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Author Topic: Diffraction limitation in 35mm lenses.  (Read 19680 times)
BJL
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« Reply #40 on: January 19, 2006, 09:09:24 PM »
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Ray,

    the pattern I have seen is that the highest aperture ratio before diffraction effects become noticeable is about twice the pixel spacing in mm. For example, Thom Hogan observes that about f/11 is the diffraction limit for the D2X with its 5.5 micron pixel pitch.

So with the 8.2 micron pixel pitch of the 5D, f/16 fits as the "diffraction limit". How does f/16 compare to f/22?

Of course f/16 with the 5D gives about the same DOF as f/10 in your 20D (viewing equal sized uncropped prints from the same viewing distance), so I do not see that you have gained or lost anything in DOF by the change from the 20D to the 5D; you just get to use slower f-stops and thus lower shutter speeds and/or higher ISO settings to get the same DOF.

P.S. Resolution comparisons between cameras in different formats are best done in terms of angular resolution of the subject, and then the physics of diffraction is simple: the smallest resolvable angle is inversely proportional to the effective aperture diameter, which is the focal length divided by the aperture ratio (f-stop).

And as I have said many times before, the DOF on equal sized prints and the speed at which the camera gathers light from the subject are also determined by the effective aperture diameter, independent of focal length and format: aperture diameter is a far more natural and convenient quantity than aperture ratio when comparing images of the same subject (including same field of view) made using different focal lengths and formats, even though f-stop is more convenient to use with ISO speed in determining exposure settings.
« Last Edit: January 19, 2006, 09:27:09 PM by BJL » Logged
Ray
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« Reply #41 on: January 20, 2006, 12:04:24 AM »
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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.


Peter,
This is the paradox. There's no doubt that f16 is not the aperture at which 35mm lenses are sharpest. Most lenses are sharper at f8 and a few of the really expensive lenses are sharpest at f5.6 and even f4.

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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.


Where's the evidence for this, considering that the pixel spacing of the 5D and earlier 1Ds cannot resolve greater resolution than that provided at f16 (now confirmed by BJL, our resident lens expert   ). If the sensor is no longer the weakest link, I'd expect to see that increase in resolution between f4 and f8 with all good lenses. Instead, what I see is just a marginal increase in the contrast of micro detail at resolutions that are far below the resolution limits of the lenses at their sharpest apertures.

My impression is, to get just a marginal increase in image quality, we have to get a substantial increase in lens quality. The sensor is still the weakest link. An indication of this is the usual fall-off in resolution at the edges and particularly in the corners of full frame images.

If you've ever looked at the Photodo MTF charts for quite a number of Canon lenses they've tested, you'll see that resolution (or more accurately the contrast at specific resolutions) falls off dramatically usually in that part of the image outside the crop area of the APS-C size sensors. A disadvantage of moving up to full frame 35mm is this expectation that image degradation might be a problem towards the edges. It can be, but my experience so far with the 5D is that resolution fall off towards the edges is not nearly as dramatic as indicated in the Photodo charts and less than my worst fears.

Finally, at the risk of antagonising BJL   , I'll use the example of the Olympus 4/3rds format. The Zuiko lenses designed for this format are by all accounts superb. Far better it would appear than their Canon counterparts. Yet, if you check out the very detailed and thorough reviews of the Olympus 8MP E-300 and E-500 at dpreview, showing comparisons with the Canon 350D and 20D, you'll see that absolute resolution is a shade less than that of the Canon 8mp cameras.

But the Zuiko lenses are, I suggest, a lot more than a shade better. Of course you could argue that the 8MP Olympus sensors (manufactured by Kodak, I believe) are just not as good as Canon sensors. In the noise department, they don't appear to be. But resolution?

Unfortunately, there are no adapters for using Zuiko lenses on the Canon 350 and 20D, so we'll never really know what a really good lens can do when coupled with a really good sensor   .
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Ray
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« Reply #42 on: January 20, 2006, 12:44:47 AM »
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Of course f/16 with the 5D gives about the same DOF as f/10 in your 20D (viewing equal sized uncropped prints from the same viewing distance), so I do not see that you have gained or lost anything in DOF by the change from the 20D to the 5D; you just get to use slower f-stops and thus lower shutter speeds and/or higher ISO settings to get the same DOF.

I've gained some 'picture' resolution, have I not? My images are now comprised of 12MP instead of 8MP. I've also gained the opportunity to use a slower shutter speed, not only because f16 is slower than f10 but also because of an ISO 50 option on the 5D.

If I'm shooting a waterfall and I've forgotten to bring my ND filter, and I'm not keen on the water looking like melted ice-cream, I just might be able to get the right effect using f16 and ISO 50   . This is an afterthought, (edited). To all you P&S shooters, if you want to get a good shot of a waterfall, forget it. You're going to be using a wide aperture and fast shutter speed, and the water's going to look like.... errh!.... ice cream?... errh! "S**t.

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aperture diameter is a far more natural and convenient quantity than aperture ratio when comparing images of the same subject (including same field of view) made using different focal lengths and formats, even though f-stop is more convenient to use with ISO speed in determining exposure settings.

And this is exactly what we've been doing in our conversation in the Medium Format section, isn't it?
« Last Edit: January 20, 2006, 02:53:08 AM by Ray » Logged
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« Reply #43 on: January 20, 2006, 04:44:00 AM »
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Ray -
It's edge performance I'm talking about when I say the sensor is no longer the weakest link =)

I stand corrected on the fact that some lenses lose sharpness when stopped down, although it seems counter-intuitive to me. I'll have to read up on it.

Cheers,
Peter
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bjanes
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« Reply #44 on: January 20, 2006, 06:23:53 AM »
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It's basically an issue of pixel pitch - the smaller the pixels themselves, the sooner diffraction effects kick in. There's an excellent article on understanding diffraction and pixel pitch here: http://www.cambridgeincolour.com/tutorials...photography.htm

From that article, a 5D will start to lose resolution to diffraction _after_ f/16. In my own tests to verify this I found that I saw improved sharpness at f/16 over f/11, but lost sharpness at f/22. With my 20D, I found that f/11 was the minimum aperture I could use before losing resolution (using the same lens, the 24-70L).

That being said, as Michael says in his 'stop down!' article, if you need the depth of field, shoot at the appropriate aperture and worry about diffraction later.

It's also worth remembering that everything has to go right to get the sharpest possible shot. In a controlled environment with plenty of time and no discomfort, it's easy to get razor sharp shots. In the field, with wind, rain, soft ground, misfocussing (remember - AF still isn't as reliable as we'd like it to be for landscape work, especially) and photographer discomfort it's easy to get it wrong!

Cheers,
Peter
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The Cambridge in Color site you mention is indeed quite good. However, one should be aware that the diffraction limited resolution calculation there is for the Raleigh limit, which corresponds to about 10% MTF. When speaking about resolution one should always give two figures: the resolution and the MTF at that resolution.

For most photographic work, the resolutiion at MTF of 50% corresponds much better to perceived sharpness. The contrast at 10% MTF is simply too low--that limit is good for resolving stars with a black background (very high contrast), but less useful for normal picture taking. To obtain the extra MTF one needs to use a a larger aperture. Roger Clark has a table on his website:

[a href=\"http://www.clarkvision.com/imagedetail/scandetail.html#diffraction]http://www.clarkvision.com/imagedetail/sca...tml#diffraction[/url]


Here is a MTF 50 plot for my 50mm f/1.8 Nikkor with the D70 produced with Imitest by Norman Koren. It shows definite image degradation at f/16 and beyond.

http://bjanes.smugmug.com/photos/17635874-M-2.jpg
« Last Edit: January 20, 2006, 08:02:33 AM by bjanes » Logged
BJL
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« Reply #45 on: January 20, 2006, 12:05:34 PM »
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Finally, at the risk of antagonising BJL ... if you check out the very detailed and thorough reviews of the Olympus 8MP E-300 and E-500 at dpreview, showing comparisons with the Canon 350D and 20D, you'll see that absolute resolution is a shade less than that of the Canon 8mp cameras.
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Differences in both sensor and approaches to in-camera JPEG processing make such comparisons useless as assessments of lens performance differences; after all, the 20D and even 350D are significantly more expensive than the E-300 and E-500.
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Ray
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« Reply #46 on: January 20, 2006, 04:35:56 PM »
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Differences in both sensor and approaches to in-camera JPEG processing make such comparisons useless as assessments of lens performance differences; after all, the 20D and even 350D are significantly more expensive than the E-300 and E-500.
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BJL,
So has anyone done any E-500/350D comparisons using only RAW images?  The obvious problem with such comparisons is variation in the quality of the converters used, for example C1 has a reputation for extracting marginally more detail from a shot than ACR.

But, for what it's worth, dpreview did do some in-camera jpeg and ACR RAW conversion comparisons with the E-500. See below:

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The first visual difference between JPEG straight from the camera and RAW converted using Adobe Camera RAW is the lack of artifacts in the ACR image, it has a much cleaner and less processed appearance with no sharpening halos around detail. Detail wise there doesn't seem to be a big advantage from the RAW image. The next difference comes in color rendition which is noticeably different, Adobe Camera RAW isn't rendering greens correctly, we can only assume this could be to do with support of the E-500 in this Beta version being only preliminary.


As regards the E-500 being a $100 cheaper than the 350D, it's not really significant in the general scheme of things after lens purchases have been taken into consideration. I mean, those Zuiko lenses are not cheaper than sometimes excellent 3rd party lenses for the 350D.
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Ray
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« Reply #47 on: January 20, 2006, 04:55:22 PM »
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For most photographic work, the resolutiion at MTF of 50% corresponds much better to perceived sharpness. The contrast at 10% MTF is simply too low--that limit is good for resolving stars with a black background (very high contrast), but less useful for normal picture taking. [a href=\"index.php?act=findpost&pid=56396\"][{POST_SNAPBACK}][/a]

Not only is any signal at 10% MTF less useful for normal picture taking, I think it would be fair to say it's of no use whatsoever if we are talking about high spatial frequencies. Even at f32, sometimes the smallest available aperture on 35mm lenses, a theoretical diffraction limited resolution of 50 lp/mm at 10% MTF would not be picked up at all by the sensor.
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BJL
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« Reply #48 on: January 20, 2006, 07:13:10 PM »
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I should also have mentioned differences in AA filters as another reason that fine differences in lens performance are hard to judge from such tests.
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As regards the E-500 being a $100 cheaper than the 350D, it's not really significant in the general scheme of things after lens purchases have been taken into consideration. I mean, those Zuiko lenses are not cheaper than sometimes excellent 3rd party lenses for the 350D.
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I mentioned prices to compare sensor costs: the E-300 and E-500 seem to have a substantially cheaper sensor. Lens costs are irrelevant to that. (I also note that you choose to compare the more expensive Olympus to the far cheaper of the two Canons!)


My bottom line is simply that there are far too many uncontrolled variables in these comparisons to conclude anything about the inherent performance limits of lenses for two slightly different formats (10% vertical, 20% horizontal difference in frame size.)
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bjanes
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« Reply #49 on: January 21, 2006, 06:26:39 AM »
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Not only is any signal at 10% MTF less useful for normal picture taking, I think it would be fair to say it's of no use whatsoever if we are talking about high spatial frequencies. Even at f32, sometimes the smallest available aperture on 35mm lenses, a theoretical diffraction limited resolution of 50 lp/mm at 10% MTF would not be picked up at all by the sensor.
[a href=\"index.php?act=findpost&pid=56454\"][{POST_SNAPBACK}][/a]


Why would 50 lp/mm at 10% MTF not be picked up by the sensor? The Nyquist for the Canon EOS 1Ds Mark II is 69 lp/mm. For the Digital Rebel 350 it is 78 lp/mm.
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Ray
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« Reply #50 on: January 21, 2006, 05:25:43 PM »
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Why would 50 lp/mm at 10% MTF not be picked up by the sensor? The Nyquist for the Canon EOS 1Ds Mark II is 69 lp/mm. For the Digital Rebel 350 it is 78 lp/mm.
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Why? I'm not setting myself up as an expert on such matters, but my understanding is a sensor is not a perfect recording device. It's not a 100% efficient and does not have infinite sensitivity. The light signal reaching it has to compete with  noise from a number of sources, including noise within the light signal itself, called photon noise.

Furthermore, Bayer type sensors cannot deliver resolution up to the Nyquist limit because of their requirement to interpolate the RGB values. You'll find somewhere on Norman Koren's site a resolution test of his Canon 10D and plotted MTF response of the recorded resolution. From memory, there was no meaningful resolution to be had beyond 54 lp/mm and the MTF response at that cut-off point was 10%. The lens he used would probably have had an MTF resonse of around 40% at 54 lp/mm. If the lens had been delivering 50 lp/mm at just 10% MTF because the aperture was f32, there's no chance that such a faint signal would have been recorded.

The Rayleigh's and Dawe's limits ot 10% and 2% appear to be only useful for astronomy. Such faint signals can be detected when peering through a telescope and maybe even recorded on digital sensors using very long exposures, multiple exposures and stacked images.

I think it's probably true to say that any signal coming through your lens that has lost more than 70% of its original contrast, is pretty irrelevant.
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bjanes
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« Reply #51 on: January 22, 2006, 08:55:24 PM »
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Why? I'm not setting myself up as an expert on such matters, but my understanding is a sensor is not a perfect recording device. It's not a 100% efficient and does not have infinite sensitivity. The light signal reaching it has to compete with  noise from a number of sources, including noise within the light signal itself, called photon noise.

Furthermore, Bayer type sensors cannot deliver resolution up to the Nyquist limit because of their requirement to interpolate the RGB values. You'll find somewhere on Norman Koren's site a resolution test of his Canon 10D and plotted MTF response of the recorded resolution. From memory, there was no meaningful resolution to be had beyond 54 lp/mm and the MTF response at that cut-off point was 10%. The lens he used would probably have had an MTF resonse of around 40% at 54 lp/mm. If the lens had been delivering 50 lp/mm at just 10% MTF because the aperture was f32, there's no chance that such a faint signal would have been recorded.

The Rayleigh's and Dawe's limits ot 10% and 2% appear to be only useful for astronomy. Such faint signals can be detected when peering through a telescope and maybe even recorded on digital sensors using very long exposures, multiple exposures and stacked images.

I think it's probably true to say that any signal coming through your lens that has lost more than 70% of its original contrast, is pretty irrelevant.
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Ray,

I checked Norman Koren's web site. The Nyquist limit for sensors is 0.5 cycles/pixel whereas 0.33 cycles/pixel is excellent performance for a Bayer camera. According to these figures, the 1Ds MII would resolve at best 46 lp/mm (cycles/mm) and the Digital Rebel around 51 lp/mm (at a relatively low MTF), pretty much in agreement with your memory.

At f/16 the lens would lay down 19, 48, and 100 lp/mm respectively on the sensor at MTF 80%, 50%, and  the Rayleigh criterion respectively. The 100 lp/mm at 10% MTF is most likely not that meaningful as you say, but the 48 lp/mm at 50% is in the range that can be recorded by the camera and one can readily see why stopping down beyond f/16 with cameras of this pixel size is detrimental to image quality.

To get MTF above 80% on the sensor, one would have to open up to nearly f/5.6, which can be done with a diffraction limited lens. If one opens up more, abberations would begin to degrade the image with less than diffraction limited lenses. Thus, the sweet spot with these cameras is not all that different than were taught applied to 35 mm cameras.  I don't claim to be an expert in this area either, but this is my best effort to conceptualize the physics involved. I would welcome other interpretations.

Bill
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Ray
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« Reply #52 on: January 23, 2006, 12:05:51 AM »
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Thus, the sweet spot with these cameras is not all that different than were taught applied to 35 mm cameras.  I don't claim to be an expert in this area either, but this is my best effort to conceptualize the physics involved. I would welcome other interpretations


Bill, here's my interpretation, at the risk of starting another film versus digital war   .

50 lp/mm on film was always something that could be achieved without too much difficulty; just a fine grained film, tripod and the usual sound technique was all that was required. Reaching 100 lp/mm was the really difficult thing, probably requiring the use of high resolution B&W films like T-Max 100 which has an excellent MTF response (100% at 50 lp/mm and even as high as 60% at 100 lp/mm).

But to break the 50 lp/mm barrier with film required the use of really sharp lenses, such as the Canon 200/1.8 at f4, its sweet spot. Now that's a really expensive lens and the best that most lenses can deliver is a slightly lower resolution at f8, but still higher than f11 or f16.

Now there's no disputing that the 5D (and 1Ds) can deliver spades of high MTF detail below 50 lp/mm, which is cleaner and sharper than the same detail on film. But it can't deliver anything at all above 50 lp/mm.

One can argue till the cows come home whether detail on 35mm film above 50 lp/mm serves much purpose. You need a very high resolution scanner to retrieve it for a start, and a lot of that detail is unavoidably obscured by grain. Nevertheless, it would seem reasonable to suppose that a lens which is capable of delivering say 100 lp/mm at 30% MTF could have an impact on a film that is capable of recording 100 lp/mm at 60% MTF. The net effect is a recorded image which has 18% of its original contrast; clearly not something that's going to hit you in the eye but something which is discernible.

But just in case I've caused confusion here, I must make it clear I am not trying to say that high quality primes are a waste of time on cameras such as the 5D. I'm saying that the ability of such high quality lenses to provide high spatial detail at relatively high MTFs (eg. 70 lp/mm at 40% MTF) is an irrelevancy. The only thing that matters is the performance of the lens up to 50 lp/mm.
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bjanes
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« Reply #53 on: January 23, 2006, 08:05:56 AM »
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Bill, here's my interpretation, at the risk of starting another film versus digital war   .

50 lp/mm on film was always something that could be achieved without too much difficulty; just a fine grained film, tripod and the usual sound technique was all that was required. Reaching 100 lp/mm was the really difficult thing, probably requiring the use of high resolution B&W films like T-Max 100 which has an excellent MTF response (100% at 50 lp/mm and even as high as 60% at 100 lp/mm).

But to break the 50 lp/mm barrier with film required the use of really sharp lenses, such as the Canon 200/1.8 at f4, its sweet spot. Now that's a really expensive lens and the best that most lenses can deliver is a slightly lower resolution at f8, but still higher than f11 or f16.

Now there's no disputing that the 5D (and 1Ds) can deliver spades of high MTF detail below 50 lp/mm, which is cleaner and sharper than the same detail on film. But it can't deliver anything at all above 50 lp/mm.

One can argue till the cows come home whether detail on 35mm film above 50 lp/mm serves much purpose. You need a very high resolution scanner to retrieve it for a start, and a lot of that detail is unavoidably obscured by grain. Nevertheless, it would seem reasonable to suppose that a lens which is capable of delivering say 100 lp/mm at 30% MTF could have an impact on a film that is capable of recording 100 lp/mm at 60% MTF. The net effect is a recorded image which has 18% of its original contrast; clearly not something that's going to hit you in the eye but something which is discernible.

But just in case I've caused confusion here, I must make it clear I am not trying to say that high quality primes are a waste of time on cameras such as the 5D. I'm saying that the ability of such high quality lenses to provide high spatial detail at relatively high MTFs (eg. 70 lp/mm at 40% MTF) is an irrelevancy. The only thing that matters is the performance of the lens up to 50 lp/mm.
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Ray,

You are correct that reaching 100 lp/mm with black and white film is achievable with 35 mm, but with color transparency film, the MTF drops off beyond 20 lp/mm as shown by Norman Koren on his web page:

[a href=\"http://www.normankoren.com/Tutorials/MTF1A.html]http://www.normankoren.com/Tutorials/MTF1A.html[/url]

Furthermore, even with B/W film, getting 80 lp/mm in the print is not easy at all as discussed by the Leica authorty Erwin Puts (the enlarger or scanner also limits MTF):

http://www.imx.nl/photosite/technical/highres.html

In their MTF charts, Leica publishes MTF at 5, 10, 20, and 40 lp/mm and does not bother to go higher, presumably because higher values are not meaningful in practical photography.  They state that the 5 and 10 lp/mm data relates to large object contrast while the 20 and 40 lp/mm data relates to small object resolution.

I am not interested if a digital vs film flame war either, but nearly everyone agrees that the EOS 1Ds Mark II gives better results than film, even though it can't do much better than 50 lp/mm. It does this by giving high MTF at the lower frequencies where it counts.

The concept of reporting camera resolution at extinction (10% MTF), as done by DPreview and some other testing sites is obsolete. As Mr. Koren states, it does not make sense to test resolution where detail vanishes. The resolution at MTF of 50% is more meaningful.

Here is the MTF at various f/stops, taken from Roger Clark's web site for green light (wave length 500 nm) plotted on a graph. A black line indicates the 50 lp/mm limit that you have discussed. One should try to maintain high MTF at frequencies below this limit, and this is not possible with f/stops much below f/16 as shown on the graph. This interpretation is consistent with my Imitest results for the Nikon D70 with the 50mm f/1.8 lens. I would agree that high quality primes are not a waste with digital, since they can deliver higher MTF at low frequencies and this can be used by digital.

Bill
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Ray
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« Reply #54 on: January 23, 2006, 11:46:56 AM »
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You are correct that reaching 100 lp/mm with black and white film is achievable with 35 mm, but with color transparency film, the MTF drops off beyond 20 lp/mm


I know   . I checked out Fuji's MTF charts for their films some time ago. Their highly regarded Provia 100F has an MTF response barely more than 30% at 50 lp/mm.

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The resolution at MTF of 50% is more meaningful.


No argument there, but one wonders why Canon still publish MTF data at only 10 lp/mm and 30 lp/mm.

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Leica publishes MTF at 5, 10, 20, and 40 lp/mm and does not bother to go higher, presumably because higher values are not meaningful in practical photography. 


But that's going to change, isn't it? Cameras like the 20D and D2X are already capable of greater than 50 lp/mm with a good lens. Doesn't Leica have a reputation for producing contrasty lenses rather than high resolution lenses?

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Here is the MTF at various f/stops, taken from Roger Clark's web site for green light (wave length 500 nm) plotted on a graph.


That's an interesting chart and confirms what I've understood for some time, namely that resolution increases inversely with f stop provided the lenses are diffraction limited at such f/stops, which of course they frequently aren't. The resolution and f/stop relationshsips on Roger Clark's graph apply to ideal lenses which are diffraction limited at the f/stops shown.

I'd like to believe my Canon 24-105 is diffraction limited at f16 and is able to deliver detail to the sensor at 40 lp/mm (if not 50) at 50% MTF. Even if this is true, there's no way this lens could have an MTF 50 response at 70 lp/mm at f11, and 100 lp/mm at f8, but this sort of performance will be needed if the megapixel race continues.

By the way, a test report of the Minolta Dimage Scan Elite 5400 I read some time ago claimed that the maximum resolution that was achieved scanning B&W film was 74 lp/mm, presumably high contrast test chart lines. Most 4000 dpi desktop scanners are probably not capable of more than 65 lp/mm.
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BJL
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« Reply #55 on: January 23, 2006, 06:40:49 PM »
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No argument there, but one wonders why Canon still publish MTF data at only 10 lp/mm and 30 lp/mm.
But that's going to change, isn't it? Cameras like the 20D and D2X are already capable of greater than 50 lp/mm with a good lens.
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One sensible approach to resolution is saying how good the contrast and such is at length scales or relevance to typical print size and viewing conditions, and figures lie 10 and 30 lp/mm, or 240 and 720 line pairs per picture height (lp/ph) are well established standard choices. But I agree that once sensors resolve to about 50lp/mm or better and lenses are often being used with formats smaller than 24x36mm, some new lp/mm levels should be chosen. Olympus has gone to 20 and 60 lp/mm for FourThirds lenses (270 and 810 lp/ph) so it is strange that even for EF-S lenses explicitly intended for a smaller 15x22.5mm frame, Canon still uses 10 and 30, instead of say 15 and 50.

P. S. It would probably be messy to compute and publish 50% MTF graphs for a lens, which would have to give the lp/mm at which 50%MTF is achieved for each value of radius from the optical axis, so MTF as a function of radius at a few well chosen lp/mm or lp/ph values is probably the only practical approach.
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Ray
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« Reply #56 on: January 23, 2006, 08:25:07 PM »
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One sensible approach to resolution is saying how good the contrast and such is at length scales or relevance to typical print size and viewing conditions, and figures lie 10 and 30 lp/mm, or 240 and 720 line pairs per picture height (lp/ph) are well established standard choices. approach.
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This reminds me of the dialog between Jonathan and Howard on the choice of DoF parameters relating to print size. Howard's view was that he would set up the shot with a specific print size in mind and that his choice of f/stop and CoC would relate to that print size. Jonathan reckoned that was bollocks   . He didn't want to reshoot a scene because the client later decided he wanted a bigger print.

My own view is, I don't have a specific print size in mind when I take a shot. However, experience tells me that several years down the track, I shall quite likely want to make larger prints, because (a) wide format printers have come down in price, ( sophisticated 'fractal' type programs relying upon massive computing power will probably do a better interpolation job than current programs, and © as I get older and my eyesight gets worse, I shall simply desire larger prints.
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Ray
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« Reply #57 on: January 23, 2006, 10:20:28 PM »
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Okay! I've learned that b in brackets means something else in this program   .

To get back on topic (and I should add that I'm not at all averse to digressions); my situation here is that my previous experience with 35mm film, in addition to hearsay and rule-of-thumb assertions that f8 delivers the crispest image, has created an impression that f16 is a resolution compromise.

I've just returned from a big shooting expedition in Nepal, Thailand and Cambodia where there were many situations where I knew I wanted the sharpest result with regard to the subject that was in focus, but (if possible) an equally sharp result with equally interesting material some distance from the focus point.

In such situations I generally stuck to f11. It now seems, perhaps specifically in regard to the Canon 24-105 lens, that this was a misjudgment on my part. To put it bluntly, I've bungled a lot of my shots.

Shall I give an example? Excuse the fact these are not fully processed images for printing. The first is the overview, with some cropping of the foreground to remove OOF elements resulting from an f11 choice of aperture.

[attachment=180:attachment]

The next crop shows the sacrifice in resolution I got by choosing f11 instead of f16. Never mind the foreground. That can be cropped, and has been. But the fourth bas relief is an essential part of the composition and it's also OOF. In case it's not apparent, there are four bas reliefs there, in increasing order of distance from the camera.

[attachment=181:attachment]

Of course, anyone might make the comment, you've got a digital camera, why didn't you take a number of shots at different apertures and focussing distances?

Okay! I've got my excuses   . My Tuk Tuk driver had been waiting about 5 hours and I'd told him I'd be just a couple of hours. Previous experience had taught me that f16 should be avoided if good resolution was desired.

I was sort of hoping when I started this thread, that I'd get feedback from some readers who happen to have some exceptionally good prime lenses and who might have carried out their own tests on a 5D to assure me that good primes will always deliver a noticeably sharper result at f8 than at f16.

It hasn't happened. Where are you people? Not interested?
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bjanes
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« Reply #58 on: January 24, 2006, 06:32:10 AM »
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I was sort of hoping when I started this thread, that I'd get feedback from some readers who happen to have some exceptionally good prime lenses and who might have carried out their own tests on a 5D to assure me that good primes will always deliver a noticeably sharper result at f8 than at f16.

It hasn't happened. Where are you people? Not interested?
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Ray,

I did post a graph showing resolution of the Nikkor 50mm f/1.8 with the Nikon D70. Granted it is not of Leica quality, but it is known for excellent results when stopped down a bit from maximum aperture. To see the evaluation, click on the lenses link on the left and then normal lenses.

[a href=\"http://www.naturfotograf.com/index2.html]http://www.naturfotograf.com/index2.html[/url]

Here is another example of that lens with the D200. The results are from Norman Korens Imitest. Uncorrected means no sharpening and corrected means standardized sharpening. The results are hardly better than with the D70, but here they are:
« Last Edit: January 24, 2006, 06:34:03 AM by bjanes » Logged
Ray
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« Reply #59 on: January 24, 2006, 08:35:19 AM »
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I did post a graph showing resolution of the Nikkor 50mm f/1.8 with the Nikon D70.
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Bill,

Yes you did. But both the D70 and the D200 are smaller format than the 5D and try to make up for it with greater pixel density and higher resolution.

My guess is that the 5D has no meaningful resolution beyond 45 lp/mm. If the 25-105 IS lens is optimised for good performance at f16, there is no resolution advantage to be gained by opening up the aperture, there's only a slight increase in MTF at resolutions up to 45 lp/mm, and with this lens such MTF increases appear to be negligible. Simply switching from ACR to Raw Shooter probably has a greater effect on image detail, at the plane of focus, than opening up from f16 to f8.

Maybe I'll shoot some Norman Koren test charts when I have the time.
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