Comment prendre de bonnes photos de laser

Taken from a email conversation:

Digital cameras for good laser photos

I have had good results with the Kodak DC260 series (now the DC290). This is a megapixel digital camera with the ability to manually control the shutter. The DC260 series can take time exposures up to 16 seconds(!). As explained below in the film camera section, it is important to be able to take long time exposures. Around 1 second is minimum — anything faster (e.g., 1/2 second, 1/4 second) might not be flexible enough for all the types of laser photos you want to take.
The DC260 is especially nice because you can pop out the Smart Media card (“film”), put it in a PCMCIA adapter, plug it into a laptop, and see the photos within a minute after taking them. If the laser photos are bad, you can do it again right away — no waiting for the photo developing.
There are certainly other digital cameras which can take good laser photos. For example, the Nikon CoolPix 990 series also has long shutter speeds and plenty of manual control.

Film cameras for good laser recordings

For film cameras, I recommend Fuji Velvia slide film. It is about ASA 50 speed, so you will have to do time exposures. Velvia has very saturated color, so it is especially good for laser. You should use slides almost all of the time since they capture the light more accurately. With film, first the negative is developed, then the print is made; in both areas adjustments can be made which are fine for “normal” photos but which ruin laser photos. Of course, once you get good slides then you can make duplicate prints out of them.

I mostly shoot graphics so the tips below are for images on a wall or screen.
Your camera should be a single-lens reflex so that you can see exactly what the lens sees. If you are shooting anything where distortion could be a problem (circles, squares) then put up a grid pattern, sight through the lens, and use a Universal Geometric Corrector or similar device to get the grid square in the lens. Do not worry about what it looks like on the wall or screen. Just get the grid OK in the lens. I have done this with raster pictures (many horizontal lines) and it is essential if you want the final photo to come out flat and square (not keystoned).
For good results, have the laser fairly close to the wall or screen. This makes the lines smaller and thus sharper. Use manual focus; focus with the lights on using a target taped to the wall or screen. The aperture should be stopped down as you want sharp focus; such as F16. Don’t change the aperture from now on. Change only the shutter speed.
When I have a new subject, or have been away from the camera for a while, I take about 5-10 shots of each image. I start with a quick shutter, 1/16 second, and go up to a manual time exposure of 16 or 32 seconds. Here’s a good tip: After a while it does not matter how long you open the shutter — a longer exposure won’t make a significant difference (technically known as reciprocity failure). So just double the shutter speed each time. Example: 1/16, 1/8/, 1/4/, 1/2, 1, 2, 4, 8, 16, 32 seconds. To avoid wasting film, use every other exposure time: 1/8, 1/2, 2, 8, 32. For the longer exposures you can just count off the seconds — you do not have to be exact.
Of course, the shutter speeds have an effect when they are fast because fast exposures may pick up only part of the laser image’s refresh. For example, if your scanners are projecting 8 refreshes per second, and you use an exposure of 1/16 second, you’ll see only half of your graphic!
And it is not enough merely to catch a single scan. For example, if you catch one-and-a-half scans you still will see a noticeable brightness difference between the part of the image which was scanned only once, and the part scanned twice. This is why long exposures are a must — you are guaranteed to catch many, many scans.
Be sure to write down the F-stop for the roll of film, and the exposure for each shot. Also, be sure that the first 1-2 photos you take AND the last 1-2 photos are with room lights on. All you care about is to get some bright frames at the start and end of the roll, so the film processor knows where to cut the frames! Otherwise, they have an all-black roll of film punctuated with colored lines. They have no way to tell how to center the colored lines.
I get the film processed the same day so that I can leave the equipment up and so all the variables are fresh in my mind. Then I can make any adjustments to the color balance (using the laser software color controls), UGC, or shutter speeds. It usually takes me two rolls for a “perfect” shot.
Work with a good lab that caters to professionals. Tell them what you are doing so they won’t think there’s something wrong with the film.
When the slides come back, I write the F-stop and shutter speed on the slides immediately. You will always lose the bracketing sheet, so write the data on the slide. You even may want to write other info such as the film type (e.g., Velvia) or the laser equipment.
For beams they should emerge from behind a hole in a cloth or photographic background paper. This is so you don’t see the projector or objects behind the projector. I don’t do beams as often so I can’t give you as many specific tips, except “bracket, bracket, bracket”!

Digital creation and editing

The final topic I want to discuss is electronic creation or editing of laser graphics.
If you use a digital camera, or scan in your slides, then you have the opportunity to fix up your laser photos or be more creative. Of course, you can adjust the contrast, brightness, saturation and other elements. But you can do much more.

Two scan heads from one

For example, if you are shooting a two-scan head beam show, just shoot one scan head, then in a program like Photoshop, flip the image and blend the two. Using the right blending mode, you will get a perfectly symmetrical image which looks realistic (double-bright where the beams overlap). You can see this technique used in one or two of the beam laser photos on the webpage at Pangolin.com where you can download “Windows wallpaper” photos.

Synthetic photos

One of the techniques I have developed is making “photographs” which really started out as drawings. In Lasershow Designer I might do a screen capture of the LD Drawing Window (enlarged to maximum size), with no grid lines, dot points, axis lines or any other background — just the laser lines. This screen capture is then taken into Adobe Photoshop. I crop to get only the laser lines, and then add various effects such as blur and noise. These help simulate what a laser photograph looks like. Sometimes I will take two versions — one sharper and brighter, the other blurred and dimmer and superimpose them to make the “glow” that can surround laser graphics.
I feel that if this technique is used appropriately, it is perfectly valid for showing clients or others what the laser images look like. The test is whether the Photoshop-created synthetic photos look essentially the same as the real laser-projected images. I feel they do.
You can see this effect very well if you get our 4-color brochure with a hand and mouse making a laser spiral on the cover. There are two versions of the brochure, one in English and one in German. On one cover, I used the Photoshop synthetic-photo technique. On the other cover, I shot a photo with a digital camera. Now remember, these photos are nearly 8.5 inches square at 1200 dpi, so you see any flaws! Yet most people would call the two images essentially equivalent.
There are other examples at our website of laser “images” which are not true laser photos but  Photoshop-created synthetic photos. Two notable exceptions are the many scanner test photos, and the cheerleader photos. The scanner test photos were taken using a digital camera since obviously the actual image on the wall is important to evaluating the scanners. The cheerleader laser photos were also taken using a digital camera. This was because for “school spirit” it was important that the cheerleaders were actually in the laser beams.