On a seperate note I have had a PM or two about rebreathers and their application to photography for the non-techie types. I do not consider myself a technical diver in my general attitude, I am MOD3 certified and dive my rebreathers regularly. However I am not an expert on rebreathers, I am a user and also a service provider for others, but I still call my tec instructor for advice before doing certain dives. EJ (Escape) is just starting his journey on the rEvo which has become pretty much the standard for a lot of film crews. I use the rEvo unit for most things, from Trimix 100m+ to playing around in the shallows doing very long dives (circa 18m). You need to bring a bailout and you need to be confident that you can spot a problem. There's a great guy doing courses in Bali for this unit. The rEvo can predict how long your sorb will last, thus making it very economical and having that reassurance factor, it is however the weakest link in th rEvo system and has had some problems (fixed for free with a few spare parts). I also train people on the Poseidon mk6/7 and that unit is much more accommodating to the not so techie type. It does it's boot up sequence (have the error code list handy) and lets you know if something isn't correct. When it has an error, it spits out a number and you fault find and reboot. Can be annoying and a lot of users do this before having breakfast incase they got thrown a curveball. The mk6/7 is also good in the respect that for shallow dives you don't require a bailout as it calculates how much air you need in your dil tank for a bailout ascent and predicts your remaining divetime based on that (No Deco and program breathing rate and tank size via PC). Below 18m your certifying agency (and likely Dive Operator) requires that you take a bailout. The computer doesn't know this and if you stay within the remaining dive time clock you should be fine to ascend without the bailout, but redundancy is recommended. I have put slightly larger tanks on my rental mk6 so that the guests can do 2 dives and still have a nice buffer of on board bailout at the end of the second dive. However it also injects diluent and oxygen at intervals which can throw off your buoyancy if you're not listening for it. Super awesome is the flashy light and vibrating mouthpiece if something isn't correct. It isn't too over the top and gives me comfort that I can pay a little less attention once i'm sure the unit is running well, not to say you should not respect it.
I still do open circuit dives. I made myself dive rebreather only for about a year, and it wore me down. I also reached a point where my skills were not improving. Switching back to OC from time to time and having kick-ass buoyancy again made me realise I still need to improve on the rebreather. So, down to the question that I get asked a lot: Do they make a difference for photography? In most cases yes. In some cases not at all. Neutrals / background:
If you're diving with the group and plodding along there's no point in using a rebreather other than to get experience and log hours. The being able to get slightly closer to fish thing isn't worth the cost of the sorb fill and O2 in that situation. I can do the same by holding my breath and being calm on Open Circuit.
If you're diving with a more liberal operator then it might be worth it even for normal dives. But then your options for operators declines quite rapidly. Being left alone for 5-10mins at 20m when everyone else has run out of NDL is great - but it can make guides nervous if they don't know your style. If you have bailout you have redundancy, but no one wants to waste time looking for the dick that was on his fancy rebreather and got lost... So don't expect to get carte-blanche even if you have a million c-cards. Absolutely no-one wants to start searching for a body, going deeper than normal depths increases your chance of dying unless your skills are top notch.
Ideally you need a rebreather buddy, but most who have looked at rebreather forums probably took the opinion that they would rather dive alone than hang out with the people who post there! They aren't all like that but there's certainly a higher proportion on know-it-all types in the tec sector than normal diving. Much like there's a lot of special folks in the UW photography world. My wife got certified on the AP Evolution+, and hated it. I have her scheduled for a Mk6 course, but she's put off by all the messing around pre and post dive. Camera, business, small child and rebreather don't mix well in a 24hr day. I remove the business operations part when i'm diving rebreather and make the child do the rebreather washing.
Big fish interactions! Mantas do not run away, stay still and they will disregard you as a part of the scenery.
Small fish interactions. Sitting still and just watching becomes fun again. Schools of fish ignore you.
Very long NDL for dives around 20m and shallower.
Quick washout of your deco - you can do your 6m safety stop at 100% O2. I regularly do 30m+ dives and stay there for most of the dive, then clear my safety stop in the last few minutes and come up with everyone else.
If you are an air-pig, you will really struggle to empty a rebreather on one dive with correct technique.
Warm air in the breathing loop stops the chills and shivers that I get on OC.
Rental mk6/ units available in many places although a lot of operators are getting rid of them as they do have the tendancy to not work correctly first time when left in the box for 6 months.
No Bubbles to trash your wide shots.... unless you dribble out of your nose or have a full loop and ascend a little.
Anti-Social. Cleaning these things is dull. Each unit is different in the effort it takes to rinse/clean it. I can do my rEvo way faster than the mk6 due to it's design. It makes a big difference and was not something I considered before I was a user. however, you are not going to get ebola if you don't disinfect the loop every day. If you have warm climate and ventilation then it should dry out before any nasties get a hold. Prior to being certified I listened to so many people say what a hugely important thing it was to keep them clean. Obviously rental units get disinfected all the time, but my personal one not so often. I can strip, wash and hang to dry my rebreather and then pull the batteries and cards from my camera by the time the first guests finish their shower.
Heavy - I travelled with my rEvo once last year, to Raja Ampat. With carbon cylinders and bailout. It was expensive! If you have a small camera rig that is carry-on sized and can rent cylinders on location then you can do it, just buy a few spare tshirts at the destination.
Time Wasting. When the negative pressure test leaks or the poseidon gives you error codes it can really mess with your day. Do you bring spare O/C gear as well? Or just rent if it breaks!?
Crap buoyancy when still gaining experience. As soon as you think you've got it under control and have had 20 mins of thinking "ooh I can do this" your unit will send you face-planting into the sand or on a jaunt towards the surface. It's user error and experience of course but you will curse like crazy through the loop (and your voice travels very far when screaming through the loop). Anyone who heard a very angry MF being shouted during a dive in Lembeh over the last few years, i'm sorry!
Anyone who has dived a rebreather and it hasn't tried to kill them yet is not experienced. You want it to try and do that to you somewhere nice an easy. I have made a lot of mistakes already and can outline them in another post for those that are interested!
As an operator, we get quite a few rebreather enquiries over the year and the #1 most annoying thing is how cheap rebreather users are (I have fallen into this trap myself when planning a trip, once!). People who sell tech as their sole business put up with it and do it because they love it, but the general consensus amongst other operators is that its a huge pain in the ass and expense for very little return. I'm still on the fence and welcome rebreather divers from a business perspective, but i'm hooked as a user. Speaking as a rebreather diver who often travels alone (and not an operator):
I need my tanks filling.
I need extra space to wash /prep my equipment.
Sometimes I need strange gas mixes which are expensive and may sit unused after I have left.
In the water I need bailout tanks and I don't want a normal aluminium 80 as that's unnecessary for normal dives and uncomfy with a camera - give me a 40 or a 30cuft please..
I want leniency with my dive profile once the operator knows i'm trustworthy.
I want potential longer divetimes away from the bubble blowers.
I want full O2 fills, from booster pumps that work well and I prefer to know they have a backup if it breaks (imagine it breaks on your 2nd day after you brought all your equipment across the world).
I want a stock of sorb on site that has not expired.
I want a helium /oxygen analyser that I trust.
I prefer to rent my small rebreather tanks onsite than lug them with me.
I want / am required to have a tec buddy when going deep.
I am high maintenance and part of a niche group whether I view myself as that or not.
With all this in mind, remember that finally getting the rebreather is not the end of the expenditure, it is just the beginning!