Getting dark backgrounds

[Phillipus2005]

@MaxBottomtime Sorry for the subject change - what are the floats you've got on your rig?

 

[MaxBottomtime]

That's my friend Kevin Lee's rig. He uses DivinyCell. It doesn't compress under water and makes his housing neutrally buoyant.

 

[Phillipus2005]

Cheers. Any idea where to buy in U.K.?

 

[MaxBottomtime]

Most boating and aircraft stores should carry it.

 

[KeithG]

Maybe I am restating the obvious...

In order to get a black background you need to ensure that the camera does not capture any ambient light. You will need to rely only on the light from your strobes. You do not want any background "sunlight" screwing up your world.

So you need to start with a "black" exposure and add enough strobe light to give the proper exposure. To get a black exposure you can lower the ISO, shorten the shutter and / or close the aperture. You will need to ensure that your shutter speed respects the response time of your strobes (i.e. do not shorten it too much)

As a quick test you can set up your camera settings and then take a picture with your strobes turned off. It should be black. This test can be done on dry land.

 

[bvanant]

While it is true that very small f-stops can lead to diffraction limited resolution, underwater that doesn't seem to be so much a worry, since the water is much less optically clean (in most cases).

Bill

 

[stuartv]

@CAPTAIN SINBAD Martin Edge's book, The Underwater Photographer, is really good and covers lots of stuff including this type of question.

Amazon.com: The Underwater Photographer (9780240521640): Martin Edge: Books

You're welcome to borrow my copy, if you want.

 

[Schwob]

@MaxBottomtime: Floats - Divinicell uncoated or coated with something?

 

[tursiops]

While it is true that very small f-stops can lead to diffraction limited resolution, underwater that doesn't seem to be so much a worry, since the water is much less optically clean (in most cases).

Bill

It makes a big difference on macro, where there is little water between the lens and the subject. Mid-range f-stops produce sharper images, albeit with less depth of field, of course.

 

[bvanant]

I have tried carefully to test that (in the water). I have the USAF test chart laminated and have shot it at all f stops (Canon 7d, 100 and 60 mm macro lens) from 2.8 to 22. Similarly I have shot the Olympus 60 mm macro lens at the same f stops. Not much sign of diffraction related softness in any of these tests. On land, in my hands at least f/16 is about the sharpest but underwater I couldn't tell. Perhaps my port is not as clean as it should be.

Bill

As for divinycell in the UK,
Diab Limited
Unit 1141, Regent Court
Gloucester Business Park
Gloucester GL3 4AD United Kingdom
Tel: +44 (0) 1452 614234
E-mail: info@uk.diabgroup.com is their office in the UK, they can tell you who stocks it.

BVA.