What "Tack Sharp" means?

[ajohnw]

I am human and i know i have limitations. I also think that in some aspects a machine is better then me. It's confusing with MF. WHy? If you AF on a subject, the machine searches for the optimal contrast if i'm not wrong, let's call it "Limit X". If you move to MF and keep half way the button and rotate the focus ring until the led flashes, What is the differnce? In my opinion you've rotated manually until you've reached that SAME "Limit X".? why dhould u bother to rotate manually when the machine does the same thing + faster? I'm not 100% convinced about this, because in Macro foto i've heard that MF rulllz. But there maybe the magnification of objects, how you see them is different than the usual lens.
Second. Go to a wedding and MF 5000 photos(if u can, congrats). And let me know why AF photos are so good, or put it another way howmany of the best photos are AF and how many MF? (ingeneral)

Much depends on the camera and the AF mode. The general advice at weddings for instance offered in various books written by professional is to focus into a subject not onto it, What they are saying effectively is to make sure you have the subject you want in focus over the area that needs to be in focus. Depth of field. Your scene for instance seems to have been focused a few feet in front of you. AF can do all sorts of odd things. I took a photo of a duck recently and the nearest part is sharply focused, the further parts aren't.

I mentioned processing. This is the sort of changes that can be made - I've over done the sharpening on purpose and haven't spent more than 1min on it so none of the adjustments are optimum. Not that a portrait at full size showing detail this well is a really a good idea but if reduced to a more normal size where pores etc weren't noticeable the processing would have an even more dramatic effect. Compare this side by side with the one I downloaded off here. Actually it looks like the AF has focused bang on the front of the ladies face to me suggesting depth of field is wasted back towards the camera. Fine if that's what you want or maybe you manually focused it like that or should have used a different F number to extend the depth of field. One eyebrow is marginally out of focus too. Not the camera, or the lens!



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[ajohnw]

On your scenes I suspect you may have been trying to limit the sky in one of the shots or trying to frame the shot as you wanted it. One way of doing that would be to AF on the tree and zoom towards wide angle until you can crop the shot later to what you actually want. Then select the smallest aperture you can get away with subject to shutter speed. You have loads of pixels in you camera so there is plenty of scope for cropping shots. If you want more footpath crouch down. Shot's don't have to be taken standing up. The nearer parts of the footpath might turn out to be out of focus but using the shorter focal length will help as will the small aperture. Exposure may become a problem due to more sky. Centre weighted may help but often they average too much to be of any use. Spot metering can be very difficult to use in practice. Insanely so. Evaluation - well it will evaluate even if some areas are over exposed and others are under. Some cameras show that problem in preview. When it happens the shot exceeds the capabilities of the camera but within limits the shot will be recoverable via raw.

Lastly some people use the histogram to expose. Experience with how the camera behaves helps in all areas and that may take several hundred shots.

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[Dave Humphries]

Hi Ana,

All i am intersted now it's the SHARPNESS of this pictures, not the composition, not the blown highlights .Anyway thank you a lot for your time and help. I need to see if the images are "tack sharp" and mine "tack sharp" is a sharp recognised by all others ~

1. Regarding portraits it's ok the sharpness, i can start shooting knowing what to look for when i check the sharpness of photos, right?

Remember blown highlights (e.g. on the nose), will lose you sharpness, so you should care.

1. YES - I'd say these are sharp enough, but as I used DPP to view them, the in camera sharpening was applied in the screen grab and there was more applied with the 24-70 lens than the 50mm lens shot, thus they both look about the same, although as John says, DoF is marginal for wheer you have focused, but we're reallly getting it a few percent that will not be seen in the final print, assuming you show the whole face in the final crop.

2. Regarding "landscape" it's still problematic, i'm sure that i've used the f/13 setting and HFD calculated:
2.1. pointing at smth that i assume is the distance - because on distance scale is written 1.5 feet | 3 feet | etc - try to imagine where 1,71 feet is :-? when i focus manual or autofocus;
2.2. recompose the scene, placing the camera parallel to the ground(assuming that the camera doesn't calculate the DOF remembering what was the angle when i focus and take into consideration the distance, or am i wrong?)
THE RESULT? Same story as the photo presented above.
Going over f/13 i've read that it's not such a good idea...(don't remember well the reason).

2.1 What is "smth"? I looked for it in the photo but couldn't find any obvious candidate.
Distance scales on modern AF lenses are very compressed and virtually useless, as you have noted

In this case, you must have mis-selected the aperture to f/8 (I rechecked the EXIF data) and not used the f/13 given in the tables on this shot.

2.2 Focus errors can be introduced by focusing then recomposing, but that applies more the closer you are to the subject.
People do say that going over a certain f-number is not good, this is technically true, but again, the differences are often quite negligible in the real world.
The camera does not "calculate DoF" at all.


Picking through a few points in your other replies:-

I think you are worrying unnecessarily about the 15% differences between an "8.5" and "10" lens on your imaginery scale of 1 to 10.
What does it matter if the photo is sharp enough for the means you will use to publish it?

Sure, we could probably have told you a prime lens (the 50mm, f/1.8) might be sharper (at some apertures) than the vastly more expensive 24-70mm, f/2.8 zoom lens - but does it matter? Many professionals prefer the versatility of using the zoom lens to "zooming with their feet", because the latter alters perspective, which may not enhance the image (if you get too close), or may not be possible (if you cannot get far enough away).

.. and besides; what is one of the essential bits of PP of many portraits?
Not showing every wrinkle and blemish on the subjects face, neck, hands, etc.
So why chase the ultimate (11/10) in sharpness?

Yes, people often buy lenses that are sharper than what they have, but only when it is holding them back in what they are shooting - I am not sure that is true in your case; do you have subjects complaining their portraits aren't sharp emough? - I doubt it.


I agree that if people are going to be guided to optimum manual focus via the red dot (contrast detector), you might as well have used AF
Although there are times when having focused accurately once, if the distance is not changing, switching to manual may avoid focus errors on subsequent shots and/or speed up frame rate in continuous shooting mode.

Cheers,

[xpatUSA]

I think you didn't understand the question here.
. . .
Again here, you didn't understand my question.
. . .
LOOK, for a beginner it's not so easy to understand what is going wrong.
. . .

OK, perdon de no entender sus preguntas. Entonces, no voy tratar explicaniones mas :-)

[Inkanyezi]

Hola Anita, disculpa si no te entiendo bien, pero quiero tratar de explicar como lo veo yo.

I'm not quite sure that I really understand the question, or the problem. I just thought that I'd add a few tidbits.

Sharpness of a lens is one thing, but sharpness is an entity that is not really that simple. There are several layers that ultimately define sharpness, and sharpness in itself, of course is subjective.

Subject matter really does matter. Some subjects lend themselves more easily to "tack sharpness", while other subjects may look less sharp, even though the lens is focused correctly and can produce a sharp image. Also lighting matters, as well as exposure, as just was pointed out. If you blow out a highlight or it is placed very close to blow out, you may lose sharpness, the subjective sharpness sensation. The size of your main subject also is a dominant factor in the sensation of sharpness. So many things together, building the image, may render it more or less sharp to the eye.

And the last step is processing. Processing often renders an image "too sharp", over-sharpened, which is also unwanted, although a tack sharp image may result.

In the process of taking the image, many things except lighting and exposure may go wrong. AF in a DSLR seldom hits spot on, but often misses, and sometimes may miss a lot. Also manual focusing is difficult and the aids for manual focusing in DSLR cameras often are far from optimal. The signal that reads from the AF module has a certain hysteresis, and the focusing screen might be too transparent to really show focus. It can also itself be out of focus, not representing the sensor plane at all.

Then if detail in the image is too small for the actual pixels of the sensor, sharpness may be killed by trying to cram too much detail into too low resolution. This frequently happens with foliage, rock structure and many other structures. When details get too close to each other, they are no longer resolved, and even details that are a bit wider apart are rendered with lower contrast with most lenses. When using wide angle lenses, therefore something close to the camera will help sharpness, the subjective impression, as distant objects may be too small to display optimum sharpness as experienced.

So for maximum sharpness, image detail should be sufficiently large and have sufficient contrast, which is governed by lighting. Large detail will always come out sharper than fine detail. Therefore, also when you pixel-peep, sharpness will not be as evident as when you look at the entire image at a suitable size versus distance.

I'll post an image here; a fairly normal touristic harbour scene, which I regard as sharp, even if it might be better. The DOF is supposed to cover most of the image area, but you can observe in it, that some areas are sharper than other. There is a blue box in the foreground, containing electrical connections, which appears rather sharp, as it is a large object. Below, the ground that is set with square stones, does not appear tack sharp, as it has too much detail to be resolved. The ship is sharp, it is large, and tonality over the white surface is rather smooth. Sharpness is perceived partially because there is large detail in the ship's name on the front, and details are rather large. Also in the background, large detail appears sharp, while finer detail, as the bicycle and the man on the dock are too small to be "tack sharp" when pixel-peeped. Those objects are however not primary subject matter and will not draw attention when the whole image is seen.

And one more thing. The relatively high sharpness in the background detracts from the foreground, so that the ship does not "pop" as it would have done with an unsharp background. Even though the image is rather sharp over most of the area, it doesn't really pop, maybe partially because it is a typical snapshot, but because there is too much unimportant detail that is too sharp. However, it is not the mass of details that renders appearance of sharpness most, but the main portion of the ship, which does not have a lot of detail, the smooth front and windshields convey sharpness more than the cobblestone that is not fully resolved.

The recipe for tack sharp might be to find the most interesting object to focus interest upon and compose it into the image and make just that object sharp, so that it stands out from the less sharp surroundings, which in turn will accentuate the sharpness of the main subject, so that it pops out tack sharp? And also image tonality might be part of the game? (The image may be viewed full size by opening it in its own window or downloaded. It is taken with an OM-D and the Pen F 38 mm f/1.8 lens at f/11.)