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Stereo photography underground


Cave passages provide a wonderful if harsh environment for stereo photography, given that the passages are predominantly linearly receding features with a good range of depth, and often with a rich variety of structure.

Click on the relevant gallery to see the other images in the sequence.

Double-click for a full-screen view.

Some technical details and viewing suggestions are given below.

Fairy Cave Quarry, Mendip (2020)

Fairy Cave Quarry is a disused limestone quarry between Stoke St Michael and Oakhill in the Mendip Hills of Somerset. Quarrying was first started on the site in the early 1920s. In 1963 the quarry was acquired by Hobbs (Quarries) Ltd., and production began on a much larger scale. Excavations cut back into the hillside above St Dunstan's Well Rising, and various caves were intercepted in the process. All the caves in the quarry are unusually well 'decorated' with speleothems, and only accessible through a guardian system to guarantee conservation. Withyhill Cave is one of the most beautiful in the country, and contains a profusion of stalactites, stalagmites, helictites and flowstone features. Thanks to Dave King (SMCC), our guardian, who also let me use his camera (an Olympus Tough-TG5) to take these particular shots.

Ogof Ffynon Ddu, Penwyllt, South Wales  (2017)

With a depth of 270 m, and more than 60 km of surveyed passages, the 'Cave of the Black Spring' is the deepest in the UK, and the second longest in Wales.  Its passages and chambers weave a long and tortuous network beneath the east side of the Tawe Valley.  From the stream sink at Pwll Byfre (above Smiths Armoury) down to the resurgence of OFD1 is more than 4 km as the crow flies, much more when the crow has to tackle the meandering Nant Newydd streamway and its various oxbows. The stream  carves its way through towering black limestone canyons, producing waterfalls, rapids, deep pot holes and scalloped walls. These photos are of the upper series in OFD2. Thanks to Phil Knight (SWCC), who helped out with this photo trip.

Swildons Hole, Mendip  (2019)

Swildon's Hole is an extensive cave system, first explored in 1901, and occupying a central role in the development of caving and cave diving on the Mendips. With nearly 10 km of surveyed passage, it is also the longest. The core of the system is a fine active streamway about 1500 m in length, with 12 sumps along the way, passable only by experienced divers. The waters resurge at Wookey Hole over 3 km to the south.  Thanks to David Lossl (MCG), who helped me out with this photo trip.

Box freestone mine, Wiltshire  (2019)

The hills around Bath have been producing high-quality building stone for nearly 2000 years. The stone, a Jurassic oolite, is termed 'freestone', a fine-grained fossil-free stone capable of being worked in any direction. Its honey-coloured hues are what gives the world heritage city of Bath its distinctive appearance. The stone was also used in Bristol Cathedral and the facade of Buckingham palace. The most extensive of the mines (which are strictly quarries!) is Box, with a labyrinth of around 100 km of surveyed passage, of tortuous complexity, and rich in industrial archeology. Since late 2020, access to the system is no longer possible. My thanks to Roger Banks and Simon Gaylard who helped out on my various photographing and surveying excursions.

Ogof Marros, Carmarthen  (2016)

The vast cave systems of South Wales - Ffynon Ddu, Dan-yr-Ogof, Daren Cilau, Draenen, Agen Allwedd - lie in the Brecon Beacons National Park. Further to the west, the same Carboniferous limestone outcrops as far west as Carmarthen. There are few systems of note in this area, although new discoveries are still being made. Ogof Marros was entered by the South Wales Caving Club by a team led by Phil Knight in 2015, and extended over numerous visits since. An awkward entrance series leads to a fine and beautifully decorated streamway, entering a larger 'master cave' before closing down in an area of massive collapse. The potential for further passage is evident. Thanks to Phil Knight for assistance in photography and surveying.

Upper Flood, Mendip  (2018)

Upper Flood is one of the new 'showcase' caves on Mendip. The entrance was washed open during severe local flooding in 1968, and the system explored since by the Mendip Caving Group. Major breakthroughs were made in 2006, and today it extends to over 4 km of known passage. Beyond a series of tight and awkward squeezes in a large boulder choke, the system opens into a sizeable streamway leading to an area of superb formations, Neverland. My thanks to David Lossl for enthusiastic support during this photo session.

Templeton, Mendip  (2021)

In 2001, Templeton was nothing more than a mild depression in a farmers field above the village of Priddy. Today, it's the most heavily engineered cave 'dig' in the country, and a testament to the ingenuity and dedication of cave 'diggers'. Twenty years of active excavation have resulted in an impressive vertical entrance shaft, festooned with fixed steel ladders and gantries, dropping 50m in eight stages to a solid floor before plunging another 30m in a narrow lateral rift, then continuing on down to the present dig face at a depth of about 100m. A powered winch hauls a massive skip up the main shaft on steel slides. Below are four more mains-powered winches to haul spoil from the depths, along with illumination and intercoms, as well as air and water pumps. Initially dropping through a layer of Triassic dolomitic conglomerate, the system breaks into the Carboniferous Oxwich Head limestone high in the main shaft. Exploration is driven by the hope of intercepting the streamway linking the Priddy swallets with the resurgence at Wookey Hole. These taken with an Olympus Tough TG-6.

Viewing suggestions

The images are prepared for 'cross-eyed' viewing. If you are not familiar with the technique, view in a darkened room at the maximum size possible, and from a distance of around 70-80 cm.  You are aiming to make your eyes converge, so looking just beyond your nose, but while actually focusing on the screen. The technique is non-intuitive because in normal vision the eyes are focusing and converging at the same distance.

The aim is to get the two images to merge into one, and it may help if you first concentrate on making any text in the image fuse into one single image. The effect may not come immediately, but persistence usually pays off. Once you can 'lock on' to the stereo image, you can look around the scene, and enjoy the stereoscopic depth. And once you know how to trick your eyes to get the required effect, you can quickly go from image to image


Most of these stereo images have been taken with a pair of identical Olympus E-PL1 digital cameras (from 2010), mounted on a tripod with a lateral separation of 6 cm.  I use two LEDs rated at 5000 ANSI lumens for illumination. During a typical 10 second exposure, I 'paint' the features that I want to pick out, skipping quickly over nearby or high reflectivity surfaces. One trial exposure is usually enough to adjust the painted areas in a follow-up exposure. I capture the images in raw format, then adjust the colour temperature and saturation using Affinity Photo. The image pairs are then aligned using a least-squares adjustment of selected features, which accounts for the principal optical aberrations including rotation and translation, but ignores the lateral residuals due to the parallax terms. I carry the cameras in a waterproof Pelican case. I use a sturdy if slightly unwieldy Benbo tripod, which provides great stability in difficult positions.

Fifty Years under the Earth

              [...being a reference to the classic memoirs of the great French speleologist Norbert Casteret, Dix ans sous terre]

My first trip underground was P8 in Derbyshire in 1971, with a team from RAF West Raynham. I continue actively today, hopefully celebrating my 500th trip later this year (2021). For the few who this will mean anything to, my UK classics have included Daren Cilau, Juniper Gulf, Smiths Armoury in OFD, Far North in DYO, and to the Agora in Langcliffe.  I'm a member of the Mendip Caving Group (MCG), the South Wales Caving Club (SWCC), the Ex-Cambridge Speleologists, and the MCRO (Mendip Cave Rescue Organisation).  Although I'm no longer doing the more serious trips, in the past three years I've enjoyed the delights of Otter Hole, Upper Flood Swallet, Top Entrance to OFD1, and the classic Yorkshire through trip Providence-Dow (45 years since my first). I was part of the recent Ogof Marros discovery team (background image here), I dig regularly at the spectacular Templeton on Mendip (in search of the hypothesised Swildons-Wookey master cave), and do some stereo photography and surveying as and when. 

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