long exposure underwater photos

[MantaRey]

I don't have the chance to do too much photography underwater. I would imagine that long exposure shots are hard because well, they are hard on land. wouldn't backscatter be a problem? not so much backscatter, but just little things in the water that move in front of the lens. you may have the camera still, but you can't block the scales and other stuff in the water. well, here anyways, some people are blessed with crystal waters. I think this would only matter if you do really long ones, like more than a second.

 

[blacknet]

Hello,

Well long exposure is not hard on land, in fact it's the history of photography. Up untill recently long exposures was quite common. As with many thing backscatter is a fuction of timing, distance and angle. In less than pristine water conditions you would have that factor to contend with. Remember with the right exposure you can eliminate objects whether on land or in the water.

Ed

 

[TheAvatar]

1. For those that do not know: two things you must consider for accurate long exposures are:
A. The accuracy of your lightmeter in extreme low light. (Most are accurate to 30s @ f/5.6 /w 100ISO film (i.e., EV0), to give an example for this situation at least.)
B. Reciprocity failure by the film. That is, the film failing to respond in the nice curve it normally maintains. That is, one would think exposing film for 10 minutes instead of five would make up for going from f/5.6 to f/8 (that relationship is reciprical, there is reciprocity), but it might only make up for going from f/5.6 to f/6.7 (This is NOT recipricol, there is reciprocity failure)!!! This is what happens at extremely long exposure times and it gets worse the longer the exposure is. (It also happens at extremely short exposure times, but we needn't worry about that underwater). In color negs/slides you also must consider differing rates of reciprocity failure between the color layers which can cause unnatural color shifts, though this perhaps is less important underwater. Soooo....

It is far too troublesome to correct for the color shifts underwater, which is why, as blacknet said, you might consider black and white for underwater. On the other hand, colors are kinda silly in aqualand anyhow. However, the overall exposure must be corrected to compensate for reciprocity failure. Soooooo...

It's better to have films that won't experience so much reciprocity failure so quickly. Nobody wants to have to think about yet another variable so let's pick some films that don't suffer so much.

Good choices (all exposure data from manufacturer, you may need to alter for yourself):

Kodak TMax 100 TMX, as blacknet suggets (B&W: No exposure correction needed for exposures up to 1/10 seconds, only +1/3 stop exposure compensation needed at 1 seconds, only +1/2 stop exposure compensation needed at 10 seconds, only +1 stop exposure compensation needed at 100 seconds)

Kodak E100G E100GX (Slide: No exposure compensation needed until up to 120 seconds, green shifting after 10 seconds)

Fuji Neopan Acros 100 (B&W: No exposure correction needed for exposures up to 120 seconds and only +1/2 stop exposure compensation needed at 1000 seconds)

Fuji Provia 100F (Slide: No exposure or color correction needed for exposures up to 128 seconds and only +1/3 stop exposure compensation needed at 256 seconds and there will be some orangeshift)

I wonder what Fuji Velvia 100F will have for reciprocity characteristics?

Here is a chart with reciprocity failure info for several types of slide film, including Velvia 50 (many of the other emulsions are older... notice the Provia is plain old Provia and not the F version):
http://www.tfkp.physik.uni-erlangen.de/yp/personal/ralf/photo/reciprocity.html

2. Shouldn't backscatter be reduced by a very long exposure without flash? The lack of flash should reduce it outright. The remaning particulates that cause backscatter should be moving slowly through the water and therefor it will be blurred, perhaps to the point of not being noticed depending on the exposure time, right?

 

[raviepoo]

blacknet once bubbled...

Use existing structures on the wreck/reef that are mount friendly. i.e. growths of cyano, corraline algae's and some mushroom corals.

I know mushroom corals are not actually coral, but won't mounting your equipment on it kill it just the same? Do you think it's OK to kill any organism to get a good photograph?

If I'm wrong about the killing part, please correct me.

 

[blacknet]

raviepoo.

The aquarium trade will chop up mushroom 'coral' for propigation so if you damage one yhou are you just helped it propigate. Same with corraline algae. Besides parrot fish will strip corraline algae off an area in record time and spread it to other areas where it grows. Also mushroom coral growths are usual rampant and have some extensive ranges on them. If you see a spot with very few then find another place to ancor.

Not really mount your equipment ON it but more around it or under it. I would much rather put something on corraline algae than a shroom.

That being said corals are very sensitive to the blue spectrum and I have yet to see a study on their effect under photography flashes I would speculate they have a nasty reaction over a period of time with prolonged flashing. Corals are also very sensitive to water flow and NOAA research suggest that a diver disrupting the water flow simply by being present disrupts coral growth.

Ed

 

[raviepoo]

I'm overly sensitive about damage to the marine enviromnet after diving with the temorary buddy from hell. He would latch on to anything handy to steady himself for a photo. Anything handy could be a sponge, or it could be a piece of live coral. I wanted to drown him.

 

[blacknet]

Hello,

I will avoid grabing on any thing if I can but if I do need to grab onto something i'll look for areas that can be used. They are actually more plentiful than most thing. Do this, on your next saltwater dive look for those areas I mentioned and see what you find.

Ed

 

[TheAvatar]

I think that the fact that there is often a lack of places to stabilize yourself in many reefs, the requirement that you stabilize yourself through expert ballast, breathing, and fin control, is one of the many extra challanges to taking the camera under the surface.