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06-02-2013, 11:19 AM   #1
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Blurry result sometimes

Hi!
Sometimes i get a result, where just no sharp objects, even if one of them in the DOF.
Just see for yourself: https://mega.co.nz/#!cpUkXb5Y!WEeDD2c8gQ4JUCuTN4J7ohRnLvMySo2XAy0q-hqNDwI , a raw file with all data keeped in it.
As you can see there is no action, but still image not sharp at all, even at 1/2500. Its not the lens problem, usualy pictures are much sharper, but sometimes images becomes like there is no DOF at all.
IS is off on both the body and the lens.
What do you think about it?

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06-02-2013, 11:32 AM   #2
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QuoteOriginally posted by Dachiko Quote
sometimes images becomes like there is no DOF at all.
At 200mm and f2.8 there isn't much DOF. You're also wide open, so the lens isn't as sharp as it could be.
06-02-2013, 11:38 AM   #3
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Morning,

I did a bit of figuring. I am taking an educated guess that the scene is about 20 feet wide, at 200mm so you are about 150 feet away, which would put the DoF at about 20 feet deep (@f2.8) (via the photographer's calculator). The lady in the background (white dress is out of focus worse than the girls in front). It looks like you were in manual mode with an M42 lens. I am guessing that focus was just missed. So, given that, we really do not know what aperture you were really at (via the aperture ring on the lens) since the lens is manual, and the body just defaulted to f2.8 for reporting purposes (it had to put something in there).

But assuming f2.8 - you could have pushed the ISO up from 320 to 800, rolled the aperture down to f5.6 or f8 and kept the shutter speed the same. That would have tripped the DOF from about 20 to almost 60 feet. At f8, you would have been in the sweet spot of the lens in terms of resolution too.

Looking at the stars on their leggings, the starts to the left are out of focus worse than the ones on the right. The more right you go the better the focus. So, I am guessing that you focused in back of the line of girls. Also, since they are standing at an angle to you the DOF will need to be large to get everyone in. I am guessing that the focus point is center frame, so that would be the girl on the extreme right. It would have been better to focus on the middle girl and then to recompose to the framing that you have.


Last edited by interested_observer; 06-02-2013 at 12:08 PM.
06-02-2013, 11:52 AM   #4
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Those pom poms look pretty sharp.

06-02-2013, 11:58 AM   #5
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QuoteOriginally posted by elliott Quote
At 200mm and f2.8 there isn't much DOF. You're also wide open, so the lens isn't as sharp as it could be.
Wow... Never throught its so severe...

QuoteOriginally posted by JinDesu Quote
Those pom poms look pretty sharp.
Only in small print
06-02-2013, 12:00 PM   #6
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For some reason I couldn't d/l your RAW file, but looking at your attachment, it must be very nearly in focus on the furthest young lady in the row. All I can think of is that phase detect AF (all brands) has a lot of strong points but it can be fooled into locking on a phantom alignment of the the 2 split images depending on repeated image detail, so nothing ends up in real focus. The other thing that can happen is when you get an AF lock, you then pause for the right moment and you move fore/aft in that period, so the subject is no longer in focus when you fully press the shutter.
06-02-2013, 12:08 PM   #7
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It is 200mm 1/2500s F2.8 ISO320.

This part is sharp. and seems the only part that is in focus.


other part of photo is all blury. at this shutter speed. It should not cause any motion blur.

F2.8 is shallow dof combine with 200mm. but still the person should be at the same focal plane as the leg. It should not be blury.

maybe you got a bad copy of the lens.
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PENTAX K-30  Photo 

Last edited by liukaitc; 06-02-2013 at 12:13 PM.
06-02-2013, 12:49 PM   #8
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Only the last girl is somewhat in focus and judging by the ground the field of focus looks flat and sharp, so it shouldn't be an issue with a tilted element.

06-02-2013, 04:23 PM   #9
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The best way to test is with a focus target. I use this to set the focus adjustment for each lens, but then have all modern lens that allow this and the camera to remember the lens. It does allow very fine testing of the the focus point and to see the depth of field.

This is the one I use.

SpyderLENSCAL - Datacolor Imaging Solutions - Datacolor Imaging Solutions

This is one from B&H, but I'm sure there are a lot of others available else where.

Focus target| B&H Photo Video
06-02-2013, 05:06 PM   #10
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Looks like the lower part of the image is sharper compares to the upper part
06-03-2013, 08:15 AM   #11
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Here is what i get with similar setup (200mm / 2.8) and same gear. 100% crop, exif must be there. Usually images looks this sharp, but once in while i get the result like one posted in the first message.
It was a bit postprocessed, but just a bit, no sharpening has been applied.
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PENTAX K-30  Photo 

Last edited by Dachiko; 06-03-2013 at 08:20 AM.
06-03-2013, 10:43 AM   #12
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How did you auto-focus? Your K-30 has several options. I use select focus, where my 4-way controller allows me to select which of the points will be used for focus.

The line of young women is at an angle to the lens. If you used auto focus and then recomposed with a subject like this, it is very possible that none would be in focus.
06-03-2013, 11:14 AM   #13
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QuoteOriginally posted by Dachiko Quote
Here is what i get with similar setup (200mm / 2.8) and same gear. 100% crop, exif must be there. Usually images looks this sharp, but once in while i get the result like one posted in the first message.
It was a bit postprocessed, but just a bit, no sharpening has been applied.
I wonder if sometimes we expect too much of 100% viewing with regard to motion blur. The old 1/FL rule was from film days with no 100% peeping; nowadays we have a couple of stops image stabilisation to help, but let's face it 200mm FL cropped to 1/7 of original size is equivalent to 1400mm FL on APS-C, so the handheld rule makes it 1.5 times worse, so about 1/2000s for pixel sharp results on a 7:1 crop like your OK (slightly soft) example which was shot at 1/1600s. There isn't much margin for error basically, so some are bound to be too soft at 100%.
06-03-2013, 12:23 PM   #14
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QuoteOriginally posted by JimJohnson Quote
How did you auto-focus? Your K-30 has several options. I use select focus, where my 4-way controller allows me to select which of the points will be used for focus.

The line of young women is at an angle to the lens. If you used auto focus and then recomposed with a subject like this, it is very possible that none would be in focus.
Usually i use central focus point and then recompose. Even if original object of focus slightly out of DOF, still focus must be somewhere

QuoteOriginally posted by SteveB Quote
I wonder if sometimes we expect too much of 100% viewing with regard to motion blur
Well... Im not that experienced, but usually motion blur easily detectable becouse of "strokes". Can it be that in 1/2500 of second i manage to shake camera in all directions to make such a perfect blur?

Looks like there is no evidence of such cases in this comunity, so its something unusual, and must be proved with another examples, to judge the origin.
Thanks to all, who parcticipate and share his points! I will try to use your thoughts to investigate this case closer.
06-03-2013, 12:37 PM   #15
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QuoteOriginally posted by Dachiko Quote
Usually i use central focus point and then recompose. Even if original object of focus slightly out of DOF, still focus must be somewhere
Absolutely, but it is hard to visualize this being the case if the focus point holds nothing but air. See this post:
https://www.pentaxforums.com/forums/general-technical-troubleshooting/223317-...ml#post2369818

I use center focus and recompose too. But you have to understand the limitations, and this is why my camera is set to selective focus where I compose, THEN select the appropriate focus point.
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