CameraTalk » exposure

Say Hello to My Little Friend: Fill Flash

Peter Ching — Wed, 20 Jan 2010 06:23:24 +0000

Scenario: you are photographing a subject in broad daylight. The camera sees a bright scene and adjusts its exposure accordingly.

Result: disappointment with your subject silhouetted against a very bright background.

Solution: Fill flash.

Instead of using your camera’s flash or a hotshoe-mounted flash simply as a means to take photos in the evening — which, for good images, requires either additional lights or expertise — bring it with you when shooting in the daytime.

Camera manufacturers calibrate flashes, knowing that users will most likely use them as the main light sources. So, using default settings when shooting with a flash in the daytime will “burst” light, hoping to equal the main light source (the sun), resulting in a flat, bland photo.

What we’re looking for is a flash setting that will achieve the balance that your eye would normally see. This would use enough light to illuminate the shadows and fill in details that would otherwise be lost due to the extremes in contrast in the scene. Voila!… Fill Flash.

Setting Fill Flash

How much you reduce the flash output will depend on the lighting imbalance in the scene and your own creative ideas. In general, you’ll probably reduce your flash output anywhere from 2/3 to 1-1/3 stops.

On most point-n-shoot cameras, look for a button with a lightning bolt symbol. Pressing that button should cycle through a range of icons indicating the camera’s flash mode. Refer to your manual to work out which is the fill flash mode. Failing that, taping over the flash using paper (tissue or other) or a coloured gel is an option.

SLR cameras with popup flashes can also be adjusted. Your manual will explain how. Often it’s a case of pressing the button that pops the flash up a second time to place the camera in a mode where the flash output can be adjusted using one of the control dials.

External flash units need to be adjusted independently from the camera.

Flash exposure adjustment is not to be confused with adjusting exposure in your camera. Exposure time is constant for a given lighting situation. Fill flash will not change the exposure.

You may have a camera that adjusts exposure if it senses a change to flash output. No worries. These cameras are programmed to do pretty much what you want anyway.

Expertise with this, as with many photographic techniques, may take a little practise.

In the sample photos above, fill flash is used on the photo on the right.

Extension Tubes Close Up

Peter Ching — Fri, 04 Dec 2009 00:53:03 +0000

EXTENSION TUBES MAKE AN ATTRACTIVE ENTRY POINT into macro photography.

These relatively inexpensive tubes have no optical elements. They work by extending the distance between the lens and the imaging plane.

As the lens is moved farther from the sensor (or film plane), the distance at which focus is achieved decreases while magnification increases. At the same time, the light that registers on the imaging plane diminishes, as it now has a longer barrel to traverse. So, longer exposure times are needed.

You’ll find that extension tubes come in various lengths to provide a choice of magnification and focus distance effects. You can stack them together for even greater effect although, in combination with some lenses, the focal distance can be too short to be physically possible.

Extension tubes, such as those produced by Canon, Nikon and Kenko, include electrical contacts that allow DSLR cameras to maintain control of the lens, enabling autofocus and aperture control.

Some of the cheaper extension tubes, many of which appear for sale through eBay, have no electrical components. Consequently their use would compromise aperture control and focusing, not to mention the absence of EXIF data in the digital files.

Extension tubes are more effective when used with lenses with longer focal lengths and less noticeable on shorter focal-length lenses, where the situation described above can occur, in which too short a focal distance can be unworkable.

One Point Or More To Focus

Peter Ching — Mon, 16 Nov 2009 02:41:51 +0000

USING THE CENTRE FOCUS POINT, especially for close up, thin depth-of-field shots, often leads to focusing errors as well as metering errors.

There are times, of course, when using the centre Focus Point is fine – for example, landscapes and other shots with very wide depth-of-field.

But for group shots and portraits, especially with narrow DOF, you’re better off selecting Focus Points that best serve the composition. Manual selection of the best Focus Point will reduce out of focus and poorly metered shots.

Trying to lock focus and recompose will likely result in focus errors. In fact, doing so misleads many users to believe their lens is back-focusing or front-focusing when, in fact, the problem is poor technique.

Lenses are not perfect, so their plane of focus is not a perfect plane. This means that, for narrow DOF shots, if you focus with your centre Focus Point and recompose, the region of the frame now occupied by the target, may not be in perfect focus for that part of the lens. Result: soft images.

Multiple Focus Points are there for good reason – to help produce sharp, correctly exposed images. Note: histograms will show whether exposure compensation is needed.

This is what Canon, Nikon and other camera manufacturers had in mind when they designed their DSLRs. Exploiting multiple Focus Points is the best way to get the sharpest images with the best metering.

Here’s the how:

Bring camera to eye
Compose and frame shot
Manually select the most appropriate Focus Point (eg, on subject’s eyes)
Hold framing steady, shoot.

If this sounds all too time consuming, a little practise will help make it second nature, such that you’ll proceed quickly and effortlessly, concentrating instead on the composition.

Multiple active Focus Points also come in handy is when using the Dep or A Dep mode – where the camera sets a focus distance and aperture to capture the chosen near and far points (Dep mode), or the range, to a given minimum level of sharpness, between the closest and furthest Focus Points (A Dep).

Multi-Point AF is your friend when tracking something that is moving unpredictably. Aside from subjects in rapid or erratic flight, the same system is a godsend for animal portraiture as dogs and horses, to name but a two, tend to move their heads around quite a bit.

Continuous mode AF with multi-points uses a multi-point algorithm to identify the subject and choose the sensor(s) that are on it. For example, if you pan past a light pole in the foreground, AF won’t generally shift off the main subject. Or if you’re following a plane flying by at upwards of 1000 kph, AF will stay “locked on” even if only a fraction of the subject is in the finder.

Filter Essentials

Peter Ching — Thu, 09 Jul 2009 01:04:43 +0000

Photographic filters are akin to sunglasses. They shield your lens similarly to sunglasses protecting your eyes. They also modify light in much the same way as sunglasses do.

Here’s an overview of some of the types of photographic filters available.

UV Filters

UV filters are the Go To filters for most people. Other than a purpose-built protective filter, UV filters have the least impact on image quality. They can be left permanently mounted to your lens so that when the unexpected happens and your new-born projectile-vomits, you need only clean the filter.

They’re called UV filters because they eliminate the haze commonly seen on a summer’s day. Commonsense suggests that colour and sharpness remain untainted because a clear filter attuned to only ultra-violet lightwaves will ignore the slower wavelength colours.

But, as with many applications of commonsense, arguments abound. Detractors point out that anything between subject and lens glass will affect image quality. They also argue that your best defence to protect your lens is your plastic lens cap.

Whatever the argument, the upside is that your $3000 lens will be shielded from untoward debris and will never wear the visible evidence of subsequent scouring efforts. The downside is that a stickler will resort to a 400% image enlargement just so they can offer you a smug “told you so”.

If you who own top-shelf glass, such as Canon’s L lenses and the faster Nikon lenses, you will want nothing less than Hoya’s Pro1D filters to maintain high optical standards. This applies equally to the circular polarising filters described further on.

Circular Polarisers

Unlike UV filters, you’re hardly going to want to leave a circular polariser on your lens fulltime. They WILL have an affect on your images. But it’s an effect you will achieve by no other means.

Take, for example, a landscape shot featuring lots of blue sky and puffy white clouds. Without a filter, your exposure is correct for the trees and farm buildings but the blue sky looks washed out and the clouds have no definition.

Enter the circular polariser. These filters work like Polaroid sunglasses – they redirect, i.e. refract, the angle of light passing through. You will not only see more sky depth and detail, you’ll also be able to eliminate reflections off glass, water or foliage.

Polarisation is most effective at right angles to the sun. At 180 degrees – in other words with the sun directly behind you – polarisation is almost non-existent.

Due the directional nature of polarisers, it’s not a good idea to use them when you want to stitch together a panorama, as the sky in each panel will be at variance with the others.

Above left with a polariser; above right without a polariser.

Above: upper half with a polariser; lower half without a polariser.

Neutral Density Filters

Neutral Density (ND) filters reduce the amount of light through the lens. They’re designed to filter out all colours equally, therefore having no effect on the colours in your images, hence the term “neutral”.

All ND filters are grey in colour – the deeper the grey, the more light is reduced. These filters come in three strengths, giving 1, 2 and 3-stop reductions in light intensity. You can stack a number of ND filters to further reduce the intensity of light.

ND filters have ‘gradings” depending on the amount of light they cut. A higher grading means lower light.

There are two commonly used notations:

ND2 ND4 ND8:
The number designates the density of the filter based on binary numbers 2=21
i.e. 1 stop of light. 4=22 i.e. 2 stop of light, etc.

0.3 0.6 0.9 ND:
Another notation in which every 0.3 will make you lose one stop of light. So a 0.3ND will cut 1 stop of light 0.6 2 stops etc.

ND filters help in at least three situations:

reduce light intensity;
allow slower shutter speed use; and
allow larger aperture use.

If the shutter speed remains the same after adding an ND filter, you’ll use a larger aperture to obtain the same exposure. Likewise, if the aperture is retained after adding an ND filter, a slower shutter speed will achieve the same exposure.

Keep in mind that a larger aperture produces a shallower Depth of Field. So, for example, if you are shooting a portrait in broad daylight and the light conditions demand high shutter speeds, an ND filter will allow you to use bigger apertures to isolate your subject via shallow DOF.

On occasions where you cannot achieve correct exposure even with the smallest aperture and fastest shutter speed, ND filters provide a means. Reduced light intensity allows either a slower shutter speed or a larger aperture. A slower shutter speed can give moving objects a blurred result (i.e., motion blur) to create a sense of motion.

Shooting a waterfall through an ND filter is a revelation. The key to achieving that milky water effect is slow shutter speed.

Above, without an ND filter.

Above, with an ND filter.

You do not want to use ND filters when different objects are lit differently and you need to expose all of them correctly.

Should you buy a Neutral Density filter? If you shoot landscapes, you DEFINITELY need to have an ND or two in your kit. ND filters provide an effect you cannot reproduce in Photoshop.

Filters available from CamerasDirect