Extending Sharpness

“The” challange in macro photography is that depth of field (DOF) - the subject area, which is depicted sharp in the image - is quite shallow. The longer the focal length, the shallower is DOF, and again, the closer you get to your subject, the shallower is your DOF. And now guess what you use for macro photography - a tele lens, from a relatively close dictance.

The only thing giving some comfort on this is closing down your aperture (applying stops f16-f22).

And still… you do not even need to get to 1:1 magnification ratio to have a DOF shallow enough so your subject would not fit into it. If you look at my gallery green tale you see that merely, or not even the heads of the depicted insects would fit into the actual DOF.

I shot my newest Lego creation with the same lens I used for most insect shots, and got this image:

Zoom in, and see how much unsharp the headlight closer to the camera is, and - at least to me - it feels somehow dumb to look at that the rear wheel is more sharp than the front one:

And here is a setup diagram to explain how it works, please consider I set sharpness on the eye of the car driver figure, and also consider, the diagram is not at all exact in terms of size proportions. The diagram shows one thing most cameras have in common: image plane is parallel to the plane of focus, and the optical angle is perpendicular to both.

The old school solution from the time before digital cameras is to shoot objects with a so-called view camera, like the Cambo SC, which offers you applying the Scheimpflug principle via the tilt camera movement. You could replace the heavy and cumbersome view camera with a tilt-shift lens, but functionality may be limited while cost wise not so…

Let me show you the image I was looking for to take for quite a long time for the sake of technical excersize. Both headlights are depicted evenly sharp, and the front and rear wheels are evelny slight out of focus.

And here is the diagram for this shot, showing the very point of the tilt camera movement, moving plane of focus out of the position parallel to the image plane. The point of the Scheimpflug priniciple is that plane of focus, lens plane and image plane intersect in one line (which is shown as a point in the diagram while looking at it from above). The DOF is approximately as wide as in case of the common macro shot, but  - with a little luck - you can fit your object into it. In the end this is not an extension of the DOF, some great and classical photographic manipulation though. Keep in mind, this technique was invented for sheet film shots, where you had to record an actual image beamed at your raw material  by a lens, and digital interpolation was out of the qustion.

So what is the alternative if you can only afford an expensive macro lens, not an even more expensive view camera nor a decent tilt-shift lens? You may apply the computer powered hardcore image manipulation: focus stacking. I will not give you step by step details, how to do it, neither will explain focus breathing which you may find a challange when shooting your raw material - you can get all this from the web. Here and now it seems enugh to say you shoot a handful (or depending on your subject even more) images from a very similar point of view (preferably only the focus setting is different between shots), and then you merge these images with a software (probably Photoshop).

My point here is to give you an idea how much you can improve your image by actually extending DOF, and what this technique means as an alternative to tilt movements, so let’s see the result:

Both headlights and both wheels are tack sharp, just like the whole Lego car, as it fits into the DOF extended by the focus stacking technique.

See some more werk shots here (in some I removed the bellows from the Cambo SC camera to make tilt movement more visible).

Thanks for reading!

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