WE KIT UP ON a small wooden bench at the back of the pick-up truck, enclosed on all sides by the impenetrable green wall of the jungle. There is no view of water; our destination is just a wooden staircase leading down into a crack in the earth.
These are certainly surreal surroundings for scuba, but I am about to experience one of diving’s freshest experiences.
The steps lead down into a pool of smooth, dark water. I slip in and dip my head into El Pit cenote.
Suddenly I feel much smaller. This tiny plunge pool is the opening to a huge world, both underwater and underground.
Looking down, I can see about 30m, but I can’t see the bottom; in front this T-shaped cavern extends away into the darkness. Welcome to the world of cenote diving!
Any of us looking to expand our photographic horizons should place a trip to Mexico’s cenotes at the top of our list. The cenotes offer two types of diving. Cavern-diving is open to all, and takes place always in view of the light from an entrance, although this still means going into some very dark spaces.
Cave-diving is the technical discipline that requires special training and equipment, but allows divers to explore the fully dark and much less visited parts of the cenotes.
Full-blown cave-diving gives a photographer access to the best cave formations, but the photographic potential of caverns should not be under-estimated. All the images in this and next month’s columns are taken during cavern-dives that any open-water-qualified diver can experience with a guide.
Cavern areas still have attractive speleothems (stalactites, stalagmites etc) and have the big advantage that the beams of sunlight that penetrate through openings make the most attractive subject of all.

THE CENOTES ARE FILLED with very clear water but are mostly very dark, which is the big photographic challenge and causes problems both for focusing and exposure.
I use back-button or thumb-focus in the cenotes. This is a mode offered by most cameras that allows us to decouple the autofocus from the shutter-release and assign it to a button you press with your right thumb.
This means that you can focus carefully when there is light at the start of the dive and leave it locked, so that the focus doesn’t struggle in darker places.
Although we will, of course, be diving with a torch, a dedicated focus light is often a hindrance in this type of photography, because its beam will show up in your pictures, being brighter than the dark conditions in the caverns.
The main challenge of the darkness is with exposures, because the required settings are way beyond what we normally use. For example, the two photos on this page are taken at ISO 1250 and ISO 2000 and a shutter-speed slowed down to a risky 1/40th and 1/13th!
Sadly, there are no magic numbers that I can tell you to plug in to work for all cenote shots. First, cenote light levels are very changeable. Second, how much each of us will adjust our aperture, shutter speed and ISO from our normal dive settings depends on our camera.
For example, newer cameras can be pushed to higher ISO values than older ones. Full-frame cameras can use higher ISOs, but also need the aperture closed more for acceptable corner sharpness.
Image-stabilised lenses and cameras can be pushed to slower shutter speeds than non-stabilised lenses. And so on.
What I can advise is that it is best to think about your settings and your camera’s capabilities pre-dive, rather than trying to make a call on what to sacrifice under pressure and underwater.
It is also sensible to compromise a little on all three (aperture, shutter-speed and ISO) rather than a lot on any one.

THE KEY TO CAPTURING beautiful beams is to position ourselves in the dark, looking out to the beams.
Crucial to success is to find a viewpoint that hides the surface and anything else brighter than the beams from the camera. This allows us to properly expose for the beams and to make them stand out.
If we have to expose for the surface, the beams will be faint and hard to see.
The other big challenge with exposure is getting it right! In the dark of a cavern, our LCD will shine brightly, making it easy for us to think that an underexposed image is correct.
Underexposing a little isn’t normally a problem when diving, because we can easily tweak the exposure in Lightroom. However, in the cenotes we will be working with higher ISO values, which means that image quality falls away far more quickly with any post-processing corrections.
I always dive in the cenotes with strobes attached to my housing, but  I keep them turned off as much as possible. Adding strobe light usually ruins the feeling of atmosphere, so unless there is something spectacular in the foreground, don’t worry about lighting it up.
The dark shapes of the caverns make for an excellent frame when shooting towards light.
Fisheye lenses are usually the default choice in caverns, because they really open up the space. All three images in this month’s column are fisheye shots.
However, when shafts of light or stalactites run close to the edges of a fisheye shot, they will bend.
Careful composition keeps bendiness to a minimum, but we can always straighten them up in post-processing using lens correction.
When planning on shooting speleotherm formations I will often favour a non-bendy rectilinear lens, and I’ll show an example of that next month.

All cenotes are on private land and require diving with a specially qualified guide. However, most guides are experienced and willing to pose for your photos, and always have phenomenal buoyancy control and excellent trim.
Note that most cenotes ask photographers to pay a little extra for taking a camera in.

Cenote scenery is captivating, but nine times out of ten it looks best with a diver in the frame to give a sense of scale and a compositional focal point.
Many serious photographers will dive with a private guide and ask them to model. Because dive-gear is 99% black, people are easily lost in the background in a dark cavern. So position the model in front of the light coming in from an opening.

The complex shape of cenote openings and the trees surrounding them mean that the best beams come at very specific times of day in each cenote, and these shift a little during the year.
All the good operators know when the beams are at their best in each cenote and will plan your diving accordingly, as long as you request it.
You should also pay attention to the weather forecast on your phone, focusing on beams during periods of sun and shooting speleothems on cloudy days.

Caption Key

Position divers against a bright background to help them stand out in the dark. Taken with a Nikon D5 and Nikonos 13mm. Subal housing. 3 x Inon Z240. 1/13th @ f/8, ISO 2000.

To catch beautiful beams, shoot from the dark to the light, hiding anything brighter than the beams from the camera. Taken with a Nikon D5 and Nikonos 13mm. Subal housing. No strobes. 1/40th @ f/10, ISO 1250.

There isn’t much aquatic life in the caverns, but the pools often contain photogenic life, such as these tetras and water-lilies. Taken with a Nikon D5 and Nikonos 13mm. Subal housing. 2 x Inon Z240. 1/320th @ f/14, ISO 400.