How can we get standardized phone photos of insects in shallow ponds with the water column in focus?
Asked 4/9/2021
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We need a low-cost, scalable way for many colleagues to take standardized photos of insect communities in shallow ponds, ideally using mobile phones. The ponds are only about 7–15 cm (3–6 inches) deep, and we want serviceable scientific record images rather than artistic shots.
Our main problem is focus: autofocus often locks onto the water surface or the pond bottom, leaving the other out of focus. We also have to deal with reflections from the water surface. What practical setup or technique would help keep the full shallow water column visible and reasonably sharp across many users?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
5y ago
2 Answers
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A place to start is with a polarizing filter to allow removal of reflections off the surface of the water. It’s probably simplest if this is hand held between the phone and the water. The user can rotate the filter as required to remove glare. Polarizing filters are commodity items, so costs can be low.
Due to the small size of phone camera sensors, depth of field is less likely to be a problem than with a DSLR.
If depth of field is a problem, a point and shoot camera with a zoom lens might be worth considering...small sensors will provide greater depth of field than larger. And a hand held polarizing filter can be held in front of the lens at least as easily.
Originally by user95237. Source · Licensed CC BY-SA 4.0
user95237
5y ago
0
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For this use case, a phone can actually be a good option. Because phone cameras have very small sensors and short focal lengths, they naturally give much more depth of field than larger cameras, so 7–15 cm of pond depth is less likely to be a true depth-of-field limit than a focus-placement problem.
The most practical approach is:
- use manual focus if possible, rather than autofocus
- set focus roughly halfway between the surface and the bottom
- use a polarizing filter in front of the phone to cut surface reflections; a simple handheld polarizer is a low-cost option and can be rotated for best effect
If the default camera app does not allow manual focus, a third-party app may. If a particular phone cannot do this reliably, a small-sensor point-and-shoot camera is another affordable option and will also provide generous depth of field.
So the key improvements are controlling focus manually and reducing glare with a polarizer, not necessarily moving to a DSLR.
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