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Author Topic: Canon 1Ds Mark III diffraction limit  (Read 9568 times)
seberri
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« on: September 11, 2007, 12:06:33 AM »
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f/16 is often an optimal aperture for landscape photography, it works very fine without any diffraction on the canon 5D, but what do you think about the new 1Ds Mark III and its smaller pixels ?
I have read somewhere (i cannot find it anymore) than f/14 will be the limit for diffraction


a good diffraction tutorial : http://www.cambridgeincolour.com/tutorials...photography.htm
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Wayne Fox
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« Reply #1 on: September 11, 2007, 01:39:14 AM »
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Interesting article.

Wouldn't that be more like the "theoretical" diffraction limit?  I'm not sure I've ever had a lens that has performed optimally at f/16, seems more like from f8 to f11.5 is more typical.  Not that I'm afraid of 16 or 22, but only go there if needed.

I always thought other factors were heavily involved as well, such as optical quality of glass and coatings (internal flare), etc.  Not sure where I picked that idea up ... could very well be an urban legend.  I swear I read it somewhere though.  Maybe this isn't related to "diffraction" limiting.

I guess we're all curious how current optics will perform with the small sensors in new 1ds Mk III.
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seberri
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« Reply #2 on: September 11, 2007, 01:45:17 AM »
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generally for large landscapes f/11 to f/16 is the best

for exemple take a look at : http://www.timecatcher.com most part of the photos are shot with canon 5D and 17-40 @f/14 to f/16
 you cant say there are not sharp enough
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dobson
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« Reply #3 on: September 11, 2007, 12:07:08 PM »
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Please correct me if I'm wrong. Here's how I see it.

Both the 5d and the 1Ds3 have full frame sensors. This means that with the same lens, the image projected onto the sensor will be identical, including diffraction effects. When printing the same size, the image will have identical diffraction blurring. The higher resolution of the 1Ds3 will show some advantage because it will show finer detail.

At higher f-stops you will be experiencing diminishing returns with the higher resolution sensor. Eventually the image will become so blurred that the 1Ds3 sensor will not be able to resolve more fine detail than the 5d. The 1ds3 should still render the blurred image more accurately, but not noticeably so.



Phillip
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BJL
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« Reply #4 on: September 11, 2007, 01:54:06 PM »
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Please correct me if I'm wrong. Here's how I see it.

... When printing the same size, the image will have identical diffraction blurring. The higher resolution of the 1Ds3 will show some advantage because it will show finer detail.

At higher f-stops you will be experiencing diminishing returns with the higher resolution sensor. ... The 1ds3 should still render the blurred image more accurately, but not noticeably so.
Phillip
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Thank you for that excellent summary: more, smaller photosites on the same sensor size never cause any decrease in resolution or sharpness; at worst, diffraction makes the gains in IQ less than they would be without diffraction. And at some point, increasing pixel counts will add little to overall resolution due to lens limitations: diffraction (particularly at small apertures) and lens aberrations (particularly at large apertures).


One note though: to make use of increasing pixel counts through making larger prints (same PPI, for example), getting the same perceived DOF on the print requires using smaller apertures, to balance the greater magnification of the circles of confusion in the image recorded by the sensor. If f/11 is the limit for adequate DOF with the print sizes made with 35mm film, or with an 8 to 11 MP sensor, then maybe f/16 or higher is needed for the larger prints invited by a 22MP sensor. So the diffraction effect grows even faster with increased pixel count when trying to show all the extra detail on big prints.
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lehtila
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« Reply #5 on: September 11, 2007, 02:48:02 PM »
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Only one more variable that I can see in this.  Sensor size is not necessarily directly related to number of sensors on a given chip size.  If Canon is increasing the size of the lens at each photosite (less wasted space on the chip) as new generation chips come out, there is bound to be some kind of effect.  This may, in fact, increase diffraction effects, because now the larger sensor picks up some diffraction pattern from the light falling on the neighbour, where a less efficient chip loses this pattern in the wasted space between photosites.  This would probably only be any kind of issue at all if we were comparing two chips of identical size and number of photosites - one that was older generation and one that was newer and with bigger lenses.  Othwise what Dobson (Philip) pointed out would still apply.
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sojournerphoto
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« Reply #6 on: September 12, 2007, 04:46:30 PM »
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Another thought is that although the projected image degrades due to deffraction at smaller apertures, a sensor with more resolution may give a more pleasing rendition as a result of more accurately recording the diffracted image. I think a similar argument can be applied to the necessary resolution of film scans, with higher dpi giving a better and more pleasing rendition of grain even though there may be no more image information delivered.

Just a thought I'd be delighted to test if someone will give me a 1Ds3...

Mike
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gdeliz
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« Reply #7 on: September 13, 2007, 10:51:10 AM »
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Depth of field for any given lens and lens setting will be the same for any FF camera. The more dense the pixel spacing the more quickly the sensor becomes diffraction limited as the lens is stopped down. The Canon 5D, for example, becomes diffraction limited at about f/12 while the new 1DSIII will be diffraction limited at around f/9. However, if the 1DSIII is stopped down to f/12 the resulting image will be no worse than and probably a bit better than the 5D at f/12.

The concept of diffraction limiting of the sensor has to be seen in the context of the maximum sized print that can be made with a given camera. This, in turn depends on one's criteria for acceptable sharpness. So, if a 240ppi print is what one considers the minimum acceptable resolution, the largest acceptable print that can be made with the 5D is about 12X18, assuming one doesn't stop down beyond f/12. ( In actual practice the 5D can be stopped down to f/16 without too much degradation.) The largest acceptable print that can be made with the 1DSIII would be about 16X24  but only if the lens is not stopped down beyond f/9. (In practice you'll probably be able to go to f/11.)

Another way of looking at this is that the equivalent mp rating of the sensor starts going down once the lens is stopped down beyond the limiting aperture. So, as the sensor size remains the same, the effect of increasing pixel count becomes one of diminishing returns, you can make larger prints with the camera but if you need maximum depth of field you will have to settle prints that are not that large if you wish to maintain the same criteria for acceptable resolution.

The bottom line is that more pixels is better(disregarding noise) but it's not a free lunch.

George Deliz
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ErikKaffehr
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« Reply #8 on: September 20, 2007, 12:11:30 AM »
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Hi,

Everything depends on your perception of sharpness. Diffraction effects all of the picture whereas depth of field affects the area which is perceived sharp. Optimal sharpness can only achieved i a single plane of focus.

Depth of field depends on eyesight, accommodation of the eye, viewing distance and image size. These dependencies are most often condensed down to a single factor called circle of confusion, COC. Essentially what this says that if a point is described with a spot having a certain diameter it would be perceived is sharp in the circumstances involved.

In film based photography a figure of 1/30-th mm was often used for COC and is normally what lens marking are calculated for. That figure is only correct for small prints like 9x12 cm or 4x5".

The issue is actually quite complex:

  If magnification is not high enough the pixel size will be smaller than the resolution of the eye, so pixel size would simply not matter. But this is also a matter of eyesight and image magnification.

  How many pixels does it take to resolve a point? Sensors are normally of bayer RGBG design. Each pixel is only detecting one color (red, green or blue) so hue and intensity for each pixel is calculated by interpolation.

  There is a antialiasing (AA) filter in front of the sensor that smudges the image. I would say that it reduces MTF for fine details or that it acts a low pass filter. The antialiasing filter may be of higher and lower quality and of different strength. Some cameras do not have AA filter but will than have problems with "moire" patterns.

  Diffraction acts as a kind of AA filter. In the few cameras that did not have AA filter (Kodak full format SLR comes to mind) moire could be reduced by using small apertures.

 I would say that in general an optimum sharpness can be achieved at about aperture 8 on a digital SLR. On a six MP camera with APS-C sensor 1/32 definitively is quite a bit soft, 1/22 may be acceptable. You would definitively loose sharpness if going past 1/16.

 Perceived sharpness is not really a function of resolution as much as of "acutance". Acutance lost in imaging can be regained by sharpening.

On a six MP camera ( Konica Minolta 7D ) and a high grade lens (80-200/2.8 APO) I could see that  there was a significant image detoriation at 1/16. The image was as sharp at 1/16 as at full aperture. I would guess that with 10 MP APS-C and weaker AA filter we could see some image detoriation already at 1/11. I would guess that similar finding would be valid for the Canon 5D and the Canon 1DsII/1DsIII as pixel sizes actually are quite similar between 5D and 6MP APS-C and 1DsII and 10 MP APS-C.

Best regards

Erik Kaffehr





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Depth of field for any given lens and lens setting will be the same for any FF camera. The more dense the pixel spacing the more quickly the sensor becomes diffraction limited as the lens is stopped down. The Canon 5D, for example, becomes diffraction limited at about f/12 while the new 1DSIII will be diffraction limited at around f/9. However, if the 1DSIII is stopped down to f/12 the resulting image will be no worse than and probably a bit better than the 5D at f/12.

The concept of diffraction limiting of the sensor has to be seen in the context of the maximum sized print that can be made with a given camera. This, in turn depends on one's criteria for acceptable sharpness. So, if a 240ppi print is what one considers the minimum acceptable resolution, the largest acceptable print that can be made with the 5D is about 12X18, assuming one doesn't stop down beyond f/12. ( In actual practice the 5D can be stopped down to f/16 without too much degradation.) The largest acceptable print that can be made with the 1DSIII would be about 16X24  but only if the lens is not stopped down beyond f/9. (In practice you'll probably be able to go to f/11.)

Another way of looking at this is that the equivalent mp rating of the sensor starts going down once the lens is stopped down beyond the limiting aperture. So, as the sensor size remains the same, the effect of increasing pixel count becomes one of diminishing returns, you can make larger prints with the camera but if you need maximum depth of field you will have to settle prints that are not that large if you wish to maintain the same criteria for acceptable resolution.

The bottom line is that more pixels is better(disregarding noise) but it's not a free lunch.

George Deliz
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bjanes
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« Reply #9 on: September 20, 2007, 09:36:38 AM »
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Please correct me if I'm wrong. Here's how I see it.

Both the 5d and the 1Ds3 have full frame sensors. This means that with the same lens, the image projected onto the sensor will be identical, including diffraction effects. When printing the same size, the image will have identical diffraction blurring. The higher resolution of the 1Ds3 will show some advantage because it will show finer detail.

At higher f-stops you will be experiencing diminishing returns with the higher resolution sensor. Eventually the image will become so blurred that the 1Ds3 sensor will not be able to resolve more fine detail than the 5d. The 1ds3 should still render the blurred image more accurately, but not noticeably so.
Phillip
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An excellent analysis, Phil. As you correctly point out, the effects of diffraction as projected on the sensor will be exactly the same for both cameras. The term "diffraction limited" can be confusing, since diffraction always sets a limit on resolution. In practice, the term is used when system resolution is limited by diffraction, rather than lens aberrations or the resolution of the camera sensor. In his excellent diffraction tutorial, [a href=\"http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm]Sean McHugh[/url] assumes the system is diffraction limited when the diameter of the Airy disk exceeds the allowable circle of confusion (COC). COC also comes into play with depth of field, and is relative, depending of the visual acuity of the observer and the distance at which the print is viewed. The same considerations come into play with Sean's diffraction calculator.

If you plug in values for 35 mm camera sensor size, default visual acuity (not stated, but apparently considerably less than 20/20), 25 cm viewing distance, and 10 inch maximal print size, the system becomes diffraction limited between f/22 and f/32. Megapixel count does not affect the calculation. If you change visual acuity to 20/20, maximal print size to 20 inches and keep the other parameters the same, the system becomes diffraction limited between f/4 and f/5.6.

These calculations involve what is "good enough" for a given print size, viewing distance, and visual acuity. Rather than trying to get an image that is good enough, one might strive to get the best possible image. This is the approach that Nathan Myhrvold took in his somewhat controversial thread posted earlier on the LL. Details aside, I think Nathan's approach is valid.

When the size of the Airy disk is larger than the pixel size of the camera, the disk will extend over adjacent pixels, blurring the image. The size of the Airy disk as related to pixel size is demonstrated nicely on Sean's web site. The 12.7 MP 5D has a pixel size of 8.2 microns and the 21 MP 1Ds MIII pixel size is 6.4 microns. With green light, the Airy disk is 5.4 microns at f/4, 7.5 microns at f/5.6 and 10.7 microns at f/8. If you want to make full use of the resolution of the 1Ds MIII with a diffraction limited lens, you probably should keep aperture at f/5.6 or larger, whereas a somewhat smaller aperture would not limit the 5D. Since real world lenses may not be diffraction limited at those apertures, your results in practice may differ.

In my own tests using Imatest, a Nikon D200 (10 MP, pixel spacing 6.2 microns) and 50 mm f/1.8 lens, I noted peak resolution at f/5.6. Many similar test results are available at Photozone.de. For example, the Canon 85 mm/ f1.2, where resolution peaked at f/4-f/5.6, and was most likely limited by the resolution of the 8 MP (pixel spacing 6.5 microns) camera used for the test. It would be interesting to see the results of this lens on the 1Ds MIII. The resolution wouldn't be that much increased in terms of lp/mm, since the pixel spacing  is 6.4 microns. However, the image would require less magnification for a given print size (its resolution in terms of lp/picture height is greater).
 
Under these circumstances, the 21 MP camera becomes "diffraction limited" when stopping down earlier than the 12 MP device. However, as Sean points out, this does not mean that the image at a given aperture will be worse with the 21 MP camera; indeed, the higher resolution camera will have fewer artifacts such as color moiré and aliasing.

Bill
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BJL
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« Reply #10 on: September 20, 2007, 10:08:12 AM »
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I would say that in general an optimum sharpness can be achieved at about aperture 8 on a digital SLR.
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That is far too much of a generalization to cover the array of format sizes, focal lengths and lens quality in the digital SLR world. It seems to be based on a common rule of thumb for 35mm format film cameras and lenses, rather than actual evidence about modern lens performance.

MTF testing at [a href=\"http://www.photozone.de/8Reviews/]PhotoZone[/url] for smaller format digital SLR lenses like Olympus E system, Nikon DX and Canon EF-S lenses often show peak MTF performance around f/4. All but some of the entry level Olympus lenses are at least as good wide open as they are at f/8, and the same is true at least for the Nikon 17-55/2.8 DX and Canon 17-55/2.8 EF-S. (At a quick search, good 35mm lenses seem often to have peak MTF at f/5.6 or f/8.)

Going in the opposite direction, lenses for medium and larger formats often show peak sharpness at f/11 or higher.
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ErikKaffehr
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« Reply #11 on: September 20, 2007, 01:07:53 PM »
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Hi,

I checked on Olympus lenses on Photozone and as far as I can see they are reaching maximum performance around f/8 on the border. The term border does not mean extreme corner so I think  that border figures are quite relevant. On the Nikon 17-55/2.8 DX and Canon 17-55/2.8 EF-S there is a similar tendency, border performance is best at f/5.6 or f/8.

What I meant by the reaching optimum quality is more that you can be pretty sure that image quality is pretty close to optimum at f/8.

Medium format lenses designed for digital like Schneider Digitar and Rodenstock HR lenses are also said to be diffraction limited around f/5.6.

Maximum performance is hard to achieve, partly because there is a significant error in focusing. Photozone does focus bracketing to find optimum focus.

Best regards

Erik


Quote
That is far too much of a generalization to cover the array of format sizes, focal lengths and lens quality in the digital SLR world. It seems to be based on a common rule of thumb for 35mm format film cameras and lenses, rather than actual evidence about modern lens performance.

MTF testing at PhotoZone for smaller format digital SLR lenses like Olympus E system, Nikon DX and Canon EF-S lenses often show peak MTF performance around f/4. All but some of the entry level Olympus lenses are at least as good wide open as they are at f/8, and the same is true at least for the Nikon 17-55/2.8 DX and Canon 17-55/2.8 EF-S. (At a quick search, good 35mm lenses seem often to have peak MTF at f/5.6 or f/8.)

Going in the opposite direction, lenses for medium and larger formats often show peak sharpness at f/11 or higher.
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BJL
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« Reply #12 on: September 20, 2007, 11:20:42 PM »
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Hi,

I checked on Olympus lenses on Photozone and as far as I can see they are reaching maximum performance around f/8 on the border.
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The 11-22 at 11mm is best wide open at f/2.8, center or border. At 22mm, wide open f/3.5 is about the same as f/8
The 50-200 is overall as good in the corners wide open at f/2.8 than at f/8, an better at the center, so better overall wide open, looking at 50mm, 100mm and 200mm.

Saying that performance is also about as good at f/8 obfuscates the ability to use lower aperture ratios (and thus get smaller diffraction spots) without significant sacrifice of resolution to lens aberrations.
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seberri
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« Reply #13 on: September 21, 2007, 12:11:38 AM »
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Photozone is testing lenses with a 350D .... their tests have nearlly no interrest
they have done so much and great work for nearlly nothing

to test 24x36 lenses you need a 24x36 camera , a 5D or a 1D (for Canon lenses of course)

... and they test only up to f/11
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Paul Kay
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« Reply #14 on: September 21, 2007, 02:20:35 AM »
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Sorry, but isn't the optimum aperture the one which most appropriately suits the subject being photographed as opposed to the test bench. Arguing over minutiae might be fascinating but misses the point IMHO!

If on the other hand the discussion could steer towards "which camera/lens combination might fulfil a type of application most effectively" (best is an appallingly overused word which is rarely put into context) I'd consider it in a more favourable light (no pun intended).
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bjanes
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« Reply #15 on: September 21, 2007, 09:32:44 AM »
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Photozone is testing lenses with a 350D .... their tests have nearlly no interrest
they have done so much and great work for nearlly nothing

to test 24x36 lenses you need a 24x36 camera , a 5D or a 1D (for Canon lenses of course)

... and they test only up to f/11
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The 350D has about the same resolution as the EOS 1Ds MIII, since the pixel spacing is about the same, so the 350D is good for testing the center resolution of the lens. The 5D has less resolution, and you must remember that they are testing the resolution of the camera system, camera + lens. Some lenses exceed the resolution of the 5D, so the 350D is a better test bed for testing the center resolution. However, to test the resolution out to the edge of the 35 mm field, you do need a full frame camera.

They do test beyond f/11 for some lenses, for example the [a href=\"http://www.photozone.de/8Reviews/lenses/nikkor_200_4/index.htm]Nikkor 200 mm f/4[/url]. However, as you go beyond f/11, the lens may become diffraction limited and you are confirming the laws of physics rather than the quality of the lens.

Bill
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Gary Ferguson
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« Reply #16 on: September 21, 2007, 03:46:46 PM »
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I use Leica M8, a Canon 5D, a Canon 1Ds MkII, and a Phase One P25 on both Hasselblad and Linhof cameras. I see little if any consistent and practical resolution difference between them.

The colour and gradation can be a little better with the Phase One, wide angles tend to draw more satifyingly on the Leica, and higher ISO noise is generally better controlled with the Canons. But pure resolution differences, repeatable and observable across thousands of frames? Little if any.

Why might this be so?

I'm no physicist but I'd suggest that the practical, image degrading, hurdles encountered in real life photography will swamp any theoretical differences, and force the vast majority of images into a pretty pedestrian spectrum of achievable image quality. If you're attentive to technique you'll average slightly better, if you're a bit slapdash you'll average slightly worse. But as reasonably competent and experienced photographers we'll all exist in a fairly narrow image quality range. Here's three factors from scores of candidates that may explain this.

1. All our theorising is only concerned with a wafer thin plane of actual focus, but as we photograph three dimensional subjects the vast majority of our image space and subject matter exists outside of this plane. There's no refuge in notions of "depth of field" either. As has been been pointed out by a previous poster, depth of field holds true only for the enprint sized photographs that were common in the 1920's and 1930's when the depth of field tables were compiled. They're designed to give satisfying results with 6x9 and 4x5 contact prints made with relatively primitive emulsions. Consequently our images are either optimised within a vanishingly slim plane, or they're outside that plane and degraded to the point where it's difficult, in resolution terms, to distinguish between an Alpa and a point and shoot. I posted an article on this site entitled "Focusing In The Digital Era" that shows examples of how fuzzy image quality is at the supposed margins of depth of field, and how stopping down one, two, three or even more stops beyond this to provide a safety margin actually delivers only small gains in resolution.

2. Our ability to accurately place that precious plane of focus within the image is pretty suspect too. In a full face portrait for example I'm sceptical that any autofocus system, or manual focus system with a realistic magnification factor, could consistently place focus precisely on the eyeball of the nearest eye. If you doubt this try replacing the model with a ruler to a comparable scale, and try to hit consistently a mark to within plus or minus three milimetres.

3. Tripods need to be reasonably portable to be useful, just look at the difference between even the best constructed tripod and a professional studio camera stand. Consequently they're simply not able to deliver the rigidity required to reliably observe the difference between a five and seven micron pixel pitch. A marketing director at Zeiss was an enthusiastic and remarkably honest lens evaluator. He concluded that he couldn't realistically distinguish between lens performance without a fluid head tripod costing more than most medium format digital backs. He even went so far as to claim that vibration was so critical that the choice of cable release could have a more material influence on real life image quality than the choice between a zoom and a prime lens. I try and remember that when my Linhof is humming tunefully in a breeze!

I don't think we should ever stop searching for improved image quality, but we should do so in the knowledge that it's unbelievably difficult to realise the full potential of even basic lenses and cameras, let alone explore the theoretical limits of the exotica that the photographic industry is now producing.
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ErikKaffehr
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« Reply #17 on: September 21, 2007, 11:55:01 PM »
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Thanks for a nice article, Gary!

I think your posting and also the articles you refer to in your posting give an interesting insight in realities of optimizing sharpness in digital cameras.

The articles "Focusing In The Digital Era" are very enlightening regarding DOF.

Best regards

Erik

Quote
I use Leica M8, a Canon 5D, a Canon 1Ds MkII, and a Phase One P25 on both Hasselblad and Linhof cameras. I see little if any consistent and practical resolution difference between them.

The colour and gradation can be a little better with the Phase One, wide angles tend to draw more satifyingly on the Leica, and higher ISO noise is generally better controlled with the Canons. But pure resolution differences, repeatable and observable across thousands of frames? Little if any.

Why might this be so?

I'm no physicist but I'd suggest that the practical, image degrading, hurdles encountered in real life photography will swamp any theoretical differences, and force the vast majority of images into a pretty pedestrian spectrum of achievable image quality. If you're attentive to technique you'll average slightly better, if you're a bit slapdash you'll average slightly worse. But as reasonably competent and experienced photographers we'll all exist in a fairly narrow image quality range. Here's three factors from scores of candidates that may explain this.

1. All our theorising is only concerned with a wafer thin plane of actual focus, but as we photograph three dimensional subjects the vast majority of our image space and subject matter exists outside of this plane. There's no refuge in notions of "depth of field" either. As has been been pointed out by a previous poster, depth of field holds true only for the enprint sized photographs that were common in the 1920's and 1930's when the depth of field tables were compiled. They're designed to give satisfying results with 6x9 and 4x5 contact prints made with relatively primitive emulsions. Consequently our images are either optimised within a vanishingly slim plane, or they're outside that plane and degraded to the point where it's difficult, in resolution terms, to distinguish between an Alpa and a point and shoot. I posted an article on this site entitled "Focusing In The Digital Era" that shows examples of how fuzzy image quality is at the supposed margins of depth of field, and how stopping down one, two, three or even more stops beyond this to provide a safety margin actually delivers only small gains in resolution.

2. Our ability to accurately place that precious plane of focus within the image is pretty suspect too. In a full face portrait for example I'm sceptical that any autofocus system, or manual focus system with a realistic magnification factor, could consistently place focus precisely on the eyeball of the nearest eye. If you doubt this try replacing the model with a ruler to a comparable scale, and try to hit consistently a mark to within plus or minus three milimetres.

3. Tripods need to be reasonably portable to be useful, just look at the difference between even the best constructed tripod and a professional studio camera stand. Consequently they're simply not able to deliver the rigidity required to reliably observe the difference between a five and seven micron pixel pitch. A marketing director at Zeiss was an enthusiastic and remarkably honest lens evaluator. He concluded that he couldn't realistically distinguish between lens performance without a fluid head tripod costing more than most medium format digital backs. He even went so far as to claim that vibration was so critical that the choice of cable release could have a more material influence on real life image quality than the choice between a zoom and a prime lens. I try and remember that when my Linhof is humming tunefully in a breeze!

I don't think we should ever stop searching for improved image quality, but we should do so in the knowledge that it's unbelievably difficult to realise the full potential of even basic lenses and cameras, let alone explore the theoretical limits of the exotica that the photographic industry is now producing.
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BJL
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« Reply #18 on: September 23, 2007, 10:19:29 PM »
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On a six MP camera ( Konica Minolta 7D ) and a high grade lens (80-200/2.8 APO) I could see that  there was a significant image detoriation at 1/16.
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I missed that observation before. This is yet another report from actual experience that
diffraction starts to reduce resolution at aperture ratio about twice the pixel pitch in microns
which is 8 microns for the 6MP Sony sensor in the Konica Minolta 7D.
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ErikKaffehr
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« Reply #19 on: September 24, 2007, 02:39:06 PM »
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Hi,

I made a small experiment. I ran a series of tests with Imatest on my two DSLR-s an KM Dimage 7D and a Sony Alpha 100. The 7D is a 6 MP camera and the Alpha 100 is 10 MP. Pixel pitch is about 7.8 microns on the 7D and 6.1 microns on the Alpha 100.

I then plotted uncorrected LW/PH for both cameras. I think it is quite obvious that this lens achieves it's peak performance about aperture 8. The Alpha looses sharpness faster then the 7D, even if it is essentially always sharper than the 7D.

Sharpness at full aperture may be negatively affected by focusing errors, I did no focus bracketing to find optimal focus.

Airy disk size for f/8 would be 10.7 micron, for f/11 14.8 micron and for f/16 21.5 micron.

Best regards

Erik


Quote
I missed that observation before. This is yet another report from actual experience that
diffraction starts to reduce resolution at aperture ratio about twice the pixel pitch in microns
which is 8 microns for the 6MP Sony sensor in the Konica Minolta 7D.
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