Pedrosa: Understanding Auto Focus and Sharpening

Albert Pedrosa
Photo mania

LAST Monday during the Lilo-an impromptu photo contest, some photographers were gathered together waiting for the afternoon activities and the hot topic was how to shoot at a lower shutter speed. You’d be amazed on how creative these guys are in finding ways to minimize movement. Of course the entire afternoon’s topic was about camera gadgets and a lot of teasing between Nikon and Canon.

Can you really shoot at lower shutter speed without a tripod? Of course, but will it be sharp enough? I’d say sometimes but in my case never. No matter how I practice shooting at lower shutter speed, I never get it done. There are those who can really shoot like a rock and unfortunately I’m not one of them. But don’t confuse your excessive hand shake with having blur photo.

There are a number of reasons why you’re getting blur or at least soft photos. Hand shake can be one but can always be defeated by higher shutter speed. You have to note that the higher the focal length, the greater the magnification of image and shake.Therefore you need to ensure that your lowest shutter speed should be equal to or more than your focal length when shooting handheld.

Depth-of-field is another possibility. When I first handled my 50mm 1.4, most of my shots were soft both the subject and the background. When shooting at lower apertures or bigger opening, depth-of-field is less. So small movements going forward or back after you focus will instantly blur your photo which is not an issue at f/3.5 and up.

You should also know that lenses are at their best at 2 stops up from their biggest aperture.

AF or autofocus comes in different modes. Nikon has AF-S, AF-C, AF-A while Canon has One Shot, AI Focus and AI Servo. Sometimes, setting this improperly for a certain scenario can degrade the sharpness of the image. AF-S or One Shot means that once the lens focuses, it stays in that position as long as you hold the trigger in half-press position. Lifting it and pressing it back again will refocus.

When autofocus is set at AF-C or AI Servo, the lens will focus on the subject and will continue to refocus as the subject move. This is not a good setting if you know your subject is stationary since the camera will try to collect data constantly and will result to inaccurate focusing. The AF-A or AI Focus on the other hand is programmed to detect if the subject is moving or not and applies the right AF mode as per requirement.

When shooting RAW, sharpening in post processing is necessary. RAW files are naturally blurred since the in-camera processing where sharpening is applied is not performed when quality is set to RAW. Only in JPEG format that in-camera processing is performed which includes the auto color, auto contrast, auto sharpening and compression is applied.

You can choose to sharpen it using Photoshop under the sharpening filters, unsharp mask or smart sharpening. Lightroom can also do that for you under the details tab in Develop module. Personally, I choose to sharpen it in Photoshop using unsharp mask.

Maybe I’ll talk more about this sharpening technique in my future articles.

Keep on shooting everyone! For comments and suggestions, email me at photography@grp.ph