Monday, July 5, 2010

It's not sharp! Are you sure it's in focus?

Morris ArboretumOne of the most asked questions I receive by email is, “My close-up photos are sharp, but the ones taken from 25 feet away or longer aren't. Do I have to have my camera focusing fixed?”

Many photographers expect that if a camera has focused properly, all their photos will look sharp.

Let me dispel that idea immediately. It's not true.
Sharpness is, to a large extent, in the “eye of the beholder.” While one person may consider a photograph sharp, another person might not. Don't ask me to define sharpness, I can't. Nikonians tried, but personally I think its definition (below) is gobbledygook.

The amount of detail that can be perceived in an image. Definition of an image in terms of focus and contrast. The combination of resolution -typically measured in terms of the number of distinguishable line pairs per millimeter- and acutance -the power to resolve detail in the transition of edges.
Sharpness depends on focus, but it doesn't end there. If the camera isn't properly focused when the photograph is taken, it never will be sharp, but even if it's perfectly focused, it might not be perceived as sharp.

Sharpness depends on:
  • Focus
  • Depth of Field
  • Distance from the Subject
  • Image Size
  • Resolution
  • Subject Motion
  • Camera Motion
  • Lighting
  • Texture of the Subject and Background
I repeat, if your photo is out of focus, it won't look sharp. You therefore need to understand that auto-focus is not without it's shortcomings. The three most important factors influencing auto-focus are: light level, subject contrast, available edges or lines on which you can focus, and camera or subject motion. You need to learn about how to positively influence your auto-focus, and if necessary switch to manual focus to achieve “sharp” focus.

Entrance to the Los Angeles County Museum of ArtDepth of Field:
Interestingly, while it may not make sense at first, according to the subject, both a shallow, or deep depth of field can make your photograph look sharp.
Depth of field refers to how far to the front or back of the lens' focus point the subject will still be in focus.

The photo of the LACMA entrance on the right has a deep depth of field, while the photo of the Lotus below, has a shallow depth of field.

For a practical method of understanding depth of field try this experiment.

In moderate to low light, look into the distance, or perhaps close-up, according to your eyes, and notice how much in focus the scene is. Then squint your eyes and notice how much sharper the scene becomes. By squinting you've effectively reduced the hole (aperture) through which you're viewing the image. That's increased the depth of field.

Garden of Eden Botanical Garden, HawaiiGenerally, the smaller the aperture, the shorter the focal length of your lens, and the further away your subject is, the greater the depth of field. Subjects which are within the depth of field are in focus.

Sometimes having the background extremely sharp due to a deep depth of field, can enhance the sharp appearance of the main subject. On the other hand, having a blurry background keeps focus on the main subject, which can cause its appearance to look extremely sharp due to the comparison to the blurry background.

Distance from the Subject:
The further away from the subject (at each focal length of your lens) the less detail your camera will be able to capture, and generally the less sharp your photo will seem.

Art Institute of Philadelphia Fashion ShowImage Size:
There's no doubt when you magnify a digital photograph beyond its original size it will increase in blurriness due to the interpolation the software will use to fill in the photograph. That being said, you generally look at photos which are enlarged from further and further back as they are enlarged more and more. The further away you are from the photo, the less blurry it becomes. Some software does a better job in reducing the blurriness than others as a photograph is enlarged, but it does become less sharp, the larger it is made, regardless of the software.

Generally speaking, resolution has the least effect on perceived sharpness. There are 4MP (megapixel) cameras, for example, which can produce wonderfully sharp photos. That being said, all things being equal, in manipulating your photo, higher resolutions will enable you to produce sharper photographs.

Subject Motion and Camera Motion:
I've put these two items together, as they go hand in hand. If you're photographing a moving subject you have several options to get a sharp photo of that subject. You can pan with the subject. Panning refers to the horizontal and/or vertical movement or rotation of your camera to maintain the main subject in the same relative location within your framing of the photograph, to eliminate the motion blur of the movement of your subject. You can also increase the shutter speed to “freeze” the subject's movement. We see that technique used in sports photography often. Of course, you can let the subject blur a bit to speak to the viewer that the subject is in motion.

The other side of the coin is camera motion. If your camera shakes and you can't compensate for it, your photo will be blurry. You can compensate for camera movement in two ways. You can use a high shutter speed which will negate shaking problem, or you can use a lens/camera with vibration reduction, or optical stabilization which will compensate for the movement. Of course, you can always use a tripod or monopod too, to eliminate camera motion.

Lighting can play a major role in the perception of sharpness in the photo by either hiding or revealing detail in the photograph. Lighting can either bring out texture, lines and edges, and other details in your subject, or flatten or smooth them out. High contrast lighting against low contrast lighting, plus lighting which brings out tiny shadow in your subject will help make your photograph look sharp.

The Grand CanyonTexture of the subject and background:
The more fine detail or sharp edges in your photograph the more likely your photograph will be perceived as sharp. Edges are of particular importance in producing an image which is considered sharp. In Photoshop, for example, one of the best tools is to use the “unsharp mask” which, increases the contrast in the photograph around all the edges in the image, which makes them appear to be sharper.

If you want sharp photographs, each of the above characteristics needs to be taken into account.

By the way, in post-processing, you can considerably improve photo sharpness, as long as the photograph is in focus to start.


Marge said...

What an incredible article Ned. I had no idea all these things influenced the sharpness of my photos. I had hesitated to ask you the question which prompted your article, and now I don't have to do so. Now I know why many of my photos aren't sharp, and others are beautifully sharp.

Debbie said...

I never thought of the idea of blurring my background to make the foreground sharp.

Where was my mind???

What a marvelous insight.

Thank you so much. Your Blog is consistently the best Photo Blog on the Internet Ned. You should win some more awards for your work. You certainly get my Blue Ribbon.


George said...

Incredible article Ned. I've had a problem with lighting and now I know why. Thanks.

Jon said...

Great article Ned. Your section on focus got me thinking about why I had trouble at times getting the camera to auto-focus. I've been studying now and I'll put the info and your article to practical use this coming weekend.


Sharon from Miami said...

Ned most of your photos I'd call very sharp, and I notice that many of your wildlife photos, and travel architectural photos, for example, have only specific parts of the photos, the main subject, really sharp, which makes them stand out.

So, how do you do it?

Ned S. Levi said...

Hi Sharon,

I post-process every photograph I make. I don't particularly change them, but I do try to make them as good as I can.

I start my processing in Photo Mechanic where I add my keywords, subject codes, general description, location and other information as well as rename them with a descriptive name, and back them up.

I then move to Photoshop. First I'll correct any lens distortion. I'll generally crop the photo to the extent necessary next. I'll color correct the photos using levels or curves, and get the balance very close. I then set the saturation to an appropriate level, then finally set the contrast and brightness if any further adjustment is needed. All these changes are made via adjustment layers.

Some of the above made be completed by add-ons to Photoshop.

Finally, the last thing I do is sharpen the photo. I use Nik Sharpener Pro. It enables me to be very specific with sharpening for the type of output the photo is for, such as a print on a specific type of paper or for display on a computer screen. It also allows me to easily sharpen only specific areas of my photo.

That's a general overview of how I do it.

Vic from Des Moines said...

Great article. Thanks Ned

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