Chris Ross

The valves will both have an m16 thread, the only thing that might be different could be placement of the o-ring so that it contacts the seating surface correctly.

How big was it? If it's quite small it looks reminiscent of a triplefin, except for the mouth, but a large mouth triplefin seems close? https://www.inaturalist.org/taxa/338587-Ucla-xenogrammus/browse_photos

In general two strobes are not additive because you generally don't point them at the subject UW, rather have the edges of the beams overlap a little in the centre so each strobe lights mostly it's own side of the image and fills in the shadows created by the other strobe. Whether you need the extra power depends. At one extreme shooting a full frame camera with an MWL lens at the recommended f16 needs plenty of power, compared shooting the same scene with a 180° diagonal fisheye at f8 or even f5.6 on m43. Likewise shooting full frame big animals at f13 with a 16-35 in a big dome that don’t get that close is also power hungry. Macro on the other hand you can shoot at f22 with a single small strobe as you are so much closer - a single MF-2 or Inon S220 can work just fine.

That's a big reason I wouldn't consider them, but you've got them already so need to deal the weight. I assume you have your floats on the closest arm to the strobe. I'm not sure what you are using for floatation but ideally if you get the strobe and float near neutral on it's own and closely linked to each other it should be less prone to torquing. However if you are using a lot more than the 200-250 gr per side that is required to offset the strobes then they'll want to torque, You could transfer the rest of the buoyancy to the inner arms closer to the housing and potentially bolt some foam underneath. 10 Bar have this: https://www.divesea.shop/shop/10bar-base-tray-float-29093#attr=3681 It could work if 400 gr is not too much. The principle is that if the buoyant part is above the non buoyant part it's stable and the closer the buoyancy is to the centre of gravity the more stable it will be.

12 and 6 o'clock strobe positions is generally not recommended for a number of reasons, lighting from below by the 6 - o'clock position strobe tends to look un-natural. Plus the bottom strobe might be a lot closer to substrate and blow it out. The general recommendation tends to be put your strobes in 9 and 3 or 10 and 2 or some variation while in portrait as well. See this video at about 9:35 for the positions: https://tutorials.brentdurand.com/underwater-strobe-positioning/amp/#wide I would also add if you are getting a lot of torque like that you might have too much flotation on your arms and could benefit from less on the arms and transfer some buoyancy to the housing possibly under the base. I had this issue with my rig which had around 1.5kg in float arms and it was difficult to twist upwards. I ended up pulling the two smaller float arms and replacing them with standard ones and diving the rig a bit negative.

I once dived with a camera that was slightly positive (new configuration) and found it really magnified the tendency for the dome to want to twist upwards, was quite a pain to use on that dive. It was maybe about 100 gram buoyant at most. I'm always clipped to my camera with a lanyard.

I have seen insects on land that can depart between pre and main flash, they are mostly small flies, very fast to react, I would think water would slow most things down enough for most subjects. The time between pre and main flash is generally pretty small. Having said that With a bit of thought and practice I would think you should be able to get manual to work for you first time.

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The website linked has some nice shots, though I should note that I looked at his wide angle shots and checked the EXIF data and it shows "flash not fired"for all that I looked at - the macro shots however all show flash fired. So all of the wide shots are natural light and they do look very well balanced . The AOIs would be a great solution for macro where you need a lot less power compared to wide angle as the strobes are so close to the subject. I am thinking they might struggle a bit for wide angle.

Shooting m43 is less demanding you are not closing your aperture down so much compared to full frame. Certainly reef scenes take the most power, but the YS-D2 has enough for m43. Diving in the tropics also involves thinking about transport, The YS-D2 is near half the weight and is almost neutral UW, if you are using the AOI housing then you likely won't need any buoyancy arms, but you'll probably be wanting them with the HF-1 strobes. On the dual strobes, while you can have them different and make it work and even if you want to have uneven lighting it's less thought to go from even light both sides to unbalanced, to me it's conceptually easier to have two identical strobes as my starting point.

It's a very powerful strobe, typically with m43 you shoot at f8 for wide angle. For full frame on the same shot probably f13-16 range depending on your setup, you just don't need as much flash power. It will certainly work, but it's quite a heavy strobe and a lighter cheaper strobe will get the job done.

You can generally get two different strobes to work though they will need to have different settings if they differ greatly in power like the YS-D2 and HF-1. In TTL they will both have the same duration which means the HF-1 will be quite a bit brighter than the YS-D2 and you'll be trying to use compensation on them to balance the lighting. Generally it's simpler if the two flashes are the same, less to think about and murphy requires that the you'll have the high power strobe on the side of the camera where you want less light. On the choice of strobe the HF-1 is probably overkill for a m43 camera.

If you are shooting super macro having the flash on manual should work well without much need of adjustment. Your distance to the subject is more or less constant so the flash power will remain constant. I found on my camera with exposure mode manual using an olympus flash in the hotshoe that I could assign flash exposure compensation to a dial (OM-1 Mk1) with the flash turned on and it would allow me to vary it. BUT - it only actually worked to change flash exposure in TTL it had no impact if the flash was in manual, be it RC manual or regular manual. Presumably OM thinks if you are in manual you want fixed flash output By the way if you are using RC this sends out flash control signals prior to the main flash in manual mode if you are varying manual power from the camera, this is how it varies the flash power from the camera. I'm not sure what you are doing with TTL, it should only have a single pre-flash and be effectively instantaneous, though RC mode TTL might be a little slower perhaps?, I've never really used RC mode much. I also don't have your trigger and it may slow things up a little and behave differently to a regular flash. I assume you have already disabled red-eye reduction as it will cause significant delay. Looking through what I can see on my camera, you can do two things. First go to full manual and change flash exposure on the flash. Second use TTL and see if you can find out why it is slow - with an olympus flash in the hotshoe I can't detect any lag or detect a pre-flash. To use full manual set the flash power before you move in to your subject on a part of the reef at the high magnification you want to use. Then approach and frame up your subject. If you are the same distance then you should be very close on exposure as long as the flash is positioned such that it is not shaded by parts of the reef. If the subject is slightly over exposed stop down a touch more. I find I rarely adjust flash power if I'm shooting the same size subjects. On your settings - I tend to shoot f10-11 most of the time as it means I'm not fiddling with flash power too much and I generally want the depth of field. The only reason to try high speed sync to get beyond 1/250 is to get your background water darker. If you use HSS then you start to significantly lose flash power.

Anything specific you struggle with on the OM-1? It will have a little less depth of field in comparison to the m43 sensor in the OM-1 and you do need to place it well.