Question about diffraction limit

pz797_mizzou · Sep 19, 2009

As far as I understand, it suggests once you pass the limit, the resolution start to degrade, meaning I can't get 18MP with 7D once I pass f6.8.

I'm planning to shoot it mostly in 9mp (mRaw), does the diffraction limit change to f11 (like 20d which is 8MP). If so, I don't see the point why people are complaining about too many MP for 7D.

--
Gallery: http://www.mizzou.edu/~pz797

Ross Murphy · Sep 19, 2009

no DLA does not change, this is not a lanscape camera and I will get one to compliment my 5D2 for my wildlife while the 5D2 does lanscape, I will shoot the 7D from f8 to f1.4
--
Image's In Light North West
http://rossmurphy.zenfolio.com/
http://imagesinlightnw.blogspot.com/

Peter 13 · Sep 19, 2009

pz797_mizzou said:
As far as I understand, it suggests once you pass the limit, the resolution start to degrade, meaning I can't get 18MP with 7D once I pass f6.8.

There is no such thing. And yes, I know that it is a very popular term. Diffraction exists at any f-stop and gets worse with smaller apertures. On the other hand, if we can somehow ignore diffraction, lenses typically get sharper with smaller apertures. The cumulative effect of those two factors is minimized somewhere between, say f/5.6 and f/8, depending on the lens. This is like trying to minimize F(x)=x+1/x. The optimal f-stop is independent of the resolution of the sensor.

BTW, IR has very detailed images taken with the 7D at f/8. All the 18 mp's are there, really.

pz797_mizzou said:
I'm planning to shoot it mostly in 9mp (mRaw), does the diffraction limit change to f11 (like 20d which is 8MP). If so, I don't see the point why people are complaining about too many MP for 7D.

Nothing really changes. You get smaller files and lose some of the info. That will results in some IQ loss, but not much, depending on how much resolution you need, and how picky you are.

People complain because they like to complain. Many just do not understand the techical side.

Lee Jay · Sep 19, 2009

Ross Murphy said:
no DLA does not change, this is not a lanscape camera and I will get one to compliment my 5D2 for my wildlife while the 5D2 does lanscape, I will shoot the 7D from f8 to f1.4

You got shot down the last time you made this wrong claim, why not learn from it?

http://forums.dpreview.com/forums/read.asp?forum=1019&message=33057152
--
Lee Jay
(see profile for equipment)

Andreas Helke · Sep 19, 2009

There is no diffraction limit with any real meaning. If you analyze MTF charts you´ll see that you already have degraded performance from diffraction if you go from 24mm f4 to f5.6 with the 18-55 IS kit lens on the 10 MP 40D.

http://www.dpreview.com/lensreviews/canon_18-55_3p5-5p6_is_c16/page3.asp

Most people find the diffraction at f11 acceptable on an APS-C camera. If it has a high resolution sensor you are already beyond that poorly understood diffraction limit but still get an increase in resolution if you use a higher MP camera. At f16 the diffraction softness becomes easily visible and for many people f22 is unacceptably soft due to diffraction.

ohyva · Sep 19, 2009

Ross Murphy said:
no DLA does not change, this is not a lanscape camera and I will get one to compliment my 5D2 for my wildlife while the 5D2 does lanscape, I will shoot the 7D from f8 to f1.4

True that the diffraction in crop1.6 sensor have the same amount softening effect than in FF when roughly 1.5 stop smaller aperture is used. But on the other hand the crop1.6 camera has the same DOF as a FF camera when 1.5 stop smaller aperture is used. So at the end both cameras perform roughly the same, but you need to use 1.5 stop bigger aperture in the cropped sensor camera. This also equalize the slight high-ISO advantage the FF cameras may have.

Most of the fast high quality lenses perform best at apertures f4...f8, so you get the very nice lanscape photos with the current high resolution cropped sensor Canon cameras, 50D and 7D. When FF lenses are used, you also get rid of most of the corner problems these lenses may have with FF cams.

Only if you want to get very shallow DOF, the FF give you advantage not possible to overcome with a cropped sensor camera. And of course the FF cameras have their advantage in WA/UWA photography. Cropped camera then have the advantage allowing you to use lighter lenses for tele photography.

Karl Gnter Wnsch · Sep 19, 2009

pz797_mizzou said:
As far as I understand, it suggests once you pass the limit, the resolution start to degrade, meaning I can't get 18MP with 7D once I pass f6.8.

Only if you pixel peep or crop to pixel level - things that usually will compromise your image quality severely anyway.

pz797_mizzou said:
I'm planning to shoot it mostly in 9mp (mRaw), does the diffraction limit change to f11 (like 20d which is 8MP). If so, I don't see the point why people are complaining about too many MP for 7D.

Don't cripple the camera! You are suggesting buying a very good DSLR and tie the virtual right arm behind the body by reducing the RAW resolution just because you fear diffraction or other ramifications of the high resolution.
--
regards
Karl Günter Wünsch
Visit my gallery at
http://www.fotocommunity.de/pc/pc/mypics/461808

Lee Jay · Sep 19, 2009

pz797_mizzou said:
As far as I understand, it suggests once you pass the limit, the resolution start to degrade, meaning I can't get 18MP with 7D once I pass f6.8.

That's a bit low. Most of the diffraction calculators out there don't take some things into account, like the AA filter and Bayer mask, plus the aberrations in the lens.

pz797_mizzou said:
I'm planning to shoot it mostly in 9mp (mRaw), does the diffraction limit change to f11 (like 20d which is 8MP).

It would go up some, yes.

pz797_mizzou said:
If so, I don't see the point why people are complaining about too many MP for 7D.

Repeat after me. There are NO f-stops at which mRaw will out-resolve native raw.

--
Lee Jay
(see profile for equipment)

jsmiller · Sep 19, 2009

I see many posts here about the diffraction limit, but many are full of inaccuracies and false claims. Some are outright nonsense. It is very simple to calculate a good approximation to the diffraction effects of a given lens (actually it only depends on the f/ratio) and camera, but quite difficult to do a detailed and exact calculation. The exact effect and its importance would require knowledge of the shapes and locations of the blades of the iris within the lens, the pixel light sensitivity as a function of position interior to it, assumptions on how to deal with square pixels, and even treatment of diffraction rings and spikes, to list a few things. There is also the question of whether the lens is truly diffraction limited at some aperture, but that is a different issue. If people are interested in the simple calculation, so that you can carry it out yourself, I will be happy to post here the basic physics and the formula. It probably gets you about 70-80% of the way to the right answer.

Joe

SteB · Sep 19, 2009

pz797_mizzou said:
As far as I understand, it suggests once you pass the limit, the resolution start to degrade, meaning I can't get 18MP with 7D once I pass f6.8.

I'm planning to shoot it mostly in 9mp (mRaw), does the diffraction limit change to f11 (like 20d which is 8MP). If so, I don't see the point why people are complaining about too many MP for 7D.

--
Gallery: http://www.mizzou.edu/~pz797

A lot of this anguishing over diffraction is due to semantics and not what happens on the photographs we take. People see the word "limit" and think that there is some sort of barrier they must not go beyond. Photographs which win international competitions, that sell well, are highly commended etc, etc - are often taken at apertures well within the so called diffraction limited zone. So it is baffling that photographers who are much less successful anguish over taking photographs in the diffraction limited zone, when successful photographers understand that all photographic settings are compromises, understand what happens, and then take successful photographs well past the misnamed diffraction limit.

All diffraction limited actually means is the aperture size where resolution is no longer limited by the design and efficiency of the lens, but by the physical properties of light passing through this aperture. Your camera doesn't suddenly explode when you pass this "limit" and even quite large print sizes don't just disappear into soft mush.

When people anguish over the diffraction limiting of the resolution in their images it is not normally on the basis of their photographs actually appearing soft, but because of some abstact concept that says they shouldn't do it. There is also a failure to understand the visual information in a photograph. The theoretical maximum resolution a lens camera is capable of only exists on the plane of focus. Away from this plane of focus this resolution rapidly drops off. Most detail within the so called depth of field is well below the theoretical maximum resolution that lens/camera is capable of. So it is a bit irrational that people anguish about less than the theoretical maximum resolution that may happen when using a smaller aperture, but at the same time are quite happy with detail within the depth of field, even though it is similarly below this theoretical maximum resolution.

The simple fact is that even with 10megapixel resolution a DSLR with a good lens is capable of recording detail that you can't even see unless a very large print is made and you look closely, or if you view it at 100% on screen. Most of the detail that makes people say a photograph is sharp or detailed is actually far coarser than the very fine detail resolved at maximum resolution.

Biggis · Sep 19, 2009

SteB said:
When people anguish over the diffraction limiting of the resolution in their images it is not normally on the basis of their photographs actually appearing soft, but because of some abstact concept that says they shouldn't do it. There is also a failure to understand the visual information in a photograph. The theoretical maximum resolution a lens camera is capable of only exists on the plane of focus. Away from this plane of focus this resolution rapidly drops off. Most detail within the so called depth of field is well below the theoretical maximum resolution that lens/camera is capable of. So it is a bit irrational that people anguish about less than the theoretical maximum resolution that may happen when using a smaller aperture, but at the same time are quite happy with detail within the depth of field, even though it is similarly below this theoretical maximum resolution.

Well put !

I'll book mark this one and use it later, because this has been stated/argued/debated before and will probably come up again.

--

I NEED TO UNDERSTAND THAT DIFFRACTION IS NOT SENSOR DEPENDENT... IT IS A LENS ISSUE" ::::I NEED TO UNDERSTAND THAT DIFFRACTION IS NOT SENSOR DEPENDENT... IT IS A LENS ISSUE" ::::I NEED TO UNDERSTAND THAT DIFFRACTION IS NOT SENSOR DEPENDENT... IT IS A LENS ISSUE" ::::I NEED TO UNDERSTAND THAT DIFFRACTION IS NOT SENSOR DEPENDENT... IT IS A LENS ISSUE" ::::I NEED TO UNDERSTAND THAT DIFFRACTION IS NOT SENSOR DEPENDENT... IT IS A LENS ISSUE" ::::I NEED TO UNDERSTAND THAT DIFFRACTION IS NOT SENSOR DEPENDENT... IT IS A LENS ISSUE" ::::I NEED TO UNDERSTAND THAT DIFFRACTION IS NOT SENSOR DEPENDENT... IT IS A LENS ISSUE" ::::

eraserhead · Sep 19, 2009

ljfinger said:
Lee Jay said:

If so, I don't see the point why people are complaining about too many MP for 7D.

Click to expand...

Because they know no better

Lee Jay said:
Repeat after me. There are NO f-stops at which mRaw will out-resolve native raw.

In fact, this can be demonstrated quite easily using the DPR lens tests. Deep into the diffraction limited regime, all lenses essentially have the same resolving power. You can check this by looking at the DPR tests, pretty much all Canon lenses tested on the 1DsIII resolve 1125 lp/ph. Thus on an APS-C camera with a 14.9mm high sensor they should logically resolve 700 lp/ph. In fact, tested on the 450D, they resolve 750. The finer pixels of the 450D have picked out more resolution even when the lens is fully in its diffraction limited regime. The 7D will do even better.

eraserhead · Sep 19, 2009

pz797_mizzou said:
I'm planning to shoot it mostly in 9mp (mRaw),

I really can't see the point of mRaw. Replacing 18MP single colour pixels with 9MP three colour ones (actually they use YCbCr) and losing a whole load of resolution on the way doesn't seem to me to be a win.

Edit: Just seen that they save space by column interleaving the Cb and Cr values, that's even more information gone.

Redteg94 · Sep 19, 2009

eraserhead said:
pz797_mizzou said:

I'm planning to shoot it mostly in 9mp (mRaw),

Click to expand...

I really can't see the point of mRaw. Replacing 18MP single colour pixels with 9MP three colour ones (actually they use YCbCr) and losing a whole load of resolution on the way doesn't seem to me to be a win.

Edit: Just seen that they save space by column interleaving the Cb and Cr values, that's even more information gone.

Agreed, though it's nice for shooting sports as the RAW buffer goes up to 24 and 9MP is more than enough for the newspaper that publishes my shots: I usually send them photos resized to 1600 pixels on the long end and that already allows me to crop significantly from 10MP, which I rarely do. mRAW will also save some card space, which is nice in this case as I sometimes shoot 400-500 images per soccer, hockey or football game.

In all other instances, I'm anxious to be able to use the full 18MP.

--
-Scott
http://www.flickr.com/photos/redteg94/

Clem Nichols · Sep 19, 2009

Is there something about a macro lens that somehow limits the effects of diffraction? I've seen many razor sharp macro images made at f30 or higher.
--
CN

Karl Gnter Wnsch · Sep 19, 2009

Clem Nichols said:
Is there something about a macro lens that somehow limits the effects of diffraction? I've seen many razor sharp macro images made at f30 or higher.

Watch it, probably those shots were taken with Nikon cameras as they report the effective aperture (factoring in extension) while the nominal aperture (as reported by Canon cameras) is the key factor for diffraction. So while you as a Canon user might use f/10 at 1:1 for a given DOF a Nikon camera would report f/20 instead for the exact same shot...

--
regards
Karl Günter Wünsch
Visit my gallery at
http://www.fotocommunity.de/pc/pc/mypics/461808

Lee Jay · Sep 19, 2009

Karl Gnter Wnsch said:
Clem Nichols said:

Is there something about a macro lens that somehow limits the effects of diffraction? I've seen many razor sharp macro images made at f30 or higher.

Click to expand...

Watch it, probably those shots were taken with Nikon cameras as they report the effective aperture (factoring in extension) while the nominal aperture (as reported by Canon cameras) is the key factor for diffraction. So while you as a Canon user might use f/10 at 1:1 for a given DOF a Nikon camera would report f/20 instead for the exact same shot...

I doubt that's it.

Does this look sharp? It's miles and miles past the diffraction-limited boundary.

--
Lee Jay
(see profile for equipment)

Biggis · Sep 19, 2009

Clem Nichols said:
Is there something about a macro lens that somehow limits the effects of diffraction? I've seen many razor sharp macro images made at f30 or higher.
--
CN

Besides what previous poster said (I don't know about how Nikon reports aperure), you should be aware that different formats (APS/FF/MF/LF) are affected differently by diffraction.

A 'razor sharp' picture doesn't really say if there is diffraction or not.... you have to enlarge the picture quite a lot to see this effect. Thumbnails seem razor sharp most of the times.

Larger formats are not enlarged as much as a smaller format if the output (print size) is the same. That is also why you can see diffraction on a high mega pixel camera but not on a lower MP camera (when e.g. viewed at 100%)

--
BigGis

woof woof · Sep 19, 2009

Does this look sharp?

No. Sorry.

woof woof · Sep 19, 2009

Why not wait until the 7D is in the shops, go and use one and look at the results. Then you can decide if it's right for you or not.

Question about diffraction limit

Well-known member

Senior Member

Veteran Member

Forum Pro

Senior Member

Veteran Member

Forum Pro

Forum Pro

Leading Member

Senior Member

Forum Enthusiast

Well-known member

Well-known member

Senior Member

Leading Member

Forum Pro

Forum Pro

Forum Enthusiast

Senior Member

Senior Member

Similar threads

Keyboard shortcuts