Further experiences with digital underwater photography and external strobes
Guido Zsilavecz
Cape Town, September 2004


Introduction

Since my previous article "Some problems and solutions for digital underwater photography", written in October 2003, I have managed to gain further experience, especially in the use of external strobes: I used my own slave trigger extensively both in local as well as international waters, acquired another strobe, and a different, TTL-emulating, trigger. My experiences using these various pieces of equipment are described in this article.

I first describe the cameras I use, and why. This is followed by a description of the strobes and their triggers, a bit about base plates and strobe arms, and then the actual experience of using this equipment.

Photo Equipment: Cameras

Canon A70.

I use a Canon A70 in the Canon housing, WP-DC700. The camera was the first digital camera at a reasonable price I considered. Having owned and used Canon EOS cameras, the user interface was familiar and logical. The camera itself offers a full range of controls, from fully automatic, through aperture priority, shutter priority to fully manual. It is a 3.2 megapixel camera, possibly not quite up to date with the now more common 4 to 5 megapixel cameras, but my images tend to remain on a computer, and even when displayed on a wall using a video projector, I have not had the need for higher resolution. The camera is small and quite robust, and offers adequate optics, with a fair zoom range, quite good macro, and optional wide and telelenses, both of which I have and like. The housing is simple, colourful, see-through, and quite robust as well. The first housing leaked, but Canon replaced it, and since then I have not had any problems.

Canon A75.

Having flooded a Nikonos on an international trip I vowed never to place all my trust in a single camera, and I bought a second Canon, the A70 enhancement A75. The only difference really is a larger screen, which is quite invaluable, and with it an enhanced button layout. The housing, now oddly called WP-DC30, has been improved as well, with a screen hood, which Olympus owners have enjoyed for quite some time. Having tried to make one for the A70's housing, and having failed due to the button locations, having this hood as standard now is a great plus. The modified and improved button layout unfortunately dictate smaller buttons, which are not the easiest to operate using 5mm cold water gloves. It does work after some practice though, and in my opinion the benefit derived from the larger screen and display hood outweigh the occasional need to fiddle a bit.

The A75 has a few extras, such as special scene modes, one of which is for underwater. It is aimed at those using only the built-in flash in the housing. Otherwise the mode is a "push here dummy" one, which I detest. Needless to say, I have yet to try it!

For both cameras I use 256 MB CF cards, and I have four: having had one card corrupted (I think due to a cellular phone), the rule is now: one dive one card. I get 154 shots using the highest resolution and finest compression I have yet to use all of this during any dive.

Others.

The only other camera I considered as an addition to the A70 before choosing the A75 was the Olympus C-5060. I did not choose it, for apart from its larger size and an array of buttons seemingly randomly distributed around the camera and requiring an equal number of hard-to-reach buttons on the housing, it was the frequent and repeated failures of units owned by friends which turned me off.

Photo Equipment: Strobes and triggers

Nikonos SB-105.

The original strobe which I inherited from my Nikonos days, the Nikonos SB-105, remains in use. The strobe is triggered by the camera using a home-made optical slave trigger, described more fully in my first article. It requires that the camera be in full manual mode, and control the exposure using both the cameras controls and the three power settings on the SB-105, namely full power, 1/4 power, and 1/16th power.

Illustration 1 shows the SB-105 setup with the A70 and the Digital Adapter. The latter, and the strobe arm, are discussed further below.

Ikelite DS-125.

To complement the SB-105 I bought the Ikelite DS-125 with the manual, 10 setting, controller. Ikelite states that their TTL sensor does not work well with small cameras like the A-series Canons, and, having used manual controls with the SB-105 anyway, I decided that this was the way to go. The flash is well made, has a built-in rechargeable battery and a "fuel gauge" which tells you how many "rolls of film" you can still take. Essentially, each of the three lights correspond to approximately one 36 exposure film using full power. With the light-sensitivity of digital cameras it is rare to need full power, so the number of shots you can get on one charge is high; it lasts me easily though several dives, and I find I do not need to recharge it at all on a weekend. The strong built-in modeling light is very useful, and does not even deplete the batteries very much.

The manual controller is a separate item, coupled with the slave trigger. You mount it above the camera in such a way that it picks up the flash, and has a cable to the strobe. The strobe is kept in the TTL setting (it has manual settings as well), and the light output is then dictated by the controller, according to the setting dialed in by the photographer.

Illustration 2 shows the A75 with the DS-125 and manual controller. The strobe arm is discussed further below.

Others.

In competition with the DS-125 was the Sea&Sea YS90DX, but it lost mainly because I dislike the very flimsy looking fibre-optic pickup, and the manual control dial is rather badly placed for use with thick gloves. Price-wise the YS90DX and DS-125 are very similar.

Digital Adapter.

With the setups described above I am still working in manual mode, something one does get used to, but the TTL my Nikonos used to provide me with was so pleasant that I simply needed to try and see if there was some way of getting it to work for my digital cameras. The Digital Adapter, created by Matthias Heinrichs (matthias@muenster.de, http://www.muenster.de/~matthias) was an option, so I bought it. The unit is small and seems quite simple, but obviously contains some magical circuitry. It is moderately programmable, although the interface (using a magnet and watching a LED light), is not obvious, and definitely not well explained on his web-site. As an appendix to this article is my hopefully improved set of instructions.

The adapter has four changeable parameters:

  • Pre-flash suppression. Up to 3 pre-flashes can be ignored.
  • Post-flash suppression. The adapter can be set to ignore a flash within 200 mili-seconds of the one that triggered it. This can be used to avoid the triggered flash from continuing to trigger itself.
  • Pre-flash delay. There are 11 settings which can be used to delay the slave flash from triggering. This can be used to reduce the flash output.
  • Post-flash delay. There are 11 settings which can be used to delay the shutting off of the slave flash after triggering. This can be used to increase the flash output.

The various triggers are shown in illustration 4, with on top left my own trigger, the manual controller on top right, and the Digital adapter at the bottom.

Photo Equipment: Base plates and strobe arms

The original base plate used with the A70 and SB-105 was the Nikonos one, and the original arm (after replacing the Nikonos arm) was a 2.5cm diameter LocLine one. On arrival of the new gear, I decided to create a whole new set. The 2.5cm LocLine was too weak to hold the strobes (it worked well under water, but was very floppy on land), so I went to the thicker 3cm diameter version. Base plates were made of PVC. An upright rod allows attachment of the Ikelite manual controller. I now have three base plates, one for the Ikelite with upright rod, one without for the Nikonos, and a double one with upright rod. The Digital Adapter uses the same method as my original trigger to attach itself to the housing, using the flash diffuser attachment found on the housing.

As the cable of the Ikelite is not a spiral one, but straight, it tends to be in the way. I finally came up with the idea of covering the LocLine with a bicycle inner tube, and running the cable up through it. I liked this so much I added the same tube to the Nikonos LocLine. The reason I like it is two-fold. The first one is cosmetic vanity: the LocLine is bright blue, the inner tube is dark grey, matching the PVC grey of the base plate better. The second is practical: the tube is remarkably grippy, both on land and under water. The inner tube to use is a 1.90/2.125 one. Illustrations 1 and 2 show the strobe arms for the individual strobes, while illustration 3 shows the dual arm. Note the torch mounted on the arm; it is attached using two cable-ties crossing the strobe and base plate and a small section of bicycle inner tube on the base plate ensures it does not slip.

To attach LocLine to base plates and strobes a friend machined some special pieces, and I created other custom bits. In illustration 4 in the middle, between the various triggers, is a piece of LocLine and a specially machined piece which fits in the upper (narrower) section of the LocLine piece, and a "washer" which fits in the other end. A screw holds the two together, and the whole unit can be used to mount strobes. The SB-105 requires a slightly different mechanism, but the one shown works very well with Ikelite and Sea&Sea strobes like the YS50, etc. Two washers, one on each side of the LocLine piece, and a large bolt, was used to mount the arm on the base plate.

Using the Equipment

SB-105 and home-grown trigger.

Given the limit of only three strobe power settings, and having to work in manual mode, I managed to get quite quickly very proficient in using this setup. Of course, the clue is the ability to see your results immediately after taking the photo, and adapting. Generally I needed to take a few shots at the beginning of a dive to get an idea of available light and subject matter, and adjust accordingly. I use 1/4 and 1/16th about exclusively, rarely requiring full power. Fine tuning is done using the aperture setting. As mentioned, this is all working in full manual mode, but, as also mentioned, the ability to see results immediately is the saving grace.

Shutter speed was kept at 1/125, with only very rare excursions down into 1/60, when light levels and subject material (specifically, distance to subject) required it.

Camera ASA level was kept at 50, and I never went higher than that; there is absolutely no need for that, as the flash has sufficient power not to require it. I never use auto ASA.

White balance was kept as Tungsten, as it gave the most realistic looking images, although often Auto did an equally good job.

In manual mode the camera's flash is manual as well, with three power settings. As the only need for that flash was to trigger the main one, I kept it at minimum power, to conserve batteries. With the Digital Adapter I now realize how nice that is, as the double flash with much greater output is actually quite distracting.

While the setup generally worked very well, it has limitations the moment you work in macro on sand. Here you simply cannot shut both SB-105 and camera down enough to avoid over-exposure, that is 1/16 power on the SB-105 and f8 on the camera (the smallest aperture available), was not enough. This was one of the reasons I wanted another flash with finer controls.

Illustration 5 shows a photo taken using an A70 and SB-105, using the home-made trigger.

DS-125 and Manual Controller.

The manual controller, the way I mounted it, is a joy to use. It has a big dial which can be operated when wearing even the thickest gloves. The strobe has a modeling light which can indeed double as a torch at night, and works well when requiring light to allow the camera to focus (although I always mount a torch on my base plates for that), but it can over-power the flash a bit during night dives and pale subjects or backgrounds (like sand).

With the manual controller having 10 settings the operation of the camera becomes simpler: leave the camera in manual, 1/125 shutter speed, and f8 aperture, and use the controller to add or subtract light. Fine tuning can still be done using the aperture, but in general the photographer does not need to operate two pieces of equipment, concentrating instead only on the controller. This is invaluable.

In general, I find the DS-125 a superb strobe, with one down-side: colour warmth. This is a known entity, and while for distance shots it adds pleasant warmth in the colours, in macro mode there is simply too much red. Given that the waters I dive in have much invertebrate life in reds, oranges, browns and yellows, this over-saturates the image. None of the A70/A75's white-balance settings compensates enough, and I must admit I have not yet experimented enough with custom white balance to try and compensate.

Illustration 8 shows a Knysna seahorse taken using an A75 and DS-125 with manual controller. Photos using the internal flash had much colder light, so the warm light of the DS-125 was in this case rather welcome.

SB-105 with Digital Adapter.

Matthias Heinrichs mentions the SB-105 as a strobe which can work with the Digital Adapter, but does not mention how well it does so. The good news is, it works quite well, but, and this is the bad news, not in short-range macro mode. That is, using the A70/A75 and the SB-105. The strobe is simply too powerful and the camera cannot shut it off fast enough. I used all the tricks possible, namely f8, ASA 50, and maximum strobe firing delay on the adapter, but could not get it to work properly. The minimum distance is about 50cm, less if the subject is dark, so moderate macro using zoom is possible. Using the strobe diffuser helps, and one can get closer than without it. Apart from that, when it does work, it does so superbly well.

With the Adapter some short-comings of the A70/A75 come to light. First of all, the photographer must now use aperture priority, and not manual mode anymore. This is because Canon decided that "if you want manual, you get manual", and hence made the internal flash power user settable. All nice and good, and a definite bonus given that I used this feature efficiently using my own trigger and the Ikelite one (although it can be set to ignore one pre-flash, by the way), but it would have been nice to have one extra setting: TTL. The reason for this is that in aperture priority the camera decides on the shutter speed for you, and given that it is dark, chooses a slow one: 1/60 when the flash is on. This is too slow for any moving objects, and will cause blurring. Furthermore, using higher speeds one could control external strobe light. This, unfortunately, is not to be though, at least not using these cameras.

An alternative, underexposing, does not seem to work. Except for -2 f-stops the picture is still over exposed, at -2, it suddenly shuts the strobe off too early. The change-over is dramatic and sudden, and I could not compensate for it.

One interesting problem was discovered using aperture priority. As now the camera flash fires more fully, my little flash shields imperfections allow some light to leak through, occasionally enough to cause the camera to shut off the flash, before the main strobe even fired! Some masking tape solves that problem, but even then does not seem to solve the over-exposure on close macro shots.

To use the SB-105 I had to suppress the pre-flash, as the strobe simply did not handle two quick flashes in succession, which means the white balance cannot be set. Thankfully the SB-105 has pleasant white light.

Illustration 7 shows a sand crab, somewhat uncharacteristically on dark, dirty sand, taken using an A75 with SB-105 and the Digital Adapter. Taken from about 1/2meter distance, note that the adapter did not cause the crab to be over-exposed, something which could happen easily as it has a bright white base colour speckled with red.

Sea&Sea YS50 TTL and Digital Adapter

Matthias Heinrichs mentions that his adapter works very well with the Sea&Sea YS60; I could not get hold of one of those, but I did manage to borrow the similar YS50, which seems to be identical except for the light output, where the YS60 is more powerful.

The idea for testing with a YS50 was that this less powerful strobe might be able to provide better macro performance. Initial tests showed that, indeed, it would be able to do so, but also not perfectly. Using a diffuser here did improve matters, but at close range the images were still quite badly over-exposed. As the trials were on land the proof of how well it would work under water required a dive.

I changed the Adapter settings here from those used with the SB-105, namely I set it to fire the pre-flash, and, because of that, had to switch off the 200 milisecond delay before becoming ready. I left the flash turn-on delay at its maximum, as it helps with close-up shots. The strobe handles the pre-flash perfectly. As it is less powerful it requires opening up the aperture earlier than with the SB-105, but in general the exposure was very good for normal range photos.

Underwater the lesser power of the flash is noticeable when attempting to capture subjects further away, but closer in it works very well. As expected, bright objects on short-distance macro are over-exposed, but darker subjects fare much better. In general, the combination of YS50 and Digital Adapter works better than using an SB-105. The small size of this strobe is an advantage over the other two strobes tested, as it is much easier to swim around with, so depending on what your photographic aim is, it may be the best solution.

Illustration 8 shows a crayfish taken using this setup.

Conclusion

The various setups tested all have their advantages and disadvantages, with some working better in certain circumstances than others. The Digital Adapter, either with SB-105 or, even better, YS50, is the easiest to use, as the camera adds sufficient light given an acceptable aperture; pretty much as any Nikonos or Sea&Sea user knows. The manual triggers, especially my own with the SB-105 is the hardest to use, as the range of settings is less than in any other setup, and hence more it is more difficult to get it right. The DS-125 with its manual controller improves tremendously on this setup, and with the power of the strobe, and its built-in modeling light, is a great strobe to use; pity then about its inherent warm light which becomes distracting on macro shots.

There is one aspect about using all these setups, something I expected and which realized itself, is that no matter what, it all still requires a fair deal of practice to get decent results time and again. This means that none of these solutions will give the novice diver an extended "push here dummy" mode. Using an external strobe immediately adds complexity, and it is recommended that the photographer know their camera very well before attempting to go this one step further. Eventually it becomes inevitable that any serious underwater photographer add such a strobe; backscatter and increased light output make it essential, but this should be tackled slowly, one step at a time, photo after photo.

Appendix: Programming the Digital Adapter

The explanations of how to program the Digital Adapter found on Matthias Heinrichs' web page is not the most obvious set of instructions, and it took me quite a while to get it right. Do read the instructions on that web page, but in order to make this easier for the next person, here are my instructions:

Attach the adapter to the cable, attached to the strobe, which must have batteries in it. The adapter uses power from the strobe, so you cannot program it without it.

The adapter has a clearly marked "window" where the reed switch and LED are located. The reed switch is turned on by holding a magnet close by. It does not need to touch the "window", as it is quite sensitive. The LED is a tiny one, which lights up bright red. The LED has two types of flashes: a short blip and a long flash.

In order to program the adapter it must be "off", that is, not expecting a flash. To switch it off, turn off the strobe and wait for twenty seconds. If the adapter had power, the LED will give a short blip to indicate it is ready. If you need to restart programming, just wait until the adapter has cycled through its menu, and wait for 20 seconds after the last long flash, until the short blip.

Entering the menu system.

Place magnet in place. Switch strobe on - there will immediately be a long flash from the LED within the window.

The menu system has four entries:

  • pre-flash suppression: Here you can select on which flash from the strobe the digital adapter must fire. The default is 1, i.e. It will fire on each flash. There are four settings, so the unit can ignore up to 3 pre-flashes.
  • post-flash ready time: The adapter can be set to ignore a flash within 200 miliseconds after a first one. This prevents a strobe from activating itself. Do not use if you want to handle pre-flashes. The default is 1, i.e. no delay, a setting of 2 indicates the delay is on.
  • flash delay before switching on: Here you can delay the firing of the strobe, in 11 steps. The default is 1, i.e. no delay. This feature allows you to reduce the strobe firing time, and hence reduce light output.
  • flash delay before switching off: Here you can delay the turning off of the strobe, in 11 steps. The default is 1, i.e. turn off once the camera flash stops. This feature allows you to increase the strobe firing time, and hence increase light output.
The latter two menu items sit under a separate "sub-menu".

Menu 1: Pre-flash suspression.

After the long flash on turning the adapter on is shown, the current selection is shown, by short flashes. Once the current selection has been shown, there is a 5 second delay to change the setting. Within that time, tap shortly to show the next selection, which is given by short blips. These blips are shown immediately. Wait until they are shown before tapping again, to select the next option. The settings rotates from 4 to 1. If happy with selection, wait until next long flash, which signals the next menu.

Menu 2: Post-flash ready time.

After the long flash, the current selection is shown, by short flashes. Once the current selection has been shown, there is a 5 second delay to change the setting. Within that time, tap shortly to show the next selection, given by short blips. Once the setting has been shown, tap again to select the next one, etc. It rotates from 2 to 1. To accept selection, remove magnet and wait for long flash.

Menu 3: Flash delay before switching on.

To go into this sub menu, on the previous long flash, place magnet and keep it there until the end of the next long one - leave until the current selection is shown, then remove. Once the current selection has been shown, there is a 5 second delay to change the setting. Within that time, tap shortly to show the next selection, given by short blips. Tap again to select the next one, etc. It rotates from 11 to 1. Be patient, and rather wait for all the blips to have shown (count with it!) before tapping again to select the next one. This may be tedious, but tapping continuously is guaranteed to confuse you! To accept selection, remove magnet and wait for long flash.

Menu 4: Post camera flash delay before switching off.

After the long flash, the current selection is shown, by short flashes. Once the current selection has been shown, there is a 5 second delay to change the setting. Within that time, tap shortly to show the next selection, given by short blips. Tap again to select the next one, etc. It rotates from 11 to 1. To accept selection, remove magnet and wait for long flash.

The default set of blips and flashes is as follows:

long flash (turn unit on, first menu)

1 short blip (default setting)

5 second delay

long flash (second menu)

1 short blip (default setting)

5 second delay

long flash (main menu end)

long flash (sub menu start)

long flash (sub menu end)

20 second delay

shot blip (end of programming mode)

If this is not clear enough, please modify if you managed to do a better job, and please let me know!

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