Backscatter *!&!*?*

[DevilDiver]

I have read allot of post from people wanting to have feedback on their pictures. One issue that is common for everyone beginners and pros is backscatter. Most common this is from using the cameras built in flash but sometime due to conditions or experience level it can be hard to avoid even with external strobes.....
I found this article explaining one technique that will reduce the chances of your photos ending up with those white specks.... Hope it helps!!!!

Strobe Aiming to Prevent Backscatter

Backscatter! All underwater photographers have experienced it. All of us hate it. It's ruined many a picture that would have been fantastic without it!
Here's a technique to help prevent it. Carl Brownd, an award winning Colorado photographer known for his wide angle work, gave a presentation to the Colorado Underwater Photographic Society to explain some of his techniques. I've tried to illustrate his technique with these diagrams.
In this diagram, you can see that with the strobes aimed at the subject, the illumination from the strobes intersects at some point between the camera and the subject.


The result is that any particulate in that path from the lens to the subject is illuminated, producing what is known as backscatter.
Carl's technique is to actually aim the strobes outward, so that just the edge of the illumination catches the subject. Carl uses what he calls the 'Rule of Thumbs' as a guide. Rest your hand, (relaxed) above the camera with your thumb pointed along the axis of the lens, like so:

Then point your strobes along the axis of your fingers. Granted, this will vary as different strobes have different angles of coverage, but just use it as a general guideline.
Using this concept, even if there is particulate matter between your lens and your subject, it is not illuminated...
Look Ma....no backscatter!

[scubaculture]

Great tip, will try it next time I get wet

[Mycroft]

Another way is to use diffusers on the strobes. Of course when using very short lenses, you have to do this to diffuse the light out to cover the whole area of the photo.

I use a pair of strobes and diffusers myself and don't have a big problem with backscatter.

[CompuDude]

Interesting rule of thumb re strobe aiming... I'll have to try that sometime.

[Puffer Fish]

That may work, if you have one seriously powerful strobe, and the water is filled with particles to reflect the light, but in general, all you will get is a very dark, terribly uneven lit image.

The standard "professional" way to prevent backscatter is to have the strobes off angle, sometimes to the point of having them almost at the sides of the object being shoot. That usually takes 2 strobes for even lighting.

I just don't see backscatter as being a major issue.

[bversteegh]

The important thing to minimize backscatter is to avoid illuminating the water directly in front of the lens - which in effect "magnifies" the size of the particles in the water. If the subject is really close like when shooting 1:1 super macro, backscatter is usually not much of an issue because the water column is so short.

When the subject is at intermediate distances (between maybe 18" and 5 feet) - you need to be more careful - don't point the axis of your strobe directly at the target, or you will get backscatter. I normally shoot dual strobes, and have found pointing the strobes straight forward, or just a few degrees out (if 90 deg is forward and 0 degrees is pointing at the camera, I point them maybe 95 to 100 degrees). I also spread the strobes out (make them wider) when the subject is farther away, but don't change the angle of the strobe relative to the camera. This minimizes the amount of water between the lens and the subject you illuminate.

You need to be very careful if you put the strobes in front of the plane established by the front of the port - significantly increases your odds of lens flare and other nasty things in your pictures.

[Gombessa]

In the first example picture, the best solution is to adjust the strobes so they intersect right at the subject (or, if possible, get a lot closer so you place the subject at the intersection point).

I don't use underwater strobes, but I wonder if anyone has thought about using highly-focused lights or lasers as "rangefinders" to help you adjust/position.

[RoyN]

That really helps alot! Thank You!

[fisheater]

Good tip. I'll give it a try in the near future.

[Puffer Fish]

Originally Posted by bversteegh

The important thing to minimize backscatter is to avoid illuminating the water directly in front of the lens - which in effect "magnifies" the size of the particles in the water. If the subject is really close like when shooting 1:1 super macro, backscatter is usually not much of an issue because the water column is so short.

When the subject is at intermediate distances (between maybe 18" and 5 feet) - you need to be more careful - don't point the axis of your strobe directly at the target, or you will get backscatter. I normally shoot dual strobes, and have found pointing the strobes straight forward, or just a few degrees out (if 90 deg is forward and 0 degrees is pointing at the camera, I point them maybe 95 to 100 degrees). I also spread the strobes out (make them wider) when the subject is farther away, but don't change the angle of the strobe relative to the camera. This minimizes the amount of water between the lens and the subject you illuminate.

You need to be very careful if you put the strobes in front of the plane established by the front of the port - significantly increases your odds of lens flare and other nasty things in your pictures.

You have some excellent examples of that in your pictures.

I would think that the only time this does not work is when using a single strobe, or using one that does not have a fairly wide angle. Over the years, the length of strobe arms, on average, have gotten shorter, and the angle of the strobes has gotton wider for wide angle lens. The combination seems to have made backscatter much more of an issue.

For those shooting with a strobe that has a rectangular flash pattern, and you are not using a wide angle lens, turning the strobe sideways also helps, as with a narrower beam, there is less light hitting particles between the lens and the object.