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Adverse Lighting Situations
Harsh shadows, blown-out highlights, uneven or aggressive lighting are many of the main reasons for lighting rejection at iStockphoto. These are often fatal problems, meaning there isn't much one can do to bring them back to life. These problems tend to come from certain kinds of lighting sources and conditions.Direct Flash
On-camera flashes can be your worst enemy. They give you little or no control over the direction and position of your light source. They tend to throw too much light at a subject, overexposing some areas and creating bad shadows in others.Use your oncamera flash wisely, and with great care. Try to diffuse the light: there are various diffusers, smaller softboxes, tubes, grids and other products available on the market, that make lighting softer, more diffused, directionally controlled and generally more pleasing.
Outdoors
Many outdoor situations suffer from similarly unpleasant lighting conditions. Depending on the season and your location, a bright sunny day probably isn't your best friend. Especially in summer time when sun travels high across the horizon, the light light range is just too big and generally too aggressive. You will end up with washed out colours, blown out highlights, harsh shadows and so on.If the sun is high overhead in a clear, blue sky, you may have to just avoid shooting for most of the day. The best times to go out into your beautiful garden is between dawn and 9:00 a.m. or so, and then anything past 5:00-6:00 p.m. The closer the sun is to the horizon, the more atmosphere the light has to pass through, which diffuses it and removes a lot of the harsh ends of the spectrum. The ideal situation is an overcast day: a cloudy sky diffuses and softens the sun's light.
If you have to shoot in bad outdoor light, there are a few things you can try to help. There are several different kinds of neutral density filters that you can attach to your lens. These block varying amounts of light from coming through the aperture. A good polarizing filter will help you maintain strong colours on a sunny day — perfect when you're in that gorgeous green meadow with all the fluffy white clouds in the blue sky. Move into the shade, or use diffusion panels and reflectors to control the sun.
White Balance
Another vital part of lighting is proper white balance. This is another area where you camera just isn't as smart as your eyes and brain, leading to images that end up looking drastically different than how you planned. Our brains can easily compensate for various colour casts caused by different light temperatures. Our cameras can't, which means that your frame may end up with strange blue or yellow tints.Imagine a piece of metal being heated. As the temperature rises, the metal becomes yellow, then orange, then red, and finally blue and white. Well, different sources of light are different temperatures as well, and just like the metal, these different temperatures cause different colour casts.
Light temperature is measured in Kelvins. Between 5000 - 6500K a light source will produce neutral light, this covers not only sunlight at midday and clear skies but also electronic flashes.
From 1000 - 4000 K illuminates Red/orange/yellow, usually from flames, tungsten bulbs and sunrise/sunset.
Fluorescent lights are a little special needing extra care to balance them; they show as a green tint with a temperature of about 4000 – 5000K.
Temperatures 6500-9000 K will illuminate your frames with blue, usually from shade, Overcast skies and so on.
Colour Temperature in Kelvins
This is when the A(uto) W(hite) B(alance) setting on your digital camera kicks in and tries to do what your brain does automatically — adjust the colour so that white is actually white. However it doesn't always get it right, and you can end up with the wrong white balance.
Lens Flares, Reflections, Chromatic Aberration & Purple Fringing
A well-timed, artistically used lens flare can add a really nice touch to a composition. More often than not though, lens flares are unintended, and such images are not acceptable. Try with different angle in relation to light source. Have your lenses/filters clean and dry.Often you get home and find annoying light reflections in the frame which you didn't catch at the time. The most common are your own camera's flash reflected at the far end of a nearyby window, glass or similar reflective surface. While it can work sometimes (and indeed rarely), it's usually not going to be accepted around here. The only real secret to avoiding these is to always check your LCD display right away, if you're shooting digital.
Chromatic abberations are our next serious contender for ruining your shot — the dreaded Purple Fringing. Again, without fiddling with theory, it's basically caused by the refractive index of the lens in relation to different wavelengths of light. Not all wavelenghts that hit the lens are focused into the exact focal plane. There's more to it, but in essence this causes those nasty purple and/or blue shifts that you see around the edges of your subject. Cheap lenses are more prone to purple-fringing, and it is emphasized by wide-open lenses at their maximum speed. You see it most in high contrast scenes with lots of border areas, especially when shooting wide-open against the light source.
Step down your lens, shift your position in relation to light source. And as always, shoot in RAW, so your options for addressing the problem later in post-processing are wider.
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