Cheap DIY neutral-density filter options for photographing a bright LCD with a webcam or phone
Asked 6/15/2020
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I need to attenuate a very bright LCD screen by roughly 6–7 stops so students can photograph it with a webcam or smartphone for a polarization/Malus’s law lab at home. Optical quality does not need to be perfect, and a little blur is acceptable. Are there inexpensive DIY or household materials that can work as a strong improvised neutral-density filter, or is it better to solve this by reducing screen brightness or controlling camera exposure instead?
Originally by user21068. Source · Licensed CC BY-SA 4.0
user21068
6y ago
2 Answers
1
There are some fairly low-cost solutions.
Lower the display brightness. Every modern computer has brightness controls buried in settings somewhere. Most monitors have buttons to control brightness, and most laptops have button or key combinations that do the same.
Most displays can dim to completely black, and it's highly unlikely that a display dimmed to that extent would overexpose a webcam.
Use a camera that can control exposure via aperture, shutter speed, ISO, or exposure compensation. Old compact cameras can be purchased for little more than the cost of shipping, much less than the cost of traditional textbooks.
Also, the cameras built into smartphones are capable of this miraculous feat. You state, "The vast majority of our students own both a laptop and a smartphone."
Use webcam software that can control exposure. Your problem may be a software defect (auto exposure + exposure compensation). Try some different programs.
Use a different webcam. If not a software defect, your webcam may be defective.
Originally by user75526. Source · Licensed CC BY-SA 4.0
user75526
6y ago
0
Generated from our catalog & community — verify before relying on it.
The simplest solution is usually not a DIY filter at all: reduce the display brightness as much as possible and use a camera with manual or semi-manual exposure control. Phones and many cameras can lower exposure through ISO, shutter speed, aperture, or exposure compensation, and that is likely to be more reliable than improvised materials.
If you still need a physical attenuator, historical/DIY approaches include liquid or dyed filter cells, but they are more of a science-project solution than a convenient student kit item.
A practical cheap material suggested in the community answers is replacement automotive side-mirror glass. Its partially reflective coating can act like a strong dimming filter. If used, it should be held very close to the lens and shielded so stray light cannot enter around the edges, since reflections can reduce contrast.
So the best path is:
- turn screen brightness down,
- use exposure control on a phone/camera if available,
- only if necessary, add a simple dimming material such as mirrored glass close to the lens.
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UniqueBot
AI6y ago
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