How to Be Miserable By Worrying About Sharpness
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Is my tongue embedded firmly in cheek? A little bit. Nonetheless as a moderator on the KelbyOne Community, I see lots of posts by nice people worrying that their images are not sharp. First the gear gets blamed, then the post-processing and maybe sometimes even the user. While camera shake is the most common reason for user caused softness, inappropriate aperture selection and use of an unsuitable autofocus method also come to mind.
The worst offender is always misunderstanding and unrealistic expectations.
How To Be Miserable in One Easy Step
Shoot an image without thinking about camera shake, depth of field and autofocus method. Import or open the image in your favourite photo editor. Zoom in to 300%. Examine the image with your nose pressed against your display. Guaranteed soft image. Must be the camera’s or lens’ fault.
Nope, this error is happening 100% behind the eyeballs. The first problem is a lack of thinking. With larger sensors such as those found in “real” cameras which have sensors larger than ¼ the size of your little fingernail, the choice of aperture and choosing the appropriate depth of field for the lens, the aperture and the subject distance do matter. You can certainly let the camera rip on full auto, but also accept that you may not get what you expect precisely.
You also need to be considerate of what your safe hand holding shutter speed is for the lens in question. The idea of using the reciprocal of the focal length is a guide, not a rule. If you are hefting a massive 150mm-600mm, proper application of the reciprocal guide would say that your minimum safe handholding speed would be 1/600 of a second or shorter, regardless of focal length selected. This may seem to invalidate the reciprocal guide, but the lens does not diminish in size or mass when the focal length is adjusted by the zoom. I respect that you may have heard different statements on this subject from different sources. To be polite, they are not correct.
The final issue and the most common problem is unreasonable expectations, magnification, viewing system and viewing distance. Consider the following accepted and reasonable guidelines.
The proper viewing distance for any image is twice the diagonal length. Let’s use an 8x10 as an example. The length of the diagonal is the square root of 8^2 plus 10^2 or in this example, the square root of 164, or just under 13 inches. So the proper viewing distance for an 8x10 is just over two feet. Yet in most every case, when photographers examine an 8x10 print, they do so from about six inches away. Normal people are less prone to do this, but regardless making a determination on the sharpness closer than the viewing distance is self-delusional.
The only time that it is ok to be this close to a photo this size is when you are hanging it on the wall.
We also find that folks bring an image into their computer and put it up on a large screen for editing purposes. This is not a bad thing until that large image is used as a means of determining sharpness. While the guides for proper viewing distance should be followed in general, if determining sharpness is part of your workflow, do not zoom in larger than life-size or 100%. Anything more requires that the image be put through a resize process which a zoom does not do. Resizing only happens in an export process and only if the user remembers to do so. Remember that the proper viewing distance for an image filling a common 27” diagonal display is over five feet away and none of us sit that far away. In fact most move in closer than normal seating distance and make any issues appear much worse. Stopping the practice of over-zooming makes most of the sharpness concerns that are not technical go away.
Lastly, using your display as a means of determining sharpness probably does not make sense unless it is a super high res display. Consider that a 1920x1080 display has enough pixels to accurately show a 2 megapixel image. Anything bigger goes through a pixel blending or pixel dropping algorithm to make the image fit full screen. This is why we can say that these displays have resolutions of only around 120 pixels per inch, or 120 dots per inch, because each pixel is effectively a dot.
This bears no resemblance to a print. A common print DPI setting is 300 dots per inch, but most all photo printers use this data feed and run their own algorithms against the data flow to produce 1440, 2880 or even 5760 dot per inch prints. This is why it is critical to resize your print ready images to the paper size that you will be printing on. Lightroom does this automatically, but other applications require that you do the resize as a step. Thus by using your display as a means to evaluate sharpness, you may be fooling yourself because the display cannot match the resolution of the sensor.
Remediation
So instead of worrying and moaning over sharpness, check your premises. If one of your thought processes is invalid, so will be your conclusions. Moreover, if you are not being planful in the making of the shot, you are at best hoping for a happy accident. Expecting technology to make up for you not doing your part is a fool’s errand. Hope is not a strategy.
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I'm Ross Chevalier, thanks for reading, watching and listening and until next time, peace.
