Focus problem underwater in HD

markyramone62

markyramone62

Member
I've been using a HVX200 / Equinox Pro10 rig shooting tourists swimming with Sealions and Southern Bluefin tuna. The subjects are unpredictable so there is little chance to compose shots. To keep things simple I keep the zoom wide and focus on infinity. Great results in standard def but now the demand for HD is increasing and I've found infinity doesn't work through the whole depth of field. HD needs careful focusing. Can anyone share their technique for shooting in HD on full wide zoom? I'd like to set and forget focus if possible as it's very hard to get a clear idea of sharp focus in the external LCD monitor. Is auto focus worth the risk?
I guess another way to phrase the question is, how do you run and gun in HD?

Mark
 
Mark,

I am not sure if there is a magic bullet for this, but here is what I do with my funky Epic housing. Set your exposure (or gain) so that you aren't shooting wide open. Try and get your exposure to at least f/4 or 5.6 which will increase your DOF. To do this, you may need to compromise on increasing gain, but you can also reduce shutter speed (increase angle). Make some estimate of the maximum distance you will need to focus taking into account water clarity and or what you are shooting. Focus for slightly less than that distance since your DOF will include some distance on either side of where you are focused. For example if your maximum distance is at say z80 in your finder, you could probably set focus at z70 and z80 would still be ok. I can't recall if it is one of the Barry Green books or in the Panna info, but I have seen a chart that will relate DOF to f/stop to the z scale on your cam.

Please post up if you find a better way.

Grant
 
For the little bit of underwater I have done, I usually set it wide and use autofocus as focusing underwater with my rig is a bit of a pain, and I have gotten some decent results. Also, as said above, try to stop down as much as possible to increase your DOF, but I know that is hard underwater as light drops off and gain on HVX/HPX is undesirable. 1/24th shutter (360degree at 24fps) will give you an extra stop, so that is a good place to start to get some extra light. Anyway, hope that helps.
 
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