the myth of DIFFRACTION

[chauncey]

Okay, I'm not the sharpest knife in the drawer but I couple of things stand out with this thread...it's two years old, that explains how I missed it, and, it seems to dwell on philosophy and psychology.
Questions like "image sharpness verses image quality and how they impact image enjoyment" belong in the philosophical arena. The importance we attribute to those qualities oftentimes cross the line into the potential psychological difficulties, a cross that dwells at my very feet.

I've yet to read a widely accepted treatise on what specifically constitutes a great image...my own belief is "if it sells for big bucks, it must be good" seems somewhat trite by comparison to others I've read.

This thread represents the minutia that to which most of us will ascribe to reach that level of image perfection, read sharp. As I said, that cross lies at my feet as well as I obsess over my sharp critters...almost to the point of...aah, never mind. To return to philosophy...how much does it matter?

[xpatUSA]

I also find this thread a little odd. My puzzlement is all this talk about how complex the mathematics of the subject is when, for all intents and purposes, all we need is:

"The ability of an imaging system to resolve detail is ultimately limited by diffraction. This is because a plane wave incident on a circular lens or mirror is diffracted as described above. The light is not focused to a point but forms an Airy disk having a central spot in the focal plane with radius to the first null of d=1.22λN , where λ is the wavelength of the light and N is the f-number (focal length divided by diameter) of the imaging optics."

source: Wikipedia, of course.

That is simple arithmetic, not "Math"! (sorry about that double emphasis, William ;-). Everything else photographically related follows from there, surely?

cheers,

[Colin Southern]

Sorry - posted this to the wrong thread. Maybe.

[Adrian]

Tresise, Here is what you said:

From the 10 Edition, The Manual or Photography page 32
"Diffraction limited optical systems are very high quality systems, free of optical aberrations which otherwise mask the diffraction effect"

So basically no camera lens you or I could buy will be free from aberrations, and these aberrations have a greater effect than diffraction. So the talk about 'seeing' the diffraction in a camera lens is not accurate, plus other real world issues come into play.

You are drawing conclusions from your text book originated posts without providing any evidence that your conclusion is correct.

The reason I (and others) have pointed out qualifications, is that you tried to add credibility to your posts by listing yours and quoting text books. It was gently poking fun as you are being somewhat pompous and judgemental. This site is not a textbook: it is a resource (and a very good one too) for people to learn about photography and exchange thoughts about it. Nowhere does it claim to be the definitive technical guide, though so far I have still not seen a rational argument from you that actually demonstrates your assertion that CIS technical information is wrong.

The reason I quoted you above is that you made an assertion in the first paragraph, in essence that ultra high quality lenses (beyond our price range apparently) are free of optical aberrations and this characteristic means the diffraction effect is not masked.

The second quoted paragraph apparently draws the conclusion that other lenses are not free of optical aberrations, hence they do mask the diffraction effect. And that this in some way invalidates the information on CIC.

Can you see that what you have done here is exactly what you criticised CIC for? You have made a statement about expensive lenses. You have then extrapolated a negative assertion to cheaper lenses, without empirical evidence. It may, or may not, be right, but it does not withstand logical reasoning without support.

You hear this kind of thing in debates all the time: whether in a court of law or politics. It is rather like saying (to use an extreme illustration): A three star Michelin chef uses the very best cooker that you and I cannot afford, so he can cook steak perfectly. And then drawing the inference: you and I cannot cook a perfect steak because we only have a cheap cooker.

It is also, unfortunately, a weakness to rely on your textbooks and professors from 30 years ago as a credibility prop for your arguments. Textbooks and professors are not infallible. I have no idea whether technical understanding has advanced in the past three decades, but I do know from practical experience in the field of law (which I have not practised for a while now!), that very often for every "expert" you find that states a definitive opinion, another "expert" will be along soon who has a diametrically opposed view. We the jury, stand on the sidelines and make up our own mind whose picture we like best.

In the end all the chatter about diffraction, aberration and so on makes no difference. We make pictures. People who look at them either like them or they don't. It is entirely subjective and the technology, whether it be a lens or a sensor is merely a tool in a means to an end. If that tool is compromised it does not matter: I can never see exactly what you see anyway - there is no fixed truth in this as every image is interpreted differently by all of us as individuals.

Kind regards

Adrian

[Colin Southern]

I'm "calling time" on this thread because - frankly - I think that the OP is just trolling;

- The opening - inflammatory - post was made over 18 months ago, with no follow-up by the OP until now (what we call a "hit and run")

- Sean - suspecting the same trolling - was non-the-less kind enough to respond in full (being qualified to do so)

- and now that we've all been suckered into Round 1, he's back for round 2.

Folks interested in this mysterious "Page 32" that the OP keeps referencing (that's actually on page 33 by the way) may also be interested to note that for some "strange reason", the OP has left off the very next sentence, which reads:

"Most non-specialist lenses are aberration limited as residual aberrations are greater than the diffraction effects, certainly at large apertures". (emphasis mine).

Or in other words, typical camera lenses AREN'T DIFFRACTION LIMITED at large apertures -- something we all know. Diffraction at small apertures are by no means as clear cut, as they allude to (if it's "certain at large apertures" then it's "uncertain at small apertures").