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03-29-2009, 05:49 AM   #1
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Focus Question Help Needed

I took several group wedding shots and had many unfocused pictures. Attached is an example of one. This particular photo was taken with AF Center but the picture looks in focus to the left side. The middle and right are way out of focus. The camera is a new k20d and the lens is a Sigma 18-50 2.8 EX DL. Shake reduction on. The speed was 1/60 and F4.0 ISO 400. I am thinking the speed was to slow and should have used higher F. But if the focus was set to center why is it out in center and right?



Last edited by izzyinstl; 03-29-2009 at 10:11 AM. Reason: trying to get exif to photo
03-29-2009, 07:27 AM   #2
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I'm thinking a combination of either back focus or decentering of the lens and/ or short depth of field and possibly field curvature of the lens.
03-29-2009, 07:27 AM   #3
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Hi Izzy...

Your exif data isn't available, so I'm not able to verify the settings.

At f3.5 the faces should mostly all be in focus, however looking at the plane (using carpet line for reference) I can gather that the left side is physically closer to you then the centre, or the right.

I'm guessing that you may have focused on the centre, but in fact have your focus set to the left (you can change this in your menu system so that it will always focus on centre...then you can recompose).

F4.0 is usually a bit better for this, and f5.6 even better. Once you get beyond that you will need flash assistance as you will run out of high ISO.

Anywho...I hope this info helps. Without a lot to go on I needed to use a lot of speculation.

c[_]
03-29-2009, 10:20 AM   #4
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f/4 would not yield enough DOF to expect all faces to be in perfect focus, unless perhaps you very carefully set focus half way between the front and back, examining the picture closely in the viewfinder to account for the curvature of the focus plane, and even then, it would probably be iffy. So realisticallty, that's not a picture that you could have expected to be in perfect focus across the frame.

On the other hand, as for why the left side might be more in focus than the right (I say might, because at the size posted, its hard to tell, but you of course can see the full size version), that could be a lens defect. You might try a more controlled test to see if that behavior is consistent.

As for the focus not being accurate at center where you tried to focus note that most DSLR's will front focus a little under tungsten lighting, and I'm guessing the camera was aiming for the flowers, not the girl's face. So the actual focus point is probably rather in front of the faces of the people at center.

03-29-2009, 10:21 AM   #5
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not sure how to get the exif on the picture so i copied from flickr

Camera: Pentax K20D
Exposure: 0.017 sec (1/60)
Aperture: f/4.0
Focal Length: 20 mm
Focal Length: 20.0 mm
ISO Speed: 400
Exposure Bias: 0 EV
Flash: On

File Size: 5.1 MB
File Type: JPEG
MIME Type: image/jpeg
Image Width: 3872
Image Height: 2592
Encoding Process: Baseline DCT, Huffman coding
Bits Per Sample: 8
Color Components: 3
Orientation: Horizontal (normal)
X-Resolution: 72 dpi
Y-Resolution: 72 dpi
Software: K20D Ver 1.00
Date and Time (Modified): 2009:03:28 14:03:13
YCbCr Positioning: Co-sited
Exposure Program: Manual
Date and Time (Original): 2009:03:28 14:03:13
Date and Time (Digitized): 2009:03:28 14:03:13
Metering Mode: Multi-segment
Color Space: sRGB
Sensing Method: One-chip color area
Custom Rendered: Normal
Exposure Mode: Manual
White Balance: Auto
Focal Length In35mm Format: 30 mm
Scene Capture Type: Standard
Contrast: Normal
Saturation: Normal
Sharpness: Normal
Subject Distance Range: Close
Pentax Version: 4.1.2.0
Pentax Model Type: 0
Preview Image Size: 640x480
Preview Image Length: 23114
Preview Image Start: 5544
Pentax Model ID: K20D
Date: 2009:03:28
Time: 14:03:13
Quality: Best
Flash Mode: On; External, P-TTL Auto
Focus Mode: AF-S
AFPoint Selected: Fixed Center
Exposure Time: 1/60
FNumber: 4.0
ISO: 400
Exposure Compensation: 0
Metering Mode: Multi-segment
Auto Bracketing: 0 EV, No Extended Bracket
White Balance: Auto
White Balance Mode: Auto (WhiteFluorescent)
Saturation: Normal
Contrast: Normal
Sharpness: Normal
World Time Location: Hometown
Hometown City: Toronto
Destination City: Toronto
Hometown DST: No
Destination DST: No
DSPFirmware Version: 1.00.00.04
CPUFirmware Version: 1.00.00.04
Effective LV: 8.0
Image Processing: Unprocessed
Picture Mode: Manual; 1/2 EV steps
Drive Mode: Single-frame; No Timer; Shutter Button; Single Exposure
Color Space: sRGB
Preview Image Borders: 26 26 0 0
Lens Type: Sigma Lens (3 255)
Sensitivity Adjust: 0
Image Processing Count: 0
Camera Temperature: 25 C
AELock: Off
Noise Reduction: Off
Flash Exposure Comp: 0
Image Tone: Vibrant
SRResult: Stabilized
Shake Reduction: On (7)
SRHalf Press Time: 0.97 s
SRFocal Length: 20 mm
Shutter Count: 3838
Dynamic Range Expansion: Off
High ISONoise Reduction: Off
AFAdjustment: 0
Black Point: 0 0 0 0
White Point: 12224 8192 8192 11104
Picture Mode2: Manual
Program Line: Normal
EVSteps: 1/2 EV steps
E- Dial In Program: Tv or Av
Aperture Ring Use: Prohibited
Flash Options: Normal
Metering Mode2: Multi-segment
AFPoint Mode: Fixed Center
Focus Mode2: AF-S
AFPoint Selected2: Center
ISOFloor: 400
Drive Mode2: Single-frame
Exposure Bracket Step Size: 0.5
Bracket Shot Number: n/a
White Balance Set: Daylight
Multiple Exposure Set: Off
AEExposure Time: 1/60
AEAperture: 4.0
AE_ ISO: 400
AEXv: 0
AEBXv: 0
AEMin Exposure Time: 1/171
AEProgram Mode: M, P or TAv
AEMax Aperture: 2.8
AEMax Aperture2: 2.8
AEMin Aperture: 23
AEMetering Mode: Multi-segment
Flash Exposure Comp Set: 0
Auto Aperture: On
Min Aperture: 22
Lens FStops: 8.5
Nominal Max Aperture: 2.8
Nominal Min Aperture: 23
Max Aperture: 2.8
Flash Status: External, Fired
Internal Flash Mode: Off, Normal
External Flash Mode: On, P-TTL Auto
Internal Flash Strength: 0
TTL_ DA_ AUp: 0
TTL_ DA_ ADown: 0
TTL_ DA_ BUp: 0
TTL_ DA_ BDown: 0
External Flash Guide Number: 22
External Flash Exposure Comp: 0.0
External Flash Bounce: Direct
AEMetering Segments: 6.5 5.6 4.1 4.8 4.0 4.0 5.6 3.1 4.6 3.6 6.0 5.8 4.1 5.1 5.4 6.0
Flash Metering Segments: 8.0 7.2 7.0 7.2 6.8 6.9 8.8 7.2 6.8 6.4 7.0 7.0 7.2 7.8 2.9 n/a
Slave Flash Metering Segments: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
WB_ RGGBLevels Daylight: 13310 8192 8192 10499
WB_ RGGBLevels Shade: 15178 8192 8192 7989
WB_ RGGBLevels Cloudy: 14111 8192 8192 9282
WB_ RGGBLevels Tungsten: 8540 8192 8192 19478
WB_ RGGBLevels Fluorescent D: 17613 8192 8192 9891
WB_ RGGBLevels Fluorescent N: 14945 8192 8192 11260
WB_ RGGBLevels Fluorescent W: 13944 8192 8192 13999
WB_ RGGBLevels Flash: 14111 8192 8192 9891
Manufacture Date: 2008:02:27
Production Code: 2.2
Internal Serial Number: 68463
Power Source: Body Battery
Battery States: 4 4
Battery ADBody No Load: 185
Battery ADBody Load: 178
Battery ADGrip No Load: 191
Battery ADGrip Load: 178
AFPredictor: -8
AFDefocus: 5
AFIntegration Time: 58 ms
AFPoints In Focus: Center (horizontal)
WBShift AB: 0
WBShift MG: 0
Compression: JPEG (old-style)
04-23-2009, 08:30 AM   #6
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I would be hesitant taking a large group portrait with anything under F8. F4 just doesn't have the correct dof for such a large amount of people. F4 would be fine if you were shooting one or two subjects standing closely together. I would also check the weight of the Focusing area..instructions on page 106 of the K20D manual if you wish to keep using the AF. I myself, prefer the manual focus, with SEL as my focus option...I also usualy use AV mode so that I can control dof. If you have proper lighting, the higher f# shouldn't be an issue. Also, if you focused on the people on the left, with such a short dof the others are bound to fall out of focus. Just my opinion, hope it helps.
04-23-2009, 08:12 PM   #7
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Location: Salem, MA
Posts: 145
Do you have the same problem at longer focal lenghts, too? Or is just at the wider end(s)?

As for this pic, I'm assumng that you stood somewhat parallel to the group. If so, I don't think it is related to DOF, curvature of the group, shutter speed, or where and what the camera might have focused on. The entire right side is blurry and OOF compared to everything on the left, in every plane. Take a look at those decorative candles on either side behind the group, almost out in infinity. It can be assumed that there in the same focus plane, set in place by the wedding hall themselves. Both sets of candles should look just about the same, yet the left set is so much sharper than the one on the right, which is just as blurry/OOF as those people on the right side. You didn't focus on those candles, of course, but that's irrelevant -- they should look similar.

Run another test, may be in daylight (if you want to eliminate CFL/tungsten as possible cause, though I don't see how it applies here). Vary the focal length from wider to longer in steps and check if and where both sides look similarly focused.
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