Focusing Aids

In the viewfinder as well as on the display it is not always easy to determine whether or not the object is in focus. For this purpose, some digital and analog cameras, depending on the make and manufacturer, provide various tools to aid the photographer, e.g. split image indicator, viewfinder focusing screen, rangefinder, focal areas and screen magnifier. The following article contains information about these tools for manual focus.

Split image indicator / Viewfinder focusing screen

Split image indicators are helpful tools for manual focus and can be found on digital as well as analog single-reflex lens cameras. While it used to be a standard setting for cameras that only have manual focus, the split image indicator is now only available as special additional gear (special viewfinder focusing screen) for high quality digital single-reflex lens cameras.

The great advantage when focusing using a split image indicator is that it works even in poor lighting conditions. It is very easy to use. The central split image indicator focuses on the desired object. By rotating the focus ring on the lens, both split images are united.

Depending on use and camera model, further focusing screens are available, e.g. grid focusing screens with grid lines and microprism rings.

Example 1: Split image indicator – incorrect focus

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Fisherman's hands – Egypt – Alexandria

Example 2: Split image indicator – correct focus

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Fisherman's hands – Egypt – Alexandria

Rangefinder

Another useful tool for precise focus is the viewfinder magnifier. This is placed over the viewfinder and magnifies part of the view. This is especially suitable for optical viewfinders on single-reflex lens cameras, as on digital viewfinders the resolution is not improved. By using a rangefinder the photographer is able to precisely measure the distance to the subject. This is especially important when the diaphragm is open and/or for capturing close ups i.e. macro images as the shallow depth of focus combined with inaccurate focusing can quickly result in an out-of-focus, unusable image.

Focal areas

Some single-reflex lens cameras aid the photographer in manual focus with an autofocus system. The focal areas the camera determines as correctly focused, light up.

Example – Aiding tool: Autofocus system

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Tracks and overhead wires – Germany – Regensburg

This is a very convenient and easy-to-use tool for focus control. In some subject scenes however, it can result in unsatisfactory results, especially if numerous image planes overlap (see example of manual focus). Low subject contrast i.e. poor lighting can result in this focusing aid being rendered useless.

Screen magnifier (digital)

Often the display's or viewfinder's resolution is not sufficient to be able to carry out precise focusing. Digital cameras with live preview mode usually have another focusing aid, the screen magnifier. Part of the electronic viewfinder/monitor is used to display an enlarged image section. The selected detail facilitates a precise distance setting. Especially in very poor lighting conditions, the quality of image seen through the viewfinder can be very poor. In these cases, the screen magnifier's image quality is also reduced. If focusing using the viewfinder is not an option, measuring the distance to subject or auxiliary lighting could be the solution.

Example – Screen magnifier

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Gorge - Spain - Mallorca
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