Thursday, 28 July 2011

GH2, built-in flash for macro use

Lightning is critical for macro photography. To illustrate this, I will present a scene I tried to photograph. I used the Panasonic Leica Lumix DG Macro-Elmarit 45mm f/2.8 1:1 Macro lens. To make sure I used the maximum magnification, I selected manual focus (MF), and moved the focus ring until I reached the closest focus distance. Then I placed the camera so that the subject came in focus. This way, I was sure that I used 1:1 macro, which means that the subject is the same size as the sensor area, 17.3mm x 13.0mm.

As a test subject, I originally intended to use a bee. However, I found that chasing a bee around while it was visiting flowers, was much too difficult. Therefore, I found a bee that had been killed by a spider's web. With the bee being suspended, it was much easier to photograph in a controlled fashion.

First, let's consider what aperture to use. The PL45 lens has a maximum aperture of f/2.8, which has been criticized as being too small. Many would have preferred it to be f/2, to make the lens more useful for portraits. In this case, I want to have some depth of field, so I try to set it to f/5.6, a point at which many Micro Four Thirds lenses reach their optimum performance.

Here is the image at f/5.6, 1/60s, ISO 3200:


As you can see, the image is in fact not very good. One wing is in focus, the other is not. The rear part of the bee is in focus, but not the front. We can easily conclude that the depth of focus is too thin: Only parts of the insect is in focus.

To get a better depth of field, let's set the aperture to f/13. Some may worry that f/13 is too small, and will give some dullness due to diffraction. That is true, but as long as you don't make a big magnification of the print, that should not be a problem. For web use, f/13 is no problem at all, and you could even try to use f/16 if needed. I have studied the diffraction effects here.

I took ten images at f/13, 1/15s, ISO 3200, and this one is the most successful:


There are some problems here. First, you can see that the image is not framed very well. I was handholding the camera, which makes framing hard. Also, while the image has much better depth of focus than the previous, it now has some motion blur effects. The shutter speed, 1/15s, is much too slow to handhold the camera, even with Optical Image Stabilization (OIS). Finally, the high ISO at 3200 makes the image a bit noisy.

There is an easy way to solve all these problems: Just use the built-in flash. It turns out that the small built-in flash does cover the entire frame when using the PL45 lens at the closest focus range. The illustration below explains why.

In the illustration, a LEGO figure is placed at the minimum focus distance of the lens. At 1:1 magnification, the distance from the front lens element is 7cm. The built-in flash covers the focal length of 14mm, which corresponds to 75° diagonal field of view.


The resulting image is this:


As you can see, the entire image frame is illuminated by the built-in flash, even at maximum magnification.

A note about the lens hood: I don't like the supplied hood. It is much too wide, and does not do a good job at keeping out stray light. So I made my own hood, composed out of three elements: A 46mm stand off ring (glassless filter), a 46mm-37mm step down ring, and finally a 37mm-28mm step down ring. This gives the ultimate protection against stray light (in my opinion), and also good protection against objects touching the front lens element accidentally.

If you use the original hood, the light from the flash will be blocked by the hood, and you cannot use the built-in flash with macro images.

Back to our bee example. Here is the same image taken with the on-board flash, at f/13, 1/60s, ISO 160:


Using the flash allows for base ISO (160), and there is no problem with camera shake. The flash light is very quick, and freezes the image instantly. We clearly see that this image is much more sharp.

On the other hand, this method is not perfect for macro images: We see that the background has become very dark. This is because the flash light spreads out, and becomes less powerful for the background at a larger distance. Also, the flash light coming from a single light source does give a "flatness" to the image, which is not optimal. The nature of the image changes completely when using the flash.

Using the built-in flash for macro is a quick and easy way to get usable macro images.

4 comments:

  1. You can brighten up the background by making the exposure closer to ambient. For your example you could have bumped the ISO to 400-800. A well-exposed image usually doesn't have much noise at 800 with a camera like the GH2, and you'll also benefit from less flash glare (because there's less flash used) and faster flash recycle times.

    Also, if you shoot with a bigger flash like the FL-36R you can use a diffuser like the Lumiquest Mini Softbox to make the light more diffuse. Taking the flash off-shoe with a sync cable gives you even more flexibility.

    It's too bad the STF-22 doesn't work well on M43. The system is ideal for macro, but there aren't any good dedicated lighting equipment.

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  2. Yes, you are right. The background could be brightened by increasing the exposure.

    I have a TTL cable, with which the FL-36R can be connected to the camera, and yield full TTL auto. That is useful for macro, but a diffuser is still good to have, as you say.

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  3. hi...at maximum magnification, you will get 2X with the PL45 instead of 1:1 you mentioned. This is due to the crop factor of the MFT.

    I also shoot at max magnification in this fashion. But to extend the depth of field, I use focus stacking.

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