Sunday, May 27, 2012

Focus stacking

This last week I have been learning playing around with 'focus stacking'. One of the difficulties when taking closeup or macro photos is the incredibly shallow depth of field; sometimes you may only have a millimetre of the subject in focus at a time -front, sharp; rear blurry. The answer is to take a number of photos focussed on different parts of the subject and then merge them altogether to get one sharp photo.

This is easier said than done. Unlike merging photos for exposure, every time you refocus the shape of the subject changes slightly, so each picture needs to be aligned not only for x and y coordinates but also for depth by adjusting magnification. All tricky stuff for software but the free program "Combine ZP" available from: does the job admirably (though it does take some learning). Here is a dandelion composited from 5 differently focused frames in 'CombineZP':
and this is a 100% crop from right of centre out towards the right edge. Note the very fine detail that 'CombineZP' has been able to maintain:

Although the differently focussed frames can be achieved by adjusting focus on the lens, it is much easier with subjects this size to use a focusing rail which allows sub-mm adjustments. All five frames were shot at ISO 100, with a 70-300 Tamron lens at 185mm and f11 for 0.7 seconds.

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