strobe positioning W/A

I do most of my diving/photography in Ireland where viz can be 20m but most of the time it is 6m or less. For about 2 years I used a Sigma 15mm (great lens) on a D70 with 2x DS125s on 5" ikelite arms. I never had a problem with strobe positioning. I have been using the Tokina 10-17FE for a few weeks now and have also added 2x 8" bouyancy arms to the esisting 5" ike arms. and am having difficulty with strobe positioning. For wide angle shots I place the 2 x DS125s back about 8-12"s from the dome port and angle out to light with the edge to avoid backscatter.

My problem is that as I get closer to the subject (close focus W/A) the centre of the frame is not being lit. Is this because the port shade is blocking the light i.e. do I need to move the strobes more forward and closer to the port? How close? I assume I still point the strobes out to avoid backscatter.

This is a common problem. You'll need to either bring your strobes in closer, or else pull them back further. In murky water, I'd opt for pulling them back.

HTH

James

if you post an example of one of the images it will be easier for others to give you their thoughts. i have only just purchased this lens so cannot personally help, but i will be taking notes of the replies.

cheers, stew

When I was shooting really wide (17mm on FF) in the Philippines using 2 x DS125's I ended up using a third strobe in the middle.

Cheers

James

Is this because the port shade is blocking the light i.e. do I need to move the strobes more forward and closer to the port? How close? I assume I still point the strobes out to avoid backscatter.

I shoot this close focus wide angle type image much of the time, even focusing as close as within 6 inches of my domed port by bringing my strobes in very close to the dome and angle the strobes to the outside. By close to the port, I mean within as close as 6 inches.

I am one of those that never uses strobe arms that extend farther than 14 inches from the port. By using the technique you described of directing the beam angle away from the port, I have very little backscatter.

Hoping this information helps,

Barry

as I get closer to the subject (close focus W/A) the centre of the frame is not being lit

Move those arms! Your principles are fine, but you have to keep the edge-light from both strobes overlapping on the subject.

Although it looks really awkward, I've also tried having one arm vertically above the dome, pulled back behind the housing, and one out to the side.

Tim

Does anyone have pictures showing the strobes position in CFWA ?? A picture says a thousand words ...

http://www.kelpfish.net/strobe.html This is a great site. I go back there once in awhile just to refresh the basics.

Ditto that! I have found his illustrations more helpful than almost anything else I've seen or read on this topic!

Does anyone have pictures showing the strobes position in CFWA ?? A picture says a thousand words ...

Martin Edge, "The Underwater Photographer" 3rd edition, has illustrations, commentary and advice.

Tim

Martin Edge, "The Underwater Photographer" 3rd edition, has illustrations, commentary and advice.

 

Tim

 

having said this, I think the live video demo of martin edge on underwatertvchannel is real cool ... where he teaches the basics of exposure on macro photography ...

thxs guys for the website on the strobe positioning for WA ... jus wondering if using a FE or a rectilinear lens affects the way the strobes are positioned ??

my internet connection in the philippines is too slow to watch the undewater tv channel, does anyone know if you can download these videos instead of watching them streaming?

Hi,

This is an interesting topic.

I need some advice regarding scatter and blurry edges when shooting CF-WA images.

Example of CFWA with a 19th century wooden wreck in background, using a Tokina 10-17 at 10mm:

I have experimented with different positions of the strobe arms, but i still get need to crop the images taken in dark water.

I was told to move the strobes closer to the housing and point them outwards (not 45 degrees as i used to), so i removed one section of the arms and had them linear with the dome, but i'm still not satisfied with the result.

Next dive i will try to pull back the strobes even further like this:

What do you guys think?

/T

Try turning the strobes about 30 degrees outwards. You may need to move them a little closer to the back of the lens, but probably not. The centre of the frame is lit by the overlapping edges of each strobe's light, the centre of each light pool is off to the side, in your example shining on the diver's head and fins. You should have more even illumination and less backscatter.

Tim

It seems that if you put your strobes close to the camera and point them our away from the camera, you are lighting the particles on the side the wide angle lens will see. If you can imagine the WA lens having a 160+ degree viewing angle and you are pointing your strobes angled out away from the center, you are going to see more back scatter. You also run the risk of creating a shadow in the middle of your shot.

I have my strobes on 2 - 12" arms so each side can go out 24" from the camera. I then angle the strobes back a bit towards the camera and that gives me very good results without getting any backscatter. The only thing I have to watch out for is that they don't get too much in front of the lens or I will end up catching one of them in the edge of the shot. You need to keep them slightly behind the camera, but I would have them angled in towards the center a bit.

24" arms are a macho myth, once promulgated by the great and the good, including Martin Edge, then debunked by experiment. Backscatter occurs when the light rays from your strobe are reflected back at the lens: by moving the strobe to point outwards, and by positioning the strobe behind the port shade, no light rays are reflected back at the lens by the particles within the field of view: they are reflected away from the lens. This works with arms as short as 8", though 12" may be better, and a field of view up to 180-degrees. It is difficult with a circular fisheye lens...

Tim

24" arms are a macho myth, once promulgated by the great and the good, including Martin Edge, then debunked by experiment. Backscatter occurs when the light rays from your strobe are reflected back at the lens: by moving the strobe to point outwards, and by positioning the strobe behind the port shade, no light rays are reflected back at the lens by the particles within the field of view: they are reflected away from the lens. This works with arms as short as 8", though 12" may be better, and a field of view up to 180-degrees. It is difficult with a circular fisheye lens...

 

Tim

 

"Macho myth" Okay.. First, it is 2 - 12" arms on both sides giving you up to 24" of extension on each side.. Second, nothing mythical about it, it works, it was is the same set up that Cathy Church uses and has taught to me. I have looked at your pictures and I'll stick with putting the strobes further out and angling them in. To each their own, but I don't have ANY problems with backscatter and I am able to get much better dramatic lighting that gives more shadows and texture to the picture.

Personally, I think that lighting is biggest area where most photographers struggle to produce high quality results.

The main mistake people make is not getting close enough. And then when they do they use too long arms or aim the strobes out - this was by far the most common problem with people's wide angle at the start of my workshop last week. Everyone lighting the edges of subjects and not the bloody subject!

I do most of my tropical wide angle with a single section of Ultralight, 8 inch section. I almost never aim my strobes outwards. There is no problem lighting a fisheye wide angle shot with a single strobe, if you know what you are doing.

Alex

There is no problem lighting a fisheye wide angle shot with a single strobe, if you know what you are doing.

Ahhh, there in lies the rub. I'm far from an expert so I bow to your opinions, But it seems to me that there are far too many variables at work here to be able to define one way as "correct". Let's see, we have ambient light level, strobe power, strobe type, strobe angle of coverage, diffused or not, water clarity, strobe position, strobe angle, subject size, subject distance, particulate size, particulate amount, particulate reflectance and probably a few others I'm forgetting. The calculus involved in solving for these is far past my ability to provide an answer much less be adamant about it.

The real variable that drives discussion here especially on this subject is that we are all in different places on that big learning curve. What passes for a good picture for some, others would throw away. We are all on the journey and the beauty of Wetpixel is that the craft continues to grow and improve because we feel a responsibility to help those with less experience while at the same time learning from others with more. I'd say RJ and Tim are both right for what they are trying to do, really shouldn't be an argument. Take a look at the Strobist website sometime, 30,000 members discussing how to use and where to put their strobes. They are on dry land and they can't agree.

As I grow in my photography I'm paying much more attention to how I use the light. I'm starting to really understand that the light is the key variable that separates world class from just another good shot. With the advent of digital photography there are thousands of good pictures being put up each week on Flickr alone that would have been cover shots when I started diving. Now it's just another picture of an anemone fish. I'd offer that the pros like Alex and the others here who consistently produce breathtaking images that separate them from the rest of us use the light they need to make the image they want. I'll bet if you picked any six of their great images the strobes are in a different place for each one.

Where do you put your strobe(s) to take a good picture? I use a 5" and an 8" arm with the strobes pointed straight ahead so I can "scissor" the strobes in & out to the position that the light just makes it to the subject without lighting the water between us. Where do you put the strobes to take a great picture? Turn one strobe down (or off) so you get some shadows and highlights and put them where they need to be to tell the story. Where do you put them for a great image? Beats the hell outta me, but when I figure it out you guys will be the first to know.

Have fun,

Steve

I second Alex's opinion on not needing for most shooting (if not all) more than two articulations in a medium short arm.

If you are shooting 4' or closer you can aim most wide beam strobes (I use one or a pair of Ikelite DS125 and now DS160) and the beam angle is more than enough to light the subject without backscatter. Aiming it almost straight ahead light a car's headlamp until maybe 1.5' or closer works fine. Maybe slightly above the lens axis and behind the "film plane" of your camera too. I position my strobe front edge equal to my housing's back. Sometimes even pulling it back further (maybe 6" behind the back?) as I move closer to a subject.

People always seem to make this WAAAAYYY more complicated than it is. Think of your flash as a paint brush (OK, a fairly a BROAD swath one) and aim it accordingly.

YMMV

dhaas