Optical geometry of smartphone camera.

[vitency]

I posted the following on a phone forum and got no replies, as expected. It's a bit out-of-the-way and technical. Thought this might be a better place since the question still interests me.

I'm using my phone to take photos of assembly procedures on my electronics workbench. However, the focus in up-close shots is not sharp.

I've always been curious about the focusing method they use. It's obviously not electromechanical servo as in digital cameras, and my guess is that the image sensors are sufficiently sensitive as to allow the use if a simple "pin-hole" lens, which effectively gives "infinite" depth-of-field. If so, I'd guess that resolution is directly related to aperture diameter. Two questions thus arise:

1. Is my guess about focusing correct, and if not what is the method?

2. Is it possible to use an external lens to sharpen the focus, and if so of what characteristics?

Many thanks for any replies and/or answers.

 

[wukunlin]

There should be plenty of resources you can find through Google on smart phone camera modules. Basically they use voice coil motors to move the lens barrel to create focused images. Most of these modules on the market cannot properly focus on objects less than 10cm away from the camera. Try treat the camera like a long-sighted person, than in theory, you will be able to improve your close up image quality.

 

[vitency]

> they use voice coil motors to move the lens barrel

Phew! Thanks for the keywords "smart phone camera modules". They led me immediately to a swag of info that I'd never come across. And voice coil motors - yes, that makes sense when I wouldn't have believed anything more orthodox.

So it's all autofocussing, I suppose, and my poor resolution is - what - bad guess on the image plane by the autofocuser?

> treat the camera like a long-sighted person

Yes, I've been moving back as far as I can, using "long shot" mode, and cropping the centre out of the resulting images.

Gonna hafta think about this for a bit ...

 

[wukunlin]

actually, close up images cannot be focused because you need the lens barrel to move farther away from the sensor for that. Since everyone likes slim phones and hate camera bulges, you sacrificed some ability to take close up shots by having slim camera modules.