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Thread started 30 Dec 2009 (Wednesday) 19:33
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7D and Diffraction (I had to test it...)

 
John ­ the ­ Geek
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Dec 30, 2009 19:33 |  #1

So... I've had my 7D for a little over a month now and in the back of my head I've been worrying a little about just how much diffraction would influence my macro photography. I've been busy and haven't had much time to test it. So today I rigged up the Canon 180mm 3.5L, the 7D, and the MT-24EX Macro Twin Lite. Mirror lock and a cable release were used. All shots were taken at 1/200 @ ISO100. All available f-stops on the 180mm Macro. (3.5 - 32)

I've hosted both the full resolution JPEGs right out of DDP, and 1024x768 100% crops out of Photoshop CS4 JPEG level 10. I won't post all 20 images in this thread, but you can see them all here:

John's 7D Diffraction Test (external link)

Feel free to download the full JPGs here (external link) and the crops here (external link) if you would like to pixel-peep them yourself.

Here is what the full frame looks like for reference. (external link)

Now for the 100% pixel-peeping, at f/3.5 the macro starts out a little soft:

IMAGE NOT FOUND
IMAGE IS A REDIRECT OR MISSING!
HTTP response: 404 | MIME changed to 'text/html' | Byte size: ZERO


But quickly sharpens up at f/4:
IMAGE NOT FOUND
IMAGE IS A REDIRECT OR MISSING!
HTTP response: 404 | MIME changed to 'text/html' | Byte size: ZERO


Here is f/6.3:
IMAGE NOT FOUND
IMAGE IS A REDIRECT OR MISSING!
HTTP response: 404 | MIME changed to 'text/html' | Byte size: ZERO


And stays pretty darn sharp through about f/11:
IMAGE NOT FOUND
IMAGE IS A REDIRECT OR MISSING!
HTTP response: 404 | MIME changed to 'text/html' | Byte size: ZERO


A little softer now, but still usable at f/16 if I were to sharpen it a bit:
IMAGE NOT FOUND
IMAGE IS A REDIRECT OR MISSING!
HTTP response: 404 | MIME changed to 'text/html' | Byte size: ZERO


The slope continues through f/22:
IMAGE NOT FOUND
IMAGE IS A REDIRECT OR MISSING!
HTTP response: 404 | MIME changed to 'text/html' | Byte size: ZERO


Until finally arrives here at f/32:
IMAGE NOT FOUND
IMAGE IS A REDIRECT OR MISSING!
HTTP response: 404 | MIME changed to 'text/html' | Byte size: ZERO


I feel that these are basically the same results I got out of my XTi, if not better, but unfortunately the XTi is dead and I can't shoot a fair comparison between the two. The happiness in my purchase has been reaffirmed.

Again, grab the full and crop zips at the top if you would like to look at every f/stop available on the Canon 180mm Macro in your own editor.

Canon Gear: 7D Gripped :: 16-35mm ƒ/2.8L II :: 24-70mm ƒ/2.8L :: 70-200mm ƒ/2.8L IS II :: 28mm ƒ/1.8 :: 50mm ƒ/1.4 :: 85mm ƒ/1.8 :: 200mm ƒ/2.8L II :: 180mm ƒ/3.5L Macro :: Extenders 1.4x II and 2x II :: Speedlites 430EX II (x2) and MT-24EX Macro Twin Lite
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Tom ­ W
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Dec 30, 2009 19:40 |  #2

Similar experience here - you can start to see it (at least at 100%) at f/11, it's stronger at f/16, and pretty bad by f/32 with the 7D. Much depends on how large you will print and/or how much you will crop as well. What's visible at 100% isn't necessarily going to show up on an 11 X 14 inch print.


Tom
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John ­ the ­ Geek
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Dec 30, 2009 19:42 as a reply to  @ Tom W's post |  #3

Yeah, I've read where people say it starts at like f/5.6, etc... Not a chance. I just needed to see it for myself.


Canon Gear: 7D Gripped :: 16-35mm ƒ/2.8L II :: 24-70mm ƒ/2.8L :: 70-200mm ƒ/2.8L IS II :: 28mm ƒ/1.8 :: 50mm ƒ/1.4 :: 85mm ƒ/1.8 :: 200mm ƒ/2.8L II :: 180mm ƒ/3.5L Macro :: Extenders 1.4x II and 2x II :: Speedlites 430EX II (x2) and MT-24EX Macro Twin Lite
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Daniel ­ Browning
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Dec 30, 2009 19:42 |  #4

Thanks for sharing your test. Even at f/16 the 7D provides higher resolution than previous APS-C Canons. Especially if you have low noise and can use RL deconvolution instead of normal sharpening.


Daniel

  
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gabebalazs
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Dec 30, 2009 20:02 |  #5

Yeah, thanks for the test. Maybe the sceptics will be silenced now. I was kinda getting tired of reading panicing comments that the 7D starts diffraction at f6.9, it's the end of the world!!! :D

I also did my own test and even before that I knew that diffraction is gradual, it's not a brick wall at f6.9. Plus the high resolution makes up for it anyway.
I've checked lab tests and the 7D still outresolves the XSi at f/16

but thanks for the test again.


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gjl711
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Dec 30, 2009 20:14 |  #6

John the Geek wrote in post #9292779 (external link)
Yeah, I've read where people say it starts at like f/5.6, etc... Not a chance. I just needed to see it for myself.

Very nice test, thanx for taking the time to post the results. And in defense of all the folks saying it starts at f/5.6, they are just plain wrong. It starts at f/4. :) It's just that your not going to be able to see it but I'm sure if you did the math, it would be there.


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gabebalazs
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Dec 30, 2009 20:18 |  #7

gjl711 wrote in post #9292957 (external link)
Very nice test, thanx for taking the time to post the results. And in defense of all the folks saying it starts at f/5.6, they are just plain wrong. It starts at f/4. :) It's just that your not going to be able to see it but I'm sure if you did the math, it would be there.

:)
I think mathematically it starts at f/6.8.

http://www.the-digital-picture.com …al-SLR-Camera-Review.aspx (external link)


5DIV | 5DIII | 80D | A7RII | Canon 24-70 2.8L II | 70-200 2.8L IS II | 24-105 f/4L IS | 16-35 f/4L IS | 135 f/2L | 85 1.8 | 50 1.8 STM | 18-135 IS STM | SONY FE 28-70 OSS | Tamron 17-50 2.8 | Tamron 150-600 | Ʃ 35 1.4 ART | Rokinon 14 2.8 | Sigma 1.4x | Metabones IV | 2x Canon 600EX-RT
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Tom ­ W
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Dec 30, 2009 20:19 |  #8

gjl711 wrote in post #9292957 (external link)
Very nice test, thanx for taking the time to post the results. And in defense of all the folks saying it starts at f/5.6, they are just plain wrong. It starts at f/4. :) It's just that your not going to be able to see it but I'm sure if you did the math, it would be there.

Probably earlier than that from a purely technical standpoint, but the resolution of the 7D won't be able to show the results until at least f/6.8. And my eyes won't be able to see it until a smaller aperture is employed. :)

If I stare at 100% crops of f/8 vs f/5.6 shots long enough, I can probably see a very, very slight difference. But it's so very small as to be insignificant.


Tom
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John ­ the ­ Geek
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Dec 30, 2009 20:20 |  #9

gjl711 wrote in post #9292957 (external link)
And in defense of all the folks saying it starts at f/5.6, they are just plain wrong. It starts at f/4. :) It's just that your not going to be able to see it but I'm sure if you did the math, it would be there.

Well, that's true. Once the 7D, mark VI comes out at a billion megapixels we'll be able to see it at f/2 (even on lenses that don't start at f/2.)


Canon Gear: 7D Gripped :: 16-35mm ƒ/2.8L II :: 24-70mm ƒ/2.8L :: 70-200mm ƒ/2.8L IS II :: 28mm ƒ/1.8 :: 50mm ƒ/1.4 :: 85mm ƒ/1.8 :: 200mm ƒ/2.8L II :: 180mm ƒ/3.5L Macro :: Extenders 1.4x II and 2x II :: Speedlites 430EX II (x2) and MT-24EX Macro Twin Lite
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Maxdave
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Dec 31, 2009 06:45 as a reply to  @ John the Geek's post |  #10

Thanks for this great test with the photos ...

May I presume the doom and gloom stories about the 50D's problems with diffraction at as low as f7 or so are also of minor consequence?

Maxdave


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canonloader
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Dec 31, 2009 06:59 |  #11

Very nice visual test. It even makes sense to me. So is this going to be the same or very near the same, for all lenses?


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JeffreyG
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Dec 31, 2009 07:22 |  #12

John the Geek wrote in post #9292779 (external link)
Yeah, I've read where people say it starts at like f/5.6, etc... Not a chance. I just needed to see it for myself.

This common misperception is because people do not understand what they read.

Pretend you have a perfect f/1.4 lens. This lens resolves infinite detail and does not get better with stopping down.

Mount the lens on a 7D and a 30D and check the performance of the image at each whole stop of aperture.

The 7D should look the same at f/1.4....f/2....f/2.8.​...f/4.....f/5.6. This is because any diffraction softening happening at these apertures will be at a higher frequency (smaller) than the pixels. Once we get past f/5.6 it does become possible to detect the effects of diffraction on our perfect lens.

On the 30D we have to go to f/11 before the theoretical effects of diffraction on our perfect lens is detectable.

Does this mean the 30D is sharper than the 7D from f/5.6 to f/11? Of course not!

The actual meaning of 'diffraction limited' is that the 7D only enjoys a theoretical higher resolution at apertures larger than f/11. The advantage is maximum to f/5.6 and the two cameras theoretically approach each other in resolution between f/5.6 and f/11. From f/11 and up they are identical in what they can resolve as both are diffraction limited.

What does this mean practically to a 7D shooter? Not much. One takeaway is that buying higher and higher resolution cameras with small sensors won't gain you much real world advantage. Above f/11 the 7D isn't going to resolve more than the old 8MP 30D. Below f/5.6 a lot of zoom lenses probably don't resolve a lot better detail in the frequencies above 70 lp/mm anyway.


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versedmb
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Dec 31, 2009 07:44 |  #13

JeffreyG wrote in post #9295489 (external link)
This common misperception is because people do not understand what they read.

Pretend you have a perfect f/1.4 lens. This lens resolves infinite detail and does not get better with stopping down.

Mount the lens on a 7D and a 30D and check the performance of the image at each whole stop of aperture.

The 7D should look the same at f/1.4....f/2....f/2.8.​...f/4.....f/5.6. This is because any diffraction softening happening at these apertures will be at a higher frequency (smaller) than the pixels. Once we get past f/5.6 it does become possible to detect the effects of diffraction on our perfect lens.

On the 30D we have to go to f/11 before the theoretical effects of diffraction on our perfect lens is detectable.

Does this mean the 30D is sharper than the 7D from f/5.6 to f/11? Of course not!

The actual meaning of 'diffraction limited' is that the 7D only enjoys a theoretical higher resolution at apertures larger than f/11. The advantage is maximum to f/5.6 and the two cameras theoretically approach each other in resolution between f/5.6 and f/11. From f/11 and up they are identical in what they can resolve as both are diffraction limited.

What does this mean practically to a 7D shooter? Not much. One takeaway is that buying higher and higher resolution cameras with small sensors won't gain you much real world advantage. Above f/11 the 7D isn't going to resolve more than the old 8MP 30D. Below f/5.6 a lot of zoom lenses probably don't resolve a lot better detail in the frequencies above 70 lp/mm anyway.

Keep in mind that there is no difference in diffraction between the 7d and the 30d. Higher pixel density does not equal more diffration. Diffraction is related to sensor size, not pixel density.

The difference is that the 18mp of the 7d enlarges the image more than the 30d so that you can see the effects of diffraction, whereas the 30d doesn't magnify the image enough to see the diffraction.

The 7d magnifies the image more so that you can see the flaws better - kind of like looking into one of those high magnifaction mirrors that show all of your skin flaws. ;)


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John ­ the ­ Geek
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Dec 31, 2009 07:46 |  #14

JeffreyG wrote in post #9295489 (external link)
This common misperception is because people do not understand what they read.

Pretend you have a perfect f/1.4 lens. This lens resolves infinite detail and does not get better with stopping down.

Mount the lens on a 7D and a 30D and check the performance of the image at each whole stop of aperture.

The 7D should look the same at f/1.4....f/2....f/2.8.​...f/4.....f/5.6. This is because any diffraction softening happening at these apertures will be at a higher frequency (smaller) than the pixels. Once we get past f/5.6 it does become possible to detect the effects of diffraction on our perfect lens.

On the 30D we have to go to f/11 before the theoretical effects of diffraction on our perfect lens is detectable.

Does this mean the 30D is sharper than the 7D from f/5.6 to f/11? Of course not!

The actual meaning of 'diffraction limited' is that the 7D only enjoys a theoretical higher resolution at apertures larger than f/11. The advantage is maximum to f/5.6 and the two cameras theoretically approach each other in resolution between f/5.6 and f/11. From f/11 and up they are identical in what they can resolve as both are diffraction limited.

What does this mean practically to a 7D shooter? Not much. One takeaway is that buying higher and higher resolution cameras with small sensors won't gain you much real world advantage. Above f/11 the 7D isn't going to resolve more than the old 8MP 30D. Below f/5.6 a lot of zoom lenses probably don't resolve a lot better detail in the frequencies above 70 lp/mm anyway.

That is a very good explanation. I think it finally makes sense to me now.


Canon Gear: 7D Gripped :: 16-35mm ƒ/2.8L II :: 24-70mm ƒ/2.8L :: 70-200mm ƒ/2.8L IS II :: 28mm ƒ/1.8 :: 50mm ƒ/1.4 :: 85mm ƒ/1.8 :: 200mm ƒ/2.8L II :: 180mm ƒ/3.5L Macro :: Extenders 1.4x II and 2x II :: Speedlites 430EX II (x2) and MT-24EX Macro Twin Lite
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Dec 31, 2009 07:49 as a reply to  @ John the Geek's post |  #15

Must say im impressed, This isnt any worse than my 30D really from what I've seen....

As in I had to push to f/22 or f/32 before i really started to notice the difference..and a pass or two of USM i bet fixes things up nicely :) and keep in mind of course that actual usable output [prints or web-sized images] wont show flaws like this either...

Nice test man!


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7D and Diffraction (I had to test it...)
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