Sharp focus

ACBart

http://www.flickr.com/photos/107644394@N02/

I read everywhere about how important tack sharp focus is, but how do I know it's sharp? I've come across some pictures that looked phenomenal, but all critics say it's not sharp or the focus is off. What is the secret? Here are some of my recent pictures. I'd love feedback. Are they sharp and is the focus good?

ACBart

Hello??? I would really love some feedback, please and thank you. :-)

elmerglue

Wow, those look pretty sharp to me. I would like to know the secret too if they say they aren't in focus.

ACBart

@elmerglue, thanks for the feedback. Hopefully I can get some definitive information as to what makes a picture "sharp". I've been able to judge focus somewhat, but definitely still a serious novice.

als

I have had a similar experience. The sharpness in your pictures may be good enough for most purposes but viewing at a large screen or print out you would notice that the closest eye is not sharp. Normally that is where your eyes are drawn in the picture. The "unsharpness" could depend on a too slow shutter speed if the dog is moving or where you have set the focus. Top left, for example, you have the focus on the ear. The old rule of thumb for shutter speed faster than 1/focal length (FX equivalent) is for still objects. The faster the object is moving the faster shutter speed to freeze the motion (less blur). Using a 200mm on your D5100 would require a shutter speed faster than 1/300s (1/ 1.5*200) compensate for VR by 1-2 stop to say 1/125s (but that's for still objects). I would use 1/250 - 1/400 for pets dependent on activity.

bruto

Sharpness is partly subjective and partly not.

Focus accuracy, sensor resolution, lens quality, diffraction and file compression all have some effect as well as simply getting it right. The perception of sharpness depends on how edges are shown, and there are instances where a lens that is not exceptionally sharp will look better because of how it renders edges.

But in addition, digital images rarely are at their very sharpest without some post processing, simply owing to the way the thing happens. How much sharpening you do will depend to some extent on taste, and what you sacrifice.

I think some people over-emphasize sharpness in the abstract at the expense of image quality.

I think you should always strive for the sharpest image you can reasonably get, but some people in the digital age have become addicted to pixel peeping and expect more at 100 percent magnification than is reasonable. As a result, some images I see that one might judge as sharp look to me as if they're over-processed. You can sharpen an image so much it looks like a paper cutout. That may be technically sharp, but it is not necessarily most pleasing.

Do note what @als says about the old reciprocal rule. For DX format, it's the effective focal length, not the numerical one, so remember to multiply your lens's length by 1.5 to be safe.

It can be hard to know just what your own lens and hand holding capability add up to, but if you can, try taking indoor pictures at shutter priority (other issues unimportant for this exercise, so leave it on auto ISO) of something that has small, round LED pilot lights or the like in it. Camera movement is hard to spot in many instances, but if you take a picture of a tiny, round light, movement will be easily spotted as elongation. Turn off the VR for the experiment, and focus directly on the light. Some lights will have a bit of halo, but ovals are a no-no.

Finally, remember that a web display of any picture will not do it any favors in sharpness. Even out of the camera, a JPG image may lose a tiny bit. The more compression, the worse it gets. If you want to study the sharpness of an image, take it in Raw form, and open it in a viewer such as ViewNX2 or Capture NXD, where you can magnify it to 100 percent.

Some loss is inevitable when you downsize a picture in compressed JPG form. If you do need to sharpen it, do so as the very last stage, after it's at its final size.