Back Focus

Term: Back Focus
Description: Back Focus, or back-focus, is the error of having a subject be accidentally out of focus, and sharp focus instead falling behind or past the subject. While images can exhibit this error even when manually focused, generally speaking a "back-focus problem" is usually referring to when the error is caused by your camera and lens' autofocus.

Back-Focus Technical Definition

The issue of back-focus is commonly seen if a fast aperture lens is used. Sometimes it is the photographer’s own fault, however: ether they accidentally focused on the background due to imprecise placement of the selected focus point, or there was actual movement in the scene. One of the most common user-error reasons for backfocus is simply that either the photographer our their subject shifted their balance just a little bit, and you were using an f/1.4 lens standing just a few feet away from each other.

Although technically any image which has focus accidentally falling behind or past the intended subject could be considered to be back-focused, when most photographers talk about back-focus issues with a particular camera or lens, they are referring to a specific problem with the autofocus system that causes the lens to repeatedly miss focus in that “back” direction.

This is an issue that can be corrected with most modern cameras’ autofocus calibration or focus micro-adjustment menu function, when performed correctly under controlled conditions.

Back Focus Distance

NOTE: The term “back focus distance”, although similar, is an unrelated photography term. It refers to the measured distance between a camera’s image sensor plane and the rearmost glass element in the attached lens.

Back-Button Focus

Also note that the term “back-button focus refers to something else too: using a button on the back of your camera to perform autofocus, instead of your shutter release. This is a camera customization that is popular among serious photographers who want to be able to perform the functions of focusing and firing the shutter independently of each other.

Related Articles to Back Focus Definition

canon 1dx markiii review

Canon 1DX Mark III Review | Living with a $6,500 Camera

Pye Jirsa
Pye is here to share his real-world experience of living with this flagship camera and test out both photo and video to see if it's worth the plunge.

Improve Focus Accuracy With Autofocus Micro Adjustments

Holly Roa
We photographers often discuss the merits and pitfalls of particular lenses, and one important area that we expect to be ‘dead-on’ is focus accuracy. However, even the finest optics are not always calibrated with...

An Inexpensive Way to Calibrate Focus on Your DSLR For Sharper Images | AF Fine Tune

Hanssie
Focus calibration doesn't have to be expensive or difficult, try this method out and see if you can save yourself some time and money.

New Sigma USB Dock Offers Level of AF Adjustments Never Before Seen

Anthony Thurston
Part of Sigma's new Global Vision initiative was the introduction of the new Sigma USB Dock, a device that allows you to update lens firmware and AF micro adjustments from your computer via a...