internal flash reflection with 15mm fisheye and a 8.5" dome in Nauticam NA-800 housing

[sherco49]

Hi
Does anybody else got this problem of reflection when shooting with a sigma 15mm fisheye and a dome port ?
the lens diameter is 72mm, and the Nauticam dome entry is 98mm, so the internal flash light goes inside the dome and reflects on the picture.
I see three solutions:
- put a piece of paper under the internal strobe to prevent the internal light to escape => not so good
- put a round piece of plastic around the lens to close the space between it and the dome entry => looks ok
- sync with cable , so no internal flash => obvious

any advice else ?
bests
Christian

 

[Merry]

Sync with cable, but also have the strobes well behind the housing arms.

 

[davehicks]

If you are using Optical triggering for your strobes you need to change the camera's onboard flash to manual power and set to a value like 1/20th. It should not take much energy to trigger strobes and if you are using Full Dump it may spill out to the dome. You won't have this issue with that setup (I use the same) if you set to a fractional power level.

Refer to your camera manual if you don't know how to do this, but after a few minutes looking at the menu / flash section should do the trick.

 

[jgttrey]

If I'm understanding the issue, it is light from the onboard flash sneaking around inside the housing, around the lens, and reflecting off the inside of the dome. Assuming that's the issue, I had the same problem.

I just cut some "donuts" out of 1 or 2mm black neoprene and put them around the lens so they block the "annulus" between the lens and the neck of the dome port. It's much easier than using some rigid plastic and it perfectly seals out the light. It's also easy to cut out several and have spares. Super easy to install because they just slide back along the lens once they contact the inner edge of the dome.

 

[davehicks]

You don't need to add donuts to your camera. This sounds like a great way to create an addition object to get pinched in an o-ring or bump Autofocus switches from Auto to Manual.

Just set your camera flash to manual 1/20 power. Done.

Nikon D800 Settings:

 

[jgttrey]

If reducing flash output solves your problem, great & no need for donut or any other further action.

But, that option did not cut it for me. In low light situations against a dark background I could still see reflections.

Perhaps you're not visualizing what i'm talking about. It's a just a flap of neoprene - donut in profile, but just a layer of neoprene. Aquatica makes one they call a "flash blocker." You can make one yourself for free. I didn't even know they had one until I'd made my own.

I've got a million dives on it (or at least somewhere between 200 and 499 according to my profile). It works perfectly.

 

[sherco49]

Thank you for your replies.
I did some tests decreasing internal strobe power in manual mode: even at 1/20, there are still some round reflections in dark situations.
So the solution looks great and easy, but doesn't fully work for me. I learned something at least !
For sure, the flash bloker presents some risks, i plan to build one wich goes on the focus ring and rotate with it: it is just in the same plan than the dome entry and so i have to set it with care and cut it without dust.
After all, i can combine both solutions...

 

[davehicks]

I'd suggest giving this a try while diving and see if you can actually see any impact on your photos. I'd be very surpised if this remained an issue in real world conditions where strobes are in use. The Nauticam housings are well engineered and if you are using an internal flash power 1/20 per the manual you should be golden. And try going even lower, like 1/100th. If your strobes still reliably trigger you're good.