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"Wasted" resolution of an "L" lens on an APC body??

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LSHorwitz1

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I am trying to understand how a specific Canon lens behaves on an APC versus a full frame body, and have been looking at the photozone.de comparisons of the Canon 24-105 L lens specifically.

The specific performance of the lens I am trying to compare is resolution. The photozone.de analysis of this lens for the APC sensor shows that the lens peaks at around 2500 line pairs per page height at its best performance. See the tables at:

http://www.photozone.de/canon-eos/423-canon_24105_4_50d?start=1

The identical lens on the full frame body shows around 3400 line pairs per page height when evaluated on a full frame body by photozone. See:

http://www.photozone.de/canon_eos_ff/420-canon_24105_4_5d?start=1

I understand that the smaller APC sensor receives a "cropped" view of the lens output, when compared to the full frame sensor. I would therefore have assumed that the smaller APC sensor should resolve, at best, 66% of the line pairs seen by the full frame. Instead it is apparently able to achieve about 75% of the resolution.

More important is the issue of whether a body such as Canon's T1i, which supposedly allows 3200+ lines of resolution, will "waste" the real benefit of an "L" lens since it apparently cannot see/use the remaining performance of the lens.

Is there an 'optimal' resolution for best achieving sharpness with an APC sensor given the above, or does the "L" lens really enjoy some type of advantage over a non-L lens even if used on an APC camera.

I specifically will note that the new Canon 15-85 non-L zoom lens, for example, appears to offer HIGHER resolution peaking at 2548 line pairs when compared to the 24-105mm L lens, and thus could imply that it is possibly a BETTER match for the APC sensor.

Am I understanding all of this correctly, or do I have some basic misunderstandings here?

Many thanks for comments.

Larry
 
Canon doesn't give "L" ratings to EF-S (crop) lenses. I have crop and non-crop cameras and the 17-55 IS (crop) and 24-105 lenses. I've never noticed but the 24-105 doesn't get "rave" reviews on the crop bodies. I love the 17-55 IS on the 40D and 7D--- not as much zoom range, but a great 2.8 lens.

Kent
 
LSHorwitz1 said:
I am trying to understand how a specific Canon lens behaves on an APC versus a full frame body, and have been looking at the photozone.de comparisons of the Canon 24-105 L lens specifically.

The specific performance of the lens I am trying to compare is resolution. The photozone.de analysis of this lens for the APC sensor shows that the lens peaks at around 2500 line pairs per page height at its best performance. See the tables at:

http://www.photozone.de/canon-eos/423-canon_24105_4_50d?start=1

The identical lens on the full frame body shows around 3400 line pairs per page height when evaluated on a full frame body by photozone. See:

http://www.photozone.de/canon_eos_ff/420-canon_24105_4_5d?start=1
Click to expand...
That's because those aren't lens tests, they're system tests, and for sharp lenses they are tests primarily of the camera body's AA filter.

For decent lenses, you should ignore the resolution portion of the PZ and DPReview tests because they are still using the AA filters in the test.

--
Lee Jay
(see profile for equipment)
 
Short answer might be surprising - 20+ lenses I have subjected to a USAF resolution test chart all out resolve the sensor. This includes tests with 5D2, 7D, 50D, and 40D cameras.

So don't worry about optical resolution. Instead, consider your lens needs and proceed accordingly. Yes, most optics that I have tried have "wasted" resolution.

Longer answer is this - the 5D2 sensor is resolution limited to 76 line pairs per mm. The 50D is limited to 92 line pairs per mm. The new 7D resolution limits at 116 line pairs per mm.

Well constructed optics, including the "consumer" grade lenses I have looked at, all easily resolve these figures from wide open.

Further, diffraction limits set in on the 7D at f/11. The 5D2 diffraction limits at f/16. The 40D and 50D limit somewhere in between.

--
Christopher Perez
  • PhotoLife Magazine November 2009 - Steampunk
  • LensWork Extended #78 Sept-Oct 2008 - In the Railyard
  • CameraWork Gallery 2007 - Palladium prints
  • The sharpest lens in my kit is a tripod
  • Cameras have no talent. Its what's behind the eyepiece that counts.
 
You are missing a few issues...

for one, the number of lines on the sensor itself are different. When looking at such comparisons. Still, if the lens is softer data will "smear" on adjoining pixels.

But, even more significantly, crop cameras have a HIGHER PIXEL DENSITY than full frame cameras. Therefore, you actually need SHARPER lenses on crop than on Full frame to resolve the same amount of detail (assuming u use ones with the same amount of MPs or close.. maybe 7D vs 5DII (not exactly.. but close enough)). Don't forget that there are many "lines" the L lens can produce which are wasted on plastic not covered with sensor ;)

The main "Waste" you get from using L lenses (or any other EF lens) on crop is that you only use some of the glass, rather than all of it (and yet you carry all of it and pay for all of it). However, that doesn't go without a candy - using only the central part of the lens means using its best area. Not only you avoid distortion and vignetting, but you also avoid using the corners of the lens where sharpness and CA are usually much worse.
 
bodies change over time so choose your lenses on the quality of the lens vs the 'current" body.

Also, one has to go way up in print size--above 16x20--to see these differences in LP resolution
LSHorwitz1 said:
I am trying to understand how a specific Canon lens behaves on an APC versus a full frame body, and have been looking at the photozone.de comparisons of the Canon 24-105 L lens specifically.

The specific performance of the lens I am trying to compare is resolution. The photozone.de analysis of this lens for the APC sensor shows that the lens peaks at around 2500 line pairs per page height at its best performance. See the tables at:

http://www.photozone.de/canon-eos/423-canon_24105_4_50d?start=1

The identical lens on the full frame body shows around 3400 line pairs per page height when evaluated on a full frame body by photozone. See:

http://www.photozone.de/canon_eos_ff/420-canon_24105_4_5d?start=1

I understand that the smaller APC sensor receives a "cropped" view of the lens output, when compared to the full frame sensor. I would therefore have assumed that the smaller APC sensor should resolve, at best, 66% of the line pairs seen by the full frame. Instead it is apparently able to achieve about 75% of the resolution.

More important is the issue of whether a body such as Canon's T1i, which supposedly allows 3200+ lines of resolution, will "waste" the real benefit of an "L" lens since it apparently cannot see/use the remaining performance of the lens.

Is there an 'optimal' resolution for best achieving sharpness with an APC sensor given the above, or does the "L" lens really enjoy some type of advantage over a non-L lens even if used on an APC camera.

I specifically will note that the new Canon 15-85 non-L zoom lens, for example, appears to offer HIGHER resolution peaking at 2548 line pairs when compared to the 24-105mm L lens, and thus could imply that it is possibly a BETTER match for the APC sensor.

Am I understanding all of this correctly, or do I have some basic misunderstandings here?

Many thanks for comments.

Larry
Click to expand...
 
Slartz said:
The main "Waste" you get from using L lenses (or any other EF lens) on crop is that you only use some of the glass, rather than all of it (and yet you carry all of it and pay for all of it).
Click to expand...
This isn't true. The entire aperture of the lens is used by each and every pixel regardless of its location in the image circle.

--
Lee Jay
(see profile for equipment)
 
I stand corrected.

though is that true for all elements?
 
you are of course correct.. I forgot my optics... the unused glass scenario is true for smaller apertures, where the central glass is used and often produces better IQ, but that's a different case :)

But, being that it's 2:30am here.. I'm a little out of focus (pun intended ;-))

In any case my point was that u'r enjoying the center of the image which is higher quality. and suffer less from corner problems when u use EF lenses on crop camera :)
 
Slartz said:
you are of course correct.. I forgot my optics... the unused glass scenario is true for smaller apertures, where the central glass is used and often produces better IQ, but that's a different case :)

But, being that it's 2:30am here.. I'm a little out of focus (pun intended ;-))

In any case my point was that u'r enjoying the center of the image which is higher quality. and suffer less from corner problems when u use EF lenses on crop camera :)
Click to expand...
In practice, that's hardly ever an advantage. The reduced enlargement of full-frame virtually always more than compensates and where it doesn't the necessary crop is more like 1.02 to 1.05, not 1.6.

--
Lee Jay
(see profile for equipment)
 
Lee Jay said:
This isn't true. The entire aperture of the lens is used by each and every pixel regardless of its location in the image circle.
Click to expand...
I also read this in another thread recently (maybe it was you :), can't remember), and I'm sure you're right, but then I don't get the whole EF-S thing.

If that's true then why does the reduced image circle allow Canon to make EF-S lenses smaller and lighter?
 
slydog said:
why does the reduced image circle allow Canon to make EF-S lenses smaller and lighter?
Click to expand...
http://www.bobatkins.com/photography/reviews/ef-s_10-22_review.html

"The EF-S design allows the rear element to be closer to the sensor then with EF lenses,
improving image quality, especially at the shortest focal lengths.

"Due to the smaller frame coverage of the EF-S lens design, EF-S lenses can be smaller and lighter than equivalent full frame designs - ..."

regards,

-rich

--
Careful photographers run their own tests.
 
The APC sensor uses the sweet spot of the lens so the lens will perform better than on a full frame camera...

The new EF-S are just as sharp as L glass but the L lenses have higher quality elements and will produce nicer photos, have better build and will last much longer..

In fact the 17-55 is sharper and has less distortions than the 24-70 but the 24-70 has much better color and bokeh...

I hope canon will upgrade the L std lenses soon.....
 
A great prime lens vs. a standard consumer zoom will show more visible picture improvement than any body upgrade.

I use the best lenses available. APS-C or FF, having the best lenses make the difference. Get great lenses first and an (expensive) FF body later - if you ever need a FF for the other qualities that you can get i.e. FpS, high ISO, water sealed etc.

The latest and most fancy DSLR body is relatively expensive and its basic picture quality will soon enough be levelled out by that of newer and cheaper models. high quality lenses will last for many, many years and give you a consistent IQ edge.
 
richj20 said:
"The EF-S design allows the rear element to be closer to the sensor then with EF lenses, improving image quality, especially at the shortest focal lengths.
Click to expand...
richj20 said:
"Due to the smaller frame coverage of the EF-S lens design, EF-S lenses can be smaller and lighter than equivalent full frame designs - ..."
Click to expand...
Yes I've heard those quotes before, and Canon's website says similar things, but that's exactly why I don't understand the above discussion.

When referring to the comment that some glass on EF lenses gets wasted on a crop sensor, ljfinger (and others) have said:
richj20 said:
"This isn't true. The entire aperture of the lens is used by each and every pixel regardless of its location in the image circle."
Click to expand...
I don't understand - these comments seem to contradict each other. Obviously I'm no lens expert, I just have a basic intuitive understanding of what happens when light passes through the lens, but I think I understand what each of these quotes basically mean. But they seem contradictory to me.

If none of the glass in an EF lens is wasted on a crop sensor, then why can EF-S lenses be made smaller and lighter?
 
slydog said:
slydog said:
"The EF-S design allows the rear element to be closer to the sensor then with EF lenses, improving image quality, especially at the shortest focal lengths.
Click to expand...
slydog said:
"Due to the smaller frame coverage of the EF-S lens design, EF-S lenses can be smaller and lighter than equivalent full frame designs - ..."
Click to expand...
Yes I've heard those quotes before, and Canon's website says similar things, but that's exactly why I don't understand the above discussion.

When referring to the comment that some glass on EF lenses gets wasted on a crop sensor, ljfinger (and others) have said:
slydog said:
"This isn't true. The entire aperture of the lens is used by each and every pixel regardless of its location in the image circle."
Click to expand...
I don't understand - these comments seem to contradict each other. Obviously I'm no lens expert, I just have a basic intuitive understanding of what happens when light passes through the lens, but I think I understand what each of these quotes basically mean. But they seem contradictory to me.
Click to expand...
They don't.

First quote means this: wide and UW lenses have short distance bitween optical center of lens and focal plane. It's shorter than space needed for mirror. So if you place such lens as it is, it wouldn't be possible to focus on infinity. To make infinity focus possible they build-in additional elements that project focal plane to sensor's plane. And with closer distance on EF-S lens less correction requered. Which degrades IQ less.

The second quote has to do with the fact that lens isn't single optical element. There's distance between apperture, front glass and rear glass, etc.

To get the same amount of light in the corner as in the center, front element should be bigger then dictates apperture. Corners is formed by light entering the lens at some angle. If front element is of the size of apperture part of it would be blocked by lens barrel. Smaller image circle of EF-S lens mean that that angle smaller, so the front element and the hole lens could be smaller too.
slydog said:
If none of the glass in an EF lens is wasted on a crop sensor, then why can EF-S lenses be made smaller and lighter?
Click to expand...
Because they requred to produce smaller image circle.

P.S. Looks like I'm for another lesson from Steve Balcombe :)
 
richj20 said:
slydog said:
why does the reduced image circle allow Canon to make EF-S lenses smaller and lighter?
Click to expand...
http://www.bobatkins.com/photography/reviews/ef-s_10-22_review.html

"The EF-S design allows the rear element to be closer to the sensor then with EF lenses,
improving image quality, especially at the shortest focal lengths.
Click to expand...
Only at short focal lengths. This is because the design doesn't need to be quite as retrofocus as it would otherwise need to be, and because the angle of view doesn't need to be as wide at a given focal length. There's no size benefit at all at long focal lengths.
richj20 said:
"Due to the smaller frame coverage of the EF-S lens design, EF-S lenses can be smaller and lighter than equivalent full frame designs - ..."
Click to expand...
Again, only at short focal lengths (under 44mm).

--
Lee Jay
(see profile for equipment)
 
The lens is just as sharp on 8mp APS-C as it is on a 15mp APS-C as it is on a 21 mp "full frame".
The first line at photozone's testing site:

! Please note that the tests results are not comparable across the different systems. This does also apply for the new EOS tests based on the EOS 50D because of differences in the sensor system (e.g. AA-filter) as well as different RAW-converters.

In comparing between tests on the 350D, the 50D, and the 5D II, you have to ignore the nominal line pairs number. Instead you have to look at the where the lens scores in the normalized "Excellent," "Very Good," "Good", ... ranges. There you will see that the same lens performs at the same level across systems.

I think it's a popular misconception that some lenses are "out resolved" by a sensor. Even the lousiest cheap lens, even pinholes, will give greater resolution on a higher resolution sensor.
 
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