Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 71,929   Posts: 1,585,235   Online: 848
      
Page 2 of 4 FirstFirst 1234 LastLast
Results 11 to 20 of 39
  1. #11
    Ian Grant's Avatar
    Join Date
    Aug 2004
    Location
    West Midlands, UK, and Turkey
    Shooter
    Multi Format
    Posts
    16,436
    Images
    148
    Quote Originally Posted by Q.G. View Post
    I

    Stopping down to f/22 (or whatever the smallest aperture is) is a way that is guaranteed to not get the best out of your lens, ever.
    The effect of diffraction is quite large: possible resolution is halved (!) about every two stops the lens is stopped down.
    DOF calculators are all wrong. One big fault they have is that they do not take this overall image degradation that stopping down causes into account, which makes the difference between 'sharp' and not sharp much smaller, hence DOF much larger, than the formulae suggest.
    So you do get huge DOF. But never "sharper final images". Never that what you paid for when you bought the lens, never what it is capable of.

    f/22, and miss out.
    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

  2. #12
    Ed Sukach's Avatar
    Join Date
    Nov 2002
    Location
    Ipswich, Massachusetts, USA
    Shooter
    Medium Format
    Posts
    4,520
    Images
    26
    Quote Originally Posted by Q.G. View Post
    ...
    What also should not be forgotten is that diffraction always reduces what a lens can do, even at larger apertures.
    **Interesting** - A possible source to contradict what I've been taught in Optical Theory - and proven by many moons of commercial Optical Quality Control work. Can you direct me to your source ? Hopefully it is NOT "everybody knows".

    Many lenses are limited by residual aberrations wide open, and the beneficial effect of stopping down will be greater than the limiting effect of diffraction. When you find the point that both aberrations and diffraction are equally bad, you have found the optimum aperture.
    Uh ... you've lost me here. Same source?

    You have to run tests to find it. Each lens design is different, and graphs only show so much. So test.
    ... And the way to "test"? ... Optical Bench? MTF --- ?

    Now if you think it worth, practically speaking, to stop a lens down to its optimum aperture, you should also not want to stop it down any further.
    So forget about DOF.
    I would not forget. Can be useful information.

    Stopping down to f/22 (or whatever the smallest aperture is) is a way that i guaranteed to not get the best out of your lens, ever.
    Of course. All the lens manufacturers make *SURE* that it will be easy to *destroy* the quality of their lenses by providing easy access to "'small' apertures. They are intent on providing built-in "booby traps" for those who don't listen to "everybody knows".

    But ... seriously ... every lens is designed around "acceptable parameters" - OPTIMAL performance may well be at the "middle aperture; "Fast" lenses tend to be "shifted" towards the larger apertures; Copy lenses may ... usually don't... offer adjustable apertures.
    Believe me. every reputable lens manufacturer KNOWS that their clients *WILL* at one time or other, use their lenses at the smallest (highest numerical) aperture and they ARE designed to "go" there (I don't know about Holga).

    The effect of diffraction is quite large: possible resolution is halved (!) about every two stops the lens is stopped down.
    Man!!! Information about THAT progression, "halving"!!??, is something I've got to see in writing.

    I hate to tell you this, but diffraction limiting is NOT directly linked to f/stops.
    This is not a simple area of optical design ... you might try googling "diffraction".

    DOF calculators are all wrong....
    No, they are not "wrong".

    One big fault they have is that they do not take this overall image degradation that stopping down causes into account, which makes the difference between 'sharp' and not sharp much smaller, hence DOF much larger, than the formulae suggest.
    So you do get huge DOF. But never "sharper final images". Never that what you paid for when you bought the lens, never what it is capable of.
    f/22, and miss out.
    Uh ... can you give me the definition of "Circle of Confusion"?
    Carpe erratum!!

    Ed Sukach, FFP.

  3. #13
    keithwms's Avatar
    Join Date
    Oct 2006
    Location
    Charlottesville, Virginia
    Shooter
    Multi Format
    Posts
    6,079
    Blog Entries
    20
    Images
    129
    Oh my

    For anyone feeling buried in jargon, semantics and fine technical arguments, look at the link to the lens test applet that I posted above, it can teach you a lot!
    "Only dead fish follow the stream"

    [APUG Portfolio] [APUG Blog] [Website]

  4. #14
    RPippin's Avatar
    Join Date
    Apr 2008
    Location
    Charlottesville Virginia
    Shooter
    Multi Format
    Posts
    277
    Images
    75
    This has been an eye opening thread for me. I understand for the first time the true meaning of the "circle of confusion". Next for me is to apply this to a better understanding of the Zone System, BTZS, and "everybody knows, meter for the shadows and develop for the highlights".

  5. #15

    Join Date
    Jul 2007
    Location
    Netherlands
    Shooter
    Medium Format
    Posts
    5,686
    Quote Originally Posted by Ed Sukach View Post
    **Interesting** - A possible source to contradict what I've been taught in Optical Theory - and proven by many moons of commercial Optical Quality Control work. Can you direct me to your source ? Hopefully it is NOT "everybody knows". [...]
    You lost me completely.

    You have been taught Optical Theory, have worked many moons in Optical Quality Control work, and do not know this?!

    Now why don't you teach me how it really is?
    Go on!



    Quote Originally Posted by Ed Sukach View Post
    ... And the way to "test"? ... Optical Bench? MTF --- ?
    Take pictures.

    Quote Originally Posted by Ed Sukach View Post
    Of course. All the lens manufacturers make *SURE* that it will be easy to *destroy* the quality of their lenses by providing easy access to "'small' apertures. They are intent on providing built-in "booby traps" for those who don't listen to "everybody knows".
    Lens manufacturers?

    Today’s high quality color films do reach resolutions in the region of 140 line pairs per millimeter with Kodak Ektar 25 leading the field at 200! The full resolution potential of these films cannot be utilized with existing depth-of-field concepts nor f-settings of f/11 and beyond.

    Carl Zeiss, Camera Lens News, no. 2, Fall 1997.

    Quote Originally Posted by Ed Sukach View Post
    But ... seriously ...
    Seriously, what have you been smoking!?


    Quote Originally Posted by Ed Sukach View Post
    Man!!! Information about THAT progression, "halving"!!??, is something I've got to see in writing.
    Go back to your books then. I bet you haven't touched them since "many moons" ago.

    But, conveniently, from the same source, theoretical limits:

    f-no. resolution (line pairs per millimeter)
    45 - 35
    32 - 50
    22 - 70
    16 - 100
    11 - 140
    8 - 200
    5.6 - 280
    4 - 400
    2.8 - 560



    Quote Originally Posted by Ed Sukach View Post
    I hate to tell you this, but diffraction limiting is NOT directly linked to f/stops.
    You definitely need to return to your books!

    I was going to suggest that you look up the formula that describes the relation between f-stop and resolution when posting Zeiss' table when i saw what you wrote here.
    I now strongly urge you to do so!

    Quote Originally Posted by Ed Sukach View Post
    This is not a simple area of optical design ... you might try googling "diffraction".
    Let's make a deal: i'll do that, and you return to school.

    Quote Originally Posted by Ed Sukach View Post
    No, they are not "wrong".
    They are.
    In many ways.

    Quote Originally Posted by Ed Sukach View Post
    Uh ... can you give me the definition of "Circle of Confusion"?
    I can. Several
    One is about the thing your head seems to be spinning in right now.



    P.S.
    Been to Google, and nothing there i didn't know.
    Last edited by Q.G.; 08-12-2009 at 12:34 PM. Click to view previous post history.

  6. #16
    BetterSense's Avatar
    Join Date
    Aug 2008
    Location
    North Carolina
    Shooter
    35mm
    Posts
    2,883
    f-no. resolution (line pairs per millimeter)
    45 - 35
    32 - 50
    22 - 70
    16 - 100
    11 - 140
    8 - 200
    5.6 - 280
    4 - 400
    2.8 - 560
    That gives resolution in lp/mm. But does it consider the large effect format size has on acceptable sharpness?

    I'm thinking a 4x5 film is 3.33 times longer than a 35mm frame so stopping down to f/32 (50lp/mm*3.33=170) should be about as damaging to resolution as f8 is on 35mm at the same sized enlargement.
    f/22 and be there.

  7. #17

    Join Date
    Jul 2007
    Location
    Netherlands
    Shooter
    Medium Format
    Posts
    5,686
    It illustrates the relation between aperture and theoretically achievable resolution.
    Which is 'hard', i.e. the way it is, without anything we (including Ed ) can do about it.

    What resolution is still acceptable, and when, is another matter.
    It depends mostly on what we find acceptable.

    Criteria for CoC size traditionally are different for different formats, for exactly the reason you are thinking about.

  8. #18
    keithwms's Avatar
    Join Date
    Oct 2006
    Location
    Charlottesville, Virginia
    Shooter
    Multi Format
    Posts
    6,079
    Blog Entries
    20
    Images
    129
    Quote Originally Posted by BetterSense View Post
    That gives resolution in lp/mm. But does it consider the large effect format size has on acceptable sharpness?
    Which is why some people mention enlargement factor in this context.... Of course, pinhole photography is an interesting albeit extreme case in point.

    ~~~

    Overall, in my opinion, far too much time is spent discussing the high frequency center resolution, to the neglect of the rest of the frame.

    Tonal and focus transitions across the frame can be more important than maximum center esolution: you can have tack sharp center resolution and crappy edges, and that effect will be especially noticeable because the viewer of the print is able to see both side by side....

    ...which brings me to a basic principle of perception that sometimes gets lost in the technicals: we are not generally able to perceive absolute resolution. I.e., your eye probably cannot tell the difference between a print from a 100 and 80 lp/mm neg at typical enlargement sizes, that kind of thing is background noise if the composition is effective. Critical detail that is lacking is usually not missed.... unless it is viewed comparatively.

    So, if you have a big falloff in resolution across the frame, that can certainly be noticed. And actually that is seen quite often. An extreme example would be the results from holgas etc. where the effect is so strong that it becomes a defining part of the composition.

    The effect of resolution falloff is manifest in the high frequency (critical detail) as well as in the tonal smoothness and perhaps also in the lower frequency characteristics e.g. the amount of swirl and general smoothness of the bokeh.

    So... apologies for the coffee-time ramble, but my point is that, in these discussions, too much emphasis is placed on the paradigm of front-to-back sharpness and how aperture selection affects the absolute resolution at frame center. There is a lot more to aperture selection than lp/mm at frame center!
    "Only dead fish follow the stream"

    [APUG Portfolio] [APUG Blog] [Website]

  9. #19
    Ian Grant's Avatar
    Join Date
    Aug 2004
    Location
    West Midlands, UK, and Turkey
    Shooter
    Multi Format
    Posts
    16,436
    Images
    148
    Quote Originally Posted by Q.G. View Post
    It illustrates the relation between aperture and theoretically achievable resolution.
    Which is 'hard', i.e. the way it is, without anything we (including Ed ) can do about it.

    What resolution is still acceptable, and when, is another matter.
    It depends mostly on what we find acceptable.

    Criteria for CoC size traditionally are different for different formats, for exactly the reason you are thinking about.
    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

  10. #20
    Ed Sukach's Avatar
    Join Date
    Nov 2002
    Location
    Ipswich, Massachusetts, USA
    Shooter
    Medium Format
    Posts
    4,520
    Images
    26
    Quote Originally Posted by Q.G. View Post
    You have been taught Optical Theory, have worked many moons in Optical Quality Control work, and do not know this?!
    No, I DON'T "know" this!

    Now why don't you teach me how it really is?
    Go on!
    Considering where you are starting from (and your attitude)...

    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.

    Polarisation, section 5, was another matter. I passed the "tests" - but I'm still not completely sure...


    Take pictures.
    Ah! Obviously an infallable way to test a lens, free from subjective judgement and preceptual bias.... NOT!

    [QUOTE Lens manufacturers?

    Today’s high quality color films do reach resolutions in the region of 140 line pairs per millimeter with Kodak Ektar 25 leading the field at 200! The full resolution potential of these films cannot be utilized with existing depth-of-field concepts nor f-settings of f/11 and beyond.

    Carl Zeiss, Camera Lens News, no. 2, Fall 1997. [/QUOTE]

    As interesting as that my be ... I doubt that it has anything to do with diffraction. Is the article available on-line ? Or ...?

    Seriously, what have you been smoking!?
    The last refuge of one insecure in his argument: an "Ad Hominem" attack.

    But, conveniently, from the same source, theoretical limits:
    The same source? Zeiss? Now I am really interested!

    f-no. resolution (line pairs per millimeter)
    45 - 35
    32 - 50
    22 - 70
    16 - 100
    11 - 140
    8 - 200
    5.6 - 280
    4 - 400
    2.8 - 560
    Nice table. Anything to do with diffraction?

    I was going to suggest that you look up the formula that describes the relation between f-stop and resolution when posting Zeiss' table when i saw what you wrote here.
    I now strongly urge you to do so!
    I understand some of the factors that influence lens design... What happened to "diffraction"?

    I can. Several
    One is about the thing your head seems to be spinning in right now.
    Well, that really says it all. There is only ONE definition recognized as "Circle of Confusion" - an important criteria in lens design.
    Carpe erratum!!

    Ed Sukach, FFP.

Page 2 of 4 FirstFirst 1234 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin