Determining optimum aperture?

[Ian Grant]

Complete rubbish and misquoted

Complete rubbish, you attribute quotes to me that are most certainly not written or said by me.

This is ALL I have said:

Tessar type lenses (135mm and over) only reach optimum performance at f22, that's intrinsic to the design, a modern Xenar 150mm f5.6 has a marked aperture scal to f64 and is still razor sharp at f45.

I'm not sure where you drag that myth from, both Schneider and Rodenstock manufacture their LF lenses to be used at f22/32 and with longer lenses f45/64.

Ian

and

Nothing you say falls into line with reality and the fact that LF lenses are designed to be used at f22/32 and have excellent resolution across the field.

Some lens designs don't achieve edge/corner sharpness until f22m andthen how do you explain the outstanding performance of an f5.6 150mm Xenar at f32 & f45, it stops down to f64 ?

Ian

So please don't fabricate facts.

These quotes are what you claim I've written:


Quote: Originally Posted by Ian Grant (there was a url link here which no longer exists)
Considering where you are starting from (and your attitude)...

That's perhaps because we cannot all be as learned as you, right?


Quote: Originally Posted by Ian Grant (there was a url link here which no longer exists)
Even though I am under NO obligation to instruct you in anything - you will just have to learn for yourself, I will direct you to:

This from one of the important text books:

What is Light? By A.C.S. van Heel and C.H.F. Velzel,World University Library - Library of Congress Catalog Card Number: 67-24448

Page 97, Section 4, Diffraction:
We can now turn to another facet in the study of light: the diffraction effects, the existence of which has already been mentioned. (See section 2 on the rectilinear propagation of light, and section 18 on the distribution of light at the focal plane of a lens upon reduction of the size of the diaphragm). To explain such phenomena, the great physicist and optician, Augustin Fresnel (1788 - 1827) developed a theory of the propagation of light, with which we begin our discussion.

Until now we have used as a model for the propagation of light, the theory of Huygens, which we define as follows.
One can imagine a wave front to originate out of the previous one by supposing each point in the latter to be a secondary source of spherical waves. The envelope of these spherical waves forms the new wave front..."


**Fascinating**. I will admit to having read this section a number of times, but I finally gained a fairly good "grasp" of what was going on.

Nice quote.
But it says absolutely nothing about this matter.
So not well chosen.

Quote: Originally Posted by Ian Grant (there was a url link here which no longer exists)
Polarisation, section 5, was another matter. I passed the "tests" - but I'm still not completely sure...

Who is?

Quote: Originally Posted by Ian Grant (there was a url link here which no longer exists)
Ah! Obviously an infallable way to test a lens, free from subjective judgement and preceptual bias.... NOT!

Who said anything about an infallible test?

But you do know (i assume, but tell me if i am wrong) that photography is a visual medium, and that what you see is what you get?
Good!

Quote: Originally Posted by Ian Grant (there was a url link here which no longer exists)
As interesting as that my be ... I doubt that it has anything to do with diffraction. Is the article available on-line ? Or ...?

Yes.
It has everything to do with diffraction (you really need to get those books out again)
And yes, it is available online.


Quote: Originally Posted by Ian Grant (there was a url link here which no longer exists)
The last refuge of one insecure in his argument: an "Ad Hominem" attack.

That's why you started by pointing out your personal qualifications?

I don't doubt your personal qualifications. So not even an ad hominem.
But given that your argument is based on authority, it is not possible to dismiss your mistake as such without touching your proffered authority.


Quote:
Originally Posted by Ian Grant (there was a url link here which no longer exists)
The same source? Zeiss? Now I am really interested!

You know it is optics 1.0.1.
So you really should know this, and not find this interesting, but old hat.


Quote:
Originally Posted by Ian Grant (there was a url link here which no longer exists)
Nice table. Anything to do with diffraction?

It is about nothing else but diffraction.

Quote:
Originally Posted by Ian Grant (there was a url link here which no longer exists)
I understand some of the factors that influence lens design... What happened to "diffraction"?

What are you asking?


Quote:
Originally Posted by Ian Grant (there was a url link here which no longer exists)
Well, that really says it all. There is only ONE definition recognized as "Circle of Confusion" - an important criteria in lens design.

Only one? You think so?
I think 'the place where your head is (was?) spinning' qualifies as a perfectly good definition.

Now just stop digging.

Well, there we are!

Based on your bragging, you should though.

That's perhaps because we cannot all be as learned as you, right?


Nice quote.
But it says absolutely nothing about this matter.
So not well chosen.

Who is?


Who said anything about an infallible test?

But you do know (i assume, but tell me if i am wrong) that photography is a visual medium, and that what you see is what you get?
Good!

Yes.
It has everything to do with diffraction (you really need to get those books out again)
And yes, it is available online.


That's why you started by pointing out your personal qualifications?


I don't doubt your personal qualifications. So not even an ad hominem.
But given that your argument is based on authority, it is not possible to dismiss your mistake as such without touching your proffered authority.

You know it is optics 1.0.1.
So you really should know this, and not find this interesting, but old hat.

It is about nothing else but diffraction.

What are you asking?


Only one? You think so?
I think 'the place where your head is (was?) spinning' qualifies as a perfectly good definition.

Now just stop digging.

At no point do you acknowledge that Zeiss, Rodenstock, Schneider and other manufacturers large format lenses are designed to give optimum performance at f22/f32, there's a vast difference between diffraction in a 50mm standard lens for a 35mm camera used at f22 and a LF lens at f22.

Ian

 

[Q.G.]

One thing to remember: the "practical limit" of any lens system is not entirely and wholly dependent on "diffraction"... it would be, IF the remaining parameters were all perfect... and the chances of that happening are not great.

Noone said that diffraction was the only limiting factor. Would be great if it was.

But, despite you not knowing, it always is there, getting worse when you stop down.
So the "f/22 and be there thing" comes at a cost. At f/22 it is the limiting factor.
And it's there, without chance for a let off. There is nothing design can do about it.

I will ask one favor: Direct me to web site where I can find Zeiss's formula for determining "diffraction limitation". Until I can check that out, I will not continue to discuss their assumptions.

Heck, no!
This is in all of your books and you should have learned this "many moons" ago..
Whether Fraunhofer, Abbe, Fresnel, Young, wave optics or Fourier optics, Kirchhoff, Keller, Dawes, Rayleigh or Sparrow, and what or who have you: whenever diffraction is mentioned this is too.

Assumptions?
Optics 1.0.1!

Why don't you apply for a job at Zeiss? Your job interview should be fun.

It is interesting that you consider "Diffraction" as one of the simple. basic phenomena. I think it is one or two notches above "basic".

Then it is perhaps interesting too that you put words in my mouth.
I never said i consider diffraction (both in or not in "") "as one of the simple, basic phenomena".

BTW... I've been considering the "tone" and syntax of your posts ... in some way, vaguely familiar. Would you happen to be posting from St. Louis, Missouri?

Ad hominem, again. You do know ad hominem means, don't you?

Apparently that too better than you do.

You are still trying to find refuge in that extremely silly "ad hominem" defence?

You made your expert knowledge the thing that gives weight to your mistaken view.
Argue using authority as 'proof' and face will be lost when you are wrong. There's no way around that.

It was your (!) choice to do so.
Don't you forget. Take a risk, bear the consequences. Don't blame anyone but you.

I hate to break the news, but, that time span is about 15 minutes.

"hate to ..."?
Your understanding of "many moons" (your words) is "about 15 minutes".
I can see why you hate to reveal that too.

About 15 minutes ago, you should have found that your books do not agree with your view.

Sounds good to me --- WHERE??

In those books you said you put down 15 minutes ago perhaps?

Hilarious. Indicative of your sharp wit, I suppose.

Who knows.
Indicative of a rather dull wit (now is that ad hominem?) that you needed it to be repeated to get it.

 

[Q.G.]

Ian,

Yes, the quote-thingy got mixed up badly.
My apologies for that.

Everything quoted should be attributed to Ed.

 

[Q.G.]

Ed,

I thought it could be HIM also.

Then you too might want to stick your nose in some books, and learn a bit.

 

[richard ide]

"Then you too might want to stick your nose in some books, and learn a bit."
That is a rather silly statement as you have no idea what I do or do not know. I know that I can produce a negative that resolves over 300 lppm with what I have at home. Diffraction be damned.
I guess you have no idea who "HIM" is. ;>)

 

[Q.G.]

Your right, Richard: i have no clue what you do or do not know.
And i am not assuming anything.

But i do know that anyone (no matter who, or what i might know or not know about him or her) who doesn't know the relation between aperture and diffraction, and the effect it has on image quality, still has a bit to learn.

I have no idea no: who is HIM?

 

[keithwms]

Alright, look here, this has gone on long enough hasn't it

Q.G. is correct that diffraction always limits resolution (actually there is one notable exception but it is technical and I will not bore you with it; suffice it to say that it's a well-known mechanism that I and many others get paid to research).

But... this is a big but... stopping down does not necessarily reduce resolution. It does at frame center, but not at the edges until you stop down really far. This is clearly seen in the flashlet I linked earlier and it also makes sense.

People need to look back at that applet/flashlet that I mentioned a few pages ago, then all will be crystal clear.

Seems to me that most of the tension in this thread comes from equating diffraction with stopping down, without completing the story in a clear way.

It's as simple as this: stopping down can actually improve off-center performance substantially. Just look at the freaking applet diddle the aperture setting between 5.6 and 11 and all will be clear! What is happening in that applet is quite typical. It applies to LF as well, look at these lovely charts....

http://www.hevanet.com/cperez/testing.html

Note that almost all LF lenses give quite poor corner performance wide open, relative to center performance (which, by the way, hardly matters for many typical LF enlargement factors). But look at the charts: if you average across the frame, almost every single lens achieves best overall performance at f/16 or f/22 or so. How important that is to you? Well you have the liberty of deciding that yourself. Like I said before, aperture selection is usually best guided by artistic vision, not by charts.

~~~

And...

it

is

really

annoying

when

people

use

so

many

quotes

Brevity is the soul of wit, y'all!

 

[Sal Santamaura]

Useful forum feature!

Ed, Ian and Richard,

Other than when others quote his posts, I've been blissfully Q.G.-free for more than six weeks. In the words of Fred Picker, "Try It!"

(there was a url link here which no longer exists)

 

[Ian Grant]

Another option Sal would be to use the quote system to list the image links & apertures used by John Sexton in every anwer to his posts.

Q.G. you should go look at Sexton's work, you don't have to like it but his technique can't be faulted and he uses f22. f32. f45 etc and just blows away everything you're trying to say, and so does the work of a huge percentage of other LF users.

Ian

 

[Q.G.]

How hard is it to accept that nature works in a particular way, despite what people, in their innocence, like or don't like?

Apparently very hard.

 

[Chazzy]

Call me practical, but the theoretical cost of diffraction doesn't interest me very much. I would much rather hear about the "sweet spot" for various lens designs based on actual use and experience. I believe Ian when he says that Tessars are best when stopped down—I have found the same—and I believe he is also correct in stating that most large format lenses are optimized for f22. But many large format lenses are surprisingly good at wider apertures—it depends on the lens. I wouldn't normally shoot an Angulon wide open, but a Super Angulon would be a different story. And of course uncorrected aberrations at wide apertures can be useful for some purposes—I love a portrait of my mother shot wide-open with a Tessar-clone.

 

[Ed Sukach]

I am not going to respond directly to "Q.G." The more he writes, the more convinced I am that it is ...HIM!!! - Posting yet again, under yet again, a different name... form St. Louis. Perhaps the moderators could check this out - I really do NOT want to form an opinion of anyone based on suspicion. I admire his tenacity, but he seems to be tenaciously abusive.

Possibly I can do something to straighten out this snarled mess. There is a basic truth here ... taken out of context, and extrapolated, there is the transferrence of a LOT of misinformation.

From an unamed source:

"But despite not knowing, it is always there (diffraction limitation) getting worse as you stop down. So the "f/22 and be there" thing comes at a cost. At f/22 it is the limiting factor, and it's there, without a chance for a let off. There is nothing design can do about it."


Truth:

in a *PERFECT* optical system (in this case, a camera lens), the final resolution WILL be limited by "diffraction". N.B. "PERFECT"!!

The easiest way to start is to draw attention to a necessary assumption: "Diffraction limitation" **IS** "always there", but it does not have an - ANY effect until it is applied to the performance of a "PERFECT" optical sytem. IF!!, n.b. "IF", you had a system capable of resoving 500 lines/ mm. you would see the ultimate resolution decreased. As far as I know, no one here HAS a "perfect" optical system - and I have never seen one in *MANY MOONS* worth of "looking". At the risk of intorducing a similie, I could install a governor on my Honda Accord to limit my top speed to 500 M.P.H. ... If that engine was in fact, "perfect" it might make it. It is not ... so there will be *NO** effect from the governor. I will NOT see my engine producing less power at 2, 5.6, 22, 11 MPH, or any less speed than 500.

My Honda Accord is DESIGNED to comply with certain design parameters - and it does that very well, thank you.

Do I feel the need to muck about with a theorectical limitation that has *NO* effect on what I am doing at the present...?, or even suggest some sort of magic to ... solve?? a problem that does NOT exist?
Not even! I do KNOW the "structure" (pretty much) of diffraction and its effects ... and I'm NOT going to worry about it.

My advice - final: Worry about something worth worrying about - "limiting dffraction" HAS been considered - and taken care of by most of the lens manufacturers. Feel fre to use any aperture you have.


Hmmm ... I wonder if it COULD be "HIM!!".

 

[Q.G.]

I am not going to respond directly to "Q.G." The more he writes, the more convinced I am that it is ...HIM!!! - Posting yet again, under yet again, a different name... form St. Louis. Perhaps the moderators could check this out - I really do NOT want to form an opinion of anyone based on suspicion. I admire his tenacity, but he seems to be tenaciously abusive.

You think you found a new refuge from your embarrasement?



The only misinformation here is
a) that you are very learned in this matter, as you have shown (and again show) not to be,

b) your implied - by offering your assumed learnedness as proof - believe that you, at any time, have been right at all,

c) the content of your attempts (continued now again) to wriggle out of this "snarled mess".

d) that you have not been abusive: your entire stance has been one of disdain. Ironically, you vehemently resent that, now that you realise that the egg is on your face.

e) that there is a basic truth here (there indeed is. One you repeatedly said you never heard or read anything about) taken out of context: your attempts to save face are the only instances of where this matter is taken out of context.

For instance; when or where was a "perfect" optical system mentioned in which diffraction is the only thing that limits resolution, except in your post above?
And how does that have anything to do with the fact that you denied - on your authority - the "basic" "truth" that diffraction and aperture size go hand in hand?
Nowhere.
And it doesn't.

So lots of misinformation spread by mr Ed Sukach.


And you follow it up with even more:

You obviously still do not grasp the concept.
No optical system needs to be perfect, since when you reduce the aperture far enough every single one (!) will be diffraction limited.
N.b. "EVERY SINGLE ONE"!!

Still optics 1.0.1

Luckily, you do apparently do know that "diffraction limitation is always there".

Just too bad that you dragged that PERFECT thingy into it.
And again started rambling about your very own perceived reality (based upon your many moons again).
There is no refuge either in alluding to a non-PERFECT world in which all you say is true. The problem is very real (that you say that you never come across anything like it again says something about you. Not about optics or lenses).
People do "muck about" with lenses that are best wide open. Those are by no means PERFECT lenses, but still only get worse when they are stopped down. And you should (! you probably still don't though) know by now what it is that makes them worse.

And your advice?
Very good: if we are to rely on lens manufacturer's, read what Zeiss had to say again.


And finally: the slimmest hope there might be that you had started to understand the matter is dashed by your "limiting dffraction" HAS been considered - and taken care of by most of the lens manufacturers."

You clearly do not understand that it cannot be taken care of anymore than gravity.
You clearly do not understand it at all.

 

[SuzanneR]

This thread has taken a decidedly ugly turn. Everyone's point has been made. A round of beers on me...