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Author Topic: Diffraction limitation in 35mm lenses.  (Read 20601 times)
kenstrain
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« Reply #20 on: January 16, 2006, 01:12:51 PM »
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Oh no! lets not go there again     Who wants to change format in this thread? Note it says "35mm lenses".  The "format" issue was done to death elsewhere on this forum recently.  Summary: it depends what question you ask what answer you get (even if the answer is right).

Ken

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To put it another way, you can use smaller F stops on MF gear, before diffraction starts to degrade the image quality.

Leif
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Ray
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« Reply #21 on: January 16, 2006, 08:18:26 PM »
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Diffraction is a non varible property. In otherwords, it is the lens opening not the f number responsible. A 100mm lens at f8 has the same amount of image degrading diffraction that a 50mm lens does at f 5.6 or a 200mm lens does at f11. It is a property decided by the lens opening.

DrGary
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That might be true, but there are a few other variables missing from your statement that make it incomplete. F stop is related to both the physical opening and the focal length; field of view is related to distance from the subject; diffraction spot size on the film or sensor is related to the sensor's format.

All my comparisons were done with the same focal length; the same distance to subject; the same FoV and the same format (35mm). The only variable was the f stop or opening which can correctly be described either way, ie. diffraction spot size is inversely proportiona to f stop, or to  give a concrete expample, the diffraction spot size at f16 is double the diffraction spot size at f8, all else being equal, which it was.
 
I think Peter has hit the nail on the head by bringing in the issue of pixel pitch. That's why I think the 1Ds2 should theoretically reveal more resolution difference between f8 and f16 with any good lens. It has supposedly greater resolving power than the 5D, although I notice that this issue seems to be hotly debated on other forums by people who own both the 5D and 1Ds2, the explanation being that the 1Ds2 has a stronger AA filter, although why it should need a stronger AA filter beats me.

I've been following the LL forum since Michael produced his controversial review of the Canon D30 several years ago and I remember well all the whinging and complaining that went on in those early forums about the D30 not being full frame.

It seems clear now, if the D30 had been full frame, maximum resolution would have been achieved at f22, with any 35mm lens no matter how good, and people like me would probably have been observing that there didn't seem to be any significant resolution difference between f22 and f32   .
« Last Edit: January 16, 2006, 11:38:11 PM by Ray » Logged
crspe
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« Reply #22 on: January 17, 2006, 04:00:08 AM »
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Diffraction is a non varible property. In otherwords, it is the lens opening not the f number responsible. A 100mm lens at f8 has the same amount of image degrading diffraction that a 50mm lens does at f 5.6 or a 200mm lens does at f11. It is a property decided by the lens opening.

DrGary
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[span style=\'font-size:21pt;line-height:100%\']NO!!![/span]
Image degrading diffraction depends only on f-stop. it does not depend on focal length.

This is a common mistake.  What is correct is that the angle of diffraction is proportional to the lens opening (i.e. at constant f-stop, longer lenses have a lower angle of diffraction due to the larger lens opening), but for the longer lenses, the diffraction starts further away and the lower angle of diffraction spreads out over the longer distance. These 2 exactly cancel out, resulting in the fact that degrading diffraction is proportional only to f-stop.

From the lens FAQ: "All lenses are diffraction limited to no more than about 1500/N to 1800/N line pairs per mm". Where N is the f-Number. Note that the focal length is not a part of this formula.

See this site for a detailed description:
[a href=\"http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm#]http://www.cambridgeincolour.com/tutorials...hotography.htm#[/url]
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Ray
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« Reply #23 on: January 17, 2006, 07:34:01 AM »
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[span style=\'font-size:21pt;line-height:100%\']NO!!![/span]
Image degrading diffraction depends only on f-stop. it does not depend on focal length.

See this site for a detailed description:
http://www.cambridgeincolour.com/tutorials...hotography.htm#
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I've got a sense of dejavu here.    You are technically correct if you define an image as a unit of area, such as square mm or square inch and don't concern yourself with the actual picture or the full image.

To understand this, you have to understand the distinction between absolute resolution and picture resolution. The formula 1500-1800/ f stop (n) does not tell you how much an image (picture with height and width) is degraded. It tells you what the absolute diffraction limited resolution will be in terms of line pairs per mm on the image. If you don't know what the field of view (FoV) is, you don't know what the picture is. If you are not concerned with the FoV, the actual picture or full image, or the size of the sensor (or format of the camera), then yes, you are right.

To take a concrete example, a 400mm lens at f45 will produce a diffraction spot size (Airy disk) that is inversely proportional in diameter to the f stop. The resolution limit in line pairs per mm will be determined by the Rayleigh's formula 1500/ f stop (for green light). That applies to all lenses irrespective of focal length, but only in regard to that unit area of image. Such statements have to be qualified.

For example, if I attach that 400mm lens to a 35mm camera, the image will be severely degraded by diffraction. If I attach the lens to an 8x10 field camera, I think most people would be very impressed with the over all sharpness of the image. But they will be different images.  The 35mm image would be a small crop or subset of the larger image. It makes a difference to the photographer. I never use f45 on my 100-400 IS zoom (it does have an f45). LF photographers use f45 frequently, producing images much sharper than any image from 35mm at any f stop.

I usually find I have an afterthought with pieces such as this. Here's something to consider. If image degrading diffraction depends only on f stop, then how is it that f stop is a relationship between the physical lens opening and focal length?

Aperture Diameter= Focal length/f stop;  F stop = Focal length/aperture diameter. Rayleigh's derived formula for diffraction resolution limits, ie. 1500/ f stop, could also be expressed as 1500 x Aperture Diam/ focal length (all in mm).
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Tim Gray
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« Reply #24 on: January 17, 2006, 10:46:28 AM »
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When doing the thought expirement of moving a 400mm lens from one format to another, what impact is there on the image circle the lens is designed for?  When you put an ef-s lens on a ff canon, you just get vignetting, not a wider fov.
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Slough
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« Reply #25 on: January 17, 2006, 02:05:14 PM »
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Unless I've misinterpreted what has been written, I disagree with what has been said. In the absence of aberrations, the resolution of a lens is defined by the aperture. Such a lens is said to be diffraction limited, and some high end and very expensive astronomical refractors are not far off being diffraction limited. The larger the aperture, the higher the resolution. That is one reason astronomers always want bigger telescopes. The other reason is of course to collect more light.

In practice few lenses are diffraction limited, especially camera lenses, and aberrations (coma, CA, spherical aberration, field curvature, astigmatism, and others ?) reduce the resolution.

Anyway, a diaphragm acts as a stop in the system, and introducing a stop is equivalent to reducing the diameter of the objective, for example by masking it off.

So an 600mm F5 lens has a higher diffraction limited resolution than a 200mm F5 lens. So if we were to photograph the same image at the same distance with both lenses, the longer lens would show finer details but would only show a crop of the image in the shorder lens.

However, the 600mm lens will magnify the image more than the 200mm lens. So if you were to photograph an image using both lenses, but move closer when using the 200mm lens so as to get the same image size, which lens would show more detail in the image? I suspect the amount of detail (lines per millimetre) would be the same. Is that the point that is being made in the preceding posts? I suppose that way of looking at it makes sense for photographers, but is very confusing for skywatchers.

And of course a medium format camera has a larger image circle to confuse matter more. (With apologies to Kenstrain who gets the heeby jeebies at the mention of other formats.)

Leif
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kenstrain
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« Reply #26 on: January 17, 2006, 03:04:17 PM »
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"I disagree with what has been said."
All of it or just a little?    

Let me disagree with much of what you said, but not all (I did not read it all).

"In practice few lenses are diffraction limited, especially camera lenses"
except at, for example, f22 when most are, very strongly, for 35mm lenses anyway.

"Anyway, a diaphragm acts as a stop in the system"
hence the phrase "stopping down" meaning to close the aperture, and the unit of f-stops too.  This is not a revelation.

"So an 600mm F5 lens has a higher diffraction limited resolution than a 200mm F5 lens. "  

I can't believe you wrote that!

Not in the conventional definition of the terms you are using.   If you want to redefine it that way you will have to understand that some others will not know what you are talking about.

Anyway by a conventional definition ....
Resolution indicates the finest detail measurable at the focal plane.  Diffraction limits the resolution of your example LENSES to about 1600/5  = 320 lp/mm approximately (lenses focussed at infinity, white light, uncoloured images, at some particular choice of contrast).  The formula was given in a post above.  

Formulae, with suitable definitions of the variables and parameters tell us all we need to know here.  Of course it is hard to find lenses that are diffraction-limited at f5 (for 35mm format).

There is no need to invoke focal length or image size or format size or time of day or any other irrelevant quantities in this discussion.

I decided not to read the following paragraphs of your post, but spotted my user name at the end....

"With apologies to Kenstrain who gets the heeby jeebies at the mention of other formats."  

Apologies accepted, thank you.

BTW I think the OP reminded us of something very useful: THINK whether the sharpness over depth in the image will fit your needs for the image you are visualising.  Know your sensor resolution expressed as an equivalent f-number. Then you can decide when to trade overall sharpness for depth of field.  Now that is where focal length comes in (squared).  Of course ignore this if you take portaits at f1.4.

But hey - the useful stuff has already been said, unfortunately along with all the  waffle.

Norman Koren has some nice tutorials on the topic too, IIRC.

Take care

Ken
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Slough
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« Reply #27 on: January 17, 2006, 03:24:44 PM »
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ken

I found your original posting rather rude, but decided not to comment. My comment on you having the beeby jeebies was a light hearted attempt to deflect your aggression. Now your follow up is extremely unpleasant. If you have some sort of personal problem, then maybe you should sort it out rather than take it out on me.

I am familiar with some optical theory and I do know what I am talking about when it comes to resolution of optics (Dawes limit and all that) which is why I'm not going to discuss the technical content of your posting. What I will say is that there are one or two valid points in your posting and that they could have been made without being so obnoxious. Some of your comments suggest that you did not read my posting properly.

If someone with some manners cares to comment, then I will respond. I happen to find the postings in this thread - Ken's rude ones excepted - extremely interesting. These issues are not at all simple which is why I explained myself as clearly as possible at the risk of sounding condescending which was not my intention.

I thought my original postings were polite and reasonable. If others disagree, then maybe they could politely say so.

Leif

BTW Are you by any chance Ken Rockwell? I'm trying to think why you would be so aggressive.
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kenstrain
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« Reply #28 on: January 17, 2006, 04:33:55 PM »
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Dear Leif,

may I sincerely apologise for the offense that I have caused, without reserve.  Please accept that I did not indend to be rude in the way which my second message clearly came over to you.  It is neither my habit nor my will to do so.  
Actually it horrifies me that I could be thought of as being rude in that way to the extent which you state. I am truely very sorry about that.  

As explanation: I was trying to be a little bit light hearted in the face of what I sincerely believe to be incorrect information that was posted.  I do not like to see, what I believe to be, errors being perpetuated.  I read the parts of your post I commented on very carefully before replying.  

When I saw your reference to heeby jeebies I assumed that you were also being lighthearted about it, and never guessed your ire at my first post, or I would not have continued.  I also thought my posts were both inoffensive, if perhaps with a slightly exasperated tone in the second one, but I clearly misjudged that.  There was no aggression in the first post, if my language conveyed such that was utterly unintentional.

I am, in fact Ken Strain, and although that is not my full name, it is my only one, so please accept the apology as personal.

Ken



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ken

I found your original posting rather rude, but decided not to comment. My comment on you having the beeby jeebies was a light hearted attempt to deflect your aggression. Now your follow up is extremely unpleasant. If you have some sort of personal problem, then maybe you should sort it out rather than take it out on me.

I am familiar with some optical theory and I do know what I am talking about when it comes to resolution of optics (Dawes limit and all that) which is why I'm not going to discuss the technical content of your posting. What I will say is that there are one or two valid points in your posting and that they could have been made without being so obnoxious. Some of your comments suggest that you did not read my posting properly.

If someone with some manners cares to comment, then I will respond. I happen to find the postings in this thread - Ken's rude ones excepted - extremely interesting. These issues are not at all simple which is why I explained myself as clearly as possible at the risk of sounding condescending which was not my intention.

I thought my original postings were polite and reasonable. If others disagree, then maybe they could politely say so.

Leif

BTW Are you by any chance Ken Rockwell? I'm trying to think why you would be so aggressive.
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Ray
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« Reply #29 on: January 17, 2006, 05:11:49 PM »
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When doing the thought expirement of moving a 400mm lens from one format to another, what impact is there on the image circle the lens is designed for?  When you put an ef-s lens on a ff canon, you just get vignetting, not a wider fov.
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Tim,
That's a good question. The image circle is enlarged as one stops down but it's doubtful whether any 400mm lens designed for 35mm could be stopped down sufficiently to avoid serious vignetting on a large format camera. This is the sort of question I think BJL could answer.

However, as regards the thought experiment, if there's a problem moving a 35mm lens to a larger format then one would simply use the lens designed for the larger format and transfer that to the smaller format.
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LeifG
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« Reply #30 on: January 18, 2006, 01:54:37 AM »
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Hi Ken: Thanks for the response. Okay, I accept that you were not trying to be rude.  

I did not understand the quote that "Image degrading diffraction depends only on f-stop." because it goes against what I know about optics. I understand the effective aperture to be the deciding factor as far as diffraction limited resolution goes i.e. the upper limit to resolution from an optic.

You are of course correct that few photographic lenses are diffraction limited unless stopped down below ~F22. Hence this is largely an academic discussion.

Regarding stopping down, it is certainly not obvious to me. Did you know that the human eye acts as a stop on a binocular, and hence in 'good light' there no light gathering advantage to an 8x binocular with a larger objective than about 20mm?

BTW When I refer to a 600mm F5 lens, what I mean is a 600mm lens, stopped down to F5.

Leif
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pcox
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« Reply #31 on: January 18, 2006, 05:08:50 AM »
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Having got out my college physics book, I will now prove that focal length does not affect resolution loss due to diffraction. *drum roll*

Now, we know that diffraction creates these 'Airy disks' which look like bulls-eyes - a central dot surrounded by concentric rings. The smaller the aperture, the bigger this central dot becomes - this is as described in http://www.cambridgeincolour.com/tutorials...photography.htm, to wit:

Quote
When the diameter of the airy disk's central peak becomes large relative to the pixel size in the camera (or maximum tolerable circle of confusion), it begins to have a visual impact on the image.  Alternatively, if two airy disks become any closer than half their width they are also no longer resolvable (Rayleigh criterion).

Some images may help, hopefully he won't mind me linking them here:

Airy disk in 2D


Airy disk in 3D


In order to figure out the maximum resolution of a lens, we figure out the angular separation of two points which are barely resolved - which for the purposes of this exercise will be two points whose central dots are just touching edge-to-edge - this will be the same as the angular size of either central peak.

The equation to figure this out is:

sinθ = 1.22(λ/D)

Where θ is the angular separation, λ is the wavelength of light (considered a constant in this exercise, and set at 500nm) and D is the aperture diameter.

For simplicity's sake, we'll make sinθ just plain old θ, as θ is so small in any real world scenario to make the difference negligible. That gives us:

θ = 1.22(λ/D)

Now, the experiment: We take two lenses, of 50mm and 100mm focal lengths, and set their apertures to f/2. Take a picture of an object 10 meters away with the 100mm lens, and one of an object 5 meters away with the 50mm lens. We'll take the wavelength of light to be 500nm as a constant.

We do this because for this experiment to be valid, the size of the image on the negative/sensor must be the same for both lenses. Since a 100mm lens gives 2x the magnification of a 50mm lens, we stand back twice the distance with the 100mm lens.

For the 50mm lens, D, the aperture diameter is 50/2 = 25mm.
This gives us:

θ = 1.22(500x10⁻⁹/25x10⁻³)
so...
θ = 2.44x10⁻⁵ rad

For the 100mm lens, D, the aperture diameter is 100/2 = 50mm.
This gives us:

θ = 1.22(500x10⁻⁹/50x10⁻³)
so...
θ = 1.22x10⁻⁵ rad

So, what does that tell us? It tells us that the Airy disk of the 100mm lens is half the angular size of that of the 50mm lens. This is critical to understanding why focal length doesn't matter in terms of diffraction. Longer lenses produce a narrower 'beam' of diffracted light - remember, the number above is in 'rad', so it's an angle, not a distance.

Even though the diffracted light has to travel further to reach the film/sensor in the 100mm lens than the 50mm lens, it's spreading out much more slowly. By the time it reaches the film/sensor it will produce a spot of light exactly as large as the 50mm lens does.

Now to prove this concretely, we want to measure what that means in terms of resolution. To do this, we want to measure the minimum distance between two points on an object that can be resolved with both lenses at the distances and aperture given.

From basic optics:
y/s = y'/s'

Where y is the separation of the points on the object, y' is the separation of the corresponding points on the film/sensor, s is the distance from lens to object and s' is the distance from lens to film/sensor.

Thus the angular separations of the object points and the corresponding image points are both equal to θ, so we get:

y/s = θ
and
y'/s' = θ

Because s is greater than the focal length of the lens, the image distance s' is approximately equal to the focal length.

For the 50mm lens, s = 5m, s' = 50mm and θ = 2.44x10⁻⁵ rad:

y/5m = 2.44x10⁻⁵
so...
y = 1.22x10⁻⁴m = 0.122mm
and
y'/50mm = 2.44x10⁻⁵
so...
y' = 1.22x10⁻³mm = 0.00122mm

For the 100mm lens, s = 10m, s' = 100mm and θ = 1.22x10⁻⁵ rad:

y/10m = 1.22x10⁻⁵
so...
y = 1.22x10⁻⁴m = 0.122mm
and
y'/100mm = 1.22x10⁻⁵
so...
y' = 1.2x10⁻³mm = 0.00122mm

Phew! So, where does that leave us? Both lenses can resolve a minimum distance of .122mm on an object, which translates to a minimum resolvable dot on the film/sensor of .00122mm at those distances and an aperture of f/2. If we change the aperture, we will get different numbers, but the important thing is that they are the same for both lenses - so we've just proved that for the same image size and the same aperture, but different focal lengths, resolution is identical.

Again, the reason for this is that the longer lens produces a narrower cone of diffraction, so even though the light has to travel further to get to the film/sensor, it ends up producing the same size spot of light in both cases.

Thus, focal length does not contribute to resolution loss from diffraction.

Cheers,
Peter
« Last Edit: January 18, 2006, 06:32:18 AM by pcox » Logged

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« Reply #32 on: January 18, 2006, 12:34:34 PM »
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I've partially read through this thread with mild interest - and feel slightly as though I may have just grown a pocket protector and found tape on my glasses.    I am curious about a couple things though...

I tend to be someone who simplifies things into general principles rather than understanding the theory behind them. So far, Peter (and others) have done a good job establishing that when you are dealing with a single format (35mm) the diffraction limitation remains at equivalent apertures (for any given framing/picture) regardless of whether you use a telephoto lens or a wide lens.

My question is - If you take the same picture (equivalent image framing) with a smaller format camera (a pocket digicam) and with a large format camera (4x5), will you run into the diffraction limits at equivalent apertures? I've always been under the impression that small format cameras were more sensitive to diffraction than the larger formate cameras (hence why none of the pocket digicams goes above f/8 and LF goes to f/64). I'm also only interested in the resolving power at the focal plane in the image - not how many lp/mm fit onto the film itself.

Is there anyone who could clarify this issue?
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« Reply #33 on: January 18, 2006, 02:58:17 PM »
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Sheldon -
It's basically a question of enlargement. If you look at a 35mm slide on a lightbox with the naked eye, you wouldn't be able to see any resolution loss due to diffraction. Blow the image up 20 times though, and it'll be easy to see.

Same for a 4x5 transparency - look at it on the lightbox without a loupe and you won't see diffraction problems either. Blow it up 20 times and you will.

The difference is that the 35mm frame needs to be enlarged just about 4 times to be approximately the same size as the 4x5 - that's why if you look at a 4x6 print from a 4x5 frame, and compare it with a 4x6 print from a 35mm frame the 4x5 print blows it away. Along with the fact that the 4x5 frame recorded a boatload more detail, you're also not enlarging the diffraction effects.

So diffraction effects are identical on all formats, it's just not as obvious because of the different enlargement requirements. That's why you can get away with f/64 on large format. Which is just as well, because since large format uses longer lenses, and long lenses have shallower perceived depth of field at the same aperture than shorter lenses, you need smaller apertures to increase your depth of field.

Hope that helps.

Cheers,
Peter

Quote
I've partially read through this thread with mild interest - and feel slightly as though I may have just grown a pocket protector and found tape on my glasses.    I am curious about a couple things though...

I tend to be someone who simplifies things into general principles rather than understanding the theory behind them. So far, Peter (and others) have done a good job establishing that when you are dealing with a single format (35mm) the diffraction limitation remains at equivalent apertures (for any given framing/picture) regardless of whether you use a telephoto lens or a wide lens.

My question is - If you take the same picture (equivalent image framing) with a smaller format camera (a pocket digicam) and with a large format camera (4x5), will you run into the diffraction limits at equivalent apertures? I've always been under the impression that small format cameras were more sensitive to diffraction than the larger formate cameras (hence why none of the pocket digicams goes above f/8 and LF goes to f/64). I'm also only interested in the resolving power at the focal plane in the image - not how many lp/mm fit onto the film itself.

Is there anyone who could clarify this issue?
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« Reply #34 on: January 18, 2006, 05:40:34 PM »
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It's basically a question of enlargement. If you look at a 35mm slide on a lightbox with the naked eye, you wouldn't be able to see any resolution loss due to diffraction. Blow the image up 20 times though, and it'll be easy to see.

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On the other hand, if we are using digital cameras, the enlargement depends on the number of pixels, not the size of the sensor. An 8mp camera produces the same size image whatever the format of the camera (assuming same aspect ratio). So we are back to pixel pitch as a significant factor in determining the point where diffraction kicks in to degrade 'image' quality.

As I see it, it all boils down to a semantic confusion of terms. The statement, 'the degree to which diffraction degrades an image is dependent only on f stop' is in fact poorly expressed. There's an ambiguity in the meaning of the word 'image'. Are we talking about the whole image, ie. a picture, or are we talking about a unit area of that image or picture?
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« Reply #35 on: January 18, 2006, 05:58:48 PM »
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Ray -
You are correct. With digital cameras it gets tricky because every camera is different - pixel pitch, pixel count and sensor size are all variable. Still, it's easy enough to figure out a rule of thumb.

Bigger sensors will have less problems as a rule because they will (generally) have a bigger pixel pitch than a small sensor. Even if they have the same or smaller pixel pitch, diffraction will be an issue, but in that case, you have lots more pixels and you won't need to enlarge the image that much to get a good size print.

Michael would brand the lot of us as pixel peepers in this discussion. Personally, I'm not that bothered by the whole issue - I want sharp images, and I happen to know that for the 5D, the optimum aperture is f/16 due to its pixel pitch.

That being said, I still get a lot of unsharp images - misfocus, camera shake, tripod sinking in soft sand on long exposures, etc. Any of these problems creates an unusable photograph. An image that's less than optimally sharp due to diffraction is rarely an unusable photograph if it's compositionally good and otherwise technically good, however. So, to paraphrase someone or other - be happy in your photography!

I wanted to put this argument to bed because there were a lot of 'facts' being bandied about, and it had degenerated into a bit of a shouting match. So I read up on it and laid out the real deal. I enjoyed it - forgot how much I liked physics in college.

If only selling and marketing your work was as easily distilled!

Cheers,
Peter
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« Reply #36 on: January 18, 2006, 08:25:16 PM »
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Michael would brand the lot of us as pixel peepers in this discussion. Personally, I'm not that bothered by the whole issue - I want sharp images, and I happen to know that for the 5D, the optimum aperture is f/16 due to its pixel pitch.

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Peter,
If the above statement is true (and my tests with the 24-105 zoom imply that it is true) it causes me to re-evaluate so many statements I've seen on this forum from 1Ds owners since the introduction of that camera. It almost became a mantra that any shortfalls in the quality of 1Ds images were due to lens deficiencies. This camera needs the finest lenses, I read time and again.

Some folks even went so far as to claim there would be no point in increasing pixel count in a future upgrade, because the 1Ds is as good as it gets and that without an upgrade to Canon's entire range of lenses there would be no point.

I don't recall reading once, from any source, that at least part of the problem might be due to the fact that the pixel pitch of the 1Ds does not allow it to capture any more detail than any good lens can provide at f16. I guess such comments would have been considered too negative.

But before I get jumped on, I will concede that a marginal increase in contrast is apparent at smaller f stops than f16. The contrast difference between f11 and f16 is just too marginal to be concerned about. Likewise between f8 and f11. But jump two stops and you have a difference which doesn't necessarily translate to more detail but does result in slightly better defined detail, or slightly more contrasty detail.
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« Reply #37 on: January 19, 2006, 04:00:16 AM »
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Peter,
If the above statement is true (and my tests with the 24-105 zoom imply that it is true) it causes me to re-evaluate so many statements I've seen on this forum from 1Ds owners since the introduction of that camera. It almost became a mantra that any shortfalls in the quality of 1Ds images were due to lens deficiencies. This camera needs the finest lenses, I read time and again.

Well, the 1Ds (mark II) has a smaller pixel pitch than the 5D, so somewhere between f/11 and f/16 you'll see the 'optimum' quality. The fact that it needs the finest lenses is true - we're getting to the point now where these cameras can outresolve all but the finest glass, and they will show up problems that have remained hidden even to film users before.

Even with this, the statement that you'll see the best quality at f/stop x is true, regardless of other problems. I know of no lens that gets worse in sharpness as you stop down, so you'll always get the best sharpness a lens has to offer by stopping down to the point just before diffraction becomes evident. It's just that with many lenses the optimum sharpness isn't as good as it could be, but it didn't matter in the past because the camera bodies didn't have the resolution to show the problems.

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Some folks even went so far as to claim there would be no point in increasing pixel count in a future upgrade, because the 1Ds is as good as it gets and that without an upgrade to Canon's entire range of lenses there would be no point.

There is something to this. At this point, I'd prefer to see an upgrade to Canon's wide-angle selection of lenses (which as a rule are nowhere near as good as they could be) than a - say - 20mp body. I suspect we'll get the camera before the lenses though, as I imagine it's easier to cram more pixels onto a sensor than it is to engineer glass to the tolerances now required and sell it at a $1500-ish price point.

That being said, it's always possible to take some of the excellent lenses out there on the market at the moment for other mounts and use them on the Canon bodies. You'll lose autofocus and auto-exposure on most of them, but the results can be pretty stunning if used properly

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I don't recall reading once, from any source, that at least part of the problem might be due to the fact that the pixel pitch of the 1Ds does not allow it to capture any more detail than any good lens can provide at f16. I guess such comments would have been considered too negative.

At f/x (where x is the optimum aperture), both the 1Ds mkII and the 5D capture bloody good detail with a good lens - certainly enough that vast numbers of photographers that used medium format film are abandoning it in favour of these bodies. Those that can't afford to go to medium format digital, anyway - which is most of us =)

If you really want excellent near-far sharpness in your photos - the sort that requires f/22 or higher for enough depth of field in an SLR - a view camera is what you need. Then you can tilt the plane of focus and achieve effectively infinite depth of field without having to worry about diffraction effects (yes, they're there, but as discussed earlier they're not nearly as much of an issue).

Cheers,
Peter
« Last Edit: January 19, 2006, 04:07:30 AM by pcox » Logged

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Ray
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« Reply #38 on: January 19, 2006, 10:47:32 AM »
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The fact that it needs the finest lenses is true - we're getting to the point now where these cameras can outresolve all but the finest glass, and they will show up problems that have remained hidden even to film users before.


Peter,
This is the paradox I'm referring to. A camera like the 5D and 1Ds might show up problems that were (previously) partly disguised by film grain, but I'm very dubious about this notion that these cameras can 'outresolve' all but the finest glass.  I would say these cameras can only outresolve mediocre lenses, lenses at the edges and cheap lenses at maximum aperture.

I've never seen an MTF chart of a 35mm lens at f16, and the reason no-one is producing them, I'm led to believe, is that all lenses (bar very cheap ones) would have a very similar performance at this f stop.
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« Reply #39 on: January 19, 2006, 02:31:27 PM »
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Ray -
I'll allow that the statement about the 5D or 1Ds outresolving lenses might have been a bit hyperbolic. However, I wasn't talking about at f/16 (although edge performance on some of Canon's wide angles does seem to be lacking at small apertures). Whereas before you could get away with relatively large apertures on less-than-world-class glass, now you really do have to stop down to get to the good stuff.

I don't really see a paradox here - there are just a lot of factors that contribute to image quality. The system is only as good as its weakest link, and the sensor - which has for so long been the weakest link in high-end digital photograhy - is now not necessarily so.

Cheers,
Peter

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Peter,
This is the paradox I'm referring to. A camera like the 5D and 1Ds might show up problems that were (previously) partly disguised by film grain, but I'm very dubious about this notion that these cameras can 'outresolve' all but the finest glass.  I would say these cameras can only outresolve mediocre lenses, lenses at the edges and cheap lenses at maximum aperture.

I've never seen an MTF chart of a 35mm lens at f16, and the reason no-one is producing them, I'm led to believe, is that all lenses (bar very cheap ones) would have a very similar performance at this f stop.
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