Backscatter

Hi,

I have a problem with backscatter between my camera and my target. I have the strobes set up wide to reduce backscatter, but for my wider-angle shots (e.g., wrecks), I have a ton of backscatter still. I generally shoot ISO100, around F6.3, and around 1/200

I have an S95 with Ikelite housing as well as two YS-01 strobes.

For the Ikelite housing, would you recommend black tape on the inside and over the front of the fiber-optic sensor? Could light getting through the front be the cause of backscatter? Do you have any example of taping done with this type of Ikelite housing?

Thanks!

That's a big question and there's been a ton of discussion in the forums. Its one of the primary issues shooting underwater and is dependent on a number of factors.

Indeed, if your on-camera flash is not blocked then it will indeed give you horrid backscatter, no matter where you place your external strobes. Its simple to test, just turn the external strobes off.

Posting a pic of your backscatter could help - basically if there's really large OOF (out of focus) blobs in the image, its likely a particle very close to the lens and you're somehow getting light right in front of the lens.

Of course visibility is a massive factor, with backscatter nearly impossible to avoid in mid-poor vis.

Strobe positioning is another factor, and people often point their strobes out slightly to light the subject with the edge of the beam, avoiding too much light hitting the water between the lens and subject. I started out with my strobes spaced far apart (for wide angle work) for the same reason, and much of the school of thought a few years ago was based on this principle. However, I find myself more often now keeping the strobes closer to the housing and pointing them outwards slightly. For example, if you space your strobes far out, but then have to point them inwards to light the subject, you'll still get backscatter. Granted the backscatter will be more side-lit and may not be as prominent. Its worth experimenting with and in the age of instant photo review, is easy to test in a few minutes (or perhaps worth a whole dive) UW.

Hope that helps. Cheers,

Chris

The more crap is in the water, the harder it is to eliminate it from a photo.

The basic concept is to not light any of the water between your camera and your subject. You want to catch your subject with the edge of your strobe's beam.

How to do this is a subject of endless debate. One thing to consider is that even if you feather your strobes out so the beam just catches the subject, you might get a hot spot in your photo if the strobe is too close to the camera.

Hi, I have a problem with backscatter between my camera and my target. I have the strobes set up wide to reduce backscatter, but for my wider-angle shots (e.g., wrecks), I have a ton of backscatter still. I generally shoot ISO100, around F6.3, and around 1/200 I have an S95 with Ikelite housing as well as two YS-01 strobes. For the Ikelite housing, would you recommend black tape on the inside and over the front of the fiber-optic sensor? Could light getting through the front be the cause of backscatter? Do you have any example of taping done with this type of Ikelite housing? Thanks!

I have to wonder:

1 - How close you are to the wide angle subject?

2 - Have you dry tested the flash?

With respect to 1, if you are more than 6 feet away from your subject I would expect backscatter, even in the most optimal conditions it can be really tough to get the light on just the subject under those conditions.

With respect to 2, using a red light for focusing, and take a test shot with just the housing and camera and see if you get any illumination from the flash, that will tell you how much light is getting through.

Steve

Ok, here's a couple of examples of my backscatter.

The reef photo is obviously more than 6+ feet away, so there is inevitable backscatter. However, it's an obscene amount, and I know it can likely be reduced.

The squid photo is less than 5ft away, yet there's tons of backscatter. This type of backscatter is the type of backscatter I usually get (except maybe more).

Does it look like the light from the camera flash is getting through?

I'm no expert, but for photo 1, I would have turned off my strobes and shot ambient light in RAW and fixed up the colour with Lightroom/Photoshop.

For the second one getting closer so as to fill the frame would be my suggestion. I always shoot RAW as it was one of the reasons I bought an S95.

I was thinking the opposite. It appears to me you need more strobe light.

That you still have backscatter suggest that the strobes are not lighting the subject, but instead the water in front or in back of the subject.

I think you need to practice your strobe placement. It appears you may have turned down the strobe power to try to avoid the backscatter. I think that was the wrong approach in these photos. The subjects need more light.

It just takes practice and experimentation. That's the beauty of digital photography. You can take all the shots you want and not run out of film.

Once you do better with the still subjects you will find it easier to get the moving ones.

At the risk of sounding rude, neither image works because the subjects are too far away. The first, and most important, way to avoid backscatter is to get close. The next is to put the strobe in the right place, pointing in the right direction. Martin Edge, in "The Underwater Photographer", explains it best.

Good luck!

Tim

At the risk of sounding rude, neither image works because the subjects are too far away. The first, and most important, way to avoid backscatter is to get close. The next is to put the strobe in the right place, pointing in the right direction. Martin Edge, in "The Underwater Photographer", explains it best.

 

Good luck!

 

Tim

 

Don't worry about sounding rude; I'm open to criticism. These clearly are not good shots, but they are a good example of the type of backscatter that I see sometimes.

Also, by turning up the strobe power, a lot of lighter-colored subjects become overexposed. If you look at the squid, its eyes are extremely bright due to the reflection of the strobe light. Is there a way I can work around that?

I've been out of the game for awhile but I thought backscatter is light reflected directly back into the shutter creating a hexagonal (shape of aperture) ghost in the image. I see mostly just lighted particulate in the photo suggesting that your subject matter was too far away. Anyway, maybe I'll tune back in a day or so and get a better understanding. BTW...that lighted particulate is really what drives underwater photogs nuts. It is hard to avoid. Generally I get the best results in turbid water by angling my strobes out (most say in) and taking off the diffusers (most say leave them on)...so go figure.

As mentioned one trick to reducing backscatter is getting closer to your subject. For wide angle you may want to consider a lens like the UWL-28. Here are two basic primers that may also help.

http://opticaloceansales.com/files/Strobe%...itioning-sm.pdf

http://opticaloceansales.com/files/Shooting%20Tips-sm.pdf

Thanks, everyone. I'll try all of your suggestions.

I'm still quite new to this and I've never really experimented on the surface with cameras in manual mode, so underwater is where I'm learning. Hope to see significant improvements with my photos.

While learning about strobe positioning it might be worth leaving one strobe turned off or in the boat for a few dives. I find it helps me to keep on top of all the settings if I keep things as simple as possible.

black tape in front of the flash on the camera is important. I've sometimes taped the majority of the front of the housing, to block the light.

black duct tape works great, and can be put over the outside, so you can still figure a way to feed the fiber optics.

Show us a pic of your housing setup.

I occasionally shoot with an S95 and an Ikelite 160 (with diffuser) with a manual controller/sensor. I do use the supplied opaque white card to reflect the light back to the sensor (so none projects forward), set the camera's flash to it's lowest power setting, and with the 100 degree beam, tend to point the flash slightly outwards. Obviously, depending on visibility, this has yield some excellent results. I will often push the ISO a little higher (400), but I have found the S95 very susceptible to noise.

As someone above mentioned, get closer- there is no substitute for this.