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05-27-2015, 07:17 PM   #1
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Strange focus issue

I have had my K-30 for a bit over 2 years now. I don't use Live View very often tho I have used it enough to be comfortable with it. I used live view Monday for several shots while visiting a civil war cemetery. I was trying out my new DA 35 2.4 lens.. I was using AF as well. When I got home I was disappointed with several shots as they appeared to be out of focus.. I use back button focus and knew that I had focused those shots. Deciding that maybe I needed to fine tune the focus on the lens I set to it. First I tried with Live view AF then MF with focus peaking. Then I tried view finder AF and MF with focus confirmation. Then I checked the images on my computer all the shots taken using LV are out of focus but all the ones taken using the VF are fine. My set up was K-30 mounted on tripod SR off, 1/25, iso 1600 f 2.8 on board flash on.center point focus and center point meter. I use back button AF so focus would not have changed since the the only buttons touched were LV and shutter, during the AF part of the check
What can cause the difference in focus?.
The first is LV AF tho both MF and AF are the same.
The second is VF AF . Both VF shots are the same.. In fact the AF was not changed when changing from LV and VF the only thing I did was turned off LV looked thru the VF and tripped the shutter button
My question is why is LV out of focus? I did just get the camera back from warranty service for the battery lug replacement.

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05-27-2015, 07:25 PM   #2
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huh that's weird as hell
05-27-2015, 07:38 PM   #3
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I have several front focus with my k5 (with my 2 af lenses) when I use LiveView, but I've used LiveView around 5 times in 2 years so isn't a problem for me..
05-27-2015, 07:38 PM   #4
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QuoteOriginally posted by Aaron28 Quote
huh that's weird as hell
Yep. It has me stumped at the moment. It is a good thing I prefer the View Finder.

---------- Post added 05-27-15 at 09:41 PM ----------

QuoteOriginally posted by PabloFP Quote
I have several front focus with my k5 (with my 2 af lenses) when I use LiveView, but I've used LiveView around 5 times in 2 years so isn't a problem for me..
I didn't know if or why it could front focus only in Live view.

05-27-2015, 08:03 PM   #5
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I noticed focus issue with CDAF quite a lot, more with sigma lenses, but some pentax lenses also have problem. Some of these lenses don't have focus problem when using PDAF. And I can confirm the inaccurate CDAF was not due to miss focus point: it happens when shooting a map on the wall, camera on tripod, remote and 3'' delay.
05-27-2015, 08:35 PM   #6
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QuoteOriginally posted by PabloFP Quote
I have several front focus with my k5 (with my 2 af lenses) when I use LiveView, but I've used LiveView around 5 times in 2 years so isn't a problem for me..
This by definition can't happen. FF/BF only applies to viewfinder AF.

However, your live view results can vary greatly depending on the size of the AF area. The spot AF in live view is generally worse than multi-point AF as far as the % of keepers goes. There's certainly a small learning curve involved, and lenses with longer throws are less likely to lock on consistently than lenses with short throws.

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05-28-2015, 08:04 PM   #7
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QuoteOriginally posted by Adam Quote
However, your live view results can vary greatly depending on the size of the AF area. The spot AF in live view is generally worse than multi-point AF as far as the % of keepers goes.
It is worth trying this week end when I try different lenses . My confusion is that both these were taken with the AF set from the live view. the focus was not changed when I switched to the view finder. It was the exact same focus as the LV had used it is just that all the pictures taken in LV look like the first and all my shots taken in View finder look like the second. This weekend I am going to work backward and see what happens when it is focused in View finder and taken in Live View. That is the only way I have not tried yet.
05-28-2015, 08:31 PM   #8
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QuoteOriginally posted by Adam Quote
This by definition can't happen. FF/BF only applies to viewfinder AF.
I have seen this with many lenses. more accurate with pentax lenses, but they are not error-free. Although I have never seen FF/BF as bad as posted photo, the lenses have focus inaccuracy always FF/BF constantly, make me believe the CDAF is not alway accurate.

One of my 50/1.4 lenses, when I tested it on K5, live view, shooting a map on the wall, I was so surprised to see F1.4 is sharper than F 1.8, and after F2.0 it get sharper again. I tested many times and got same result. eventually I turned the camera to MF, and found AF wan't very accurate.

05-28-2015, 08:36 PM   #9
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QuoteOriginally posted by grahame Quote
I have seen this with many lenses. more accurate with pentax lenses, but they are not error-free. Although I have never seen FF/BF as bad as posted photo, the lenses have focus inaccuracy always FF/BF constantly, make me believe the CDAF is not alway accurate.
It won't necessarily be 100% accurate, but it should never require a fixed adjustment to compensate for a margin of error. Live view AF essentially works by scrolling through all possible focus settings and picking the setting with the highest contrast. Due to poor micro-adjustments or too few measurements, it's possible for the camera to select the wrong point of focus. This is all fairly strongly tied to the AF area you select, though. Like with PDAF, CDAF requires a nice contrasty target. If you choose a target that isn't equidistant from the camera in its entirety, you also cant predic't what part of it the camera will focus on.

Overall, the K-5's live view implementation is usable but not the best. Significant algorithmic improvements were made in the K-30/K-50 and again in the K-3/K-S1/K-S2 that dramatically increased the performance. I'm fairly close to using live view about as often as I use the viewfinder now. On the K-5 I rarely used live view off a tripod.

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05-28-2015, 08:45 PM   #10
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QuoteOriginally posted by Adam Quote
Overall, the K-5's live view implementation is usable but not the best.
That is very true. But I thought the issue might be slow, but still be accurate.
And it FF/BF always happened to these lenses, and always FF or BF consistently on tripod. I saw similar issue on K-01, although it is better in general. BUT, it is not alway the same lens has FF/BF issue on K5 and on K-01.
I understand the mechanism of CDAF, so I am very confused.
06-29-2015, 07:22 PM   #11
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My DA35mm2.4 AL has a slight back focus issue but just barely. I tried a fresh battery and no flash it is a touch better but still not right. I didn't have this issue till the camera went in for a battery retainer repair. I guess it will just be used with the VF . That is how I used it most of the time anyway. Now it is the only way.
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