mind that each lens my need different adjustment. I'm not sure if the K-r lets you save different adjustments for each lens. The later models do, so your probably does, too.
09-19-2013, 08:18 AM   #11
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QuoteOriginally posted by Takumar55 Quote
Yes. And also keep in mind that each lens my need different adjustment. I'm not sure if the K-r lets you save different adjustments for each lens. The later models do, so your probably does, too.
The K-r has only one adjustment, but it seems that the same adjustment is needed for all of the lenses I've tried so far (which is just about all the lenses I have: DA35/2.4, Tamron 28-75, Tamron 18-250 and, on the manual side, an A50/1.7).

A big point of confusion, though (at least for me) is that the adjustment is named "AF Fine Adjustment", while what it is actually controlling is the "in focus" indicator. In other words, with a name like that, one would assume that manual focus lenses would not be affected. So, IMO, it should be called something like "Focus Indicator Fine Adjustment" (or some appropriate abbreviation so it'll fit on the menu screen).

Now, away from semantics and back to my issue, I had to adjust to -10 to get consistent and accurate operation of AF and the focus indicator (in MF mode). Since this is the maximum adjustment, I'll have to live with it, I suppose. I'm also considering installing an aftermarket (split-prism style) focusing screen, so in doing that, perhaps I'll be able to shim it to minimize or eliminate the need for such an extreme adjustment setting.
09-26-2013, 06:41 AM   #12
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QuoteOriginally posted by wedge Quote
The K-r has only one adjustment, but it seems that the same adjustment is needed for all of the lenses I've tried so far (which is just about all the lenses I have: DA35/2.4, Tamron 28-75, Tamron 18-250 and, on the manual side, an A50/1.7).

A big point of confusion, though (at least for me) is that the adjustment is named "AF Fine Adjustment", while what it is actually controlling is the "in focus" indicator. In other words, with a name like that, one would assume that manual focus lenses would not be affected. So, IMO, it should be called something like "Focus Indicator Fine Adjustment" (or some appropriate abbreviation so it'll fit on the menu screen).

Now, away from semantics and back to my issue, I had to adjust to -10 to get consistent and accurate operation of AF and the focus indicator (in MF mode). Since this is the maximum adjustment, I'll have to live with it, I suppose. I'm also considering installing an aftermarket (split-prism style) focusing screen, so in doing that, perhaps I'll be able to shim it to minimize or eliminate the need for such an extreme adjustment setting.
The adjustment is valid both for the focus indicator as well as autofocus. They are one and the same thing, the only difference is that in autofocus a motor turns the focus instead of your hand and just stops turning when focus is reached. (In principle at least, in practice it is a bit more clever than that)

Whatever adjustment you make for the focus confirmation will also result in the same adjustment for autofocus.

I have a K-r and I also had to set it all the way to -10 and actually it would have been better if it could go to -11.
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