Wednesday, November 16, 2011

Still learning

I commented about the photos that someone had taken in the Auditorium of the gala for ADIS and said that in the dim lighting it was difficult to get a sharp picture without using flash.

There are three factors to balance, the ISO speed at which you set the camera to, the shutter speed and the aperture. In good daylight you can set a low ISO and combine that with a small aperture and a fast shutter speed. That is the perfect combination because setting a low ISO gives you a clean image, a small aperture provides sharpness throughout and a fast shutter speed avoids the problems of camera shake and motion blur.

It is when the light is low that things get difficult.

With a powerful flashgun it is possible to get good clear pictures even in pitch darkness at relatively large distances. However, using flash in the Auditorium creates problems. First off it is very distracting to the performers and to the audience. It is also tricky to get the level right when you are sitting in the audience because that is going to be determined by the nearest object to you.  So, for example at a concert, the band members at the front would be correctly exposed but those towards the back would be in darkness.

In order to avoid these problems, I prefer not to use flash but rather rely upon the light in the Auditorium. That is where it gets awkward because even with the stage well lit I need to use almost impossible ISO levels to get an exposure.

I would like to be able to set the speed to ISO 2,000 maximum because then I can clean the images up reasonably well.  However, at that speed I have to either go for the maximum aperture of my 70-200mm lens or try and take shots at ridiculous shutters speeds that even image stabilisation finds difficult to cope with. And, even if I avoid the effects of camera shake by using a tripod, any movement of the subject will blur the images at these very slow shutter speeds.

Each time I go to a performance, I experiment with the settings that I am going to use.

At the latest concert for Santa Cecilia I set the ISO to 4,000 which gave me exposures of about 1/30th to 1/100th second at f5.6 (bear in mind I am often using my lens set to 200mm where you would normally set a shutter speed faster than 1/200th of a second). For the shots from the balcony I changed to f8 to gain greater depth of field which slowed the shutter speed down further.

The results I got were mixed.  It was impossible to get perfectly clean images even using software to remove the digital noise so inevitably  I lost some detail on all of my shots. The problem was made worse in those pictures where the light background had the greatest effect on exposure because for those pictures I had to try and lighten them up using software.  When you try and correct an underexposed picture, the digital noise increases, the colour balance is affected and you loose even more detail. You can see this in those photos where the band members suits have taken on a bluish purple tinge.

I know that I haven’t got it right yet, this is what we would call “a work in progress”.

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