Interesting thread on MF forum. Here is an excerpt:

Thread Location:
http://luminous-landscape.com/forum/index....ic=26025&st=160

Excerpt:

http://www.openphotographyforums.com/forum...p?t=6103&page=3

See reply 23
It's an extreme sample, but sort like stories have been appearing on several sites.
I tested a 1DsIII a while ago and also found that f11 was noticable softer that f8 and this was with a 70-200 f2.8 L IS.
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Frank,
Makes sense to me. When I moved from the 8mp 20D to the 5D, I was surprised I could use F16 with minimal loss of resolution with the 5D. With the 20D I would hesitate to stop down beyond F8 because I knew there would be a trade-off. I'd be sacrificing sharpness for the benefit of additional DoF.

The 1Ds3 has similar pixel density to the 20D. Resolution (ie. lp/mm) does not care about sensor size, only pixel density or pixel pitch. The same principles that apply to the 20D will apply to the 1Ds3. Softening of the image will appear at the same F stops using the same lens.

Effect of diffraction in combo with pixel density?

It's just the matter of diffraction.

In perfect, diffraction-limited lens, using ideal values for the Rayleigh limit, and applying the contrast theory of Kühler, resolution for the average wavelength of light (0,555 micron) is:

Aperture resolution
1,4 550 lp/mm
2,0 385 lp/mm
2,8 263 lp/mm
4,0 185 lp/mm
5,6 135 lp/mm
8,0 94 lp/mm
11 69 lp/mm
16 48 lp/mm
22 30 lp/mm
32 21 lp/mm

So theoretically, in case of 1Ds3 sensor (which resolution is 78 lp/mm), diffraction should affect image quality for apretures smaller than f8.

Just for anyone unaware of this topic, you can read about it here:
http://www.cambridgeincolour.com/tutorials...photography.htm

Given the above quote, the "practical" diffraction is dependent upon print size or monitor size and distance viewed from image. So you could use f16 and get an image where your eyes cannot see the diffraction, such as shooting a 1ds3 at f16 and printing it in a magazine at 4x6 inches (or whatever size cancels the eye perceiving the diffraction). From my experience, and from reading, the sweet spot is virtually always between around 5.6 and 11, and most full frame cameras, and maybe even MF (If I recall correctly) is around f8--please correct if wrong. It's just what I remember and what I go by.

Since most people here are interested in landscapes, this would mean figuring out from the above link what your camera's best aperture is, and using it when you can, where "when you can" is the operative phrase. For instance, if you're aiming at the ground 3 feet in front of you and you want the ground and background mountains crisp, you won't be using f8 at 30mm (It may not happen whatever you do, but you get my point).

Diffraction simply means, for practical application, that you will be getting a softer image, all things being equal, which they are not.
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The reason I started this thread is because I am interested in what people had to say about diffraction issues and the comparison between the 20D, 5D, and 1DS MKIII. The reason I am interested in this topic is because I do a little product photography, and the higher the f stop the better when rendering an entire product in focus. If the above is true, then I'm wondering if the 5D would be a better camera for product photography than the 1DS3 in the studio, where DoF and sharpness are most important, in respect to print size and detail quality?

I just wanted to be clear about what I was thinking on this topic and what my interest is for posting it.

Yes, 5d is a better camera for product image, I can work with 16 aperture on 5d, 1dsIII is only until 11 or 8, as for crisp image with small apertures - 5d or even full frame with 6mp like light Phase

Doesn't this all depend on out put size and not 100% screen viewing for lpm? I mean smaller denser pixel count ceases to be denser if it has to be stretched further right? Same with D of F.
Just my feeling, I stopped worrying about the mathematics of photography when I stopped accounting for bellows extension.

Kevin.

VERY WELL SAID.

Not really: for equal sized prints at f/16 (or any aperture) the 1DsIII will give sharper images: equal diffraction effects (l/mm), higher sensor resolution (l/mm).

Diffraction merely limits the improvement in resolution that you get at a given f-stop from an increase in sensor resolution, it never decreases resolution or sharpness in any real sense like "lines per mm", in either the image recorded by the sensor at the focal plane or on prints of equal size.

Bingo. If you're always shooting at f/22 the 1DsMk3 may not provide any resolution advantage in actual output, but to think that it will actually be worse than the 5D makes no sense.

Wouldn't a 90mm TS-E lens solve whatever DoF issues there might be in dealing with the diffraction of the 1Ds3? A 1Ds3 + 90mm TS-E for product shots seems like the best of all worlds.

CHeers!

This website has produced or referenced a considerable amount of material on these issues recently. For example you may wish to have a look at my recent contribution:Noise About Noise. While this was in the works, Michael published: Martinec; and also see more recently Osuna and Garcia

The diffraction effect of narrow apertures is a lens issue and completely separate from the resolution of a sensor. As for the latter, yes the 1Dsmk3 has smaller photosites than a 1Ds or 5d, but the image detail using the same lens and the same f/stop is AT LEAST as good, as far as I can see from all the testing I've done.

BJL,
Could you provide further explanation for this point of view.

If we accept that at F16 all good 35mm lenses are very substantially diffraction limited (it wouldn't be too inaccurate to state that all lenses are equal at F16), then it's clear, as you state, that diffraction at F16 will limit any improvement in resolution from an increase in sensor resolution.

Yet you also state that at F16 the 1Ds3 will still provide sharper images (than the 5D, for example) . I agree that a higher resolution sensor will never provide less resolution, whatever the F stop. However, that it might still provide more resolution despite this strong diffraction limitation at F16 is interesting.

Since I already have a bunch of Minolta lenses, there's a strong possibility I might buy the Sony 24mp A900 that will probably be shown at Photokina this year and available before the end of the year.

It would be interesting to see some comparisons at F16, between the 5D (or D3) and the 1Ds3. I suspect that any resolution advantage of the 1Ds3 at F16 would be insignificant at any print size, after appropriate interpolation and sharpening.

Go read a book on how MTF curves work. System MTF is the product of the MTFs of each component in the system, not the smallest individual component's value. If f/16 limits lens MTF to 50% at a given linear frequency, then increasing sensor MTF from 50% to 60% will still increase image MTF by 5%. There is obviously a principle of diminishing returns involved, but the amount of benefit from upgrading is non-zero. There's also other improvements in play (less noise, etc.) that make the degree of benefit more significant.

Which book do you recommend that deals with sensor MTF response? I've seen many MTF curves of film resolution in my time, but few of sensor resolution.

My impression is that sensor MTF does not fall off so rapidly as film does with increasing resolution, so the basic formula 1/S=1/F+1/L does not necessarilly apply. This is certainly the impression I get when viewing line charts I've shot to compare resolution. The lines remain strong and clear almost to the cut-off point.

However, if the sensor MTF of the 1Ds3 at 40 lp/mm is noticeably greater than that of the 5D or D3, then one would expect a marginally contrastier image from the 1Ds3 at F16.

On the other hand, since it is reported that the 5D has a weaker AA filter than the 1Ds3 and since the D3 has lower pixel noise than the 1Ds3, I'd like to see the comparisons. Seeing is believing.

Ray, "it is reported" by who? Someone who makes the filters? Someone who knows how to take them apart and appraise them? Someone who was told something by one of these parties?

How do you know the D3 has lower pixel noise than the 1Ds3? I'd be curious to know where this is reported? Much of this depends on exposure, as I demonstrated in my article on this website.

Please note I said MTF in general, not sensor MTF. Since there are multiple factors involved--lens, AA filter, sensor MTF, sensor noise, etc.--a comparison should look at all of them.

No need to read a book, only a little thought is required. The sensor can't resolve anything beyond Nyquist, so MTF must drop to essentially zero at that point; it resolves quite well any contrast variation of more than a few pixels in spatial wavelength, and so the sensor MTF will be a steeply decreasing function of spatial frequency starting from say 1/3 to 1/2 Nyquist, and which vanishes around Nyquist.

Thus, all other things being equal, an increase in sensor resolution (via decreasing pixel pitch) will result in the spatial scale corresponding to the Airy disk diameter being pushed further from Nyquist and thus increasing overall system MTF, since the sensor MTF ceases to be the weakest link in the chain. As Jonathan says, at some point the law of diminishing returns sets in, and further decrease in pixel pitch results in only marginal gains in system MTF, because the sensor MTF curve flattens out at about 1/3 to 1/2 Nyquist.

One can also probably formulate these notions in terms of a quantization error of spatial discretization of the signal, which would lead one to a quantitative formulation of sensor MTF. I'll have to think about that at some point...

So which camera will provide more detail at f16, the 5D or 1DS3?

I dunno; all other things are not equal (in particular the AA filter).

Mark,
I recall Michael commented on this after his initial appraisal of the 1Ds3. Some time later, Jack Flesher reported that he was surprised the 1Ds3 images required so much sharpening, more sharpening than the 5D and 1Ds2, and concluded that the 1Ds3 AA filter was unusually strong.

As regards the pixel noise of the D3, it would have to be less than that of the 1Ds3 otherwise Michael would not have been able to report that D3 images have lower noise than any other 35mm camera on the market.

I understand from Emil Martinec's article on noise that the greater number of 1Ds3 pixels compensates for the slightly higher noise of the individual 1Ds3 pixels so that the 1Ds3 image as a whole has about equal noise to the D3 image.

Jonathan, I too was curious about your commendation to read a book on this. There is tons of (free) material on the web about MTF insofar as it relates to lenses, and some but less on sensor resolution issues, but I guess much like Ray I haven't seen all this brought together from a systemic perspective in a book. But you apparently would think it has given your recommendation to Ray. So if you happen to know the title of a book which does this, it could be of more general interest to a number of us.

Doug, with all the factors involved (lens, scene, pixel pitch, sensor design, AA filter, firmware, blah, blah) I think it's an impossible question to answer without doing empirical tests. From the work I did, frankly I'd be surprised if there were "hit-you-in-the-faces" differences at f/16 using say a lens with maximum aperture of f/2 ~ f/5.6. The main advantage of the 21 MP sensor is the additional 35% or so resolution - nice elbow room for cropping when we can't fill the frame with the desired composition at capture.

Surely that would not make sense and would make having much higher pixel density pointless. I suspect that what the report means is that when images are viewed at 100%, the effect of the 1DsIII AA filter is stronger. That would make much more sense.

People tend to confuse viewing an image at 100%, and the appearance at a given print size.

Well, where do the results I reported in my Noise article stand in relation to these observations about D3 vs 1Ds3 noise? (Hint: "it depends"...............)

As well, you may recall Michael's first comment on the 1ds3 AA filter was not the last word on that matter.

As for Jack Flesher's observation about the amount of sharpening needed for 1Ds3 images - this of course is rather subjective so I'm not disputing Jack's findings - especially as he is referencing the 1DsMk2 which I haven't tested myself, but I find my 1Ds3 images sharpen just as well as my previous 1Ds images did using the default settings of PK Sharpener Pro - i.e. I haven't found myself wanting to increase the opacities of those sharpening layers for the 1Ds3. And I recall at the time the 1DsMk2 appeared, some users complained the images weren't quite as sharp as the old 1Ds images.................etc., etc..

Norman Koren discusses some of these factors in a tutorial on his web site. The classical additive reciprocal formula for combining MTFs works only at low contrast, around 10%, and does not apply to a more useful contrast such as 50%. If you had the MTF50s for the various components in a system, you couldn't just multiply the individual values to obtain the system MTF 50 since the individual component MTFs above and below 50% also affect the system response at 50%.

As Norman explains, you would need to perform a Fourier transform to separate the individual MTFs into the frequency domain and multiply these components. Having done this, you would then need to convert back to the spatial domain using a complicated process known as convolution. The process would be further complicated by the fact that the MTF of real lenses is different in the meridional and saggital planes.

In practice, it is simpler to determine the system MTF 50 by observation using such tools as Imatest. For 35mm style digital, many such results are posted on PhotoZone. For example, Klaus has tested the Zeiss 50 mm f/2.0 Makro-Planar lens on the Nikon D200.

This plot incorporates the test results and also shows the MTF 50 for an ideal lens as well as the Nyquist limit of the camera. Optimal MTF for this excellent lens is at f/4.0. For other lenses, the optimum may be at f/5.6 or even f/8. Beyond that, diffraction is the limiting factor.

Bill

Click to view attachment

I'm travelling in Northern Queensland at the moment, sheltering from the colder winter of Brisbane and taking a few photos. I'm using a 5D as my primary camera and the 40D as back-up. The 40D is also attached most of the time to my 100-400 zoom. At F8 it should provide sharper and more detailed results than my 5D when a 600mm lens is required with full frame.

If the 40D were full frame, it would be a 26mp camera with a slightly greater pixel count than the 1Ds3 and pretty close to the much anticipated Sony A900.

Since I have my eye on the 24mp Sony as a possible future purchase, I thought I would do a bit of testing and comparisons between the 5D and 40D whilst out shooting today.

I used the 100-400 at 400mm, the TS-E 90/2.8, the 50/1.4 and the Sigma 15-30, all at F16, and other apertures, and all at the same focal length and from the same position.

It's not looking good. My suspicions so far are confirmed. You can't get more resolution than the 5D at F16, no matter how many pixels, unless you increase sensor size, or remove the AA filter (perhaps).

The following scene was chosen for its low contrast. I upressed the 5D shot, cropped to the 40D FoV, to the same file size as the 40D. I applied no further sharpening after upressing. Both images were converted with mostly identical settings, default sharpening, 50 clarity, 30 vibrance, but I forgot to equalise WB.

I'm searching for any low contrast detail in the 40D image that is not present in the upressed 5D image. I can't find any, but it will take some time to work through all the comparison shots I took.

Here's the first comparison, at 400mm and F16.

Click to view attachment Click to view attachment

I'm working on an uncalibrated laptop, so apologies if the color sucks or the brightness/contrast is off.

Interesting - as you were writing (I think) I was looking at Imatest - some very interesting results there - though dated - still relevant to this discussion:

Imatest Results 1Ds, 1DsMk2, etc

Ray, from what you describe above it's not clear to me you are doing this, but in case you aren't, let me suggest you'd get more definitive answers to your testing doing things (both capture and post-capture) one variable at a time, all else equal, and using test scenes which have the kind of surface texture and edges allowing you to get a quite reliable visual impression of sharpness and resolution.

Also, there may be issues trying to infer the quality of a 24MP Sony image from a Canon D40 sensor as more factors than MP determine pixel quality. If you're not in a panic and you want to be sure you're making the right purchase, wait till the 24MP beast hits the market and gets tested by the usual gurus - then you'll know "for sure".

I found it hard to assess the images you posted, because of the subject matter and their size at my display resolution (1200*1600).

I'm not sure what you're looking at, the 40D crop on the second pair has loads more detail than the uprezzed 5D shot.

The other question to ask yourself is whether you always intend to shoot at apertures narrower than f8. A 5µ sensel is not going to be diffraction limited at f5.6 or wider, and there will be a definite benefit to the higher resolution.

Part of the problem is the number of variables. Up-rezzing itself introduces yet another variable.

Interesting indeed. If we compare the 1Ds2 with the 20D using the DPR data analyzed by Koren (so same lens (50mm) at same aperture (f9) and hopefully other testing parameters similar), the 20D has 23% higher resolution in lp/mm, despite having only 12% smaller pixel pitch.

Yes, and that I think raises a more general proposition about ranges and limits. Within certain ranges of pixel pitch, one can generalize that more PPI (higher MP per sensor size) will outresolve fewer PPI despite the incremental downsides of somewhat smaller pixels, the question being at what lower limit of pixel pitch, all else equal (if it ever is in practice) does this become the decisive variable.

Mark,
This is just one shot; the first scene I used for a test, on my way up the mountain. I'll proceed to post additional shots. If I don't find any difference of significance in any of my comparisons, I'll shoot newspapers. Okay!

Okay! The next comparison of the top of Wallaman Falls near Ingham (the tallest waterfall in Australia, incidentally) was taken with the Canon 50/1.4 at F16.

I've concentrated on the rocks in sunlight. 100% crops still show no greater detail from the 40D.

Click to view attachment Click to view attachment

Looking forward to your future findings Ray!

OK, now you're into the kind of subject matter that makes it easier to see what's going on or not going on. The issue here, going back to one of my previous posts (discussing ranges and limits), however, is whether by using f/16 the diffraction of the lens has become the binding constraint, such that differences between the sensors get over-ridden by the limitation of the lens. It would be, perhaps, more telling to see a comparison of these rock-face shots if the aperture were somewhere in the range of f/2.8~ f/4 (based on the "rule-of-thumb" that optimal image quality resides about 2 f/stops above the maximum aperture - maybe someone else has better data on the optimal f/stop range for this lens).

Erwin Putts has posted some interesting test results showing image sharpness with and without image stabilization. He compares the Imatest resolution handheld vs that obtained with the use of a tripod.

It would be interesting to extend these observations to a high resolution camera such as the 1DsMIII to determine how much sharpness you can actually get in the field with hand-held and image stabilization. IOW, can you really make use of the resolution of this camera under field conditions?

Bill

Good article. I think he's by and large correct. I'm not a great fan of a tripod in field conditions - I find it an encumbrance, and only use it when it is just plain unavoidable. I can't complain about the sharpness of my 1Ds3 shots magnified to 13*19 or with cropping considerably larger, particularly those using the 24~105 lens. Stabilization works VERY well. I have not done a stationary eyeball-to-eyeball test of exactly the same scene handheld vs tripod, but they would be darn close at shutter speeds down to 1/100th with the 24~105 - that I have no doubt about. Using the 70~300 is a different story - hand-holding at the higher focal lengths is dicier, so with that lens I use a tripod below 1/300th or so. Given how clean the 1Ds3 images are with real ETTR exposure, in lower lighting I'd pump the ISO so I could increase the shutter speed before resorting to the tripod. But I know there's a fair bit of skepticism out there about this approach. BTW the images I shot for the Noise article were all done WITH a tripod. For testing it's just plain dumb not to, unless one is testing the need for the tripod !

Hey! This was incidental testing on my trip to Australia's highest waterfall. There's a limit to the amount of testing I'm prepared to do.

It seems fairly clear, so far, if I buy the 24mp Sony A900 I'm going to have to hone my skills at focus bracketing if I want to improve on the DoF and resolution that the 5D can provide at F16.

Ray, I'm still confused as to why you say that the 40D has no greater detail. I downloaded your 100% crops and did a spatial frequency analysis. Here is the Fourier transform of a 256x256 portion of the same area from each image:



Nyquist is out at the edge of the square, low frequencies are in the middle. Black is no power, bright is lots of power. What you see is that the 40D has much more power at high spatial frequencies, indicating more detail (and it's not just noise power, that is a soft grey background that goes all the way out to the edges; I'm talking about the extent of the bright blob above that background). If the 40D were not resolving any more than the 5D, the extent of the bright disk would be the same for the two images. This just reaffirms what my eyes are telling me, that the 40D is getting way more detail.

Thanks for this thread. It allowed me to update my ignore user list.

Ray, take it easy - don't fall off the mountainside. Sounds like a nice place. To keep in mind if I ever get to that part of the world.

Ya - in those conditions I agree - limits to testing - but twirling the aperture ring a few notches ain't a big-time stress factor, even in the upper atmosphere. Anyhow, whatever, however. As you can and want.

I don't believe the sensor is the determinative factor for what you want from good focusing technique - for any quality DSLR. And I remain to be convinced that what you see from the 40D is necessarily a reliable guide to what you will get from a Sony A900. That remains to be seen.

Are you saying that none of those lenses shows any improvement in resolution as one opens up from f/16, even with the 40D? If so, I suggest that you need to seriously reconsider your choice of lenses! There is good evidence that in at least one other SLR system, most or all lenses have higher resolution at their optimal apertures (between f/4 and f/8) than is allowed by diffraction alone at f/16.

Exactly. Back to ranges and limits again: what's the binding constraint: whether we're talking a 40D, a 5D, a 1Ds3, a D3, a D300 - the sensor is most unlikely to be the binding constraint, but f/16 probably is, and if so, these comparisons aren't saying much about either absolute or comparative resolution for these sensors.

Yes, if you go back to that Zeiss D200 plot I posted, the Nyquist of the camera is 82 lp/mm and maximal observed MTF50 was 71 lp/mm at f/4. At f/16 the ideal lens MTF50 is 48 lp/mm (for green light) and the observed MTF50 was 56 lp/mm. The MTF above the ideal is most likely due to sharpening, which has a marked effect on MTF50.

The link below is from my own test using the D200 and Imatest. The results are shown without sharpening (uncorrected) and with standardized sharpening (corrected). If you want to compare lenses or diffraction effects, it is best to disable sharpening. Generally speaking, the best you can do with a Bayer arrar camera is 75-80% of Nyquist. The best results with this lens were at f/5.6 and I suspect the results for Ray's Canon 50mm f/1.4 would be similar. You can look up the results with that lens and the EOS 350 on PhotoZone.

Bill

http://bjanes.smugmug.com/photos/53712086_UaE9x-O-1.gif

OK, if one posits that diffraction is setting in somewhere between f8 and f11, shouldn't we attribute the downslope there and beyond to diffraction effects, or is there more going on?

If it's just diffraction, then the uncorrected MTF50 drops by about 1/3 between f11 and f22, while the aperture is dropping by 1/2. The effect of stopping down is to change the size of the Airy disk relative to Nyquist, so if diffraction limitation were a hard cutoff one should see MTF50 drop in proportion to f number rather than more slowly as it does.

Assuming that the limiting effect is diffraction and not any optical aberrations of the lens, if the effect of diffraction on MTF50/Nyquist is dependent only on pixel spacing/Airy disk size, and I don't see offhand why it shouldn't be (the question is how big is the diffraction blur on the scale of the sampling array), then stopping down by two stops should have the same effect as halving the pixel size -- both change the ratio of the pixel spacing to the Airy disk size by the same amount.

Thus halving the pixel size at f11 should have the same effect on MTF50 relative to Nyquist as keeping the same pixel size and doubling f number, and as we have seen the MTF50 goes down by less than a factor of two. This says to me that increasing pixel density even beyond the point where diffraction limitation sets in, will result in a net gain of resolution (as I and others were arguing before), at least for a while. Less than double the resolution, for sure, but more than nothing (the simple linearized model I am suggesting would say that one gets 4/3 the resolving power). But maybe the model is too naive?

Emil,

I don't know if the model is linear or what, but am merely reporting observed results. Since you are the physicist, I would accept your interpretation. In any event, if you stop down to f/16 with the tested camera and lens, you lose MTF. If you look at the results on PhotoZone, you will see that this is generally the case with similar pixel spacings.

Bill

The power spectrum of natural images decreases in proportion to more or less the inverse of the square of the frequency. The highest value, is of course, the DC entry.

If the power spectrum did not fall we could kiss compression schemes such as wavelet, mpeg, h.264, etc., good bye.

Just came across this thread...

Ray, in these shots of the rock face the 40D looks clearly sharper to me. ejmartin's analysis confirms this. Do they not look different to you?

Yes, but I presume that Bill was shooting a test target, which have sharp edges or sinusoidal variation with spectral power out to high frequency. A proper test target used in a proper test methodology should not in and of itself limit the MTF as a function of spatial frequency, otherwise the testing methodology is flawed. Are you saying that Bill's measured MTF50 is inaccurate?

MTF simply tells you how much of the spectral power of the scene is transferred to the recording medium. It is not a function of the spectral power distribution of any particular scene you wish to photograph (including a test chart), and doesn't care whether that power is large or small, it just says how much of that large or small power gets through.