View Full Version : What is considered "tack sharp"?
Mar 5, 2011, 02:28 PM
this term is subjective of course but i just want to get some opinions on the sharpness that i get from my canon EFS 18-135mm 3.5-5.6 lens. this is a screen grab of a photo i took this morning that i'm viewing at 100% in PS. is this considered sharp? (no pp sharpening done)
this is a screen grab of the pic at 25%.
i think this is pretty sharp, can L lenses produce even sharper images? just curious, thanks.
Mar 5, 2011, 02:49 PM
having never used the 18-135mm 3.5-5.6 I am not quite sure how sharp it *can* be, but your sample appears more than sharp enough.
And yes, L glass (And lots of non L glass; primes and 17-55 f/2.8 come to mind) can be quite a bit sharper.
Besides, "sharpness" is not the only reason people buy L lenses. Example: I got a 70-200 f/2.8LIS for a number of reasons, including but not limited to zoom range, advanced IS, constant fast 2.8 aperture, build quality, weather sealing for the snow here in MN, etc. Sharpness was just a nice bonus!
All that aside, if your camera and lens AF do not play nice then it doesn't matter how sharp your lens is.
Mar 5, 2011, 03:05 PM
If you really want to test sharpness, it's best to focus manually on something that does not move. A swing suspended in the air is not the best subject for this kind of test. Use a tripod, mirror lock-up, and either a shutter release cable or 2-second timer. Use live view to zoom in 10X and focus manually on some absolutely stable subject with lots of micro-detail, such as a piece of newsprint taped to an outside wall in good light.
Your photo of the swing ought to be sharp enough for most uses, but yes, images can be much sharper than that.
Mar 5, 2011, 03:49 PM
I think there is no simple answer to this. Tack sharp to me means that the smallest elements in the photo do not bleed across pixels or that edges are defined by one pixel.
By this definition it is clear that many lenses would deliver sharp images to a 1MP camera and that no lens would deliver sharp images to a 1,000 MP camera.
Your photo shows your lens is sharp for your camera.
BTW, if you look in the corner of the image it might appear softer. Only a few lenses are equally sharp edge to edge.
Don't worry about it too much, if it looks good to you its good.
Mar 5, 2011, 03:58 PM
It all depends on your intended output. And how important "sharpness" really is to the individual image.
How big are you planning on printing? Are you going to be cropping the image? Does your image rely on "tack" sharpness for the message you intend to convey with it?
There are many famous photographs that are compelling on every level that aren't really *tack* sharp. For example, many of Henri Cartier-Bresson's most famous images are a bit blurry, this for example:
Yet it is an amazing image that speaks volumes.
If you want to see how sharp your particular lens/camera combo is, then you need to shoot in a controlled environment. Indoors where wind isn't an issue. On a decent tripod. Tripping the shutter with a remote release.
Sharpness is somewhat dependent on gear. It is somewhat (moreso?) dependent on technique. It's importance is dependent on subject and intended output. You are the only one that will be able to determine if your current lens/camera is delivering what you want it to deliver.
Remember that format also plays a large role in this. Crop format vs full frame. Medium format vs 35mm "full frame" format. Large format vs medium format. Certain lens/camera combos can push you to the extremes of what a given sensor size/film size can produce, but each format has very real limitations. No 35mm equivalent camera/lens combo, regardless of price, is going to approach the detail possible with a large format film camera. The physics just doesn't make it possible. But you have to decide which compromises you are willing to accept in price/convenience/immediacy/capability/versatility/image quality.
While it is possible that an "L" lens will produce sharper images than your current lens, it is also possible that improving your technique by using a tripod, using a remote release, paying more attention to your exposure choices (ISO/aperture/shutter speed) could result in sharper images. Totally possible that your technique is good and that a gear upgrade makes sense, but I'd think about the other things if this is really a big decision for you. Would also make sense to consider how important *tack* sharp images are for your creative vision and intended output.
Mar 5, 2011, 11:40 PM
Tack sharp is a 30" x 40" print that did not need uprezzing and looks perfectly detailed at arm's length. Pixel peeping will always reveal flaws in any image, but in today's digital world most shots never make it past web sized jpegs and your lens appears to do a fine job of that, even with a non-static subject.
I upgraded lenses to achieve faster apertures, and fine glass has a special way of rendering images with color and clarity and creamy bokeh that is unparalleled by standard grade lenses. There is a measured difference in sharpness, as well. My ultimate test is water droplets against a blue sky, since that's my niche.. but the only way to judge sharpness across the board is with something like the dpreview mtf (http://www.dpreview.com/lensreviews/canon_70-200_2p8_is_usm_ii_c16/page4.asp) image tests, although I would recommend you do the tests yourself, dp can be rather slanted..:p
Mar 6, 2011, 01:18 AM
educational as always, thanks for the input guys. yeah, i think the sharpness on my 18-135 is good enough for me, but as others have said, upgrading to the L lenses brings other benefits, not just sharpness. having a fixed aperture will probably be my next upgrade. thanks again.