How far off-axis does my strobe NEED to be?

[lairdb]

(Apologies if my search-fu was weak.)

Since I can't dive it to test different distances right now -- how far away does my strobe really need to be to acceptably reduce backscatter?

Some background: I've got an older Ikelite DS51 and DS-Sensor, and an Ikelite tray and arm. In fact, pretty much exactly what's pictured in the DS-Sensor documentation:

...except my camera is about half that size. Which is probably why I don't carry the whole rig any more; it's just less fun to dive with. I bring the camera by itself (currently a Nikon W300) but it's really along just in case the mermaids show up -- the pictures aren't great under real-world conditions.

So: I'm thinking about fabricating a more compact tray/strobe-mount -- leading to the question: how far away does the strobe really need to be? Do I really need it to be a foot away? Or 6 inches? Or is 4 enough?

I see pictures like this...

...and I start thinking I can get away with it being pretty close.

Thanks. (Yes, I realize there are a lot of subjective judgements involved, and that if I was "serious" I'd get a better camera, more arms, better strobes, etc. -- but I appreciate your humoring me that I'd like to use what I have and get slightly better-lit nudibranchs and whitemouths.)

 

[tursiops]

The reason to move the flash away from the camera is mainly to reduce backscatter from particles in the water. If that is of no concern to you, then the flash can be close to the camera. But if backscatter concerns you -- and it should -- then the rule of thumb is to have the flash-to-camera distance be no less than the camera-to-subject distance; this gives a 45 deg offset, which is good for backscatter reduction. If you only shoot macro, the flash can and should be close. Most solve the dilemma by having an articulated strobe arm so you can easily position the strobe where you need it, unlike the pix you show of the light on the tray. That is awful.

 

[lairdb]

The reason to move the flash away from the camera is mainly to reduce backscatter from particles in the water. If that is of no concern to you, then the flash can be close to the camera. But if backscatter concerns you -- and it should -- then the rule of thumb is to have the flash-to-camera distance be no less than the camera-to-subject distance; this gives a 45 deg offset, which is good for backscatter reduction. If you only shoot macro, the flash can and should be close. Most solve the dilemma by having an articulated strobe arm so you can easily position the strobe where you need it, unlike the pix you show of the light on the tray. That is awful.

Yes, backscatter is my principal issue. (I momentarily blanked on that term and used “snow” — I’ll edit that in case anyone else reads.)

Same distance is an interesting rule of thumb. The arm “shown” in the picture does articulate, but it’s pretty awkward and bulky, compared to a camera not much bigger than a dinner roll.

Edit: found a photo of the old-style Ikelite arm that shows the articulation:

 

[tursiops]

This was the picture I meant as awful, not the Ikelite rig.

 

[davehicks]

Those are both awful.

Don't be put off by a longer set of folding arms versus a fixed strobe. It will fold up small and you can balance your rig to be near neutral underwater. The advantages of being able to position your arms are critical to taking good pictures.

 

[Mike1967]

I have that same tray with a flex arm on it, works pretty good.

 

[jonhall]

I have that same tray with a flex arm on it, works pretty good.

Same here. I'm not an expert photographer but am happy with one flex arm - but if I was trying extend the light even more, the SeaLife setup allows for adding more quick connect flex arms. The flex arm is one of the cheaper pieces of equipment SeaLife has.

 

[Jim Lapenta]

I had the loc line flexible arms that link together. One of the problems I found was that they tended to drift and weren't as user friendly as you'd think they would be. Plus I never trusted being able to have the camera handed to me by them. I spent $$$ bucks on a set of ultralight arms and the difference was amazing. They allow the strobes to get in tight and at angles not possible with the loc-lines. Arms - ULCS
I have 4 - 12 inch sections with clamps and use foam blocks for buoyancy adjustments.

 

[sea_ledford]

This is the magic sauce:

Stobe(s) pointing straight forward, with the font of them inline with the camera sensor. Distance from camera to strobe equal to distance from lens to subject.

Of course it is a pretty limited setup, but the take-away is to aim your strobe so it doesn't illuminate the water column between the lense and the subject. The further away from your camera the strobe is, the more options you have. With the sea life arm, it has a quick disconnect on the strobe end, so you can just take the strobe off and hold it by hand. Position is then only limited by shoulder flexibility and arm length!

 

[lairdb]

Stobe(s) pointing straight forward, with the font of them inline with the camera sensor. Distance from camera to strobe equal to distance from lens to subject.

That seems to be the consensus rule -- although it flies in the face of compact and convenient.

With the sea life arm, it has a quick disconnect on the strobe end, so you can just take the strobe off and hold it by hand. Position is then only limited by shoulder flexibility and arm length!

I've thought about that -- a dock/undock arrangement that would be a compact package when docked, but I could pull it off with the other hand when needed.

I suppose I'm just hunting for a niche arrangement that may not exist -- it seems as though as soon as you get away from this

...there's no real functional step that's much short of this

Even the "awful" example from above

is still 4x the size of the camera alone and demands one or both hands for most of the dive.


Just as a thought exercise, I suppose I'd define what I'm looking for as

• an attachable external strobe,
• preferably supporting TTL,
• on a foldable arrangement so it could be used folded or unfolded,
• and the folded arrangement fits a drysuit pocket.

(I'm either looking for something the market doesn't desire; wouldn't be the first time -- or there's an unmet need here and quite a few smart people missing it.)