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Achieving a greater depth of field - Focus Stacking


In Principle

At, say, x4 the depth of field is around 0.08mm using f8. At x20 with a microscope objective it will be around 0.01 to 0.02mm. Below left is a single image taken of a mosquito head. As can be seen depth of field is negligible. The camera is moved forward on a rail 0.01mm and another shot taken, then again and again until reaching the back of the insect. We now have 190 single images, each with a number of pixels which are sharp. Using specialist software, e.g. Helicon Focus, all images are checked for sharp pixels and accumulated to create one composite image. Below right.


One image taken near the tip of the proboscis with a x10 objective lens sited on extension tubes. This is one of around 190 images taken at 0.01mm intervals
from the tip to the back of the insect.

This is a composite image made from 190 images taken at 0.01mm intervals from the tip of the proboscis to the back of the insect.
 

In Practice

Using a manual rail and advancing the camera with a slight twist of the knob can be a rather hit and miss process. I still use on occasions a manual rail in the field. On a tripod the advancement can be checked using live view. I prefer using both in the field and studio the automatic StackShot. It is very precise. Using the control box I set the position of the first shot in the sequence and then select the final shot at the end. Select the interval distance between shots (I have worked these out by trial and error for different apertures and lenses) and then just push the button to go. Stand back and the photos are taken and the camera advanced automatically.


Note the battery pack on the left to drive the StackShot
Photographing eggs on a butterfly orchid.

Eggs on the lip of the butterfly orchid flower. Shot taken in the
field, left, magnified about x3.

StackShot control box

StackShot in the field, France

When working in a studio setup the StackShot is setup on an old microscope stand for stability. As well as the camera being connected to the StackShot it is also connected to a laptop. Increasingly I am using a Microsoft Surface Pro tablet in the field. Not only do the images go straight to the computer where they can be stacked in Helicon Focus software but also for a large Live View using the Canon Utility software. This also gives access to all the necessary camera controls like aperture change and precise functioning of the macro flash. I use a Canon 7D Mk2 and the USB3 connection provides rapid download of the files. I rarely use Raw files only JPG as there are few benefits to Raw in this situation. Invariably you need a quick check on the composite to look at outcomes and make any changes to lighting etc. Raw stacking takes a long time. 100 image stack with JPGs on my HP Envy 12Gb RAM is around a minute or less. With Raw it could be 4-5 minutes. The animal will have moved on!

I try to work with live material only and use a range of narrow glass tanks for both aquatic and terrestrial organisms. Once they have settled down you can start the stacking.

 If you want to know much more please check out my book Extreme Close-up Photography and Focus Stacking