The whole question of lens sharpness...

Started Jun 12, 2013 | Discussions thread
John1940
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Re: Sharpness in Reasoning ...
In reply to Basalite, Jun 17, 2013

Basalite wrote:

Detail Man wrote.

You seem to enjoy "sparring" over silly things like where or not any display monitor does or does not have exactly 2,400,000 pixels, and attempting to dismiss outright the thoughts of others - but you are yourself noticeably evasive about the important and central point which renders your bold claims of "objective knowledge" patently hollow - that "sharpness" (like "brightness" and "image quality") are indeed nothing more than subjective terms and phrases which are descriptive only of the implicitly subjective human visual perceptual experience.

Here you betray the subjective, ethereal nature of what you are trying to present as objectivity:

Increasing contrast also doesn't improve sharpness or detail, even if *apparent* sharpness tends to go up.

http://www.dpreview.com/forums/post/51645102

You could still (as I have requested) attempt to provide an objective defintion of what you mean by "sharpness". Otherwise, what you are doing is simply imagining that all the world must surely perceive reality precisely as your eyeballs happen to, or they are otherwise most certainly in error.

What is so difficult to understand? Viewing a high resolution image at 100% on my 27 iMac, or any other good monitor, is like viewing an enlarged negative or slide under a loupe or on a piece of enlargement paper in the darkroom. It's the best way to determine whether an image is sharp. A monitor also does not need to have 300PPi resolution to make that so.

You seem to be forgetting that all images (on any display media) differ in their appearance and characteristics depending upon viewing-size and viewing-distance - decimating your assertion. In fact, your proposed magnification of view (involving re-sampling effects and artifacts at all magnifications other than "100%") at best is depecting something that you claim does not even exist:

"Nearby details?" No such a term. It doesn't even make sense in the context of the discussion.

http://www.dpreview.com/forums/post/51645848

A print, and especially so with the digital processes of today, can easily make a less than take sharp image look "sharp." It is a poor, inefficient and backwards way of determining the true sharpness of a digital image.

I am no particular fan of printed images - but you persist in using an objectively undefinable term.

To assist you in your perhaps unlikely future meditations upon the nature and (the possibility of any) objective meaning of the term "sharpness" that you persist in slinging around as "objective truth", have a look at this statement by Bob Atkins relating to the findings of E.M.Grainger and K.N.Cupery:

... the subjective sharpness of a print corresponds to the area under the MTF curve between the spatial frequencies of (0.5 x magnification) and (2 x magnification) when spatial frequency is plotted on a logarithmic scale.

http://www.bobatkins.com/photography/technical/mtf/sqf1.html

Note that this finding rips a wide and gaping hole in your assumptions that "sharpness" (as subjectively perceived by human visual systems) is independent of the spatial frequency response of the human visual system as affected by viewing-size and viewing-distance, as well as the composite system spatial frequency response and the signal/noise ratio as a function of spatial frequency of the recorded, processed, and displayed image-data. Perhaps food for thought ...

I like to "pixel peep" - but I don't foolishly imagine that doing so allows me to see some overarching and invariant objective perceptual truth. Let me know if you would like to see further indications that your wielding of the ethereal term "sharpness" constitutes little more than a fool's errand.

DM ...

Bloody hell, is this all the nonsense you think one needs to determine what is and isn't sharp? How on earth did I get through all those years in the darkroom without all that?

I hope for your own good you don't view the rest of your life with such unneeded and ridiculous complexity.

Basalite, I'm wondering whether you are just being argumentative with Detail Man or simply do not understand how monitors work and, secondly, how easy it is to test lens sharpness (to some reasonable level) with something like a Nikon 800E if the lens has the Nikon mount.

If two lenses are much sharper than "36 MP" (equivalent) but one is three times sharper than the other, you cannot tel the difference with the 36 MP 800E. And, you can use any decent calibrated HDTV monitor to verify that. But, you have to zoom in to "actual pixels" in order to do side-by-side image comparisons. You will have to scroll both images to the same part of the full 36 MP since the monitor can only display about 2 MP at a time (divided by two since you will be showing two lens results at a time).

If, on the other hand, one lens has less sharpness in the image corners that is detectable by a 36 MP sensor, for example, then when you look at a 2 MP window of each 36 MP image by scrolling to that area for both images, you will see the difference.

This is an easy test to do. The sharpest lens I use regularly is a Canon EF-s 60mm f/2.8 macro. If I test any other lens such as a travel zoom that I can set to 60mm, it's easy to see the IQ I am giving up at that focal length for the zoom lens's convenience. That's why I usually take the macro with me during traveling also.

John1940

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