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Author Topic: Lens Diffraction - When is it an issue with Medium Format Lenses?  (Read 13299 times)
theguywitha645d
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« Reply #20 on: December 06, 2011, 08:04:05 AM »
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Theory is all very well but why not just do a test at different apertures with YOUR lens and back, and decide for yourself where the acceptable limit is?


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hjulenissen
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« Reply #21 on: December 06, 2011, 08:19:15 AM »
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Theory is all very well but why not just do a test at different apertures with YOUR lens and back, and decide for yourself where the acceptable limit is?
With no theoretical background, it is very hard to interpret the results. Perhaps a given image looks "sharp" to me when viewed @0.75 meters on a 27" computer monitor using default Lightroom development when shooting my 85mm on a crop-camera @ f/6.3 and 1/200s and "base" ISO using a nice stand and focused on a reasonably  shallow object at 10 meters. Would it make sense for me to find a soap-box and proclaim loudly that f/6.3 should be "good enough for anyone, anywhere"?

Are my results "good" and "as expected"? Do my results indicate that there is a flaw in my methods or my equipment? Are my expectations too low? Too high? Can I extrapolate my findings to all possible combinations of camera settings, motifs and light conditions, or do I need to accumulate field-experience with every single one before making up my mind?

I agree that good, relevant, hands-on empiry is always a good thing, and that arm-chair photography seldom results in nice images. I do believe that theoretical analysis and practical experience should be combined for optimal results.

-h
« Last Edit: December 06, 2011, 08:25:18 AM by hjulenissen » Logged
BartvanderWolf
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« Reply #22 on: December 06, 2011, 08:29:09 AM »
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Theory is all very well but why not just do a test at different apertures with YOUR lens and back, and decide for yourself where the acceptable limit is?

Hi Graham,

I agree that experience based on empirical observations is useful. However, it may not be immediately clear how to translate that experience to situations that have not been tested yet. That's where the theory can help to predict behavior well in advance, and take appropriate measures in advance.

By using the theory one can also simulate all sorts of scenarios that may be difficult to test, until confronted with them at the decisive moment. I think it's better to be prepared than sorry ...

Cheers,
Bart
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ErikKaffehr
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« Reply #23 on: December 06, 2011, 11:00:26 AM »
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Hi,

You can just shoot a series of images at different apertures and compare them, for instance using Lightroom´s 'Compare View'. This will demonstrate the deterioration of the image, than you need to decide how much deterioration you are willing to accept.

Best regards
Erik

With no theoretical background, it is very hard to interpret the results. Perhaps a given image looks "sharp" to me when viewed @0.75 meters on a 27" computer monitor using default Lightroom development when shooting my 85mm on a crop-camera @ f/6.3 and 1/200s and "base" ISO using a nice stand and focused on a reasonably  shallow object at 10 meters. Would it make sense for me to find a soap-box and proclaim loudly that f/6.3 should be "good enough for anyone, anywhere"?

Are my results "good" and "as expected"? Do my results indicate that there is a flaw in my methods or my equipment? Are my expectations too low? Too high? Can I extrapolate my findings to all possible combinations of camera settings, motifs and light conditions, or do I need to accumulate field-experience with every single one before making up my mind?

I agree that good, relevant, hands-on empiry is always a good thing, and that arm-chair photography seldom results in nice images. I do believe that theoretical analysis and practical experience should be combined for optimal results.

-h
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mmurph
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« Reply #24 on: December 06, 2011, 12:35:27 PM »
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Hi,

You can just shoot a series of images at different apertures and compare them, for instance using Lightroom´s 'Compare View'. This will demonstrate the deterioration

Good advice. I like theory now because anything physical hurts!  Tongue

You might also print a portion of each image at the size you will most likely print at. Some things that look terrible on the screen look fine on paper. And visa versa.

If your target size is 24 inch x 30 inch, or whatever, size the image in Photoshop, then print out an 8x10 sample of each of the images - from the center, corners, etc. 

Or better, I run cheap dye inks that are about $20 a liter in a calibrated Epson 7600 ($500 printer, $100 for Claria match OCP dye inks.)

I run my "proofs" off at 24"x30" (4x5) to be able to really see the image - my final output is almost always a print. (Fine art stuff now.). It costs less than $.30 for that size print on 170 weight proofing paper. Less than $.05 for the ink.

Great way to learn!

When I settled on default papers about 5 years ago, I ran the same image on 8.5x11 on more than 40 papers. Then at 24x30 on at least 10. Settled on 1 standard proof paper, 1 standard print, and 3 premium (normal, high end, b&w.). Sorry - wandering here! Huh

Cheers, Michael
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Wayne Fox
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« Reply #25 on: December 06, 2011, 05:59:30 PM »
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Hi,

You can just shoot a series of images at different apertures and compare them, for instance using Lightroom´s 'Compare View'. This will demonstrate the deterioration of the image, than you need to decide how much deterioration you are willing to accept.

Best regards
Erik


And while testing, dial in some varying sharpness settings, and perhaps even take them to photoshop for further sharpening and prints.

 As you have mentioned, current sharpening can offset the visual artifacts of diffraction quite nicely in many circumstances.  I shoot at f/22 all the time and have printed some large prints that look terrific.
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bjanes
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« Reply #26 on: December 06, 2011, 09:01:40 PM »
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And while testing, dial in some varying sharpness settings, and perhaps even take them to photoshop for further sharpening and prints.

 As you have mentioned, current sharpening can offset the visual artifacts of diffraction quite nicely in many circumstances.  I shoot at f/22 all the time and have printed some large prints that look terrific.

Wayne,

The prints may look terrific, but you have effectively reduced the resolution of your IQ180 to perhaps that of a 6 MP dSLR. Still, you can take some very nice shots with a 6 MP camera.

Nathan Myhrvold puts it succinctly:

"Now, I don’t think anybody would be very excited about turning their EOS 1Ds Mark II, or Canon 5D or other full frame camera into a 2 megapixel camera. It sounds pretty drastic, but that is exactly what you do when you stop down to f/22 – the diffraction limit imposes this condition. If you shoot with a full frame 24 x 36 sensor at f/22 you are throwing away a lot of resolution. There is no getting around this – it is fundamental in the physics of light."

For some subjects, excessive detail may detract from the impact of the image. Can you imagine Monet's water lilies presented with photographic reality.

Regards,

Bill




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EricWHiss
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« Reply #27 on: December 06, 2011, 10:58:05 PM »
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Theory is all very well but why not just do a test at different apertures with YOUR lens and back, and decide for yourself where the acceptable limit is?

That's exactly what I did
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hjulenissen
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« Reply #28 on: December 07, 2011, 12:33:47 AM »
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Hi,

You can just shoot a series of images at different apertures and compare them, for instance using Lightroom´s 'Compare View'. This will demonstrate the deterioration of the image, than you need to decide how much deterioration you are willing to accept.

Best regards
Erik

My point was that there are many variables in-between camera aperture setting, and me being satisfied with the end-results. If I am going to ignore every piece of theoretical understanding I may have, I would strictly have to investigate every single one of them. My life is too short for that, therefore I try to combine theory with practice. One example may be that I assume that the results at f/6.3 will be an intermediate of the results at f/5.6 and f/7.1. Or that the deterioration due to diffraction at small apertures will be similar in two lenses. Or that the images shown on my computer display tells me something about how the image will look on paper.

I do agree that shooting at different apertures to get a qualitative feeling for how it affects images is a good thing.

-h
« Last Edit: December 07, 2011, 12:37:43 AM by hjulenissen » Logged
ErikKaffehr
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« Reply #29 on: December 07, 2011, 12:42:05 AM »
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Bill,

Wayne has a good point. Don't forget that we discuss diffraction or parts of the image being out of focus. With deconvolution sharpening, even with unknown PSF, we can improve much on diffraction and less on out of focus. Diffraction is more like a broad peak, with most of the energy at the center. Out of focus is more like an uniform disk with aberrations added depending on construction of the lens.

We had a lengthy discussion here on LuLa forums regarding deconvolution that you, Wayne ;-), me and many other were involved in: http://www.luminous-landscape.com/forum/index.php?topic=45038.0

This is just one sample from that discussion:
http://www.luminous-landscape.com/forum/index.php?topic=45038.msg378744#msg378744

Best regards
Erik

Wayne,

The prints may look terrific, but you have effectively reduced the resolution of your IQ180 to perhaps that of a 6 MP dSLR. Still, you can take some very nice shots with a 6 MP camera.

Nathan Myhrvold puts it succinctly:

"Now, I don’t think anybody would be very excited about turning their EOS 1Ds Mark II, or Canon 5D or other full frame camera into a 2 megapixel camera. It sounds pretty drastic, but that is exactly what you do when you stop down to f/22 – the diffraction limit imposes this condition. If you shoot with a full frame 24 x 36 sensor at f/22 you are throwing away a lot of resolution. There is no getting around this – it is fundamental in the physics of light."

For some subjects, excessive detail may detract from the impact of the image. Can you imagine Monet's water lilies presented with photographic reality.

Regards,

Bill





« Last Edit: December 07, 2011, 12:43:48 AM by ErikKaffehr » Logged

Wayne Fox
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« Reply #30 on: December 07, 2011, 01:20:22 AM »
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Wayne,

The prints may look terrific, but you have effectively reduced the resolution of your IQ180 to perhaps that of a 6 MP dSLR. Still, you can take some very nice shots with a 6 MP camera.

Nathan Myhrvold puts it succinctly:

"Now, I don’t think anybody would be very excited about turning their EOS 1Ds Mark II, or Canon 5D or other full frame camera into a 2 megapixel camera. It sounds pretty drastic, but that is exactly what you do when you stop down to f/22 – the diffraction limit imposes this condition. If you shoot with a full frame 24 x 36 sensor at f/22 you are throwing away a lot of resolution. There is no getting around this – it is fundamental in the physics of light."

For some subjects, excessive detail may detract from the impact of the image. Can you imagine Monet's water lilies presented with photographic reality.

Regards,

Bill
Well, I've shot with nearly every digital camera since my Kodak DCS 520 and 560, and have many images taken with decent sensors such as the original 1Ds.  I'm not a scientist, but I do know none of these printed large (90" pano for example) can come close to what I see with the phase backs, even at  f/22.  they're just absolute mush at that size and the phase files look terrific ... even up close.
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John R Smith
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« Reply #31 on: December 07, 2011, 04:04:08 AM »
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My approach to this is a purely practical one. For almost all the Zeiss 'C' lenses which I use, the best MTF is at f8, according to the factory data.

Now, I find I can see almost no loss of IQ at f11, but I do gain a bit of useful DOF over f8. So I tend to use f11 as my working aperture pretty much most of the time. If the light is really bright and I need the DOF I will use f16 just now and then, but you can certainly see a fall-off in the centre at f22 so I avoid it. That's for the normal run of lenses - on my 120mm S-Planar f22 is useable but f32 and f45 are pretty hopeless, really. The oddball lens is the 250mm Sonnar, which has its best MTF wide-open at f5.6. The DOF is pretty skinny, though. That's it - having discovered those things some while ago I no longer worry about it.

John
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hdomke
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« Reply #32 on: December 07, 2011, 05:15:26 AM »
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Quote
why not just do a test at different apertures with YOUR lens and back
I agree. Any suggestions on a practical way to do that?
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ErikKaffehr
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« Reply #33 on: December 07, 2011, 05:32:22 AM »
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Hi,

Find a good subject, like a dollar bill and photograph it with different apertures using the best technique you have.

My test, below was done with a 100 mm lens at 3.0 meters. I also varied "defocus" by moving the camera in 3cm steps.

http://echophoto.dnsalias.net/ekr/index.php/photoarticles/49-dof-in-digital-pictures?start=1

Last page shows effect of deconvolution sharpening with Lightroom and Topaz InFocus.

In general, the more you have, the more do you loose.

Best regards
Erik


I agree. Any suggestions on a practical way to do that?
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theguywitha645d
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« Reply #34 on: December 07, 2011, 08:04:03 AM »
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I agree. Any suggestions on a practical way to do that?

take some pictures at different apertures and print them large. Not difficult at all really.
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KLaban
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« Reply #35 on: December 07, 2011, 08:15:28 AM »
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And above all do relevant tests. Pictures of dollar bills or brick walls aren't going to be of much help to a landscape photographer.
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theguywitha645d
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« Reply #36 on: December 07, 2011, 08:16:01 AM »
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Wayne,

The prints may look terrific, but you have effectively reduced the resolution of your IQ180 to perhaps that of a 6 MP dSLR. Still, you can take some very nice shots with a 6 MP camera.

Nathan Myhrvold puts it succinctly:

"Now, I don’t think anybody would be very excited about turning their EOS 1Ds Mark II, or Canon 5D or other full frame camera into a 2 megapixel camera. It sounds pretty drastic, but that is exactly what you do when you stop down to f/22 – the diffraction limit imposes this condition. If you shoot with a full frame 24 x 36 sensor at f/22 you are throwing away a lot of resolution. There is no getting around this – it is fundamental in the physics of light."

For some subjects, excessive detail may detract from the impact of the image. Can you imagine Monet's water lilies presented with photographic reality.

Regards,

Bill






That is the silliest thing I have read in a long time. Like Wayne, I have shoot MFD at f/22 and that claim is so wrong on so many levels. So you are saying we are seeing great images, but actually they are really not good, we are just not seeing it? So if you cannot see the loss of quality, then why the stress on quality that cannot be observed?

I have a feeling the folks stressing absolute technical perfection really do not shoot and print their work. Only the working photographers seem not to be bothered by small working apertures. And if resolving power is really that important to people, I would like to note that my backgrounds and foreground have more resolution at small apertures than large ones--that is what DoF does...

This is one of the funniest conversation I have seen on LL in a while.
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theguywitha645d
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« Reply #37 on: December 07, 2011, 08:16:53 AM »
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And above all do relevant tests. Pictures of dollar bills or brick walls aren't going to be of much help to a landscape photographer.

But forgers and masons may benefit...
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ErikKaffehr
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« Reply #38 on: December 07, 2011, 09:39:38 AM »
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Hi,

You need to have fine detail down to pixel level, and it needs to be reproducible. A dollar bill shot at 300 cm with a 100 mm lens will have enough detail.

BR
Erik

And above all do relevant tests. Pictures of dollar bills or brick walls aren't going to be of much help to a landscape photographer.
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bjanes
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« Reply #39 on: December 07, 2011, 09:46:07 AM »
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That is the silliest thing I have read in a long time. Like Wayne, I have shoot MFD at f/22 and that claim is so wrong on so many levels. So you are saying we are seeing great images, but actually they are really not good, we are just not seeing it? So if you cannot see the loss of quality, then why the stress on quality that cannot be observed?

I have a feeling the folks stressing absolute technical perfection really do not shoot and print their work. Only the working photographers seem not to be bothered by small working apertures. And if resolving power is really that important to people, I would like to note that my backgrounds and foreground have more resolution at small apertures than large ones--that is what DoF does...

This is one of the funniest conversation I have seen on LL in a while.

It may appear funny to you, but it is based on the laws of physics. Nathan Myhrvold is no crank, but a genius with a PhD in physics form Princeton University. He is not only an accomplished scientist but an accomplished photographer and gourmet cook--a true renaissance man. That is why I chose to quote him. Of course, one can stop down further with a MFDB than a full frame dSLR, but a few calculations are instructive.

The pixel pitch of the IQ-180 is 5.17 μ, the resolution is 7816 x 10380 pixels, and the sensor dimension is 40.4 x 53.7 mm. The Airy disc diameter for light at 530 nm is 28.5 μ. The sensor becomes diffraction limited when the Airy disc diameter is 1.4 to 2 times the pixel pitch. Diffraction limited resolution of a lens at f/22 is 70 lp/mm at the Rayleigh limit (about 9% MTF) and 33 lp/mm at 50% MTF (figures from Roger Clark). Rayleigh resolution in an astronomical telescope can separate binary stars in this high contrast setting, but is not very useful for terrestrial photography, where an MTF of 50% is more reasonable.

One can use these figures to calculate the resolution of the IQ-180. The Rayleigh resolution at f/22 is 2840 x 3375 lp; since it takes 2 pixels to resolve 1 lp, that corresponds to 2702 x 3592 pixels or 43 MP. For a MTF of 50% the figures are 2702 x 3592 pixels or 9.7 MP.. For the Canon 1DsMIII that Dr. Myhrvold quoted in his post, the Rayleigh resolution at f/22 is 1687 x 2351 lp 17 MP. The MTF 50 resolution is 803 x 1204 lp or 3.9 MP, somewhat better than his prediction of 2MP.

One needs to correlate these figures to the perception of sharpness. According to David Pogue's tests, megapixels are not as important as often believed, so it is reasonable to get good results at the 9.7 MP you would get with the IQ-180 at f/22.

Regards,

Bill
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