# What distance should there be between two shots for a stereogram?

Back in the day I had a stereoscope with a stereogram. The effect was fascinating.

These days I have a few rolls of cheap, expired slide film and a film camera with a 50mm and a 100mm lens.

If I were to build a jig for my tripod so that it allowed me to take stereograms, how big should it be? I imagine some very basic horizontal bar that allows the camera to be mounted either left or right from the center. How far should these two positions for the camera(s) be apart to get a good effect? How does it change depending on the focal length?

Let's assume scenes without too much change in them, so that using a single camera could work.

I'm looking for a concrete distance as I do not want to shoot through an entire roll of film before knowing what's going on.

Let's say the focal length is 50mm or 100mm, the subject is 1, 5 or 10m away. What should I choose as a distance in these scenarios?

• It would depend on the distance to the subject matter. Longer distances would call for greater separation. You'll just have to try and see what works best. Commented Jan 14, 2015 at 21:00
• That makes sense. I edited my question to provide more information. I don't want to waste an entire roll just to get the settings right.
– null
Commented Jan 14, 2015 at 21:13
• Roll of film? For what? Wrapping food? Commented Jan 15, 2015 at 18:15
• @Jasmine to not expose the film to light all the time ;)
– null
Commented Jan 15, 2015 at 18:32

## 2 Answers

It depends on the effect you want.

If you want a natural view, the separation between the images should be about 6.5 cm/2.5 inches, equal to the distance between the average person's eyes. However, if you do this, the stereo effect is limited to relatively nearby objects (6.5 m/20 feet), and objects that are too close will give a "double vision" effect rather than a stereo effect.

If you want a scale-independent view, you should adjust the separation based on the distance to the subject. A good rule of thumb is that the separation should be around 1/30 the distance to the subject. This lets you create stereograms of things like mountains.

Separation is largely independent of focal length, though you need to be careful about using telephoto lenses when producing stereograms: if the foreground or background shifts too much between the pictures, a person viewing it cannot combine the two images into a single view.

The technique I use is to take three images: the second image has a separation from the first that seems right for the subject, while the third image is separated from the second by about half as far. This gives a "separation bracketing" effect: I can use whichever of 1-2, 1-3, or 2-3 gives the best appearance. Note that I'm usually hand-holding and judging distance by feel; if you're using a tripod and measuring everything out, you may not need to bracket.

If you want the scenes to look natural: the distance should be the same as between your eyes - about 8cm. This is independent of the subject distance.

If you use a larger separation, you're effectively simulating the perspective of a giant; I remember seeing an early 3D IMAX movie where they shot a scene with a 2m distance between the cameras, overlooking a boat in a canyon. The people in it looked like tiny toy soldiers.

I am not sure whether this only holds for a normal perspective or also independent of focal length.