LSD (Light Shaping Device) for Underwater Photographers
(July 2011)

In 2010, the Canadian underwater photographer Keri Wilk surprised the community of underwater photographers with a set of amazing pictures. The featured main objects on those were illuminated, while the rest of the photo was pitch black. He later explained the principles behind his work in a comprehensive article.

In his shots, Keri used homemade snoots on his strobes, similar to the ones used in studio photography. The problem however, according also to Keri himself, is the difficult and limited nature of this type of work – in order to maintain the effect and stop the light from diffusing, the snoot has to get fairly close to the object, therefore rendering its usage on fearful objects pretty much impossible.

Later on, some photographers started using fiber optics, which made the task of bringing the light to the main objects a bit easier.

The main cons of the conventional snoots and fiber optic systems are therefore:

  • The device has to be in close vicinity of the object, which is likely to scare it away.
  • The light, lacking direction, can easily diffuse.
  • There is a considerable loss of light.
  • When using snoots on strobes with central pilot light and concentric flash tube (which is the configuration of most underwater wide-angle strobes!) it often happens that the flash illuminates a different area than the pilot light, which makes framing a fairly difficult task.

A couple of months after the spot macro shots were published, however, I was contacted by a then barely twenty years old Slovenian underwater photographer, Oskar Marko Musić. He described an incredible idea that would enable one to illuminate objects selectively from a greater distance – and thus avoid scaring them away! By that time, he had already filed for patent pending, yet generously welcomed me to develope a similar device using his idea.
By the formal name of Light Shaping Device in underwater photography (LSD), Oskar developed his on a Seacam 250 Digital strobe, whereas I did it on a Seacam 150 Digital.

Both devices, more or less same by design, differing only in execution, saw the light of the day at pretty much the same time – at the end of October, 2010. It was then that I first tested my LSD in the sea. Even then, it was a good run, although it did display some minor malfunctions that needed to be fixed. Still, the device was promising to pay off the effort and the considerable financial input.

When the LSD was finally fully optimized, Oskar asked me to formally test it and publish the results on the internet. I gladly accepted the suggestion, and due to having quite a lot of experience with my own LSD by then, I got around to handling his fairly quickly.

LSD is basically composed of three modules.
The first one, attached directly to the strobe, is a light collector. Its function is gathering the light onto a small circular matted area. It is very important that the pilot light and the round flash tube illuminate the matted area evenly, with minimal light loss. This is the part that caused us most trouble - the light from underwater strobes, emitting in a wide angle, has to be recollected and concentrated on a small area. This is incidentally also the part that Oskar's LSD and mine most differ in. My collector is based on a truncated cone, made of Plexiglas. The light is collected on the basis of total reflection inside the cone. At first, Oskar used the same solution, but he later replaced it with a highly reflective white coating. This reflects light better and spreads it evenly over the diffuser, all the while minimizing the weight and size of the device.

The second module is a kind of aperture, not meant for determining brightness, but the shape of the projected light spot.

The core of the invention, however, is the third unit – the lens – used for projecting the light spot from a greater distance. Both LSDs have interchangeable lenses (70 and 100 mm) that project light from a different distance.

The maximum diameter of Oskar's LSD matted area is 44mm, using the included apertures it can be reduced to 25 or 10 mm. The illuminated area cannot be smaller than the diameter of the aperture. Since the light is being projected, the smallest and brightest light circle with the sharpest edges is achieved once the object we're illuminating is in focus of the LSDs lens. The lenses are attached as to project the illuminated matted area in 1:1 ratio. Working distance in air of a 70 mm lens is therefore 125 mm and 185 mm with a 100 mm lens. Underwater, that distance is increased by 33% (making the distance 166 mm and 246 mm respectively). In other words: if the far edge of a 100 mm lens of the LSD is 185 mm away from the object (we're talking air), the diameter of the light circle with which the object is illuminated will be equal to the diameter of the used aperture. Insofar as we move away from the object with the LSD, the circle expands, the brightness is reduced and the edge between the dark and illuminated area becomes softer. If we come closer, the light circle also expands, but I would advise against such action. The illumination becomes uneven and a darker area appears in the middle (due to the projections of the round flash tube).

In connection to said, two terms have to be defined:

  • Working distance: the distance between the far edge of the LSD and the focal plane, where one can get the smallest and brightest light spot with the sharpest edges. Shorter distance is not advisable, as the illumination becomes uneven.
  • Useful range: the distance further of focal plane (= working distance) up to the point where one feels the illumination is still useful according to needs. Further distancing from the focal plane expands the optical figure, softens the edges, and the illumination decreases by the inverse square law.
Seeing as LSD is used for projecting a light spot onto an object, let me expressly say that the shape does not necessarily have to be a circle. Oskar also offers three squares with 10, 20 and 30 mm sides for his LSD, and can on request make any custom shaped figure that can be fit inside a 44 cm diameter circle.

As we can see, in theory, LSD undoubtedly has many advantages over conventional snoots and optical fiber systems:

  • Objects are illuminated from far away, which avoids scaring them.
  • For the same reason, LSD can also be used in ambiental underwater photography, using wide-angle lenses and dome ports.
  • Light is focused and disperses minimally with distance.
  • Less light loss.
  • Strobe illuminates exactly the same area as the pilot light.
  • Illumination is possible in any figure, not just a circle.

But let us not forget the core of this review – practical testing of LSD underwater.
I used Oskar's LSD on a Seacam 250 Digital strobe (as the prototype had been designed for it) and took pictures with my Nikon D2x in a Seacam housing plus Sigma 150 mm f/2.8 macro lens and Tokina 10-17 mm f/3.5-4.5 fisheye in combination with a small dome port.
LSD is, as far as the length is concerned, in the same league as the fairly large Seacam 250 strobe (200 mm with a 70 mm lens and 260 mm with a 100 mm lens), but I found it almost neutral and well balanced underwater. When working alone, using longer arms with multiple joints is advisable, as it gives one more freedom to direct LSD. I was using the arms I usually use in ambiental underwater photography with a fisheye lens.

Keri tells us in his article that he worked using strobes on tripods (Gorillapod) that he triggered with the main strobe on the housing via an external slave sensor. That way, he had more freedom for framing. As for myself, I figured out it was more efficiently to work with the LSD and strobe attached on the strobe arms where the joints aren't as firmly tightened. That way, I could finely direct the strobe with my arm. A patient assistant (a  buddy diver) is of course the greatest of help, holding the strobe and directing it to one's liking. While testing LSD, I was partially working alone and partially with Oskar's assistance.

Working with LSD, one has to keep in mind the direction as well as distance. The size of the light spot, its brightness and the sharpness of the edges all depend on the distance. Many parameters have therefore to be taken into account when working with the LSD, which calls for an amount of experience and practice.

When shooting alone, I directed the camera perpendicular to a random neutral surface (e.g. sandy seabed) and focused it. Then, I used my arm to direct the strobe until seeing the light spot of the pilot lamp in the desired position in the picture. Of course the object had to be held in focus the whole time. Moving the camera back and forth, the light spot moved in and out of the desired position. Once the LSD was set, I began hunting for objects in the viewfinder. Once I'd caught one and illuminated it with the pilot light, it was automatically in focus that I'd set beforehand. I had to do only a few minor focus adjustments and I could take the picture.
Directing LSD is therefore most of the work, whereas shooting afterwards comes quickly. Of course, if we're not completely satisfied with the frame, light spot or the transition between the light and dark, we have to do the whole process of directing LSD again.
If the optical axis of the LSD is near the optical axis of the camera's lens, the illumination is a nice circle. This technique is to be used especially when taking pictures of more two-dimensional objects (e.g. the eye of the fish). When taking pictures of three-dimensional objects (such as a nudibranch or a shrimp), a higher position should be taken when directing LSD, giving us a more elliptical illumination.

In order to successfully work with the LSD, a powerful pilot light is needed. LED pilot lights, built into modern underwater strobes, usually suffice; problems surface only when shooting in shallow water in a sunny weather, when the ambient light is too strong to see the light spot. Of course, experience comes handy in that situation – the light spot, even though not any brighter than the surrounding area, can be seen as a somewhat warmer spot. I could say this is the main disadvantage of the LSD in comparison to conventional snoots and optical fiber systems, seeing as those have to be brought right next to the object. LSD, on the other hand, is made to be successfully used only from the aforementioned working distance (when the light spot is in focus) or further, but not any nearer due to uneven illumination.

As for light loss, I'm glad to say it is minimal. Both lenses have a 50 mm diameter, so we could say all in all we have a 70 mm f/1.4 and 100 mm f/2 lenses. I illuminated an object (a hermit crab) with a slower 100 mm lens. Optimal parameters were ISO 100, f/11, Seaflash 250 powered to 50%. Then I took away the LSD and illuminated the object again, from the same distance, with the same parameters. The picture was of course burned up, but by only one to two f-stops at most in my assessment. With a 70 mm lens, the light loss would be about one f-stop.
LSD also works great with fisheye lenses. Working distance is large enough to hide the device behind the lens' viewing angle and illuminate the objects in the foreground with a spotlight. I would suggest, however, the use of a small dome port in wide-angle photography, since it gives us more freedom to position the LSD.

All in all I can say I had a very pleasant experience with Oskar's LSD. All the theoretical advantages in comparison to conventional snoots and optical fiber systems turned out to be true in practice also.
I recommend the LSD to all advanced photographers, interested in creative techniques of illumination.

Let me just emphasize again: LSD is suitable for experienced photographers only! Working with it isn't simple and can easily complicate a photographer's mission. It does, however, contribute greatly to the appearance of our final products, which is in the end the only thing that really matters.
Sharp and soft edge of a light spot.


A shot of a goby's eye in daylight. Without LSD, such a picture could only be taken at a night dive.   The goby was floating mere 10 cm above the light sandy bottom.

LSD is currently available for Seacam 250 and 150 strobes, but it will be soon made available for most popular underwater strobes like Sea&Sea, Ikelite, Subtronic ... . In case the LSD isn't made available for a particular strobe, an adapter for one can be custom made in cooperation with the client.

LSD is a large and complex accessory, so its price is also considerably higher than that of ordinary snoots. The final retail price of the device had not yet been calculated by the time this article was written.

LSD can be ordered directly from Retra Underwater Technology.
For any further information please contact Oskar directly.

The reviewer Borut Furlan (on the left) and the inventor of LSD, Oskar Marko Musić.