What focal length lens do I need to record a mouse crossing a 33-inch walkway with a Basler acA1300-200um?
Asked 4/12/2018
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I need to capture video of a mouse walking the full length of a 33-inch runway for later motion analysis. The camera is a Basler acA1300-200um with a 6.1 × 4.9 mm sensor. I tried a Zeiss Makro-Planar 60mm f/2.8, but it gives too narrow a field of view unless the camera is placed very far away. I’m looking for a lens that can cover the whole walkway from a practical distance and ideally keep distortion/aberrations low enough for analysis work.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
8y ago
2 Answers
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First -- I was not aware that Balser made a film camera. Could it be that your are interchanging the word "film" for video?
I strongly suggest that for now, ignore lens quality deficiencies such as aberrations until after you nail down the camera and lens combination that will best do this task. Let me add that I doubt that lens aberrations of any kind will be a deterrent. In other words, modern camera lenses are generally good to go for most projects (exceptions noted).
The focal length of a lens dictates the size of images of object and the angle of view. Reading between the lines, you found that the 60mm yielded too much magnification and too narrow a field of view forcing you to step back to 20 feet.
Now subject distance and focal length are intertwined proportionally. If you mount a 30mm, the field of view will widen and the image size will half. In other words, mount a 30mm and you can image form 10 feet. Mount a 15mm and you can move in to 5 feet. Their are limits as how short a lens you can mount. The danger is, too short a lens and the image will be vignette (dark corners).
Originally by user44949. Source · Licensed CC BY-SA 4.0
user44949
8y ago
0
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Your 60mm lens is simply too long for this small sensor if you need to see the whole 33-inch walkway from a reasonable distance. Focal length controls field of view: a shorter lens gives a wider view and lets you work closer.
For this kind of setup, the first priority is getting the right framing and working distance. Modern lenses are usually good enough that optical aberrations are unlikely to be the main problem, especially compared with using the wrong focal length.
So instead of another macro lens, look for a much shorter focal length lens matched to the Basler sensor and mount. An industrial/C-mount lens in the wide-to-normal range is the direction to explore. Also pay attention to distortion if you’re doing measurement; low-distortion machine-vision lenses are often a better fit than still-photo lenses for this kind of task.
In short: choose a significantly shorter focal length than 60mm, optimize the camera distance and framing first, and treat lens aberrations as a secondary concern unless testing shows they affect your software results.
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