Nature photography with magnification: Experiments with flash duffusers

Introduction

Electronic flash is ideal for macro photography. The flash duration is very short, meaning that any subject and camera movement should be frozen. This article gives measurements of the duration for a YN560. For example, at 1/2 power, the duration was 1/1359s and at 1/4 power, 1/2809s. At the same time, by placing a bright source of light close to the subject, it allows a small aperture at reasonable ISO to be used. When photographing subjects at reproduction ratios close to 1:1, depth of field is critical, so I like to keep the aperture at around F16.

The downside of electronic flash is that it can give very harsh lighting. This results from the relatively small size of the flash tube with respect to the subject distance which makes the lights highly directional. The light falling on the illuminated side contrasts strongly with dark shadows on the other side. Diffusing the flash in some way ameliorates this and aims to provide softer, less directional and contrasty lighting. A search on Google comes up with loads of ideas for both DIY and commercial solutions. So, I decided to try out some of the ideas with the sorts of subjects I like to photograph. There are two factors to consider here: firstly, achieving attractive lighting, but secondly, the setup has got to be practical when taking photos of wild insects in the field.

Target

I set up a target consisting of a couple of freshly caught flies from the garden - a male hoverfly, Syrphus ribesii, and a Muscid, Phaonia tuguriorum, pinned through a fresh leaf to provide a typical background. Then an X-Rite Colour Checker Classic colour card was positioned so that the bottom left three squares are visible above the flies. These are three very pale grey panels which I will use to adjust the white balance during RAW processing so we can assess the effect various diffusers are having on the colour of the flash.

Exposure

All the shots were taken with my Canon EOS R in manual mode with a 100mm F2,8L Canon macro lens set to manual focus at 1:1. The aperture was set to F16 and the ISO to 200. I bracketed the exposures for each shot by adjusting the flash power up and down and chose the shot where I could discern the three shades of grey from the colour checker. The shutter speed was set to 1/200s - the fastest flash sync speed for this camera. On the whole, these chosen shots where the lightest of the three grey panels was not blown, looked somewhat underexposed to me, so I also cropped out the Syrphus and increased its exposure (in RAW processing) by 2/3 of a stop. I will present the whole image (reduced in size) and the crop (reduced to 1300x3000 pixels).

Yongnuo YN560 IV

Yongnuo 560 IV flash and RF605C wireless trigger

The flash head tilts up, but not downwards, so sitting it in the hot shoe on top of the camera, it won't depress enough to direct it at the focus point at 1:1. It would probably still work, providing it was set near its wide angle beam focus setting, but that would waste a lot of the light. So I mounted the slash beside the camera using a flash bracket and a small ball and socket.

This allows the flash head to be aimed and positioned closer to the focus point. However, there needs to be a way to trigger the flash. For this I used a Yongnuo RF605C wireless trigger on the camera's hot shoe.

YN560 at 1/16 power

As expected, the lighting is quite harsh with a strong shadow and strong specular highlights on the thorax and wing tips of the Syrphus.

If you search for 'flash diffuser' on Google, one of the things you will find in quantity is plastic caps to fit over the flash-head. I got one of these free with one of my Yongnuo guns.

The sort of "diffusers" are pretty useless! The textured plastic will scatter the light and therefore reduce the amount of light reaching the subject. But the size of the light source hasn't changed, so the directionality is the same and will result in very little change to the harsh contrast between the lit side and the shadow.

YN560 with plastic cap at 1/8 power

Comparing these images with the previous set, we can see that, as expected, the plastic cap "diffuser" has made very little difference, although it cut the light by around a stop. The shadows and the specular highlights on the Syrphus and pretty much unchanged. I do think that the plastic has affected the colour balance a bit - giving a slightly warmer image.

To actually achieve decent diffusion of the light, it is necessary for the light source to be much larger so that light rays reach the subject from many different angles. One way to do this is to build some sort of funnel shaped structure with the flash gun at the narrow end and a panel of translucent diffuser material at the wide end. Here is an example on YouTube by Reinhard Biller. I actually built something like this a long time ago for my Olympus T32 flash that I used with my Olymput OM2 macro gear. I refitted it for the YN560 just by modifying the size of the neck that fits round the flash head. It is made of cardboard lines with aluminium foil and the diffusing sheet on the front in tracing paper.

This will fit in the camera's hot-shoe because it was designed to point downwards.

YN560 with cardboard diffuser, 1/4 power

This time the light has been diffused substantially, the shadows are much softer and the specular highlights have also been toned down significantly. Altogether a more appealing image.Again, I think the colours are a little warmer than the raw flash. We have lost about 2 stops compared to the raw flash. Whilst the results are good, this is not a very practical device as it stands. It is rather fragile and would be ruined if it got wet. This could be tackled by using different material, e.g. foam core board and stronger joints, e.g. stuck using a hot glue gun. However, it is rather bulky and unwieldy, although not heavy, and would be difficult to manoeuvre amongst vegetation.

Another idea is to attach the diffuser around the end of the lens and illuminate it using a flash mounted on the hot-shoe without anything in between. I quite like this example, which is very easy to make. I tried this out, but found itr to be quite impractical for insects in the field. Firstly, it projects some way in front of the lens and tends to hit the vegetation the insect is sitting on and so disturbs it. Secondly, it blocks the view of the area you are trying to move in on and so makes it rather hard to find the subject. When you are working around 1:1, nothing comes into focus in the view finder until you are very close. So it is essential to be able to see where you are going and before you start looking through the view finder - which will be at the last minute.

Another idea is some sort of bounce card attached to the flash gun which is pointed more or less upwards and the light then bounces off a surface tilted at 45 degrees something like this example. There is no reason why this can't be combined with a diffuser screen placed in front of the reflector. I made the reflector part from the plastic cover of a file folder with aluminium foil stuck to the front. On the back, I attached a couple of pieces of soft wire with duct tape so that it can be positioned and will hold its shape. It is attached to the flash gun with a couple of wide rubber bands. The diffusing sheet on the front is garden fleece.

Mounted on the flash bracket, it can be positioned close to the subject.

Here are the results:

YN560 with DIY diffuser, 1/2 power

This has produced a good degree of diffusion, although it is obvious that the flash is placed to one side (to the right), so that there is some shadow on the left. The specular highlights on the thorax and wing are nicely softened. The garden fleece seems to provided a good, neutral diffuser. I cannot remember where I saw the tip about using this material as a diffuser, but it seems a pretty good idea, especially as you can easily add more layers to increase the amount of diffusion (there are 4 layers here). The combination of the bounce and the diffusion os taking 3 stops compared to the raw flash. This turned out to be a fairly practical design. The front of the diffuser remains behind the lens, so it doesn't interfere with the vegetation or get in the way of the view. The main problem was being aware of the shade it casts. Hoverflies and other insects are rather sensitive to being shaded and will often go if the shadow of you or your equipment falls on them.

Here are some hoverfies from the garden taken using this setup: