What am I doing wrong? Aperture Priority Mode on Canon DR XT

odinsride

macrumors 65816
Original poster
Apr 11, 2007
1,145
0
I am new to SLR photography, and was trying to figure out the Av setting on my camera. I bought the field manual and was reading that you can change the aperture to make the background blurred or in focus.

Well I tried this Av mode just now with a big styrofoam cup on my desk and my speaker about 3 feet behind it.

First of all, I could never get the speaker to be in focus at all, no matter what Aperture I set.

Secondly, every shot I took turned out blurry, because the shutter speed was slow in this Av mode and I couldn't hold the camera still.

I tried using the flash, increasing the ISO, everything. But I keep ending up with shots where everything is blurry, even the main subject.

What gives? In auto mode I always get clear pics. Are the manual modes really the way to go?
 

robbieduncan

Moderator emeritus
Jul 24, 2002
24,638
61
Harrogate
Are you sure you're setting the aperture correctly? To get selective focus like you are describing you want the lens open so small aperture numbers. This should result in faster shutter, not slower, making hand holding easier.
 

odinsride

macrumors 65816
Original poster
Apr 11, 2007
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Are you sure you're setting the aperture correctly? To get selective focus like you are describing you want the lens open so small aperture numbers. This should result in faster shutter, not slower, making hand holding easier.
Well I was really just experimenting right now. I wanted to see if I could get everything in the scene in focus if I wanted to. I'm setting the aperture just as the manual describes. Even at the lowest aperture the shutter speed was too slow for me to hold the camera still.
 

Kamera RAWr

macrumors 65816
May 15, 2007
1,022
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Sitting on a rig somewhere
How close are you trying to focus to the cup? Perhaps it can't focus because you're too close? Perhaps the reason the speakers in the background are never in focus is because when you have a lower f/number it's probably blurring the background and when you have a higher f/number, depending on lighting, maybe the shutter speed is too slow to hand hold a sharp shot. Just my .02 :eek:
 

robbieduncan

Moderator emeritus
Jul 24, 2002
24,638
61
Harrogate
Well I was really just experimenting right now. I wanted to see if I could get everything in the scene in focus if I wanted to. I'm setting the aperture just as the manual describes. Even at the lowest aperture the shutter speed was too slow for me to hold the camera still.
If you want everything in the scene in focus you need a small aperture (so a big aperture number). This lets less light into the camera making the shutter speed slower. If there is not enough light available you won't be able to hand-hold. That's just the way it is.
 

odinsride

macrumors 65816
Original poster
Apr 11, 2007
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How close are you trying to focus to the cup? Perhaps it can't focus because you're too close? Perhaps the reason the speakers in the background are never in focus is because when you have a lower f/number it's probably blurring the background and when you have a higher f/number, depending on lighting, maybe the shutter speed is too slow to hand hold a sharp shot. Just my .02 :eek:
I was sitting about 3-4 feet from the cup, zoomed in to just the top half of it. It appeared to be focused in the viewfinder, hell the AF thing even beeped.
 

robbieduncan

Moderator emeritus
Jul 24, 2002
24,638
61
Harrogate
OK, what focal length are you using?

I've set up a little scene with a cup close to the camera and a speaker behind it (the cup is about a foot from the camera, the speaker around 4 feet further on). Using a 35mm lens the speaker is pretty much in focus (and the cup too) at f20. It's noticeably out of focus at f8. At ISO 200 in the amount of light in my room right now f20 is a 13 second exposure. At ISO 1600 that drops to 2 seconds. Neither is hand holdable (I'm cheating and using a tripod).

Without moving the tripod and switching to a zoom lens at 17mm I get an exposure of under 1 second and the entire scene is in focus at f20. At 85mm the exposure goes to 1.6 seconds and the speaker is out of focus at f20...
 

odinsride

macrumors 65816
Original poster
Apr 11, 2007
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0
I suppose the best I could say is to post a pic or two with EXIF data... other than that, I'm not completely sure what the problem is :eek:
Well I already deleted the pics since nothing turned out, and now I'm charging the battery, but I'll try messing with the settings again tomorrow and post the results. Thanks
 

odinsride

macrumors 65816
Original poster
Apr 11, 2007
1,145
0
OK, what focal length are you using?

I've set up a little scene with a cup close to the camera and a speaker behind it (the cup is about a foot from the camera, the speaker around 4 feet further on). Using a 35mm lens the speaker is pretty much in focus (and the cup too) at f20. It's noticeably out of focus at f8. At ISO 200 in the amount of light in my room right now f20 is a 13 second exposure. At ISO 1600 that drops to 2 seconds. Neither is hand holdable (I'm cheating and using a tripod).

Without moving the tripod and switching to a zoom lens at 17mm I get an exposure of under 1 second and the entire scene is in focus at f20. At 85mm the exposure goes to 1.6 seconds and the speaker is out of focus at f20...

I tried shooting at 55mm. I should have written down the settings I tried. I'll do that once my battery is charged and I try again. Thanks for the help
 

odinsride

macrumors 65816
Original poster
Apr 11, 2007
1,145
0
Ok here's some shots I took.

First image (low aperture number)

http://www.flickr.com/photos/sitheris/933955366/

Camera: Canon EOS Digital Rebel XT
Exposure: 0.077 sec (1/13)
Aperture: f/4.5
Focal Length: 34 mm
ISO Speed: 1600
Exposure Bias: 0/2 EV
Flash: Flash fired

Orientation: Horizontal (normal)
X-Resolution: 72 dpi
Y-Resolution: 72 dpi
Date and Time: 2007:07:28 08:46:21
YCbCr Positioning: Co-Sited
Exposure Program: Aperture priority
Date and Time (Original): 2007:07:28 08:46:21
Date and Time (Digitized): 2007:07:28 08:46:21
Shutter Speed: 242512/65536
Metering Mode: Pattern
Color Space: sRGB
Focal Plane X-Resolution: 3954.233 dpi
Focal Plane Y-Resolution: 3958.763 dpi
Compression: JPEG
Image Type: Canon EOS DIGITAL REBEL XT
Owner Name: unknown < P d
Camera Serial Number: 2520718507
Custom Functions: 20, 0, 256, 512, 768, 1024, 1280, 1536, 1792, 2048
Model ID: 2147484041
Tag::Canon::0x0013: 0, 159, 7, 112
Tag::Canon::0x00AA: 10, 463, 1024, 1024, 644
Image Width: 3456 pixels
Image Height: 2304 pixels
Macro Mode: Normal
Image Quality: Fine
Canon Flash Mode: On
Continuous Drive: Single
Focus Mode: One-shot AF
Canon Image Size: Large
Easy Mode: Manual
Contrast: High
Saturation: High
Sharpness: High
Metering Mode: Evaluative
Focus Range: Not Known
Canon Exposure Mode: Aperture-Priority AE
Lens: 18 - 55mm
Max Aperture: 128
Min Aperture: 304
Flash Activity: Flash did not fire
Photo Effect: Off
Color Tone: 0
Focal Type: Zoom
Scaled Focal Length: 34
Focal Plane Size: 907 x 605
Flash Guide Number: 2097168
ISO: 1600
Measured LV: 65508
Target Aperture: 22.62741699797
Target Exposure Time: 0.077616113254593
Flash Guide Number: 2047.96875
F Number: 4.5
Camera Type: EOS Low-end
Auto Rotate: None
Image Width: 3456
Image Height: 2304
Image Width (As shot): 3456
Image Height (As shot): 2304
Shutter Count: 7172
Color Temperature: 5200°K
Sensor Width: 3516 (52-3507 used)
Sensor Height: 2328 (19-2322 used)



Second Image (High aperture number)

http://www.flickr.com/photos/sitheris/933955242/

Camera: Canon EOS Digital Rebel XT
Exposure: 2.5 sec (5/2)
Aperture: f/20
Focal Length: 34 mm
ISO Speed: 800
Exposure Bias: 0/2 EV
Flash: Flash fired

Orientation: Horizontal (normal)
X-Resolution: 72 dpi
Y-Resolution: 72 dpi
Date and Time: 2007:07:28 08:44:46
YCbCr Positioning: Co-Sited
Exposure Program: Aperture priority
Date and Time (Original): 2007:07:28 08:44:46
Date and Time (Digitized): 2007:07:28 08:44:46
Shutter Speed: -86634/65536
Metering Mode: Pattern
Color Space: sRGB
Focal Plane X-Resolution: 3954.233 dpi
Focal Plane Y-Resolution: 3958.763 dpi
Compression: JPEG
Image Type: Canon EOS DIGITAL REBEL XT
Owner Name: unknown < P d
Camera Serial Number: 2520718507
Custom Functions: 20, 0, 256, 512, 768, 1024, 1280, 1536, 1792, 2048
Model ID: 2147484041
Tag::Canon::0x0013: 0, 159, 7, 112
Tag::Canon::0x00AA: 10, 599, 1024, 1024, 571
Image Width: 3456 pixels
Image Height: 2304 pixels
Macro Mode: Normal
Image Quality: Fine
Canon Flash Mode: On
Continuous Drive: Single
Focus Mode: One-shot AF
Canon Image Size: Large
Easy Mode: Manual
Contrast: High
Saturation: High
Sharpness: High
Metering Mode: Evaluative
Focus Range: Not Known
Canon Exposure Mode: Aperture-Priority AE
Lens: 18 - 55mm
Max Aperture: 128
Min Aperture: 304
Flash Activity: Flash did not fire
Photo Effect: Off
Color Tone: 0
Focal Type: Zoom
Scaled Focal Length: 34
Focal Plane Size: 907 x 605
Flash Guide Number: 2097168
ISO: 800
Measured LV: 65508
Target Aperture: 16
Target Exposure Time: 0
Flash Guide Number: 2047.96875
F Number: 20.2
Camera Type: EOS Low-end
Auto Rotate: None
Image Width: 3456
Image Height: 2304
Image Width (As shot): 3456
Image Height (As shot): 2304
Shutter Count: 7172
Color Temperature: 5200°K
Sensor Width: 3516 (52-3507 used)
Sensor Height: 2328 (19-2322 used)


The first turned out okay, but the second one is blurred. Any suggestions?
 

miloblithe

macrumors 68020
Nov 14, 2003
2,072
28
Washington, DC
f/20 is pretty high. I think the kit lens might get soft overall at that kind of aperture.

Also check out this site:

http://www.dofmaster.com/dofjs.html

at 34mm and f/20 focusing 3.5 feet away:

Subject distance 3.5 ft

Depth of field
Near limit 2.61 ft
Far limit 5.32 ft
Total 2.71 ft

In front of subject 0.89 ft (33%)
Behind subject 1.82 ft (67%)

only things 1.8 feet behind the subject should be in focus.
 

odinsride

macrumors 65816
Original poster
Apr 11, 2007
1,145
0
f/20 is pretty high. I think the kit lens might get soft overall at that kind of aperture.

Also check out this site:

http://www.dofmaster.com/dofjs.html

at 34mm and f/20 focusing 3.5 feet away:

Subject distance 3.5 ft

Depth of field
Near limit 2.61 ft
Far limit 5.32 ft
Total 2.71 ft

In front of subject 0.89 ft (33%)
Behind subject 1.82 ft (67%)

only things 1.8 feet behind the subject should be in focus.

Thanks for the link and explanation. Still have a lot of learning to do I guess. :p
 

beatzfreak

macrumors 6502
Jan 11, 2006
346
0
NYC
Ok here's some shots I took.



Second Image (High aperture number)


Camera: Canon EOS Digital Rebel XT
Exposure: 2.5 sec (5/2)
Aperture: f/20
Focal Length: 34 mm
ISO Speed: 800
Exposure Bias: 0/2 EV
Flash: Flash fired

Metering Mode: Evaluative


The first turned out okay, but the second one is blurred. Any suggestions?
If you're hand holding at 2.5 sec shutter speed, it will be blurry. Set the camera on something solid and use the self-timer.

Also, your metering mode is evaluative, try changing it to partial. Check the manual to see how to do this.
 

seenew

macrumors 68000
Dec 1, 2005
1,568
0
Brooklyn
to check and see what your aperture is going to leave in focus, there is a button on the bottom right side of the camera, right where the lens connects, that when you push it, the aperture closes down, but it doesn't take a picture. Hold this down to see how the picture will be focused.
 

odinsride

macrumors 65816
Original poster
Apr 11, 2007
1,145
0
One thing I've noticed is that on Av mode, I get a much lower shutter speed than on Full Auto mode, using the exact same shot and aperture. Apparently Full Auto mode is making adjustments to the settings that I'm not in order to get faster shutter speed. What am I missing? I set the ISO as high it goes and still can't get the shutter speed as high as full auto mode.
 

robbieduncan

Moderator emeritus
Jul 24, 2002
24,638
61
Harrogate
One thing I've noticed is that on Av mode, I get a much lower shutter speed than on Full Auto mode, using the exact same shot and aperture. Apparently Full Auto mode is making adjustments to the settings that I'm not in order to get faster shutter speed. What am I missing? I set the ISO as high it goes and still can't get the shutter speed as high as full auto mode.
Either:

1) It's not using the same aperture (check the details)

2) It's using a different metering mode which results in a different exposure calculation.

3) It could be intentionally underexposing a bit and using the exposure compensation to bring it back up

4) Probably other stuff I've not thought about