What is Focus Stacking?

Published: 13th Jan 2009
Updated: 29th Nov 2009

Focus stacking put simply is taking a number of pictures of the subject, while moving the plane of focus for each shot but changing the framing of the shot as little as possible. Then software is used to combine the in focus sections of the images you shot to obtain a composite image with more of the subject in focus than you could with a single shot.

Why not just stop down the aperture?

You soon realise this is not an option when you start to shoot at extreme magnification - at 10:1 and more, even stopping down to F22 will not generally get you enough DOF for more than a very flat subject - three dimensional subjects like small insect faces are too deep for one shot to get everything in focus.

The main reason though is that at proper macro magnification (1:1 and beyond) stopping down a lens will soon start to cause diffraction. The more magnification, the sooner this starts to degrade your photographs.

The reason diffraction starts to become a problem is that the aperture marked on the lens actually appears to become smaller from the camera's point of view as you add extension between the camera and the lens. This is known as the effective aperture.

The formula is:

Effective Aperture = Marked Aperture x (Focal Length + Total Extension) / Focal Length

As an example, with a 20mm bellows lens and 200mm of bellows extension for 10:1 magnification, the lens is set to f8.0 then:

Effective Aperture = 8 x (20 + 200) / 20 = f88

An effective aperture of f88 is very small, and is enough to cause diffraction on any modern camera (well any camera with less than medium-large format sized film/sensor.)

If the lens can open up to say f2.0 then the numbers are quite different:-

Effective Aperture = 2 x (20 + 200) / 20 = f22.

An aperture of f22 is still just into diffraction territory on smaller sensor DSLRs like my Olympus, and APS sized sensors, but only to a small degree. This lens would be quite usable for stacking on a DSLR at f2.0 but at f8.0 will produce a seriously degraded image. (At this extension/magnification).

Okay so how do I do it??

Well, there are two ways of doing this - Method 1 in the field with live bugs; you can try to get a small number of shots closely framed, the first with the eyes of the bug in focus, then move forward by 1-2mm and grab another shot with the wings/torso in focus etc. In my experience, 2 or 3 shot stacks of wild bugs can be done but longer stacks rarely work well! Here is a short tutorial from a much admired photographer on this type of focus stacking.

Method 2 is the way I currently do my bug portraits. It involves killing the bugs and shooting them in an indoor studio, with completely controlled lighting, and a mechanism to shift the camera or the subject on an extremely small scale to adjust focus. This latter method is what I will focus on in these articles.

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4 Comments so far. Post a comment

You have some incredible pictures. Thank you for sharing. However, I do not think one should kill something in order to photograph it, even a bug. I think this also devalues the image/work you put into it as it is clearly simpler to photograph a dead insect than a live one. I hope you consider a new approach. I do appreciate your honesty in your technique.

Mike at 19:39 on 28th Nov 2009

Mike,

I understand your point of view. However you should understand, these deep stacks are simply not possible without completely immobilising the insect. There is no practical alternative. These images would be impossible without the technique.

Laurie at 01:44 on 29th Nov 2009

Laurie, you have done some amazing work here. I've been getting into photography lately and hanging on one of the well known boards looking at a lot of pictures. I've seen some spectacular stuff, even seen some stacking work. But you've really captured some incredible detail in your shots and it measures up to just about anyone. Keep up the great work!

Peter Atwood at 01:45 on 29th Nov 2009

Laurie, thank you for all your articles on stacking. They are very informative and well written. I hope to give it a shot one of these days...

Your images are super!

Steve

Steve Hanzek at 01:47 on 29th Nov 2009

What is Focus Stacking?

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