On every photo safari the second most common question (just after "what ISO are you using?") is "do you think this image is sharp?" To paraphrase an old saw, "If you have to ask, ..." But seriously, evaluating sharpness is a big part of assessing the quality of your images, so we'll take a closer look at it in this post...

The term "tack sharp" is used to refer to images that are "as sharp as a tack." Typically these images jump off the screen at you. The first image accompanying this article, of a lion cub on a termite mound is quite sharp. Like any image right out of a digital camera (without in camera sharpening applied) there is some slight softness due to the built-in low pass (anti-aliasing) filter found in almost all digital camera. That is compounded by the relatively high ISO (1600 on a D300), which when removed takes some of the detail with it. So I'd classify the image as sharp, but not razor sharp.

Note: To get a better sense of the relative sharpness of the images, click on them and then click "Original" to see the 1600 pixel version that was uploaded (still not the full 12MP image capture, but enough to show clearly the differences). Otherwise it may be tough to see the differences just from the previews.

The second image is the kind I get asked about most. It is an image the photographer really loves and wishes were truly tack sharp, but for whatever reason it didn't happen. In this case there is no secret as to why. I was shooting a moving lion at 1/30 of a second hand held from a truck after sunset (ISO 6400). No matter what I do to this image after the fact it'll never become tack sharp. That doesn't mean it won't make a great print (canvas or art paper come to mind as options) or a great image for a slideshow. But it does mean I wouldn't submit it to a stock photo agency or a nature magazine. Sometimes there just isn't anything you can do with the equipment and situation you have in front of you.

Aside from emotional attachment the other most common issue with assessing sharpness is the camera LCD. There is so much variation between the way that cameras display their images, the quality of their LCDs, the operation of their zoom functions, and lighting conditions in the field that except for obvious out of focus or blurry images the camera is not the best place for most people to judge sharpness. You need to get the image to a screen that you can trust. A related problem is comparing sharpened images with raw images. Unless you turn it off JPEG images are always sharpened before you see them. Raw images don't start sharpened so depending on your image viewer you may be looking at an image which simply suffers from the blurring effect of the anti-alias filter. That's why it is a good idea to set your preview sharpening in Camera Raw or Lightroom or DigitalPro or whichever other image browser or editor you use before trying to asses sharpness--even if you don't use their built-in sharpening capabilities and instead use nik or Photokit to do your actual sharpening.

In my case I run an action that applies either Dfine or Noise Ninja for noise reduction and then nik Sharpener Pro to each of my raw images when I begin to work on them. But for tack sharp images you can really tell they are sharp even before that step. Look at the image of the adult male lion. You can see the blood vessels in his eyeballs clearly. It is obvious that the image is just about as sharp as it can get.

Of course knowing which images are sharp is only a small part of what you need to know to be successful. The more important skill is understanding why an image is not sharp and what you need to do to fix it. Unfortunately many photographers don't worry about sharp images until they are in the field. The time to start worrying is when you first select a camera and lens. Take the time to put a piece of newspaper on a wall and shoot some images. Experiment with f-stop and shutter speeds (and different focal lengths on your zooms). Try on and off tripod. Then set up some cans or bottles angled diagonally away from you and take some more images to see where your camera is focusing and whether the bottle you focused on is the sharpest.

If you find a pattern of softness with certain lenses or certain focal lengths, before your big trip is the best time to address the issue with servicing or a lens upgrade. And you can also determine how slow you can hold the camera before you stop getting sharp images. It is different for each of us--and depends on how fast the subject is moving as well--so there isn't any exact rule that predicts the shutter speed you'll need.

For more tips on diagnosing your images you can read our article on Troubleshooting your Digital Images.--David Cardinal