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So finally ... the new Leica DG 100-400mm f/4-6.3 OIS
#51
interesting that the different wavelengths of light effectively cause different resolution limits. Going back to the 100-400, from the tables Klaus linked to at luminous landscapes (https://luminous-landscape.com/wp-conten...TABLA3.jpg) we can see that at blue wavelengths at 400mm then lens should be able to resolve enough detail for a 16MPix sensor, however at red wavelengths it will not.

 

Sounds like Panasonic have designed a surf lens (not to be used at sunset!)

 

Smile

 

All kidding aside, I wonder if this is noticeable in use? 

#52
Quote:No, but but system resolution can in simple form be calculated with the old formula for this:

 

1/(system resolution) = 1/(lens resultion at specific f-stop) + 1/(sensor resolution)

 

For ease of use we are assuming that we are talking base iso for a sensor, and in that case sensor resolution is in principle equal to the nyquist frequency, plus or minus 5 to 15 % depending on de AA-filter stack being used.although fro ease of use we can ignore this.

 

Generally speaking, in the olden days, we worked all of this back to lp/mm, and for a 16 MP MFT sensor you then end up at approximately 133 lp/mm, for a 20 MP MFT sensor at base iso that is 150 lp/mm. If we assume a 10% reduction due to the AA-fiter, this then becomes approximtely 120 lp/mm and 135 lp/mm.

 

For diffraction based maximum lens resolution, we used to use the so-called Rayleigh criterion, and that amounts to using a wavelength of 512 Angstrom and an MTF of approximately 9%, which for normal shooting purposes is average. Note that MTF-50s are therefore typically a lot lower. Anyway, at F/1 the Rayleigh limit is about 1600 lp/mm, based on the Airy disk size, the diffraction circle size of a point, one gets at these parameters.

 

Because of diffraction, we then roughly get the following diffraction limits for perfect lenses at different f-stops, all based on the Rayleigh criterion:

 

F/1: 1600 lp/mm

F/1.4: 1143 lp/mm

F/2: 800 lp/mm

F/2.8: 571 lp/mm

F/4: 400 lp/mm

F/5.6: 286 lp/mm

F/8: 200 lp/mm

F/11: 145 lp/mm

F/16: 100 lp/mm

etc.

 

Now, there is no such thing as a perfect lens, and off-axis performance of a lens deteriorates as well, and at large apertures a lens is generally not at its best. However, many of the high quality lenses do rather well when stopped down a few stops, and some even get close if not equal diffraction limits at those f-stops, at least in the optical centre.

 

Because lenses tend to be best when stopped down a bit, generally speaking, and because diffraction gets worse with stopping down, what often happens when you measure lens resolution, is that the resolution starts at a specific point, gets higher, and when diffraction becomes teh limiting factor, lens resolution goes down again. You get a parabolic or elliptical type curve, with the top lying often at the f-stops a few stops away from maximum aperture.

 

The so-called diffraction limit of sensors, essentially is the aperture at which point a sensor cannot resolve beyond teh diffraction limit, purely caused by the fact that lights bend. It is a bit more complex than that, because sensor wells are indeed wells, and create shadows depending on the angle of the incoming light, but roughly this is correct. For MFT sensors at 16 MP and 20 MP these sensor diffraction limits are F/12 and F/11 respectively, but to get the most out of this you generally need to stop down  a full aperture less, so F/9 and F/8. it doesn't mean you can't take a picture, or can't get a usable image, but this is about making optimal use of what is available; the resolution of the sensor does not alter regardless.

 

As many testers use MFT-50 for their resolution findings, I have also calculated a set of MTF-50 diffraction limits. Here it is;

 

F/1: 760 lp/mm

F/1.4: 543 lp/mm

F/2: 380 lp/mm

F/2.8: 271 lp/mm

F/4: 190 lp/mm

F/5.6: 136 lp/mm

F/8: 95 lp/mm

F/11: 69 lp/mm

F/16: 48 lp/mm

etc.

 

I have created a few tables in which I also calculated the system resolution for different sensors, and perfect lenses, based on teh two diffraction limits I mentioned here (rayleigh criterion and MTF-50).

 

First, Panasonic Lumix GF2, a 12 MP MFT camera:
[Image: attachicon.gif]Panasonic GF2.jpg

 

Olympus O-MD E-M10 Mark II (16 MP, same as O-MD E-M5, etc.):
[Image: attachicon.gif]OMD-EM10-II.jpg

 

Olympus Pen F, 20 MP (same as Panasonix GX8):
[Image: attachicon.gif]pen-f.jpg

 

In short, as you can see, at F/4, 12 MP and MTF-50 maximum resolution is 72 lp/mm, at F/4, 16 MP and MTF-50 it is 78 lp/mm and at F/4, 20 MP and MTF-50 it is 84 lp/mm. Similarly, at F/5.6 it is 62 lp/mm, 67 lp/mm, and 71 lp/mm respectively. At apertures larger than F/4 lenses tend to have a lot of residual errors and resolve less, and as you can see at F/5.6 diffraction already starts to become signifcant (for any lens and any system).

 

Even so, resolution is well above what we used to have with film, as I mentioned before, in other posts.

 

HTH, kind regards, Wim
It does not help, Wim. You are mistaken about diffraction of light.

you quote from unknown source these numbers:
F/1: 1600 lp/mm

F/1.4: 1143 lp/mm

F/2: 800 lp/mm

F/2.8: 571 lp/mm

F/4: 400 lp/mm

F/5.6: 286 lp/mm

F/8: 200 lp/mm

F/11: 145 lp/mm

F/16: 100 lp/mm



The visible light spectrum covers a range of wave lengths of about 400nm (violet) to about 700nm (a red close to infra red).

Red light diffracts much stronger than blue light. Meaning: you get to a diffraction limit (based on the rayleigh criterion) much, much sooner with red light than with blue light.

I mentioned e-line before, a blue-ish green used in semiconductor lithography in the 60's and 70's (and probably 80's still) where the diffraction limit at f2.8 was 536, for f4 375 and for f5.6 268 l/mm.

The numbers you quote are from a colour more towards blue.

G-line (part of the UV spectrum, 435.8nm) has a diffraction limit of 672 l/mm for f2.8, for f4 470 l/mm and for f5.6 336 l/mm.

Just to place the wavelength you seem to quote about into perspective.

[Image: 2000px-Fraunhofer_lines.svg.png]

In real photography life, however, we never photograph with light just from the blue and violet spectrum. And if we did, we would get pretty low resolution with bayer and Fuji-X sensors (due to the CFA).

 

In reality, we photograph with "white" light. And that is why we get to see diffraction softening at much, much bigger apertures than if we were shooting with just a blue light source like where your numbers come from.

 

Chris, to answer your question: Yes, we do see diffraction softening due to longer wavelengths like yellow, orange and reds in everyday images. Those wave lengths are part of white light. So even if you were to photographs a green towards white subject only, like an american bank note, those longer wavelengths are part of the light spectrum going through the lens and they will spread out due to diffraction. Only subjects from saturated green or blue which go towards black (so not lighter parts than saturated green or blue) will not be affected by diffraction of longer wave lengths.

#53
"My opinion is correct but I have to keep in mind the possibility it could be wrong

Others opinion is wrong but I have to keep in mind it could be correct"

 

Averroes

 

(sorryif any grammatical or translation errors since  I have translated myself from Arabic)

#54
Toni, again, not everything is opinion. What I wrote about is just plain facts, based on the physics of light. Not my "opinion". Mixing up facts, not understanding their their context, and making your own supposition based on the incorrect understanding can or will lead to an opinion not supported by facts anymore. Like taking resolution numbers from a single colour from the visible light spectrum (a blue) and then saying those are the diffraction limits for photographic lenses.

 

<span>opinion |<span style="margin-left:.3em;">əˈpɪnjÉ™n| </span></span><span style="font-size:15px;color:rgb(119,119,119);"><span>noun</span></span>

<span><span style="font-weight:600;">1 <span>a view or judgement formed about something, not necessarily based on fact or knowledge<span>: </span><span style="font-style:italic;">that, <span style="font-weight:600;">in my opinion, is right</span>| </span><span style="font-style:italic;">the area's residents share vociferous opinions about the future.</span></span></span></span>

 

<span><span style="font-size:15px;color:rgb(119,119,119);margin-left:0em;"><span>fact |<span style="margin-left:.3em;">fakt| </span></span><span style="font-size:15px;color:rgb(119,119,119);"><span>noun</span></span></span></span>

<span><span style="margin-left:0em;">a thing that is known or proved to be true<span>:<span style="font-style:italic;">the most commonly known fact about hedgehogs is that they have fleas | </span><span><span>[ mass noun ] </span><span>:  a body of fact</span>.</span></span></span></span>

 

<span style="margin-left:0em;">Facts supported by evidence:
</span>

<span><span style="margin-left:0em;"><span><span>[Image: 162810_roz.png]</span></span></span></span>

#55
Quote:interesting that the different wavelengths of light effectively cause different resolution limits. Going back to the 100-400, from the tables Klaus linked to at luminous landscapes (https://luminous-landscape.com/wp-conten...TABLA3.jpg) we can see that at blue wavelengths at 400mm then lens should be able to resolve enough detail for a 16MPix sensor, however at red wavelengths it will not.

 

Sounds like Panasonic have designed a surf lens (not to be used at sunset!)

 

Smile

 

All kidding aside, I wonder if this is noticeable in use? 
 

In film photography, we never did worry about this, we just used the Rayleigh criterion, which essentially uses green light with a wavelength of 5120 Angstrom or 512 nm. Green light was chosen because that is what the human eye is very sensitive to.

 

It does indeed make a difference when pixelpeeping, as visible light ranges roughly from 390 to 700 nm, although you could argue it goes from 380 to 750 nm. That is approximately a doubling of wavelength, and halving of resolution, roughly speaking.

 

It will still resolve enough at 400 mm, I can assure you, because the resolution of teh sensor does not actually change, it is the total system resolution that changes because the diffraction limits changes. However, the better a lens is, the closer it gets to the diffraction limit, and certainly at the smaller apertures almost all lenses will be diffraction limited.

 

Do also note that MP limits as discussed are really system MP limits, based on resolution at specific apertures for a lens and sensor system.

 

I'll see if I can work out a few examples to show you what I mean. However, that has to wait till the weekend - away from home for work currently, and limited in what I can do as a result.

 

Kind regards, Wim
Gear: Canon EOS R, Canon EOS 5 (analog), 11 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, extension tubes, an accessory plague, and an Olympus OM-D 1 Mk II, Pen F and Panasonic GM5 with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....
#56
Quote:Just catching up on the thread. I think perhaps a better way to think about diffraction is there is a point where it starts to visibly "soften" the image, and there is a later point where it is the final limiting factor. Photographers tend to refer to the former, whereas I think Wim is referring to the latter.

 

There are times where it is still advantageous to work well into diffraction limited region. Anyone tried planet imaging? My scope would be, in photographic terms, 2000mm f/10. With barlows (think of them as functioning like teleconverters) I also tried 4000mm f/20, and 6000mm f/30. Of the three, the best results were obtained around f/20, as I was into the noise of my sensor at f/30, and the subject was too small at f/10. The sensor had just over 4 micron pixel pitch if you want to work out an effective MP to compare with photographic sensors, but I think that was in the rough ball park as 18MP APS-C from memory.
 

Probably something along those lines indeed. When do we think an image is "soft"?

I actually created 60cm x 90 cm prints from images taken with my first dslr, an 8MP 350D, and if you don't come to close, they are more than sharp enough. Smile

With proper exposures at lower isos, images taken with an MFT camera are way sharper, actually Smile.

 

There are similar problems with macro photography, where DoF at high magnifications is more important than resolution. I think it is always a trade-off.

 

Kind regards, Wim
Gear: Canon EOS R, Canon EOS 5 (analog), 11 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, extension tubes, an accessory plague, and an Olympus OM-D 1 Mk II, Pen F and Panasonic GM5 with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....
#57
Believe me what is now a fact might at any moment become a misconception.

Of course you know that some discoveries that won Nobel prize at the time proved wrong later on and those were facts no opinions.

I constantly verify and update my knowledge, whenever anyone doesn't agree with me my first reaction is "could he be right?" And something he is

I am not saying anyone is wrong here (coz I didn't read the lengthy discussion)I am just asking everyone to always be ready to update and verify his knowledge.
#58
Quote:In film photography, we never did worry about this, we just used the Rayleigh criterion, which essentially uses green light with a wavelength of 5120 Angstrom or 512 nm. Green light was chosen because that is what the human eye is very sensitive to.
 
It does indeed make a difference when pixelpeeping, as visible light ranges roughly from 390 to 700 nm, although you could argue it goes from 380 to 750 nm. That is approximately a doubling of wavelength, and halving of resolution, roughly speaking.
 
It will still resolve enough at 400 mm, I can assure you, because the resolution of teh sensor does not actually change, it is the total system resolution that changes because the diffraction limits changes. However, the better a lens is, the closer it gets to the diffraction limit, and certainly at the smaller apertures almost all lenses will be diffraction limited.
 
Do also note that MP limits as discussed are really system MP limits, based on resolution at specific apertures for a lens and sensor system.
 
I'll see if I can work out a few examples to show you what I mean. However, that has to wait till the weekend - away from home for work currently, and limited in what I can do as a result.
 
Kind regards, Wim
The Ratleigh criterion does not use a specific focal length. The angular resolution of an optical system can be estimated from any wavelength of light and the diameter of the apparent aperture. 
 
In your former example, you used a blue light source diffraction table, not green.

However, in photography we usually use white light.
#59
The whole discussion is entering the theoretical realm really.

Here's a good background article that remains readable for most of us:

http://www.cambridgeincolour.com/tutoria...graphy.htm

At the bottom of the article is also a nice calculator - you should select the "advanced" option to make the most of it. Play around with the settings and be happy ever after.

 

In practical terms, using the standard 16mp sensor, the MTF50 peak performance is usually reached around f/2.8 (on MFT at 16mp). From there on dampening effects are limiting the resolution potential - that is on pixel level (using a gray target - which includes the blue spectrum, FWIW). As far as I'm concerned there can only be one physical effect responsible for this and it is diffraction - as a result of a number of SYSTEM factors.  

Now does it matter that the (practical) peak is reach at f/2.8 (on MFT) ? Not really because the "plateau" spans till about f/8 before it collapses. At the end of the day this is the only relevant info for MFT users. Can we do something about diffraction? No, we can't.

 

I will close this thread now - it was about the Leica 100-400mm ... just in case somebody still remembers.  Big Grin

 

Feel free to open a new one though.

  


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