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Old Oct 4, 2010, 2:34 PM   #31
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Er, the sweet spot of the image circle. The whole lens is used to project the image on the focal plane, not just the middle bit.

But this whole episode shows why I wish Canon made L lenses for crop cameras. Not that you cannot get a crummy copy of an L, but the odds are lower.
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Old Oct 5, 2010, 11:09 AM   #32
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Er, the sweet spot of the image circle. The whole lens is used to project the image on the focal plane, not just the middle bit.

But this whole episode shows why I wish Canon made L lenses for crop cameras. Not that you cannot get a crummy copy of an L, but the odds are lower.
If that were the case then one could use EFs glass on FF bodies and not get just plain blocked out portions in the corners like what was shown here. The arguement of distortion in the corners of FF cameras also would not exist nor the traditional views of vignetting on FF bodies even with L glass. I would not shoot my 70-200 at f 2.8 on my 1Ds MKIII for this simple reason, too much vignetting. I could however shoot it at 2.8 on a MKIII and a 50D and not get the least amount of vignetting.
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Old Oct 5, 2010, 1:32 PM   #33
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An EF-S lens projects an image circle too small for the FF sensor. But the whole of a lens is used to project its image circle. There are millions of rays of light hitting the lens which focusses them onto the film plane, forming a circle.

When using a small sensor with an EF lens you are using the middle part of the image circle, not the middle part of the lens.
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Old Oct 6, 2010, 6:29 AM   #34
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So which part of the image is in the "middle image circle" Im assuming the middle outward to the end of the sensor be it 1.6, 1.3 or FF. Has to be the middle or you would be getting the center of your image cropped instead of the fall off at the edges where the vignetting becomes apparent. So what projects in the middle of the image circle? The middle of the image I presume. Where does the middle of the image come from? The outer edges of the lens of the middle of the lens? I would have to say the middle.
With that being said and using the means of deduction the center of the lens projected outward to the end of the sensor edges results in only the portion of the lens which covers from the center to the edges being used in the image capture.
Same reasoning applied to why the EFs image is too small for a FF sensor explains why the EF image is larger than need or used and the outer edges are cropped off on a crop sensor resulting in using the middle of the lens and vignetting gets cropped.

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Old Oct 6, 2010, 2:07 PM   #35
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It's difficult to describe in a short post how many ways you've got this wrong.

Think of it this way. An object in the real world illuminated by a light source has millions of rays of light (doesn't matter whether we are talking of waves or particles) bouncing off of it in ALL directions. This is why you can see things from more than one angle.

Some of those rays will get captured by a lens (cornea or camera lens) and that lens, if focussed will bend those rays so that they are focused on a plane behind the lens. Each point on the object will reflect off a huge number of rays, and those rays will be passing through different parts of the lens but be focussed at a single point back on the image plane.

This is true for every part of the image circle drawn by the lens. The WHOLE lens draws every point contained within the image circle.

If you don't believe me, find yourself a high-school or undergraduate physics text book.

The reasons that you get chromatic aberrations, vignetting, etc is that lenses are not perfect. They don't always focus the rays departing from a point in the world back onto a single point on the image plane. These links should give you a bit of an idea:

http://www.lightandmatter.com/html_b...ch04/ch04.html

http://www.cambridgeincolour.com/tut...era-lenses.htm
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Old Oct 6, 2010, 5:08 PM   #36
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If this were the case then all lenses would be wide angle and you would be able to capture an image behind you, all images would be round and all sensors would exhibit vignetting and cut off in the corners. Experience like the example given with the 70-200 tells me different.
Ive made my point, you have made yours and its evident we are not going to agree so the best we can do is agree that we disagree.
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Old Oct 7, 2010, 1:34 AM   #37
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LOL, okay dude.
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