Close-up photography
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Macro 3D Basics
(Thanks to John Roberts)
As a general rule, the smaller the object to be photographed in 3D, the more demanding the requirements of the equipment. The basic requirements are as follows:
- A means of precisely controlling the elevation and angle of the two shots. ormally, youll want the two shots to be exactly parallel. Compensation for the offset in the two photos is taken care of when you set the stereo window.
- Precise control of the baseline. Initially, you may get by taking a batch of pictures and picking out the pair that gives the proper depth, but eventually youll want to be a little more scientific about it. For objects one to several inches across, I like to control spacing to within about a millimeter.
- Control of the background, for when the object of interest does not take up the entire field of view. With focus at macro distances, distant objects will be badly out of focus. You may also want to allow more depth in your subject by eliminating infinity. I have some pieces of plain cloth of various colors, which I drape behind the subject. If the cloth is far enough back, it is entirely defocused, making a uniform background. If its close to the subject, it still eliminates infinity.
- Proper lighting is important. In macro stereo photography, its usually desirable to get the depth of field as great as possible, so you will usually set the aperture very small. To get reasonable exposure times, you therefore need a bright light source. I havent had much luck with incandescent lights - even halogens add a lot of red to the photo (this could probably be corrected by use of the proper filter). Ive been using natural sunlight, which has its own problems during the winter or on windy days. If you use a flash, it is important that the flash unit not move relative to the subject between the two photos, because this would cause the shadows in the two images not to match. A fixed mount above or to the side of the camera (with connection to the camera with a flash cable) is ideal.
- Proper exposure can be very tricky in macro photography. There are formulas that can be used, but its easiest to use a camera that takes care of it automatically. I usually use a Minolta camera in autoexposure mode. This particular model (X-700) takes a final exposure reading *after* stopping down, so it can compensate for any inaccuracies in the stopping down process. It also uses TTL (through the lens) flash exposure control, so the duration of the flash is controlled by the illumination on whats in the field of view of the camera - *much* easier when you can do it. For best results, I suppose the distance from the object to the background should be relatively small compared to the distance to the flash. For special lighting situations, keep in mind that macro makes it even harder than usual.
For the first two requirements, a regular stereo slide bar can be used, especially if the magnification is not very great. Some people have built macro slide bars out of wood. I use a microwave tuning mechanism that I picked up at a hamfest. It has very precise gearing to control motion, and a millimeter scale with a vernier for 1/10 mm precision. Theyre pretty expensive new, but if you see one used, you ought to be able to get a good price.
Base Separation for twin-camera macro photography
The following table suggests the base separation between the two exposures for correct 3d macro photography:
| Distance to Subject | Camera Separation |
|---|---|
| 30 | 2.0 |
| 24 | 1.6 |
| 18 | 1.2 |
| 12 | 0.8 |
| 6 | 0.4 |
