articles/Nature/capturingdragons-page5

Capturing Dragons by Andy Astbury - part 5 of 1 2 3 4 5 6

by Andy Astbury Published 01/02/2009

BUT - your problems don't stop there either!

Lenses all suffer from a phenomenon known as 'diffraction limitation' whereby once you pass a certain f-number, your images begin to get 'soft' all over. This is due to the properties of light and the way it interacts with the edges of the aperture diaphragm. Once a diffraction-limited image arrives at the sensor, the area of the individual pixels on that sensor comes into play, as the detail of the image may be spread over more than one pixel. As soon as this happens yet further complications arise because there are twice as many 'green' pixels as there are red and blue, and also, red light is more diffraction limited than blue light.

On my own D2Xs I get razor-like sharpness at f11 - but even one third of a stop beyond that, it begins to show small amounts of diffraction softening. A very good friend and colleague of mine uses a Canon 40D body and can quite happily shoot away all day at f16! (This remark contains so much underlying importance that we have written it up at the end! - Ed.)

The way that the sensor size changes the DoF does not make a huge difference - at a subject distance of 30 inches using a 180mm lens, the Canon at f16 will yield 0.33'' DoF and the Nikon at f11 will give me 0.24" DoF. To my mind, 9/100ths of an inch isn't worth changing systems for!

You can now perhaps begin to see that for me, the background is as important as the subject, and I make constant use of my camera's depth of field preview button to very carefully check that my background is going to be just the way I want it.

The background in the side-on view of a Black-tailed Skimmer is not quite to my liking as there is a little too much definition in the darker areas, and is just one example of how things can go wrong with the background if great care is not taken before the shutter is activated.

I had already done some tighter head shots of this dragon and the background is more than acceptable on them, but because I had pulled away to just over 5 feet to take this particular image of the whole insect I omitted to open the aperture a stop or so. Because the increased subject distance here is now a greater proportion of the subject to background distance the f10 aperture I was using on the much tighter shot is now bringing too much DoF to bear on the background.

I took this shot in a hurry to be honest, as I could tell this Black-tail was getting fed-up with me and would be gone within seconds - 10 frames later he was; I had realised my error, but didn't have the chance to correct it.

Above right is another image which has been something of a let down, this time due to my miscalculation. I was trying to portray the way in which Black-tailed Skimmers settle on a perch and then 'hunker down' slightly as if trying to 'hide in plain sight' - and I was very pleased with the way it turned out from that respect. I know some would say that the face hidden by the petal is a fault but for me it's the whole point of the image.

he background is flawless - it's actually a bed of nettles about 5 feet behind the subject - but the error is in the foreground. I think that it's inevitable there be some focus fall-off in the foreground if the subject is facing out towards the viewer, but in this case the composition is let down by too much focus fall-off on the upper, orchid flower-head. At the time I took the image I was convinced that there would be slightly more sharpness to that individual bloom but as it is, it's slightly over-powering.

• Capturing Dragons by Andy Astbury page 1
  
• Capturing Dragons by Andy Astbury page 2
  
• Capturing Dragons by Andy Astbury page 3
  
• Capturing Dragons by Andy Astbury page 4
  
• Capturing Dragons by Andy Astbury page 5
  
• Capturing Dragons by Andy Astbury page 6
  

There are 37 days to get ready for The Societies of Photographers Convention and Trade Show at The Novotel London West, Hammersmith ...
which starts on Wednesday 17th January 2024