Re: Diffraction limit for APS-C DLSRs

Discussion in 'Digital Photography' started by Kennedy McEwen, Jan 4, 2011.

  1. In article <>, Alfred Molon
    <> writes
    >At what aperture does diffraction start limiting significantly the
    >resolution with the current brand of APS-C DLRs (with 12, 16 and 18MP)?
    >
    >Is F11 still fine, can you go up to F16 or F22?


    Work it out yourself.
    Radius of the Airy Disc is about 1.22 x L x f/#, where L is the
    wavelength of light, say 0.55um for the middle of the visible band.

    The closest that two points can be resolved by the lens is when the edge
    of one disc is just at the centre of the other, which means the points
    are separated by one Airy Disc radius, and you need two pixels in that
    distance to be able to resolve the separation.
    so 2p = 1.22 x L x f/#
    f/# = 1.64 x p / L

    For 18Mp APS-C the pixels are about 4.2um pitch, so the *maximum* useful
    f/# is about f/12.5.

    So f/16 won't resolve any more than f/11 in practice.
    --
    Kennedy
    Yes, Socrates himself is particularly missed;
    A lovely little thinker, but a bugger when he's pissed.
    Python Philosophers (replace 'nospam' with 'kennedym' when replying)
     
    Kennedy McEwen, Jan 4, 2011
    #1
    1. Advertising

  2. In article <>, Alfred Molon
    <> writes
    >In article <>, Kennedy McEwen
    >says...
    >> So f/16 won't resolve any more than f/11 in practice.

    >
    >Thanks. So roughly one should go beyond F11, unless perhaps DOF is
    >needed, which however comes at the expense of available resolution.
    >

    I hope that was a typo - "shouldn't go beyond f/11 unless..." ;-)

    >One more question, what effect does the diffraction have - is it a low-
    >pass filter?


    Diffraction is a low pass "ramp" filter - the contrast reduces fairly
    linearly with spatial frequency gradually tapering off towards the
    cut-off frequency of 1/(L x f/#) above which there is zero contrast.

    >If so, sharpening could solve (partly) the problem at the
    >expense of SNR.


    Sharpening can partially compensate, particularly where the MTF is still
    significantly greater then zero, but obviously can't recover contrast
    when diffraction has attenuated it to zero in the first place - at and
    above the diffraction limit.
    --
    Kennedy
    Yes, Socrates himself is particularly missed;
    A lovely little thinker, but a bugger when he's pissed.
    Python Philosophers (replace 'nospam' with 'kennedym' when replying)
     
    Kennedy McEwen, Jan 4, 2011
    #2
    1. Advertising

  3. Kennedy McEwen

    Peabody Guest

    Kennedy McEwen says...

    > For 18Mp APS-C the pixels are about 4.2um pitch, so the
    > *maximum* useful f/# is about f/12.5.


    > So f/16 won't resolve any more than f/11 in practice.


    Just to be sure I understand... So, an APS-C camera of five
    years ago with, say, 8mp resolution would be less subject to
    diffraction limiting, although of course it has less
    resolution to start with. But for such a camera, f/22 might
    actually be a usable non-limiting setting?

    I'm just looking for reasons to keep my XT. :)
     
    Peabody, Jan 5, 2011
    #3
  4. Kennedy McEwen

    Peter Irwin Guest

    Peabody <> wrote:
    > Kennedy McEwen says...
    >
    > > For 18Mp APS-C the pixels are about 4.2um pitch, so the
    > > *maximum* useful f/# is about f/12.5.

    >
    > > So f/16 won't resolve any more than f/11 in practice.

    >
    > Just to be sure I understand... So, an APS-C camera of five
    > years ago with, say, 8mp resolution would be less subject to
    > diffraction limiting, although of course it has less
    > resolution to start with. But for such a camera, f/22 might
    > actually be a usable non-limiting setting?



    The difference between 8 and 18 megapixels should only be a hair
    over one stop. 18 megapixels is only 1.5 times the resolution of
    8 megapixels. (I say only 1.5 times, but then again 6x4.5cm film
    is only about 1.5 times a linear improvement on 24x36mm film.)

    > I'm just looking for reasons to keep my XT. :)


    If your camera is working for what you want to do with it, then
    that should be enough reason to keep it.

    Peter.
    --
     
    Peter Irwin, Jan 5, 2011
    #4
  5. In article <>, Peabody
    <> writes
    >Kennedy McEwen says...
    >
    > > For 18Mp APS-C the pixels are about 4.2um pitch, so the
    > > *maximum* useful f/# is about f/12.5.

    >
    > > So f/16 won't resolve any more than f/11 in practice.

    >
    >Just to be sure I understand... So, an APS-C camera of five
    >years ago with, say, 8mp resolution would be less subject to
    >diffraction limiting, although of course it has less
    >resolution to start with. But for such a camera, f/22 might
    >actually be a usable non-limiting setting?
    >

    Pretty much, although it won't be as far as f/22 though f/16 would be
    worth using. In general, the lower the resolution of the rest of the
    system, the higher an f/# you can use before diffraction becomes the
    dominant resolution limitation. Also, don't forget that this is the
    maximum f/#, beyond which diffraction actually degrades the camera
    resolution. Some diffraction blur will be visible a stop or so lower
    although, as already mentioned, this can be partially compensated by
    sharpening at the expense of increased noise.
    --
    Kennedy
    Yes, Socrates himself is particularly missed;
    A lovely little thinker, but a bugger when he's pissed.
    Python Philosophers (replace 'nospam' with 'kennedym' when replying)
     
    Kennedy McEwen, Jan 5, 2011
    #5
  6. In article <>, Pete D
    <> writes
    >
    >
    >"Alfred Molon" <> wrote in message
    >news:...
    >> In article <>, Pete D
    >> says...
    >>>
    >>> Totally impractical for the range of lens sizes I use.

    >>
    >> Why? You just buy the filters in the size of your largest lens and one
    >> (step up) adapter for each (smaller) lens size you have. Adapters cost a
    >> few Euro or dollar each.

    >So how many will I need to go from my 77mm down to my 49mm?


    One. ;-)
    I have one that came with my Zuiko 18mm f/3.5, but its not for sale.
    http://www.mir.com.my/rb/photography/hardwares/classics/olympusom1n2/shar
    ed/zuiko/htmls/18mm.htm
    --
    Kennedy
    Yes, Socrates himself is particularly missed;
    A lovely little thinker, but a bugger when he's pissed.
    Python Philosophers (replace 'nospam' with 'kennedym' when replying)
     
    Kennedy McEwen, Jan 7, 2011
    #6
  7. Kennedy McEwen

    nospam Guest

    In article <>, Pete D
    <> wrote:

    > >> Totally impractical for the range of lens sizes I use.

    > >
    > > Why? You just buy the filters in the size of your largest lens and one
    > > (step up) adapter for each (smaller) lens size you have. Adapters cost a
    > > few Euro or dollar each.

    >
    > So how many will I need to go from my 77mm down to my 49mm?


    one ring, although you might be better off with two if you have lenses
    between those two sizes.
     
    nospam, Jan 8, 2011
    #7
  8. In article <080120110811089174%>, nospam
    <> writes
    >In article <>, Pete D
    ><> wrote:
    >
    >> >> Totally impractical for the range of lens sizes I use.
    >> >
    >> > Why? You just buy the filters in the size of your largest lens and one
    >> > (step up) adapter for each (smaller) lens size you have. Adapters cost a
    >> > few Euro or dollar each.

    >>
    >> So how many will I need to go from my 77mm down to my 49mm?

    >
    >one ring, although you might be better off with two if you have lenses
    >between those two sizes.


    You can buy a whole set for a few dollars/euro/pounds.
    http://cgi.ebay.com/120643691309
    http://cgi.ebay.com/150540750157
    http://cgi.ebay.com/330396934335
    http://cgi.ebay.com/370468290744
    --
    Kennedy
    Yes, Socrates himself is particularly missed;
    A lovely little thinker, but a bugger when he's pissed.
    Python Philosophers (replace 'nospam' with 'kennedym' when replying)
     
    Kennedy McEwen, Jan 8, 2011
    #8
  9. In article <>, Pete D
    <> writes
    >
    >
    >"Kennedy McEwen" <> wrote in message
    >news:...
    >> In article <>, Pete D
    >><> writes
    >>>
    >>>
    >>>"Alfred Molon" <> wrote in message
    >>>news:...
    >>>> In article <>, Pete D
    >>>> says...
    >>>>>
    >>>>> Totally impractical for the range of lens sizes I use.
    >>>>
    >>>> Why? You just buy the filters in the size of your largest lens and one
    >>>> (step up) adapter for each (smaller) lens size you have. Adapters cost a
    >>>> few Euro or dollar each.
    >>>So how many will I need to go from my 77mm down to my 49mm?

    >>
    >> One. ;-)
    >> I have one that came with my Zuiko 18mm f/3.5, but its not for sale.
    >> http://www.mir.com.my/rb/photography/hardwares/classics/olympusom1n2/shar
    >> ed/zuiko/htmls/18mm.htm

    >
    >
    >What a monster.


    What a brilliant, high performance lens though. I use it on my Canon 5D
    regularly as it still out-performs any equivalent.
    --
    Kennedy
    Yes, Socrates himself is particularly missed;
    A lovely little thinker, but a bugger when he's pissed.
    Python Philosophers (replace 'nospam' with 'kennedym' when replying)
     
    Kennedy McEwen, Jan 10, 2011
    #9
  10. Kennedy McEwen

    John Turco Guest

    Kennedy McEwen wrote:
    >
    > In article <>, Alfred Molon
    > <> writes
    > >In article <>, Kennedy McEwen
    > >says...
    > >> So f/16 won't resolve any more than f/11 in practice.

    > >
    > >Thanks. So roughly one should go beyond F11, unless perhaps DOF is
    > >needed, which however comes at the expense of available resolution.
    > >

    > I hope that was a typo - "shouldn't go beyond f/11 unless..." ;-)
    >
    > >One more question, what effect does the diffraction have - is it a low-
    > >pass filter?

    >
    > Diffraction is a low pass "ramp" filter - the contrast reduces fairly
    > linearly with spatial frequency gradually tapering off towards the
    > cut-off frequency of 1/(L x f/#) above which there is zero contrast.
    >
    > >If so, sharpening could solve (partly) the problem at the
    > >expense of SNR.

    >
    > Sharpening can partially compensate, particularly where the MTF is still
    > significantly greater then zero, but obviously can't recover contrast
    > when diffraction has attenuated it to zero in the first place - at and
    > above the diffraction limit.



    Kennedy:

    Lately, I've noticed something about your public replies: Their posting
    times are >earlier< than messages you're responding to!

    Your computer's clock is in need of adjustment, perhaps?

    --
    Cordially,
    John Turco <>

    Marie's Musings <http://fairiesandtails.blogspot.com>
     
    John Turco, Jan 12, 2011
    #10
  11. In article <>, John Turco
    <> writes
    >Kennedy:
    >
    >Lately, I've noticed something about your public replies: Their posting
    >times are >earlier< than messages you're responding to!
    >
    >Your computer's clock is in need of adjustment, perhaps?
    >

    Interesting! That post does seem to have a time stamp before Alfred's
    post it replied to, however it is the only example I have noticed on a
    brief check of a few recent samples. Can you point me to any others?

    My clock is OK at the moment, however it does resync to my ISP server
    every hour - I guess that the time server could have been out on that
    previous post, but unlikely. Also, I believe that the time I sent the
    message was close to the time stamp on it. Perhaps Alfred's post that
    it was in reply to was time stamped later than when it was actually
    sent.
    --
    Kennedy
    Yes, Socrates himself is particularly missed;
    A lovely little thinker, but a bugger when he's pissed.
    Python Philosophers (replace 'nospam' with 'kennedym' when replying)
     
    Kennedy McEwen, Jan 12, 2011
    #11
  12. > Interesting! That post does seem to have a time stamp before Alfred's
    > post it replied to, however it is the only example I have noticed on a
    > brief check of a few recent samples. Can you point me to any others?
    >
    > My clock is OK at the moment, however it does resync to my ISP server
    > every hour - I guess that the time server could have been out on that
    > previous post, but unlikely. Also, I believe that the time I sent the
    > message was close to the time stamp on it. Perhaps Alfred's post that
    > it was in reply to was time stamped later than when it was actually
    > sent.
    > --
    > Kennedy


    You could try NTP - it's available for many operating systems, including
    Windows:

    http://www.satsignal.eu/ntp/setup.html

    Better than syncing every hour.

    Cheers,
    David
     
    David J Taylor, Jan 12, 2011
    #12
  13. In article <igjrd5$9q1$-september.org>, David J Taylor
    <> writes
    >> Interesting! That post does seem to have a time stamp before
    >>Alfred's post it replied to, however it is the only example I have
    >>noticed on a brief check of a few recent samples. Can you point me
    >>to any others?
    >>
    >> My clock is OK at the moment, however it does resync to my ISP server
    >>every hour - I guess that the time server could have been out on that
    >>previous post, but unlikely. Also, I believe that the time I sent the
    >>message was close to the time stamp on it. Perhaps Alfred's post that
    >>it was in reply to was time stamped later than when it was actually
    >>sent.
    >> -- Kennedy

    >
    >You could try NTP - it's available for many operating systems,
    >including Windows:
    >
    > http://www.satsignal.eu/ntp/setup.html
    >
    >Better than syncing every hour.
    >

    Doh! What do you think NTP does?

    As it is, NTP is built into the Mail and News software I use. The
    reason it "syncs" every hour is because that is what I have configured
    it to do, which is more than adequate and certainly good enough to catch
    changes to and from daylight savings time.

    Further, having looked at Alfred's previous message it has the following
    header info:
    NNTP-Posting-Date: Tue, 04 Jan 2011 10:56:07 -0600
    From: Alfred Molon <>
    Newsgroups: rec.photo.digital
    Subject: Re: Diffraction limit for APS-C DLSRs
    Date: Tue, 4 Jan 2011 20:56:04 +0100
    ...
    X-Received-Date: Tue, 04 Jan 2011 16:56:08 UTC

    From the NNTP Posting Date, we see it was received by Alfred's News
    Server at 16:56:07 GMT and, from the X Received Date, received by my
    News Server at 16:56:08 GMT, one second later. Yet Alfred's computer
    time stamped the post as 19:56:04 GMT, some 3hrs later than it was
    received by the servers.

    In fact, the headers of all of Alfred's posts in this thread up to that
    of Tue, 11 Jan 2011 06:47:37 GMT show this 3hr discrepancy!

    As I suggested earlier, that is precisely where the discrepancy has
    arisen: at some stage Alfred's computer gained at least 3hrs, but has
    now been corrected. Any response, not only my response, to such posts
    within 3hrs would appear to be out of sequence.
    --
    Kennedy
    Yes, Socrates himself is particularly missed;
    A lovely little thinker, but a bugger when he's pissed.
    Python Philosophers (replace 'nospam' with 'kennedym' when replying)
     
    Kennedy McEwen, Jan 12, 2011
    #13
  14. "Kennedy McEwen" <> wrote in message
    news:...
    []
    >>Better than syncing every hour.
    >>

    > Doh! What do you think NTP does?


    NTP does not "sync every hour", it has an adaptive poll interval between
    about 1 minute and 20 minutes according to the system requirements, and it
    alters the clock rate to provide better accuracy than simply stepping the
    clock.


    > As it is, NTP is built into the Mail and News software I use. The
    > reason it "syncs" every hour is because that is what I have configured
    > it to do, which is more than adequate and certainly good enough to catch
    > changes to and from daylight savings time.


    It's very unlikely that your software includes full NTP - it certainly
    doesn't if it has a sync interval setting. More likely your software has
    SNTP - simple SNTP.

    []
    > As I suggested earlier, that is precisely where the discrepancy has
    > arisen: at some stage Alfred's computer gained at least 3hrs, but has
    > now been corrected. Any response, not only my response, to such posts
    > within 3hrs would appear to be out of sequence.
    > --
    > Kennedy


    I'm glad that you've resolved the issue.

    [Posted at 09:20 UTC]

    Cheers,
    David
     
    David J Taylor, Jan 13, 2011
    #14
  15. In article <igmg41$hkf$-september.org>, David J Taylor
    <> writes
    >
    >"Kennedy McEwen" <> wrote in message
    >news:...
    >[]
    >>>Better than syncing every hour.
    >>>

    >> Doh! What do you think NTP does?

    >
    >NTP does not "sync every hour", it has an adaptive poll interval
    >between about 1 minute and 20 minutes according to the system
    >requirements, and it alters the clock rate to provide better accuracy
    >than simply stepping the clock.


    It is set to one hour intervals because, as I pointed out to you, that
    is how *I* have it configured and, since my clock wasn't out in the
    first place, it couldn't "provide better accuracy".

    >I'm glad that you've resolved the issue.
    >

    I didn't have an issue to resolve, however I have identified that any
    issue lay elsewhere.
    --
    Kennedy
    Yes, Socrates himself is particularly missed;
    A lovely little thinker, but a bugger when he's pissed.
    Python Philosophers (replace 'nospam' with 'kennedym' when replying)
     
    Kennedy McEwen, Jan 13, 2011
    #15
  16. > It is set to one hour intervals because, as I pointed out to you, that
    > is how *I* have it configured and, since my clock wasn't out in the
    > first place, it couldn't "provide better accuracy".

    []
    > --
    > Kennedy


    To clarify, that's SNTP you are using, as NTP automatically sets the best
    poll interval, and does so dynamically. Other features of the NTP
    algorithms provide better accuracy.

    Cheers,
    David
     
    David J Taylor, Jan 14, 2011
    #16
  17. In article <igp43e$2f0$-september.org>, David J Taylor
    <> writes
    >> It is set to one hour intervals because, as I pointed out to you,
    >>that is how *I* have it configured and, since my clock wasn't out in
    >>the first place, it couldn't "provide better accuracy".

    >[]
    >> -- Kennedy

    >
    >To clarify, that's SNTP you are using, as NTP automatically sets the
    >best poll interval, and does so dynamically. Other features of the NTP
    >algorithms provide better accuracy.
    >

    To clarify, you can't make something that wasn't out more accurate.
    I suggest you direct your advertising campaign to those who need it.
    --
    Kennedy
    Yes, Socrates himself is particularly missed;
    A lovely little thinker, but a bugger when he's pissed.
    Python Philosophers (replace 'nospam' with 'kennedym' when replying)
     
    Kennedy McEwen, Jan 14, 2011
    #17
  18. > To clarify, you can't make something that wasn't out more accurate.
    > I suggest you direct your advertising campaign to those who need it.
    > --
    > Kennedy


    Just a correction in your terminology, Kennedy. Your software is not
    using the full NTP, but the simplified SNTP.

    Cheers,
    David
     
    David J Taylor, Jan 14, 2011
    #18
  19. In article <igqa9c$qh3$-september.org>, David J Taylor
    <> writes
    >> To clarify, you can't make something that wasn't out more accurate.
    >> I suggest you direct your advertising campaign to those who need it.
    >> -- Kennedy

    >
    >Just a correction in your terminology, Kennedy. Your software is not
    >using the full NTP, but the simplified SNTP.
    >

    And a correction in your assumptions David. My PC clock wasn't and
    isn't at fault so adding unnecessary crap certainly isn't going to help.
    Go shove your software where its needed.
    --
    Kennedy
    Yes, Socrates himself is particularly missed;
    A lovely little thinker, but a bugger when he's pissed.
    Python Philosophers (replace 'nospam' with 'kennedym' when replying)
     
    Kennedy McEwen, Jan 15, 2011
    #19
  20. > And a correction in your assumptions David. My PC clock wasn't and
    > isn't at fault so adding unnecessary crap certainly isn't going to help.
    > Go shove your software where its needed.
    > --
    > Kennedy


    Why so impolite? I never said your PC clock was at fault and NTP is not
    "my" software, but it is widely used to keep PCs and servers in sync.
    That's all. No need to get upset about it. It sounds as if I caught you
    on a bad day! Sorry!

    Cheers,
    David
     
    David J Taylor, Jan 15, 2011
    #20
    1. Advertising

Want to reply to this thread or ask your own question?

It takes just 2 minutes to sign up (and it's free!). Just click the sign up button to choose a username and then you can ask your own questions on the forum.
Similar Threads
  1. SimonLW

    Is 8MP the limit for APS size sensor DSLRs?

    SimonLW, Sep 26, 2005, in forum: Digital Photography
    Replies:
    16
    Views:
    448
    Dirty Harry
    Sep 29, 2005
  2. Giuen
    Replies:
    0
    Views:
    1,421
    Giuen
    Sep 12, 2008
  3. Chris Malcolm

    Re: Diffrection limit for APS-C DSLRs

    Chris Malcolm, Jul 19, 2009, in forum: Digital Photography
    Replies:
    8
    Views:
    332
    Chris Malcolm
    Jul 23, 2009
  4. David J Taylor

    Re: Diffrection limit for APS-C DSLRs

    David J Taylor, Jul 20, 2009, in forum: Digital Photography
    Replies:
    11
    Views:
    711
    Kennedy McEwen
    Jul 23, 2009
  5. Kennedy McEwen

    Re: Diffrection limit for APS-C DSLRs

    Kennedy McEwen, Jul 20, 2009, in forum: Digital Photography
    Replies:
    1
    Views:
    603
    Kennedy McEwen
    Jul 20, 2009
Loading...

Share This Page