Macro photography under water

Principles, techniques, skills
by  J Floor Anthoni (2005)

Due to the nature of light under water, the underwater photographer works mainly close to his subject, plagued by stringent compromises between available light, film speed and depth of field. It is often said that macro photography because of its simple setup under maximal strobe light, is the easiest and most successful technique for beginners. But there are problems. This chapter aims to give you a full understanding of the techniques of close-up (macro) photography.
Underwater photography is most successful when close to the subject but where does portrait photography become macro photography? An introduction with historical notes.
Some theory of optics to further your understanding. Macro lenses, extension tubes, teleconverters, close-up diopters. How to aim your camera.
strobe light
Macro photography needs a lot of light and your lighting setup must be flexible to deliver it correctly. How to recognise problems and how to fix these.
Aquarium photography can be improved with a few tricks.
For comments and suggestions, e-mail the author. Read tips for printing.
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There is no precise definition of where portrait photography ends and macro photography begins. Macro is the Greek word for large, and it is used for making subjects appear large. A practical way for defining macro photography is by the strength of the lens, or how nearby it can focus. In the old days, a minimum distance of one metre (one diopter) was considered enough, but most lenses will now go to 0.5 metre (2 diopter). Portrait photography ends at about one metre using a 100mm lens. If you want to go any closer, the lens must be mounted further from the camera by means of bellows or extension tubes. One can also make the lens stronger by placing closeup lenses of 1-4 diopters in front.

Modern zoom lenses and digital cameras can focus subjects very close to the lens and this has brought macro photography into the hands of many. The Nikonos RS 50mm macro lens was a technical feat for its time, being able to auto-focus down to 16.7cm (6 diopter range). Such lenses are formidable work-horses as they give such a wide range of enlargement.

One could also define macro photography as where mixed light photography ends and maximum strobe light begins.

Beginning underwater photographers often enter the arena with severely limited camera equipment and this is still very much the case today, even with digital cameras in underwater housings. The salesman never tells them what the camera won't do and what its limitations are under water.

One of the problems found with cameras with separate viewfinders or sportfinders is that of parallax. An obstacle could protrude in the line of sight without the photographer noticing, but this is but the least serious of problems.

Surely the biggest problems plaguing the underwater photographer is that the strobe light is difficult to control. It so happens that the intensity of the light diminishes quadratically with distance, which creates high uncertainty. So by taking photos at a fixed distance, with a fixed intensity of light is one of the ways to increase success. This makes fixed-distance macro photography an easy start for beginners, yielding colourful pictures that can be entered into competitions.

The arrival of the Nikonos IV and V who were able not only to meter ambient light, but also to control the strobe, was a major leap forward even though the more thoughtful photographer used self-controlled thyristor strobes before that. It was now possible to attain even lighting with variable distances, and this greatly enhanced the chance of success. However, these cameras were still not able to focus automatically such that most evenly lit photographs were usually out of focus.

Understandably, non-amphibic reflex cameras with automatic focusing, TTL (Through The Lens) light metering and strobe control, housed in separate underwater housings became popular. Their only disadvantages were often clumsily placed controls, an excessively large housing (to accommodate several brands), and optics not correcting for the water interface. But very good photos could be taken with them.

The Nikonos RS (Reflex System) came out in the beginning 1990s but was taken off the market in 1996, even though it remains today the most sophisticated underwater camera system ever made, delivering also the sharpest images with the most comfortable controls. It is truly a formidable work-horse.

It is clear that macro photography is done in many ways, using the various camera systems, but underlying it all is the theory of lenses, depth of field and the limitations imposed on lighting systems. With this general knowledge, we hope you will be able to improve your chances of success.

In the chapter on film and lens we have introduced the concepts of optics, focal distance and the various types of lenses, and here we will build further on this knowledge. Let's first get back to the basics of optical theory.

basic optical lawsThe drawing shown here captures the basic law of optics defining where an image is focused. On the right the subject with distance s to the lens. On the left the focal plane with distance o to the lens which is made up of a shift of and focal length f of the lens. The drawn dashed paths of light are special cases:
  • all light parallel with the optical axis pass through the lens and focus in its focal spot f inside the camera. This also works in reverse and light exiting the lens in parallel with the optical axis will have come from a symmetrical spot f outside the lens.
  • all light rays going through the middle of the lens are not refracted (bent) and pass straight through.
In this manner one can construct in a graphical way the basic law of optics: 1 / f = 1 / o + 1 / s  (discovered by Descartes)

The physicist Newton formulated the basic optics law noticing that the distance from focal plane to focus (of) is inversely related to the distance from subject to the equivalent focus outside:  of x sf = f x f
With Newton's formula one can quickly calculate how far to move the focal plane to focus on a distant object.

Note! The standard lens is defined as the diagonal of the frame. In the case of 35mm film, this is 43.3 mm, reason why both the 50mm and the 35mm lens can be considered standard. For a 60 x 60 mm medium format, the diagonal is 85mm and this is indeed the standard lens for this format. The standard lens is considered not to cause distortion of depth. A wide angle lens by comparison, creates the impression of space by placing subjects seemingly further away. By contrast, a telelens makes subjects seem nearby and closer together, thereby seemingly stacking them.

From simple trigonometry, one can see that the magnification is given by: m = o / s
So the further the lens from the focal plane (o becomes larger as s becomes smaller), the more magnification is achieved. Obviously for a 1:1 magnification, o = s  and this happens precisely when d = f . A 35mm distance ring should thus achieve 1:1 magnification for a 35mm lens.

One may ask how many diopters a 35mm lens is. The diopter is defined as one for a lens with focal distance of 1 meter. In general, the diopter strength = 1 / f  (in metres). Thus for a 35mm lens f = 0.035 and its diopter strength corresponds to 1/0.035=28.6. Likewise a 50mm lens is 20 diopters and a 100mm lens 10 diopters.
Thus the wide angle lenses are the strong lenses whereas telelenses are weak. Strong lenses give bigger magnification as long as they are placed close to the subject. For the highest of magnifications (as in a microscope) one needs lenses with very short focal lengths, placed very close to the subject. They also need to be very small in diameter. The latest technology of multiple strand optical cables can indeed place the camera at a fly's eye.
extension tube for NikonosExtension tubes
The standard primary (not zoom) lens is extended outward by means of extension tubes which are water tight. There is no standard for such extension tubes, but they usually come in three sizes which can be combined, or one size in combination with lenses of different focal lengths (e.g. 28, 35, 80mm). The picture shown here gives the general idea. It is a commercially available extension tube for Nikonos III, IV, V cameras. The framer is necessary because these cameras have inadequate focusing arrangements. For this kind of bracket one must mount the strobe directly above the camera to avoid one of the side poles casting a visible shadow. When the strobe is placed towards above-left, the lefthand post needs to be sawn off.
The fixed distance extension tube works well, as scientists use it to document nudibranchs and other small creatures. They often carry two Nikonos cameras with extension tubes set for different enlargements. But one is never sure where the camera focuses precisely. Furthermore, subjects often do not tolerate a frame pushed onto them. So, on the one hand one wishes the frame to precisely indicate the plane of focus, but on the other hand one wishes to place the subject just outside the frame.
This can be done to some extent with the lens' internal focus ring which runs from 0.8m to infinity (1.25 diopter). For a standard 35mm lens of 28 diopters, this is but a small change of around 5% in distance. Depth of field follows also along this logic: the larger the magnification, the more critical depth of field becomes.
Close-up lenses
For housed SLR (Single Lens Reflex) cameras, the obvious way to go macro is by placing a close-up lens in front of the primary or zoom lens inside the underwater housing. The following focal distances (in cm) above water now apply:
1D 2D 3D 4D 5D
infinity 100 50 33 25 20
1.0m   50 33 25 20 17
0.9m   47 32 24 20 16
0.8m   44 31 24 19 16
0.7m   41 29 23 18 16
0.6m   38 27 21 18 15
To make your own table of focal distances, use the formula: diopter = 1 / s - 1 / c  where c is the camera adjustment from infinity down to wherever, in metres. This translates to: 1 / s = diopter + 1 / c  For underwater distances, multiply by 1.33.

From this table a very clear picture emerges:

A teleconverter is a special lens placed in between camera and camera lens. It virtually extends the focal length of the lens, usually a primary lens (not zoom). Thus a 2x teleconverter extends a 50mm primary macro lens to a 100mm lens with the same properties such as focusing between infinity and the nearest closeup distance. The result is a two times enlargement as if one were truly using a 100mm lens.
The advantages of extending the focal length this way are: But it may also have disadvantages: Note that modern lenses for SLR cameras have teleconverters and wide angle converters in-built. A 13mm fish eye lens for instance presents to the camera a standard lens. This is also done in 'short' telelenses.
Tip: although you are shooting with the smallest apertures, depth of field in macro photography is deceptively critical. In accordance, aiming the camera becomes very critical too. Always identify where the plane of interest lies and aim your camera so that it forms the focal plane.

Tip: a true macro lens which focuses over a 4-6 diopter range is by far the preferred tool. It needs a sharp teleconverter to extend its range.

Tip: with a good quality 50mm or 100mm macro lens one can take surprisingly sharp and good pictures at distance (2-5m) successfully by using a wide aperture (f4-5.6) and placing the strobe far out with a strong warming filter in front of it. At such distance, most of the subject will be in focus. Because of the wide aperture, scatter will be faint and in large overlapping patches, almost invisible. The macro lens used at distance, allows you to get close enough to shy fish.

mating red pigfish
f034704: mating pigfish (Bodianus unimaculatus) at dusk, showing their mating colours. Shown here is the uncropped image taken with a 50mm macro lens at 2m distance f4, lit by strobe light with a colour correction filter. The picture is sharp. The picture was composed to symbolise how close the fish were to the surface.
a large sleeping parrotfish
f047913: this large parrotfish (70cm) sleeping at night, was taken with a 50mm macro lens from 2.5m distance at f4 and f5.6. The same technique as described on left was used. Note how the fish has solidly wedged itself in place. An interesting detail is that this shallow niche faced the brunt of the waves head-on, but inside it should be tranquil. How do they find these places?
tight closeup of gorgonean polyps
f041324: in this tight closeup of gorgonean polyps, one must focus by moving the camera in and out, often with autofocus disabled. It is important that all items of interest are in the same focal plane.
polyps on a fleshy coral
f046833: extreme closeups reveal a new level of interest like these tiny 8-armed polyps on a fleshy coral. One can often take advantage of side-lighting because there is too little room for frontal lighting.

think in planes


Illusive depth scale
How can you check that where you think or the camera thinks the focal plane is, is indeed where the lens focuses? When working with 8mm lenses and even 5mm wide angle lenses in Super8 cameras, this becomes very critical. One would think that this is easy to check, but without very special instruments, it becomes nearly impossible. One of the problems is that objects nearer by, become enlarged, and thus appear sharper. To overcome this and other problems, I invented the Anthoni optical illusion scale which you can print here (250KB). It is made by a BASIC program of which you find the full description here as part of a chapter on calibrating your lens for unsharpness and depth of field.
Essentially this scale has a number of radiating lines that appear parallel. The markings on this scale are such that they appear equally widely spaced over the entire range. Having eliminated these two virtual sharpness effects, the point of focus can now be read accurately. If you want to check whether infinity is indeed in focus, place a 4 diopter closeup lens in front and focus the camera on a point 25cm distant on the depth scale.
With this scale (a waterproof version) you can now verify where your macro lenses focus underwater. It is a very handy tool to have and entirely free. This is what it looks like, with red markers at 15, 20, 25cm. 

What the camera sees with a wide aperture, enables you to establish the focal point precisely.

strobe light
One of the attractions of macro photography is that ambient light no longer plays a role, simply because there is far too little to achieve satisfactory depths of field and as one enlarges more, ever more light is needed. So the strobe light is adjusted to match the smallest aperture (f22-45) on the lens. As the magnification factor increases, one rapidly needs more light according to the formula Light = ( magnification + 1 )2  (squared), as shown in the table below

magnification factor 1:2 1:1 2:1 3:1
lens to focal plane mm 52 70 105 140
extension ring thickness mm 17 35 70 105
lens to subject mm 105 70 53 47
extra light needed mm 2.25 4.0 9.0 16.0

For the situation under water, a factor 1.33 should be applied to the lens to subject distances in above table.
the ideal macro lens dimensionsBecause of the clumsy size of underwater housings and their ports, there is little or inadequate room to let the strobe light in for near-frontal lighting. As a result, very tight closeups have to make do with side lighting or back lighting. Here is where some small digital cameras inside very compact housings, have an advantage. Also the old Nikonos V with its small 35mm primary lens, offers an advantage. Don't count this 'obsolete' camera out yet, for large and sharp magnifications.
The message here is that you need to alleviate this problem by making adaptations to the hardware. Use a small strobe and special brackets. In macro photography with a macro lens, the strobe is constantly moved outward/inward, left to middle to right, and is often taken off the bracket for side and back lighting and for admitting light into narrow confines.
strobe distance
Because the amount of light is at a  premium, one would be tempted to place the strobe as close as possible to the subject, but this results in large differences in intensity between the nearest and furthest side, and it also makes the background very dark. If one places the strobe too far back, there could be an insufficient amount of light and it all appears to come from a small spot, resulting in harsh lighting with harsh shadows.

The secret is to work with a small strobe, placed back sufficiently to still appear large (some need a diffuser), while lighting nearest and furthest point in the focal plane with the least difference. By pointing the light a little too far to the opposing side, one uses the environment as reflector to bring light in the shadows while also lighting less of the near side. Understandably, when shooting at variable distances, this compromise must be rearranged each time, resulting in constant adjustment of the strobe. How easy you can do this, makes a large difference to your chance of success.
the size of the light mattersThe diagram illustrates the effect of a small strobe or a strobe placed backward too far. A small strobe behaves like a point source, creating harsh shapes and shadows because the light cannot reach the sides. A large light source as used to be common with bulb flashes, creates soft blending shadows and gives objects that three-dimensional look. It also makes scatter less obvious. The challenge is to create a large light source which can also be placed nearby.
Note that in the drawing the subject is brought closer to the light source to make the light source appear larger, but this of course exacerbates uneven lighting between the near and the far side. What is needed is a larger reflector while keeping the strobe away from the subject. Note that in supermacro photography (linear enlargement larger than 1:1), the strobe must be placed proportionally closer to the subject.

the position of the strobe in macrophotography is critical and creative


a tropical whelk at night
f046627: this tropical whelk (5cm) was photographed with a single strobe placed centrally above. Reflection from the environment brings enough light to soften the shadows.
tropical crayfish in a recess
f046410: this painted crayfish was not easy to reach. A large SB104 strobe casts light around legs and feelers, bringing some light there.

one or two strobes?
When the light comes mainly or exclusively from one source, one ends up with deep black shadows that are undesirable. So how can this be alleviated? The immediate solution is to have two strobes, one set to full power and the other to 1/3 or 1/4 power to fill in over the shadows. This has the disadvantage that another strobe needs to be mounted where space is at a premium. It can also make images look less natural. Furthermore, macro photos are often taken in recesses where only small equipment can get to. 

So let's review our options without a second strobe:

ring lighting
In scientific and medical photographs one often uses a ring light to minimise annoying reflections from wet tissues. The ring light is a long strobe tube bent in a circle and mounted around the lens. One can tape parts of the tube to accentuate light from one direction. Such a device has not been available for under water. For a better solution, see aquarium photography below.

modelling light
A modelling light is a small torch mounted on or inside the strobe. It allows one to judge whether the strobe has been aimed correctly and whether the lightfall is optimal. It also provides the light necessary for auto-focusing. It is an absolute must to have and enhances one's photography considerably. Place it low on the strobe such that the strobe points a little too high, thereby avoiding overexposure in the foreground.
Now that bright white LEDs (Light-Emitting Devices) are becoming more readily available, the modelling light can become conveniently small, yet bright enough for auto-focusing.
Tip: you must be able to easily switch your modelling light off and on because in mixed light photography it projects an unwanted spot. Also when zooplankton bugs are swarming in front of the lens, switching it off gets rid of them temporarily.


sidelighting and backlighting
Transparent subjects benefit greatly from sidelighting or backlighting and macro lenses create great opportunities but a few problems must be addressed:
With small subjects that are close to the lens, you will be able to hold the detached strobe to the side and behind the subject, but invisible to the camera. It is worth trying.
a back-lit hydroid tree
f036622: a densely set hydroid tree (Solanderia sp) invited for back-lighting, which was done by the photographer, but a shrub this size could better have been lit by the buddy, holding the strobe further out.
a comb jellyfish reflected by the surface
f046112: a comb jellyfish reflected by the water's surface. This stark photo was taken with the sidelighting technique discussed above.

Tip: for backlighting you need a long strobe cord that somehow is curled up when not used for backlighting.
Tip: you must be able to detach your strobe easily.

Aquarium photography should be so easy because one won't need to dive. It also allows one to stay warm and dry, while still within macro-distance from subjects. But there are problems.
transparent shrimp
f032018: a 4cm transparent shrimp (Palaemon affinis) photographed through aquarium glass with a Nikonos RS underwater camera outside and a small strobe inside. This gives best results.
glare eliminated with complementary polarisers
f016731: in the fish market we could demonstrate how John dories can extend their mouths to catch fish. Two complementary polarisers were used to eliminate glare. This technique is also suitable for medical photography.

Complementary polarisers
Reflections can be eliminated almost completely with two linear polarising filters rotated 90 degrees between them. One is placed on the strobe and the other before the lens. Although nearly two f-stops of light are lost, so are the reflections, which makes this technique eminently suitable for rockpool, aquarium, scientific and medical photography.
The idea behind it is that reflected light has not interacted with substance and consists thus entirely of the polarised light emitted by the strobe. Because the polariser in front of the camera is turned by 90 degrees, it blocks this light, which can be tested by sending test flashes and rotating the one on the camera until all reflections disappear. Magical!
To make it work, buy a sheet of polarising plastic and cut a rectangle to cover the strobe window. Sometimes the glass from polarising sun glasses can do the trick. For the camera just buy a linear polariser, which should be in your camera kit already. 
The technique works equally well under water to show deep colours on shiny fish, but the loss of two f-stops is rather off-putting. Also fish glare a lot less underwater than above.
A single polariser can also be used in natural light fish photography, as the sunlight underwater is polarised vertically by the water surface. To counteract reflections, turn the polariser on the camera horizontally. Although it does give better results, one loses nearly two f-stops and a high quality polariser that stands corrosion from salt water is impossible to find.