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Author Topic: Lens Diffraction - When is it an issue with Medium Format Lenses?  (Read 22661 times)

hjulenissen

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Re: Lens Diffraction - When is it an issue with Medium Format Lenses?
« Reply #40 on: December 07, 2011, 01:16:34 PM »

...and I and my clients would rather my images were reproducible.

Photographing dollar bills will tell me how diffraction impacts my photographs of dollar bills and frankly I could care less.
The extreme "hands-on" take would be that testing camera settings when photographing pine trees say nothing about the results you will get when photographing birch trees. I dont think anyone are that fundamentalist.

The extreme "hands-off" take would be that everything worth knowing about photography can be studied by reading a book on physics, optics or the golden ratio. I dont think anyone are that fundamentalist.

Most of us try to patch together a coherent understanding/method based on _both_ personal experience and what we may read or calculate.

-h

"Experience keeps a dear school, but fools will learn in no other." Benjamin Franklin
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hjulenissen

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Re: Lens Diffraction - When is it an issue with Medium Format Lenses?
« Reply #41 on: December 07, 2011, 01:22:51 PM »

That is the silliest thing I have read in a long time...
I think that it is actually a slippery slope to compare diffraction artifacts to pixel density artifacts. I would be hesitant to claim that this or that f-number corresponds to this and that number of megapixels, or that there is a hard limit beyond which the benefit of adding more megapixels are exactly zero. Nature and physics seems to generally "dislike" hard limits or rectangular functions.

But if a 180MP image contains no more details than a 6MP camera could have, so what if it looks good? I believe that people have had exhibitions and national geographic pages using 6MP cameras, the limiting factor for most of us is between the ears, or luck or travelling budget, or ...

-h
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hjulenissen

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Re: Lens Diffraction - When is it an issue with Medium Format Lenses?
« Reply #42 on: December 07, 2011, 03:01:37 PM »

...placing too much importance on tests, reading books on physics, optics and particularly the golden ratio.
Or walking around with misconceptions stemming from doing a lot of hands-on testing but not understanding the physics behind it, or the issues with non-blind subjective testing.

People who reject science are particularly easily fooled by people who sells snake-oil.

-h
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ErikKaffehr

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Re: Lens Diffraction - When is it an issue with Medium Format Lenses?
« Reply #43 on: December 07, 2011, 03:21:14 PM »

Hy,

Physics and chemistry are obviously important, without that our planet would not support 7 billion (US) people, nor would we have cameras, computers and forums like this. I don't know if Neanderthal art was very profitable.

It's OK to be an artist but do have some respect for the folks that develop the tools you have. No lens, camera or sensor could have been created ever without a massive amount of science. OK, there have been a few lenses crafted by hand, without good knowledge of optics. But since the Petzval lens (daddy of all Tessars) all lenses are based on science.

This is a good read: http://www.lensrentals.com/blog/2011/08/lens-geneology-part-1

Best regards
Erik

Or walking around with misconceptions stemming from doing a lot of hands-on testing but not understanding the physics behind it, or the issues with non-blind subjective testing.

People who reject science are particularly easily fooled by people who sells snake-oil.

-h

theguywitha645d

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Re: Lens Diffraction - When is it an issue with Medium Format Lenses?
« Reply #44 on: December 07, 2011, 04:12:24 PM »

Really, you know, there is no big deal about any of this stuff.

With almost all the stock MF lenses, the widest aperture will be crap - it is just there for focusing - and the smallest aperture will also be crap. (We are not talking Leica here, and amazing wide-open performance, neither are we discussing LF lenses and the capability to use f64).  So if the biggest hole and the smallest hole should be avoided, that leaves the ones in between. It's pretty safe to assume that the hole in the middle of the range (around f8) will be the best to use. So use f8, but if you need a bit more DOF then f11 will be just fine too. On the other hand, if you would like a softer background for portaits, open her up to f5.6.

That's pretty much it, really. What else are you going to do?

John

John, you are right, there is no big deal about this stuff. I would rather have a perfect image rather than perfect resolving power.

The documentary work I do in low light handheld with MFD, the widest aperture is great. I find that some of the limitation like vignetting can add to the image and some of the "bad" aberrations are still better than handshake. Many of my medium-format lenses are actually very nice wide open. My smaller format lenses are far worse--although their max aperture is also larger.

And since the science has been brought up, the funny thing is that it does not say shoot only at f/11. The aperture range is actually determined for the format and the lenses ability. Except for a few lenses where maximum aperture is really just for focusing, the optical designers are making the apertures within the useful range.
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bjanes

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Re: Lens Diffraction - When is it an issue with Medium Format Lenses?
« Reply #45 on: December 07, 2011, 05:49:48 PM »

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.

Erik,

An excellent demonstration! I have tried to use authoritative references to back up my calculations, but nothing beats actual data in a well done test. So far in this thread you are the only one to present actual images. The subjective impression of the IQ of an image is the most important factor in the end, but it is good to back up the impression with quantitative data such as MTF. You could add Bart van der Wolf's resolution chart to the setup to check resolution and aliasing. Thus far, none of our MFDB colleagues have taken up the challenge.

The results of the Topaz InFocus deconvolution restoration look good and have less artifact than the SmartSharpen method. I did buy InFocus when Bart recommended it and it was on sale, but I haven't used it much. It takes a bit of work to get the parameters right, and I will have to crank it up and work with it a bit more.

Regards,

Bill
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EricWHiss

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Re: Lens Diffraction - When is it an issue with Medium Format Lenses?
« Reply #46 on: December 07, 2011, 07:37:48 PM »

Hmm, I don't know you from Adam, but I'll hazard a guess that you make your living as a scientist rather than an image maker?

Some of us have both Art and Science backgrounds.  Me? I test my stuff so I know what I'm going to get and what I can and can't do with it. Saves a lot of time.  And I have degrees in both fine art and physics and worked in both professions. What's wrong with that?  The people who don't have the time/energy/experience to test all benefit from those that do.  You must have some interest in this otherwise you wouldn't read...   
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theguywitha645d

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Re: Lens Diffraction - When is it an issue with Medium Format Lenses?
« Reply #47 on: December 07, 2011, 08:29:06 PM »

Pentax 645D, D FA 55mm, ISO 200, f/22. The scene. 100% crop (and I am unsure if it is from the plane of focus). A plot of a small section of the image which is also inset in the plot. The image is resolving features 12 micros or a less on the image plane.
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Doug Peterson

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Re: Lens Diffraction - When is it an issue with Medium Format Lenses?
« Reply #48 on: December 07, 2011, 08:34:01 PM »

I don't agree at all. Neither a lens or a sensor will care about if you photograph a Dollar bill, or details on a redfern or twigs on a dead tree 200 m away.

But I want to have my test reproducible.

Macro vs. Infinity lens performance are not the same. A lens may well be much sharper at infinity than it's closest focus distance (or vice versa). The sharper the lens the less diffraction can be tolerated if the goal is to get the sharpest image the system can produce.

Also in macro photography the effective aperture regarding diffraction are not the same as the marked aperture of the lens.

e.g. here is an extreme macro example where diffraction kicks in at a lens marking of f/2.8 and is severe by f/5.6.
http://www.captureintegration.com/2009/08/25/extreme-macro/

Yet another vote for real-world testing in situations as close to your actual intended use as possible.

Doug Peterson (e-mail Me)
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Alan Klein

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Re: Lens Diffraction - When is it an issue with Medium Format Lenses?
« Reply #49 on: December 07, 2011, 10:50:17 PM »

When I shoot Landscapes with my Mamiya RB67, I want everything in focus from front to rear.  So I work with the Hyperfocal distance, figure out what aperture I need, and then stop down one more stop for good measure.  Is this right?  Is this wrong?
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EricWHiss

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Re: Lens Diffraction - When is it an issue with Medium Format Lenses?
« Reply #50 on: December 07, 2011, 11:32:40 PM »

Pentax 645D, D FA 55mm, ISO 200, f/22. The scene. 100% crop (and I am unsure if it is from the plane of focus). A plot of a small section of the image which is also inset in the plot. The image is resolving features 12 micros or a less on the image plane.

Interesting - to me that image is too soft for my purposes.  I wonder if you have tried working this image using the detail slider in Lightroom or ACR or one of the other deconvolution programs?
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ErikKaffehr

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Re: Lens Diffraction - When is it an issue with Medium Format Lenses?
« Reply #51 on: December 07, 2011, 11:44:53 PM »

Hi,

The recommendation was to shoot it at 3 meter distance with a 100 mm lens, so it's hardly macro. The reason I suggested the Dollar bill is that it has a lot of fine detail and is quite challenging in many ways.

Of course, my posting was a one liner, but it refers to this posting: http://www.luminous-landscape.com/forum/index.php?topic=59978.msg484272#msg484272

Your point is very valid. Thirty times focal length is still a bit on the short side for testing lenses.

Best regards
Erik

Macro vs. Infinity lens performance are not the same. A lens may well be much sharper at infinity than it's closest focus distance (or vice versa). The sharper the lens the less diffraction can be tolerated if the goal is to get the sharpest image the system can produce.

Also in macro photography the effective aperture regarding diffraction are not the same as the marked aperture of the lens.

e.g. here is an extreme macro example where diffraction kicks in at a lens marking of f/2.8 and is severe by f/5.6.
http://www.captureintegration.com/2009/08/25/extreme-macro/

Yet another vote for real-world testing in situations as close to your actual intended use as possible.

Doug Peterson (e-mail Me)
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ErikKaffehr

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Re: Lens Diffraction - When is it an issue with Medium Format Lenses?
« Reply #52 on: December 08, 2011, 01:00:31 AM »

Alan,

What is right or wrong can only you decide, if you are happy, you are happy.

Using the hyperfocal distance is not without problems. The question is which hyperfocal distance you use?! Hyperfocal distance and DoF essentially are about the acceptable amount of unsharpness. So hyperfocal distance calculation is essentially based on an acceptable amount of unsharpeness criterion, normally called CoC (Circle of Confusion). When lens is at hyperfocal distance, everything from infinity to half hyperfocal distance will be at least as sharp as the criterion.

The problem is that your eyes may be more demanding than the criterion.

Here is a very good article about adapting hyperfocal focusing for high resolution work: http://optechsdigital.com/Alpa_and_Hyperfocal.html

When I shot 67 on film I normally used the f/8 markers for depth of field when shooting at f/16.

Best regards
Erik



When I shoot Landscapes with my Mamiya RB67, I want everything in focus from front to rear.  So I work with the Hyperfocal distance, figure out what aperture I need, and then stop down one more stop for good measure.  Is this right?  Is this wrong?

Rob C

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Re: Lens Diffraction - When is it an issue with Medium Format Lenses?
« Reply #53 on: December 08, 2011, 04:06:58 AM »

When I shoot Landscapes with my Mamiya RB67, I want everything in focus from front to rear.  So I work with the Hyperfocal distance, figure out what aperture I need, and then stop down one more stop for good measure.  Is this right?  Is this wrong?




If it works, it's right.

What else are you reasonably going to do?

Rob C

hjulenissen

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Re: Lens Diffraction - When is it an issue with Medium Format Lenses?
« Reply #54 on: December 08, 2011, 06:28:03 AM »

Hmm, I don't know you from Adam, but I'll hazard a guess that you make your living as a scientist rather than an image maker?
Neither, actually. In what way does my occupation make my arguments more or less valid?

Both "hands-on" and "hands-off" approaches can be done in stupid ways, and easily ridiculed. Do you want to ridicule one but not the other?

-h
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ErikKaffehr

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Re: Lens Diffraction - When is it an issue with Medium Format Lenses?
« Reply #55 on: December 08, 2011, 06:44:03 AM »

Hi,

Doug's posting referred to oneliner. The original posting clearly indicated that the Dollar bill was shot at three meters with a 100 mm lens.

Best regards
Erik

Eric, the above is the opening line of my original post to this thread.

Doug's post highlights the importance of relevant testing.

I've nothing against testing as such, hell, I do my own, but I make damn sure it is relevant to my own work!


Doug Peterson

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Re: Lens Diffraction - When is it an issue with Medium Format Lenses?
« Reply #56 on: December 08, 2011, 08:26:14 AM »

The recommendation was to shoot it at 3 meter distance with a 100 mm lens, so it's hardly macro. The reason I suggested the Dollar bill is that it has a lot of fine detail and is quite challenging in many ways.

Of course, my posting was a one liner, but it refers to this posting: http://www.luminous-landscape.com/forum/index.php?topic=59978.msg484272#msg484272

Your point is very valid. Thirty times focal length is still a bit on the short side for testing lenses.

My apologies for missing that detail.

I guess my general issue with "lab" tests is that they only tell you the answer to questions you know to ask. The "known unknowns" as Cheney would say. Often the "unknown unknowns" are often the ones that bite you in the butt.

At Capture Integration we get a lot of odd-ball testing requests from photographers who are going to use the camera exclusively for landscape. Generally I try to convince them going out and shooting a landscape is the best way to determine how a camera will perform when shooting a landscape :-). Ideally with the different equipment you are considering and alongside someone who knows where the pitfalls/misuse/mistakes/limits of each system are (e.g. don't stop down that canon lens to f/22).

theguywitha645d

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Re: Lens Diffraction - When is it an issue with Medium Format Lenses?
« Reply #57 on: December 08, 2011, 08:27:35 AM »

Interesting - to me that image is too soft for my purposes.  I wonder if you have tried working this image using the detail slider in Lightroom or ACR or one of the other deconvolution programs?


You mean soft at 100%? 100% is not a real world viewing condition. So you have made a 3 foot print? Besides, I this is a low contrast scene I shoot as a test, the test I mention in the thread, to see what the result would be at f/22 and a bunch of other apertures to show the effect of diffraction. Result: diffraction is overstated.
« Last Edit: December 08, 2011, 08:40:17 AM by theguywitha645d »
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theguywitha645d

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Re: Lens Diffraction - When is it an issue with Medium Format Lenses?
« Reply #58 on: December 08, 2011, 08:38:20 AM »

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


Nathan may be a genius, but optics and imaging are not his fields. It would not be the first time someone making statement about something outside their field have made errors.

But anyway. Perhaps you can add to the discussion by showing examples of this megapixel equivalency hypothesis. Numbers are not results, especially if the underlying model has errors.
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bjanes

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Re: Lens Diffraction - When is it an issue with Medium Format Lenses?
« Reply #59 on: December 08, 2011, 09:44:43 AM »

Nathan may be a genius, but optics and imaging are not his fields. It would not be the first time someone making statement about something outside their field have made errors.

But anyway. Perhaps you can add to the discussion by showing examples of this megapixel equivalency hypothesis. Numbers are not results, especially if the underlying model has errors.

Perhaps you should read his article and then point out where he made errors. Your own results seem to verify the hypothesis (vida infra).

Pentax 645D, D FA 55mm, ISO 200, f/22. The scene. 100% crop (and I am unsure if it is from the plane of focus). A plot of a small section of the image which is also inset in the plot. The image is resolving features 12 micros or a less on the image plane.

Your test shot does show light and dark bands likely representing resolved areas of the bark or other tree structures. Aliasing and demosaicing artifacts as well as excessive sharpening can produce false detail, but diffraction at f/22 should have eliminated most aliasing and I assume we are seeing true resolution.

Resolution is measured in lp/mm or cycles/mm--that represents peak to peak. Measuring peak to peak, I get 25 μ which would be 40 lp/mm. You seem to have measured peak to trough. From my previous calculations, the resolution of a diffraction limited lens at f/22 is 70 lp/mm at the Rayleigh limit and 33 lp/mm at 50% MTF. Your resolution is somewhere between these two values and is consistent with theory. The Nyquist frequency of your sensor is 84 lp/mm and you are achieving considerably less in your shot. A statement regarding resolution is incomplete unless the contrast achieved for that resolution is stated. Resolution at 50% contrast (MTF 50) correlates best with perceived sharpness.

BTW, what software did you use for your measurement? Photoshop extended? Anyway, nice work.

Regards,

Bill  

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