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04-01-2008, 08:49 AM   #1
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So - what actually is sharp?

Maybe you can accuse me of pixel peeping but I have been trying to ascertain how sharp my K10D is with a variety of lenses (in particular the sigma 10-20) - and I am stuck.

How sharp is sharp? How do you judge? How much do you magnify the image to judge? Is it all subjective? What should I compare it with? Are there any standards?

Obviously I am lost in a maze. Any help would be appreciated.

04-01-2008, 09:55 AM   #2
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QuoteOriginally posted by ukbluetooth Quote
Maybe you can accuse me of pixel peeping but I have been trying to ascertain how sharp my K10D is with a variety of lenses (in particular the sigma 10-20) - and I am stuck.

How sharp is sharp? How do you judge? How much do you magnify the image to judge? Is it all subjective? What should I compare it with? Are there any standards?

Obviously I am lost in a maze. Any help would be appreciated.
Sharp is very subjective in one sense, and objective in another. The subjective sharp is that as long as the printed/displayed image is sharp to you, the lens is sharp. This will depend highly on how large the final product is.

I am coming to the conclusion that with my K10D, I can bring an image shot at the lower ISOs to 20x30 inches (or the equivalent magnification cropped). However, some of the lenses in this world will not support that degree of enlargement, which is why you see some rather expensive glass in my signature.

My personal opinion is that the K10D is lens limited for my purposes. If you only want to update your Flickr site with pics so the family cn see them, you will be perfectly happy with a lens that focuses and exposes correctly, and costs a whole lot less than my DA series of lenses, the least expensive of which cost me about C$700.

I realize that this does not even come close to answering our question, but that is because only you, in the end, can answer it. I don't pixel peep, but I do examine corners with detail to see the enlargement I can get away with.
04-01-2008, 10:03 AM   #3
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Well, to me 'sharp' means that the pictured object (and anything else at the focal plane in the frame) displays accurately what the eye sees - straight lines or curves - as captured and magnified up to the resolution capability of lens,sensor or film or all. Since most images are not of flat objects or scenes one has to choose what is most important for the viewer in a given picture and apply the above test.
04-01-2008, 10:06 AM   #4
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to me sharp is the ability to clearly read printed text on an image magnified 150% or more


the standard goes up as focal length goes up

ie, a 100mm lens i would expect to be perfectly legible even at 200% magnification, but something like a 10mm i can forgive if things start getting blurry after 100%

04-01-2008, 10:30 AM   #5
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Longer focal length has higher magnification so the text has to be clearer. However, if you use a 100mm and a 10mm to take the same piece of newspaper at the same magnification, they will look more or less the same, given they have similar optical quality.

So I think that's not a good way to measure sharpness of a lens. Sharpness of a lens is determined by resolving power and contrast. You can look at the MTF info as the standard.

However, I don't usually do pixel peeping. As long as the subject in focus looks sharp to me (at 100% zoom in), then I would determine that's a sharp lens. Soft lens is easier to categorize. When you look at a soft picture, you can see the dreamy look; some even has the halo/glowing effect around the subject. Some low end lens can even be too fuzzy/blurry.

User error in focusing can also misrepresent the sharpness of a lens, so don't make a hasty decision. Curvature of field of a lens also misleads user about the sharpness. If you take a flat picture (like a piece of newspaper), these lenses would have sharp center while the corners will be much softer. That's not saying the lens is bad. It just means the lens is not very suitable for a flat subject.

Personally, I think comparing two lenses against each other is the eaiser way to decide which lens to keep.
04-01-2008, 10:46 AM   #6
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thats a difficult question, it seems very subjective and i believe the most common cause is simply experience. someone who has only used a very poor kit level lens and get a mid level lens would go on about how amazingly sharp it is when a shooter with a selection of hq lenses would complain that the same lens was not as sharp as the other lenses he used.

also what is tack sharp, amazingly sharp, sharp as a knife etc. all fuzzy expressions.

in its simple form though, sharp refers to the part of the image that is in focus and within the dof.

for me, what i consider really sharp is when i use a large aperture and can tell from the k10d lcd at 0 magnification if the shot is in focus or not and what part of it is. my voigtlander 125 is like this, the in focus area jumps out from the oof part. also the produced image is so sharp that is will cause moiree in certain viewers like the canon program i used to print. i had taken a picture of my nephew and his t shirt was full of moiree, you know those tshirts if you look very closely you can see they have vertical lines, those lines were resolved so clearly that the image couldnt be viewed at less than 50% of full size. i actually had to do a slight gausian blur on the tshirt before printing.

so for me, if i see fabric cause moiree on the k10d screen, then its a sharp lens. (the fa limiteds also do this, btw)
04-01-2008, 01:35 PM   #7
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Thanks fellows - that does help.

If I understand what you are saying:

YES - it is subjective
BUT - we all have our own criteria about how we define sharp
SO - we impose our own objective standards (they may be semi-empirical but that is OK)

Perhaps if I posted an image that I considered reasonably sharp (bear in mind that I do not have any really expensive glass yet) you could comment?

Thanks Gary
04-01-2008, 01:37 PM   #8
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post away

but LINK to us the original resolution file (dont post it, it will destory everyones bandwith, just post the link)

04-01-2008, 01:47 PM   #9
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sharp = detail, the more detail, the sharper the image
04-01-2008, 02:02 PM   #10
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QuoteOriginally posted by ukbluetooth Quote
How sharp is sharp? How do you judge? How much do you magnify the image to judge? Is it all subjective? What should I compare it with? Are there any standards?
here is one old and proven method : take a picture of your... significant other... then show some certain parts of the face @ 100% magnification (no PP) and tell that it
was posted online for the whole world to see... now if you will live to post here tomorrow that was not sharp enough... move on to the next one... lens I mean, keep the human.
04-01-2008, 05:32 PM   #11
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To give you a sense of where lenses roughly sit in relation to one another in this subjective (but measurable) field, have a look over at the lens reviews at Welcome to Photozone!. Klaus measures many lenses using a standard test to show their relative resolutions (potential sharpness). Also some pictures there to help you compare.
04-01-2008, 06:27 PM   #12
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You guys like to sound complicated huh?

THIS is sharp: https://www.pentaxforums.com/gallery/images/1074/1_double06.jpg

j/k. But you can only define image sharpness relative to other images, or to the theoretical limit (that is, something 1px wide from the sensor point of view shows up as a perfect 1px line on the image file). Foveon gets close to that.

Short version: an image or area is sharp when it is using* all the available resolution**

*using as in "showing detail"
** from the lens/sensor combination

Last edited by ricardobeat; 04-01-2008 at 06:28 PM. Reason: weather
04-01-2008, 06:36 PM   #13
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IMHO, this is sharp;

taken with M 85 f/2 @ f11 - 1/3200

04-01-2008, 07:31 PM   #14
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QuoteOriginally posted by metalfab Quote
IMHO, this is sharp;

taken with M 85 f/2 @ f11 - 1/3200
this is an 800X600 image

i would not judge sharpness based off that.
04-01-2008, 07:38 PM   #15
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The floodgates have opened, everyone post your latest 'sharp' photos to irritate gooshin!



All JPEGS taken with Super MC Takumar 135 f/3.5, very minimal PP:









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