Can you photograph a real scene with orthographic projection instead of perspective?
Asked 10/25/2014
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Is it physically possible to capture a real-world scene as an orthographic image, rather than the usual perspective projection from a camera lens? I'm asking because a concept like opposite-facing display panels on a sphere would only match correctly if the recorded view had no distance-based magnification. Is there any optical way to do this for a real 3D scene, or is it only approximated in practice?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
12y ago
2 Answers
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Different lens systems have different attributes. Most lenses used for photography show things that are closer as being larger - mostly because this is how we, humans, expect to see the image. These lenses are known as entocentric.
There are lenses known as telecentric lenses that can be designed with the property that that objects do not show any magnification based on their distance (flip side, there's also pericentric lenses which more distant objects appear magnified, but that's a tangent).
Telecentric lenses are used in processes involving machine vision, meteorology, and industrial processes (lithography).
Edmund Optics has an example of this and more detailed information at What is Telecentricity? which includes the following image:
Note with the telecentric lens, as described, the two objects are the same size which is independent from the distance they were photographed at.
Another useful tutorial on the telecentric lens design can be found at opto-engineering: Telecentric lenses tutorial: Basic information and working principles. This provides another telecentric photo on the right:
Note the tube no longer shows the perspective and the background behind it is clearly visible.
Using a telecentric lens at an angle would then give the orthographic projection image on the media.
Originally by user13451. Source · Licensed CC BY-SA 4.0
user13451
12y ago
0
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Not perfectly for an arbitrary 3D real-world scene, but you can approximate it or achieve it under limited conditions.
Normal camera lenses are entocentric, so nearer objects appear larger. Telecentric lenses are designed so magnification does not change with object distance, which is why they’re used in machine vision, industrial inspection, and similar applications.
However, a true orthographic view of a 3D scene runs into occlusion/parallax: objects in front still block objects behind, and a finite camera position means viewpoint-dependent visibility. So for a non-flat scene, you cannot perfectly capture a complete orthographic image of everything unless the camera were effectively infinitely far away.
In practice, you can get close enough when:
- the scene is flat or nearly flat,
- depth variation is small,
- the camera is very far away relative to the scene depth, or
- the required accuracy is limited by resolution.
So the answer is: telecentric optics can remove distance-based magnification, but for a real 3D scene they do not eliminate occlusion and viewpoint limits. Perfect orthographic capture is not generally possible; only approximated or valid for restricted scene geometry.
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