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03-15-2009, 09:36 PM   #1
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slight blurriness at 100% magnification

My pics look a little blurry when I blow up the focused object to 100% magnification. Is it due to lens mis-focusing or monitor calibration issue? Or is it normal and I just need to take a few steps back from the monitor when using 100% magnification? I'm using PPL to process the RAW files.

03-15-2009, 10:04 PM   #2
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QuoteOriginally posted by wasim_altaf Quote
My pics look a little blurry when I blow up the focused object to 100% magnification. Is it due to lens mis-focusing or monitor calibration issue? Or is it normal and I just need to take a few steps back from the monitor when using 100% magnification?
Maybe. Due to the Bayer CFA on most sensors, there will always be a little bit of softness in the image, which software usually tries to compensate for with sharpening. If you resize it to 50%, does it look perfectly sharp on its own?

Can you post a sample, either with full EXIF or the settings you used in PPL?
03-15-2009, 10:37 PM   #3
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A lot will depend on what lens and FL you are using as well.
03-15-2009, 10:49 PM   #4
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Could be focus, could be camera shake, could be the lens isn't quite up to par at whatever aperture you are using.
Are you using auto focus or manual?
Your AF could be slightly misadjusted.

03-16-2009, 09:11 AM   #5
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QuoteOriginally posted by Quension Quote
Maybe. Due to the Bayer CFA on most sensors, there will always be a little bit of softness in the image, which software usually tries to compensate for with sharpening. If you resize it to 50%, does it look perfectly sharp on its own?

Can you post a sample, either with full EXIF or the settings you used in PPL?
How do I go about loading the EXIF data? Does it accompany the JPEG? Here are some samples, taken with different settings, cropped to 100% on the focused object. These were converted to JPEG in PPL and cropped in PPB.

Last edited by wasim_altaf; 04-04-2009 at 07:00 PM.
03-16-2009, 09:17 AM   #6
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QuoteOriginally posted by Wheatfield Quote
Could be focus, could be camera shake, could be the lens isn't quite up to par at whatever aperture you are using.
Are you using auto focus or manual?
Your AF could be slightly misadjusted.
Lens is DA-40mm, shutter speed was generally high and shouldn't have required SR. I was using auto-focus, using both AF-S and AF-C mode. Actually, I was trying out focusing with the AF-button only, with focus-by-half-pressed-shutter disabled. Don't know if that had anything to do with it, however.
03-16-2009, 09:20 AM   #7
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QuoteOriginally posted by Damn Brit Quote
A lot will depend on what lens and FL you are using as well.
DA-40mm. I don't know what FL stands for, unfortunately. (Focal length?) I did vary the aperture, though.
03-16-2009, 09:23 AM   #8
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That just looks defocused. Look at the second shot -- some of the the water in the back is sharp, the bird isn't. I think the answer is as simple as this: you haven't really nailed the focus on any of these shots.

Either way, even with a super sharp lens, no motion blur, and perfect focus, a photo from a Bayer sensor camera will always be slightly blurry at 100%. It's just the way the technology works. For instance, I've found that my 6 MP camera has about 4.5 MP of real resolution.

03-16-2009, 10:38 AM   #9
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QuoteOriginally posted by Erik Quote
That just looks defocused. Look at the second shot -- some of the the water in the back is sharp, the bird isn't. I think the answer is as simple as this: you haven't really nailed the focus on any of these shots.
That's what I was afraid of. Shots were taken only after auto-focus confirmation. I noticed the unfocused bird on the camera LCD and took multiple shots just to be sure after the first one. I should try another set with focus-by-halfpressing-shutter method.
03-16-2009, 10:39 AM   #10
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QuoteOriginally posted by wasim_altaf Quote
Lens is DA-40mm, shutter speed was generally high and shouldn't have required SR. I was using auto-focus, using both AF-S and AF-C mode. Actually, I was trying out focusing with the AF-button only, with focus-by-half-pressed-shutter disabled. Don't know if that had anything to do with it, however.
Focusing via the AF button with focus-by-half-pressed-shutter disabled should work fine, so that shouldn't be the problem.

Based on your samples I'd say the camera is back focusing as the water looks more in focus than the birds. It's also possible in AF-C that your composition momentarily shifted and the focus point was on the water or transitioning from the water to the bird or vice versa when you let off the AF button to stop focusing (though the water doesn't look in focus either).

I'd try to test your focus adjustment by doing something like this. Set the camera on AF-S and select the center AF point, so you're sure which point is being used. Set maximum aperture for the lens (wide open - ie, f/2.8 on the DA 40mm). Set up three objects with flat surfaces and fine detail (books, dvd boxes, filter cases, etc...) in a staggered line like this...


To detect a large error, you may need to increase the distance between the objects on the near/far axis (maybe one or two feet apart rather than inches as shown).

Then shoot 'em straight on, focusing on the middle object from about ten feet away.
If your lens is back focusing the object further away will look better than the center or nearer one, like this...


Properly focused, the center object will appear in best focus like this example (at a different focal length, but it shows what I mean )...


To adjust focus on the K20D, you enter the custom menu, and near the bottom of the list is #35. AF Adjustment - activate that, and enter the "On" submenu, and here you can adjust your focus... "Apply All" is a global adjustment which will change how your camera focuses for every lens, while "Apply One" will be an adjustment applied to just that model of lens (ie. the DA 40 only). I found that most of my lenses needed -6 or -7 adjustment, so I set Apply All to -7, and I can go up and down from there as needed for an individual lens, but a new lens should be close without adjustment. When setting the adjustment,
  • Higher adjustment numbers (+) move the focus closer to the camera
  • Lower adjustment numbers (-) move the focus farther away.
03-16-2009, 11:47 AM   #11
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I wouldn't be in a rush to assume any sort of malfunction regarding the focus, which is indeed off. Cameras are not mind-readers, whether in AF-C or AF-S and whether activating focus by shutter button or AF button. The camera is going to focus on what it feels like focusing on, not necessarily what you want it to. before you even start thinking about whether the camera is defective in the sense of *missing* focus as oppsoed to simply not reading your mnd, you need to work on figuring out how to get the camera to at least try to focus on the thing you want it to focus on. That might mean selecting the focus point yourself, or at least verifying in the viewfinder that the camera has chosen the most appropriate one. But it also means realizing that just because the red dot lights up right on top of your subject, that doens't mean it actually focused on the bird - the AF sensor is larger than the red dot, so it may actually have focused on soemthing above or below or off to the side. When trying to nail focus on a small object with anything other than a featureless sky behind it, you often will want to use manual focus - that's just how it is.
03-16-2009, 04:58 PM   #12
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we've talked about this before...

QuoteOriginally posted by Marc Sabatella Quote
I wouldn't be in a rush to assume any sort of malfunction regarding the focus, which is indeed off. Cameras are not mind-readers, whether in AF-C or AF-S and whether activating focus by shutter button or AF button. The camera is going to focus on what it feels like focusing on, not necessarily what you want it to. before you even start thinking about whether the camera is defective in the sense of *missing* focus as oppsoed to simply not reading your mnd, you need to work on figuring out how to get the camera to at least try to focus on the thing you want it to focus on. That might mean selecting the focus point yourself, or at least verifying in the viewfinder that the camera has chosen the most appropriate one. But it also means realizing that just because the red dot lights up right on top of your subject, that doens't mean it actually focused on the bird - the AF sensor is larger than the red dot, so it may actually have focused on soemthing above or below or off to the side. When trying to nail focus on a small object with anything other than a featureless sky behind it, you often will want to use manual focus - that's just how it is.
Sometimes it just isn't practical to use MF and only AF will do, so, I would like to pin down exactly what the center focus on my K100 is focusing on, and how big that point is.

Personally, I'd like to know that if I have the Pentax focus screen ( o ) centered on an object and the object was filling the ( o ) in the viewfinder, that the focus point is in there, somewhere, but Pentax doesn't seem to disclose that data,
Brian
03-16-2009, 08:55 PM   #13
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QuoteOriginally posted by Marc Sabatella Quote
I wouldn't be in a rush to assume any sort of malfunction regarding the focus, which is indeed off. Cameras are not mind-readers, whether in AF-C or AF-S and whether activating focus by shutter button or AF button. The camera is going to focus on what it feels like focusing on, not necessarily what you want it to. before you even start thinking about whether the camera is defective in the sense of *missing* focus as oppsoed to simply not reading your mnd, you need to work on figuring out how to get the camera to at least try to focus on the thing you want it to focus on. That might mean selecting the focus point yourself, or at least verifying in the viewfinder that the camera has chosen the most appropriate one. But it also means realizing that just because the red dot lights up right on top of your subject, that doens't mean it actually focused on the bird - the AF sensor is larger than the red dot, so it may actually have focused on soemthing above or below or off to the side. When trying to nail focus on a small object with anything other than a featureless sky behind it, you often will want to use manual focus - that's just how it is.
Good point. These were tiny objects against vast, empty background. The cropped area was Those pigeons almost blend in with the water. The seagull, though small, was practically out to infinity. It looks more in focus with increasing DOF. But the whole set has holes in it, as you've pointed out. A little troubling, nevertheless.

I'll give heliphoto's test a try, probably for both nearfield and farfield.
03-16-2009, 08:59 PM   #14
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QuoteOriginally posted by heliphoto Quote
Focusing via the AF button with focus-by-half-pressed-shutter disabled should work fine, so that shouldn't be the problem.

Based on your samples I'd say the camera is back focusing as the water looks more in focus than the birds. It's also possible in AF-C that your composition momentarily shifted and the focus point was on the water or transitioning from the water to the bird or vice versa when you let off the AF button to stop focusing (though the water doesn't look in focus either).

To adjust focus on the K20D, you enter the custom menu, and near the bottom of the list is #35. AF Adjustment - activate that, and enter the "On" submenu, and here you can adjust your focus... "Apply All" is a global adjustment which will change how your camera focuses for every lens, while "Apply One" will be an adjustment applied to just that model of lens (ie. the DA 40 only). I found that most of my lenses needed -6 or -7 adjustment, so I set Apply All to -7, and I can go up and down from there as needed for an individual lens, but a new lens should be close without adjustment. When setting the adjustment,
  • Higher adjustment numbers (+) move the focus closer to the camera
  • Lower adjustment numbers (-) move the focus farther away.
Thanks, I'll try this out. Is it a close focus test or distant (infinity) focus test?

Wasim
03-16-2009, 09:48 PM   #15
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QuoteOriginally posted by wasim_altaf Quote
Thanks, I'll try this out. Is it a close focus test or distant (infinity) focus test?

Wasim
I tend to find it useful at about 10 to 15 feet (or less with a shorter focal length). Beyond that, the difference is too minor to really detect, but you could use cars in a parking lot or something similar to test on a large scale. For infinity, I'd shoot a building that's far enough away for the lens to need to be infinity and look for sharpness.

BTW, once again Mark S. has read the details of a post completely before answering, while I miss key points ... Now, rereading that those are 100% crops in the first post (which I missed earlier), I completely agree that it would be extremely easy for the camera to lock onto something other than your intended (very small) target.

I still recommend you spend some time testing your focus since you have a K20D. The ability to adjust AF is the #1 thing about the K20D which makes me glad I upgraded to it. It can make a fantastic difference. Also, in the process of testing your focus, pay attention to what point the camera focuses on... I found my K200D center point would actually focused on a point at the bottom of the ( ) or just below, rather than in the center of these marks as you'd expect. Learning exactly where the camera is sensing, can let you be more accurate with focus point placement to get the focus you want.
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