Why do endoscope cameras have such a short usable focus range compared with backup cameras?
Asked 1/4/2019
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2 answers
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Low-cost endoscope/borescope cameras often list a focus range like 3–8 cm or 3–40 cm, while car backup cameras seem to keep objects in focus from a few centimeters away to very far away.
Why is the usable depth of field so much more limited on endoscope cameras? Is it mainly because they are designed to focus very close to the tip, or are there other optical reasons such as focal length or aperture?
I'm trying to inspect tight spaces like inside walls, and I'd prefer a camera that stays acceptably sharp over a wider range of distances.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
7y ago
2 Answers
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There's only ever one perfectly-in-focus theoretical distance from the camera. But, because perfect isn't necessary to actually appear in focus, there's a broad range — depth of field, as you correctly define it — which is "good enough" for the viewer in a given situation. Because this is perceptual, the exact limits are fuzzy — you can read more about it here. What exactly determines depth of field?
The nutshell answer to your question is: because of how this all works out, apparent depth of field is larger when the "exact" in focus part is set to be further out. When you focus very close, depth of field is minimized.
The endoscopic cameras you are looking at are meant to focus very close — sometimes right at the tip of the device. They're meant for working in small areas. By contrast, car backup cameras are meant to perceive things relatively far — usually multiple feet — from the camera. So, they can be set to provide more effective depth of field.
Originally by user1943. Source · Licensed CC BY-SA 4.0
user1943
7y ago
0
Generated from our catalog & community — verify before relying on it.
Endoscope cameras are usually optimized for very close work, and close focusing greatly reduces depth of field. In photography terms, only one distance is perfectly focused; everything nearer or farther is progressively blurrier. What looks “in focus” is just the acceptable range around that point.
Why backup cameras seem to have more “infinite” depth of field:
- They’re typically focused much farther out.
- Short/wide lenses increase depth of field.
- A smaller effective aperture also increases depth of field.
Why endoscopes often don’t:
- They’re meant to see objects very near the tip.
- Focusing very close gives much shallower depth of field.
- Their tiny optics are designed around close inspection, not broad near-to-far sharpness.
So yes: the main reason is that endoscope cameras are intentionally set up for close-focus viewing in confined spaces, while backup cameras are set up for wider scenes and farther subject distances. If you want more of the scene to stay sharp, look for a borescope/endoscope with a longer stated focus range or “adjustable focus,” but very close-focus use will always trade away some depth of field.
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