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Old Mar 15, 2009, 1:31 PM   #1
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I have owned the XSI since June of 2008. It has been taking great pictures until recent. I have noticed alot of blurred pictures.

Shooting with the kit lens 18-55mm IS.

I did some controlled test shots and every one that is f/36 is blurred.

My set up:

XSI with 18-55 II lens IS was turned off zoomed in to 55mm
Tripod used with remote timer.

1st shot with auto.

P mode 1/250 5.6 iso 100
1/125 8.0 iso 100
1/6 36 iso 100

Same setup for Tv, Av, and Manual.

Focus was center point.

Like I said previous, all the f/36 shots were blurred. I had focus lock/confirmation. Everything looked good in the viewfinder. Hit the timer and I get a blurred picture.

I attached some pics for review. Appreciate any help.

Boomstrike

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Old Mar 15, 2009, 2:28 PM   #2
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f/36? Image quality is going to start degrading before you get that far. I wouldn't use anything above around f/16 unless you have to for DOF purposes.

See this article on diffraction limitations:

http://www.cambridgeincolour.com/tut...hotography.htm


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Old Mar 15, 2009, 3:11 PM   #3
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P.S.

If you click on the "Blur Index" for your lens and adjust the sliders, you'll see that optimum sharpness occurs between around f/8 and f/11 on the long (55mm) end of your zoom range using an EOS-20D to test with. After that the image is going to start degrading as you stop down the aperture more.

http://www.slrgear.com/reviews/showp...ct/1114/cat/11

IOW, softer images trying to shoot at f/36 would be expected. That test was done using a Canon EOS-20D. With a higher resolution model like the XSi, image degradation is probably going to occur even sooner in the aperture range (because of smaller photosites for each pixel with a higher resolution sensor).

Just because you have the ability to shoot at f/36, doesn't mean you want to. You'll get softer images due to diffraction at apertures that small, and you'll probably want to stick to around f/8 or f/11 unless more DOF is needed (taking image degradation into consideration).

BTW, your camera will always Autofocus with the aperture wide open, only stopping down to the set aperture when the photo is taken. So, focus is not the problem (it's going to focus the same way, regardless of the aperture you set). You're likely seeing soft images from diffraction trying to shoot at f/36.



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Old Mar 15, 2009, 3:51 PM   #4
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Ditto.
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Old Mar 15, 2009, 4:19 PM   #5
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How sturdy is the tripod? If it's a cheap one, you may also be seeing a bit of blur from mirror vibration as your shutter speeds get slower. I'd try it with Mirror Lockup engaged to see if diffraction is the only issue or not. It looks like it's settable via a Custom Function with your model.

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