Holiday Diver – IMPROVE YOUR PHOTO SKILLS

Backscatter – those dreaded white-blobs that appear when taking wide-angle shots!

No matter what skill level the photographer the age-old problem of ‘Backscatter' will at some time rear its ugly head and ruin countless photos! But what is backscatter and what is its cause?

All of us who dive quickly come to the realisation that colours disappear as the depth increases, with red being the first to go! To bring back colour all one has to do is switch on a torch and hey-presto all the colours by some ‘magical phenomenon' reappear within the beam covered by the artificial light source. It therefore stands to reason that to bring back the true colours onto film or for that matter the digital image some artificial light-source is required. Therefore those of us who wish to produce colourful images taken deeper than about two metres resort to using an electronic flash. Whilst this solves the problem of restoring colour to our pictures it also brings to the front a much greater problem – that of ‘backscatter' or to put it simply a number of out of focus ‘white-blobs' that are most apparent from the direction of the light source used and especially noticeable in areas shown of uniform colour – for example the surrounding blue or green water.

What are these white-blobs? Think back to those cold autumn days, you look outside to see thick fog rolling in. The weather forecast states that visibility is down to 30 metres – the fog is so thick you seriously consider not venturing out, let alone driving your car. Underwater – it is considered superb diving conditions should the viz be 30 metres! So what gives rise to limit visibility underwater – firstly, water is denser than air and secondly, being most important to us as underwater photographers – there are many suspended microscopic particles in the water. It is these suspended particles that when illuminated by the camera's electronic flash throw back their reflected image to be recorded on film or digitally. This is most apparent with cameras that have a built in (close to lens) flash – with the flash-light illuminating particles that are head-on to the lens and so close as to be out of focus – hence a multitude of ‘white-blobs' and another ruined picture.

From what I have said earlier it would seem that the solution to the problem would be to distance the flash from the lens by means of using an external flash with adjustable or bendy long arm. However these particles when magnified show that they are mainly circular in shape and perform a function similar to a mirror. So, although illuminated from the side some light is reflected back towards the camera lens, giving rise to the appearance of ‘white-blobs' – to a much lesser degree but still very visible.

To minimise backscatter further it must be understood that the suspended particles between our subject and the lens should (1) Be kept to a minimum and (2) Not be illuminated at all. Complicated, not in the least! By using as wide an angled lens that is suitable for the subject as possible - this cuts down the subject to lens distance and consequently the number of suspended particles in that water column (by allowing you to get closer to your subject). By pointing the flash so that the nearest angle of flash-beam (not the centre) just sweeps across the front of the subject – as to not illuminate the particles between the lens and subject, this does alleviate much of the problem. Also the direction of light beam must be pointed at the actual subject distance and not the apparent subject distance – then a shot will be taken of the subject with little if any ‘backscatter'. When this fails to achieve the required satisfactory result or if you mess it up – and we all do it! There is but one redeeming method left – referred to and now used by me.

The ‘Last Resort' or ‘Cheats Method'. Before going into detail, cast your eyes over the picture with diver and Turtle above. There is no backscatter; a slight overexposure has been corrected; colour has been restored and the image is pin-sharp. By the way the Turtle was added later! How was this achieved? I think I gave the game away by naming it ‘the last resort or cheats method'. The secret is to have a PC, scanner, printer and very good photo-editing software. I use Serif PhotoPlus 9 (Professional Digital Image Editing) that allows me to be able to salvage many bin-destined images. Perhaps it is wrong for me to refer to photo editing on the computer as ‘the cheats method' as basically it is only copying methods that have been used for many years in the professional darkroom by a few experts. However one thing is certain - it allows me to at least adjust and put the finishing touches to any image. It also gives me the opportunity to retrieve and turn a completely unusable shot into one that would grace many a magazine page! One other benefit – no longer do I have to risk the chance of having original slides being lost or damaged when being forwarded for publication as my images can now be burnt onto CDs with the original slides or negatives always remaining in my possession.

To recap:

If you wish to avoid that ‘evil disease' known as ‘white-blob' or backscatter when shooting wide-angle.

1. Use an external flashgun and position it as far away as is possible from the camera lens.
2. Adjust it so that the flash arm is either at an angle of up to a maximum of 45° from the horizontal to the left or right of the camera's lens (when viewed from behind).
3. Do not forget to take into account the magnifying effect of water and aim at the actual distance not the distance your eyes are telling you the subject is at!
4. Finally, position the flash unit itself to point so that the centre of beam is pointed to the rear of the subject and not directly at it! You are trying to achieve no illumination to the area of water between the subject and camera lens.
5. If your flashgun has a ‘modelling light' that can be seen through the camera's viewfinder, aim this to just illuminate your subject. Tip: Better still – secure with elastic bands a small but bright torch (for example TUSA's TL-240 torch) to the side of the flashgun that is nearest to the camera – when this illuminates the subject your flashgun should be in the perfect position to fully minimise the effects of backscatter .

Even if you have no intention of wanting to have your pictures appear within the pages of a glossy magazine Serif PhotoPlus 9 (photo editing software) can, with practice give you images that you will be proud of!