How can I get shallow depth of field on a smartphone using an attachment?
Asked 2/11/2019
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I’m looking for a smartphone-compatible lens or adapter for a machine-vision research project. The goal is to achieve noticeably shallow depth of field, ideally with only a limited distance range in focus, while still being usable from a few meters away out to much farther distances. I understand that depth of field will increase as focus distance increases, but I’d like the strongest background separation possible from a phone-based setup. Are there any smartphone lens attachments or adapters that can do this reliably?
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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You can use a Depth of Field Adapter. It basically projects an image of the scene onto ground glass that you can record with your cellphone. It is used to "convert" the depth of field and field of view of one format into another. Disadvantages include reduced light transmission and the potential to capture the texture of the focusing screen.
There are adapters that blur the texture of the focusing screen by moving it with a motor. You can also experiment with not using a focusing screen, but results will be inconsistent.
Originally by user75526. Source · Licensed CC BY-SA 4.0
user75526
7y ago
0
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Simple clip-on smartphone lenses usually won’t give you dramatically shallow depth of field. Smartphones use very short focal lengths and small sensors, which naturally keep much of the scene in focus.
If you need a stronger shallow-DoF effect, the most suitable option mentioned is a depth-of-field adapter, such as a Beastgrip-style DoF adapter. These work by projecting an image onto a focusing screen/ground glass, letting the phone record that image and mimic the depth of field and field of view of a larger format.
Trade-offs: they reduce light transmission, can introduce visible focusing-screen texture, and may be less consistent depending on design. Some versions use a moving screen to blur that texture.
By contrast, add-on tele or macro smartphone lenses may increase blur a little, but generally won’t offer the kind of controllable shallow depth of field you’re after, and macro options often imply very limited focus distance.
So: for meaningful shallow depth of field on a smartphone, look for a dedicated DoF adapter rather than a basic clip-on lens.
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