Like many compact digital camera users moving to a digital single lens reflex camera for the first time, I expected images from my Canon XSi/450D DSLR to come out of the camera tack sharp.

I was in for a rude awaking. Images appeared soft, especially when viewed at 100 percent on my computer monitor.

We novice DSLR users may think soft images are caused by a faulty focusing system. However, this is not the main reason images look soft.

Aperture size and image softness

Soft images can be caused by using a large lens aperture that results in shallow depth of field. Depth of field is the amount of sharpness in front and back of where you focus on the main subject. Sharpness increases when using smaller apertures.

Find the lens “Sweet Spot”

Each lens has what photographers refer to as “sweet spots,” a small range of aperture sizes that produce the sharpest images.  The actual sizes vary from lens to lens, but they are typically found in the middle of the aperture range.

For example, I’ve found that the sweet spot for the XSi 18-55mm IS kit lens is between f5.6 and f.11. These apertures work particularly well for landscape scenes containing foliage. For the Canon 55-250mm IS lens the sweet spot is between F8 and F11.

The aperture to select within this range can vary depending on the focal length used and distance the lens is from a subject. Like so many things in digital photography, it’s best to take plenty of photos and experiment to find optimal settings.

Sharpen during post-processing

Image before and after sharpening. 100% crop.

Images taken with a DSLR need more post processing than compact digital cameras.

An important, usually last step in the editing process is sharpening. Sharpening brings out subtle detail if present in the original image.

I use unsharp mask and XSi images sharpen nicely revealing captured detail. Sometimes I selectively sharpen an image by using the appropriate editing tool to select it.

Incidentally, sharpness in a DSLR is turned down by default so images can be edited with no sharpening artifacts. Many who shy away from photo processing, increase the in-camera sharpening setting.