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Old Feb 10, 2008, 9:38 PM   #1
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I recently bought a 40D and matched it with a 500 F4. Close shots seem very sharp but distance shots are hit and miss - especially on cloudy days. I'm thinking of taking both in for servicing.

I've attached two examples. The first was quite far away in reasonable light. The second was closer under cloudy skies. I just noticed that the second picture is more than 1mg smaller than the first - even though it was half the distance away.:roll:

Thanks for any advice.

Jim

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Old Feb 10, 2008, 9:39 PM   #2
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Last edited by killdeer0007; Sep 13, 2009 at 5:06 PM.
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Old Feb 10, 2008, 10:18 PM   #3
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First one looks fine to me. And if i am right its cropped heavily....its going to appear like hit or miss when ur cropping heavily for a picture.

The second one looks like a shake apart from a missed AF. I would try to shoot something closer without cropping.

The crop sometimes takes away the quality of the image. And it would be great if u can post the EXIF for the second shot.

And u can increase the contrast a bit. It looks a bit too flat.

here is one heavily cropped and to me it appears hit or miss like urs..but viewing a normal picture without cropping looks fine to me



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Old Feb 14, 2008, 6:47 AM   #4
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Depends what you are calling further away, but if you approach infinity then you will always find a lens getting softer. Another thing that happens at range is you are using less of the pixels so definition is lost.
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Old Feb 14, 2008, 8:47 PM   #5
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There are a few general things to consider when facing sharpness issues.

* Was the shutter speed appropriate for the both the subject motion and the lens?
In the unlikely event that you were hand-holding these shots, the rule-of-thumb minimum shutter speed should have been 1/500 second (w/o image stabilized lens) just to try and offset camera shake.

* Lenses have a sharpness "sweet spot" usually about half way between the minimum and maximum aperture.

* With a long lens, the depth of field is very shallow even at small apertures, making spot-on autofocus performance more difficult.

* The farther away something is from the lens, the less pixels there are available to image any particular feature -- as pointed out by Mark1616.

The cloudy days might tend to have a negative effect by requiring a lower shutter speed and/or a larger lens aperture. The lower contrast may make it more difficult to get good focus -- in addition to requiring a larger aperture.

As far as the lower file size on the closer picture goes, image file size of JPEGs is highly affected by image detail. Areas of low detail/contrast compress better than areas of high detail. Could be that the very low over-all detail of the second pic just compressed more efficiently than the first pic.

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