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PhotoPlus February 2015 | 77

Quick Fix

Quick Fix

Circle or square?My camera seems to have

two alignment markings for attaching lenses. One is a red circle, the other is a white square. Why is this? Jill Marks Andover

Angela says Crop-sensor

Canon D-SLRs, like the 100D, 700D and 70D, have smaller image sensors (than full-frame bodies like the 6D and 5D Mk III). They can accept both EF-S lenses, designed exclusively for APS-C-format D-SLRs, as well as EF lenses, which can be used on both APS-C-format and full-frame bodies. These have white square and red circle alignment markings, respectively. Note, however, that you can’t fit EF-S lenses to full-frame bodies.

Why so soft?When I narrow the aperture of

my lens to f/22 or f/32 to extend the depth of field, images seem to be really lacking in sharpness. Is this normal?Clayton Woods, North Carolina

Hollie says When the

aperture of a lens is set to a very narrow value, light is diffracted as it passes through the tiny hole created by the diaphragm blades. Some lenses cope with this better than others, but the resulting lack of sharpness in images can be very noticeable.

One solution is to press the AEL (Auto Exposure Lock) button after you’ve swivelled the camera, as this will capture and lock in a new exposure setting. Another option is to switch to one of the alternative Centre-weighted, Partial, or Spot metering modes, all of which update in real time as you swivel the camera to recompose the shot. However, the last two of these modes are best used when you want to base the exposure on a single area or point within the scene.

As their names suggest, Centre-weighted metering biases the exposure to suit brightness at the centre of the frame, but also takes the periphery into account to a lesser degree. Partial metering bases the exposure solely on the central area of the frame, while Spot metering works in the same way as Partial metering but uses a relatively tiny dot at the centre of the frame, typically just 2-4% of the overall image, making accurate metering tricky in inexperienced hands.

But there’s a catch. In the default Evaluative metering mode, metering is locked at the same time as autofocus when lightly pressing and holding the shutter button, at least in One Shot (single) rather than AI Servo (continuous) autofocus mode. Also, the iFCL (intelligent Focus Colour Luminance) metering system of current and recent Canon D-SLRs greatly biases the exposure value to the colour and brightness of the object that’s lined up with the active autofocus point. This usually works very well, especially for tricky subjects like heavily backlit portraits, but is also prone to two errors. Firstly, if the autofocus point happens to fall on a particularly bright or dark point in a scene, the metering system will result in a picture that’s too dark or too bright, respectively. Secondly, as exposure is locked at the same time that autofocus is achieved, changes in the overall brightness of the frame won’t be taken into account when you swivel the camera to recompose the shot.

Metering modeThe default Evaluative metering mode can throw up a few surprises in general landscape shooting.

Switching to Centre-weighted metering can give more predictable results, especially if you’re autofocusing on a single point then swivelling the camera to recompose the shot. Partial or Spot metering give the greatest precision, though the latter can be tricky to use.

Highlight Tone PriorityOne common problem is that bright highlights in scenes can tend to get washed out to white. For

situations where you want to retain as much detail as possible in highlight areas, most Canon D-SLRs have a Highlight Tone Priority setting, available via one of the shooting menus or as a custom function. When used, the Auto Lighting Optimizer is disabled.

Auto Lighting OptimizerCurrent and recent Canon D-SLRs have an Auto Lighting Optimizer setting, which can help to avoid

exposure errors. It aims to correct brightness and contrast automatically, so that highlights aren’t too bright and shadows aren’t too dark. Most cameras have low, standard and high settings, and the ALO can also be switched off altogether.

Exposure CompensationCheck images in playback mode, while you’re shooting. If pictures are too dark or too bright,

apply positive or negative exposure compensation respectively, and reshoot. Check again and apply greater or lesser amounts of exposure compensation as needed. Switch off Auto Lighting Optimizer, as this can counteract the effects of exposure compensation.

Make the most of meteringSTEP BY STEP