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Image Sharpness: Resolution v. Acutance

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    User_Removed
    26 Jan 2013 - 7:39 PM

    There is an extremely interesting article in the 2 February issue of Amateur Photographer in which Professor Bob Newman explains the science behind achieving the best levels of sharpness in a photograph.

    The crux of it comes down to getting the best compromise between resolution and acutance - both are required but, to an extent, they are mutually exclusive.

    He looks at sensor resolution (for best results you want some to spare) and lens performance (even medium quality lenses are as good as any current sensor can make use of) and the use of software for "sharpening" (very easy to overdo it and make the image worse).

    He stresses the need for a tripod, even at fast shutter speeds and suggests that normal AF systems are simply not good enough to ensure accurate focus. (He suggests focussing on an object at the back of the zone you want to be sharp).

    However, the learned professor clearly has not read everything posted here by Chris as he still mixes up his dpi and ppi (as, indeed, did AP's technical editor in his testing of the Canon 6D last week). Funny how, having been converted to that cause by Chris, I have now become a zealot and notice every time a guru gets it wrong!.

    But, all in all, a very interesting article that should help us to work towards a better representation of sharpness in our photographs.

    Last Modified By User_Removed at 26 Jan 2013 - 7:39 PM
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    pentaxpete
    26 Jan 2013 - 7:43 PM

    Just use a PENTAX then you have no trouble with sharpness !!

    User_Removed
    26 Jan 2013 - 7:57 PM

    The key to everything to do with sharpness.

    Get this right and then is all in the post-production sharpening algorithms...

    Wink

    Last Modified By User_Removed at 26 Jan 2013 - 7:58 PM
    User_Removed
    26 Jan 2013 - 8:14 PM


    Quote: The key to everything to do with sharpness.

    Get this right and then is all in the post-production sharpening algorithms...

    Wink

    Unfortunately, Mike, that link takes us to one of the "Cambridge in Colour" pages.

    'Nuff said.

    keithh
    keithh  1022720 forum posts Wallis and Futuna29 Constructive Critique Points
    26 Jan 2013 - 11:00 PM


    Quote: 'Nuff said.

    sadly one feels that statement will prove to be erroneous.

    Wink

    theorderingone
    27 Jan 2013 - 11:16 AM


    Quote: He stresses the need for a tripod, even at fast shutter speeds and suggests that normal AF systems are simply not good enough to ensure accurate focus. (He suggests focussing on an object at the back of the zone you want to be sharp).

    You see, that's why this article wasn't featured in 'Practical' Photography. Wink

    Carabosse
    Carabosse e2 Member 1139385 forum postsCarabosse vcard England269 Constructive Critique Points
    27 Jan 2013 - 11:28 AM

    Even AF depends on where you point the camera! Wink

    Using the AF to get things about right and then switching to MF, using enlarged view, can work very well. It does, of course, depend on having an EVF on your camera.......

    LenShepherd
    LenShepherd e2 Member 62425 forum postsLenShepherd vcard United Kingdom
    27 Jan 2013 - 11:43 AM

    One point made in the article is modern cameras increasingly have enough resolution to make an A3 print and to still see the finest detail viewing from about 15 inches. There ought perhaps to be a qualifier that when you do this the depth of field effect is reduced.
    Apart from dpi v ppi I am not sure that the professor understands that the "common 300 dpi standard" is based on 75 dpi minimum separately for C, for M, for Y and for K (black) to avoid moire when printing magazines.

    MichaelMelb_AU
    27 Jan 2013 - 12:31 PM

    I would not argue with a professor - and judging by the article abstract supplied by the Left... the professor is right on most of things - I got to understanding of the sharpness balance by long (and winding) practical way. One thing I consider to be slightly different to what the prof says though. Poor optics shows up as fast as poor sensor - here it just depends on what "medium quality" lens means. For one man it is a kit lens supplied with the camera, for the other - 500$ piece from Sigma or Tamron.
    As for terminology - I would not care less about it if the essence of the article is right. No one is perfect.

    Last Modified By MichaelMelb_AU at 27 Jan 2013 - 12:33 PM
    User_Removed
    27 Jan 2013 - 12:51 PM


    Quote: He stresses the need for a tripod, even at fast shutter speeds and suggests that normal AF systems are simply not good enough to ensure accurate focus. (He suggests focussing on an object at the back of the zone you want to be sharp).

    You see, that's why this article wasn't featured in 'Practical' Photography. Wink

    Good Point.

    The article is trailed on the cover of AP with the byeline "How to Achieve Your Sharpest Pictures Ever"

    I guess that most of us do seriously compromise that ideal much of the time for reasons of practicality.

    However, nice to know how to do it when you really want to.

    mikehit
    mikehit  46102 forum posts United Kingdom9 Constructive Critique Points
    27 Jan 2013 - 1:24 PM

    Did he mention using mirror lock up (or LiveView) and turning off IS?

    User_Removed
    27 Jan 2013 - 3:08 PM

    Yes - he did mention Mirror lock-up and did recommend turning off IS when using a tripod.

    Probably what I took out of the article, above all else, was that achieving the maximum possible sharpness demands careful attention to a number of parameters when taking the photograph - steadiness, focussing, lens aperture, sensor resolution, etc, etc, etc, etc. and that, basically, if you fail to achieve maximum sharpness at the capture stage, no amount of software processing will restore what never existed. On the other hand, indiscreet processing can ruin what you did capture.

    Last Modified By User_Removed at 27 Jan 2013 - 3:08 PM
    thewilliam
    27 Jan 2013 - 3:17 PM

    I thought that acutance was something produced in a film image by a developer.

    Like a few other readers, I accept that havibg loads of pixels isn't enough on its own. Good pictures are the result of care and attention

    User_Removed
    27 Jan 2013 - 3:25 PM


    Quote: I thought that acutance was something produced in a film image by a developer.



    There was a film developer called Acutol (or something like that) that produced a higher level of acutance than a standard developer.

    MichaelMelb_AU
    27 Jan 2013 - 10:01 PM

    In what looks like long time ago I remember making developers for film and paper myself. I bought chemicals separately - and had a set of them, then read books looking for recipes. And there were plenty - for contrast, acutance, detail, softness, some of them were introducing slight sepia tint in papers, others were good for small grain. And there was hunt for "holy grail" of developer - the universal all-in one. Pretty much like with modern digital cameras. Creativity always finds something to get attached to. The best acutance depended greatly on process cleanness and strict compliance to prescribed temperature. We are so lucky in digital age having possibility to manipulate it post-process.

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