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There is a rather common scenario where I'm shooting a horizontal subject from above with the image plane being parallel to the subject. I need to be able to adjust the camera-subject distance without disturbing the camera orientation (somewhat like the movement of a photo enlarger lens).

Ideally I'd have a latitude of 50cm (20") which is somewhat longer then the macro rails I've seen on sale offer

Also focal-length zoom is not an option here since the subject is not flat and a fixed normal FoV needs to be maintained

The camera in question is a 35mm DSLR.

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    What's the distance you need to adjust by?
    – mattdm
    Jun 4, 2011 at 20:48
  • Also, are you interested in a DIY solution, or do you want to buy something, or both?
    – mattdm
    Jun 4, 2011 at 21:45
  • I would expect a reasonably-priced solution to be available, It doesnt feel like that esoteric a problem
    – anon
    Jun 4, 2011 at 22:25

2 Answers 2

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Do you use a zoom lens? It should give you this functionality.

UPDATE: now, you mention that you need a fixed perspective. By changing the distance to the subject you essentially change the perspective. You probably mean that you need to fix the Field-of-View (FoV). If what you need is really a fixed perspective, then your only option is changing the focal length (via lens change or use of a zoom).

UPDATE 2: A height variance of 0.5m is a lot. If you are OK with the macro rails or bellows solution, then you can just raise your tripod on some blocks, books or something similar to the approximate height. Then, you use the rails for fine tuning.

Then, if I may, I'd continue arguing that if your perspective is not necessarily fixed, then the FoV becomes meaningless. You can use a zoom lens to capture the whole item from a certain height.

If you are trying to simulate a normal vision, then your perspective is important and is determined by the FoV of the eye. In this case, you probably do need to use a certain lens from a certain height.

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  • no, these shots need to be taken with a specifc (normal) focal length
    – anon
    Jun 4, 2011 at 21:35
  • yes you are right, I meant the FoV - corrected
    – anon
    Jun 4, 2011 at 23:52
  • the perspective/fov requirement is to avoid depth-distortion of individual objects in the scene, changing the camera-subject distance while maintaining focal length will affect the apparent depth relations between the different objects but would preserve each one`s "natural" look I suppose it can be thought of in terms of comparing different-sized crops depicting the same object.
    – anon
    Jun 5, 2011 at 11:29
  • all of the above of is of course under the premise that the height of each object is in the same order of magnitude as its own length/width and those are small compared to the overall size of the scene
    – anon
    Jun 5, 2011 at 11:35
  • @anon - my feeling is that you tend to make a simple thing too complicated. Unless you have a very specific requirement to use a very specific equipment, then bringing the camera to the neighborhood of the precise required point (as I suggested in the answer) and making fine tuning with a zoom will get you to the result you want.
    – ysap
    Jun 5, 2011 at 14:11
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A "macro focusing rail" might do the trick.

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  • Ideally Id have a lattitude of 50cm (20") which is somewhat longer then the macro rails Iv seen on sale offer
    – anon
    Jun 4, 2011 at 21:07
  • 2
    @anon, you can edit your question to add that information, which is pretty crucial. That'll help get better answers.
    – mattdm
    Jun 4, 2011 at 21:44

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