DIY Add on diopter

Started Oct 26, 2013 | Discussions thread
Stephen Barrett Contributing Member • Posts: 683
Re: DIY Add on diopter

Hello dickiedoo,
Good job!
For an approximate measurement of the focal length, just hold your closeup lens close to a wall and adjust the distance until you get a focused image on the wall. Something outside a window will do, or even a lamp on the other side of the room.
The focal length is approximately the distance from the centre of the lens to the wall. You can improve the accuracy by repeating the measurement with the lens direction reversed and then averaging the two measurements. If you want the strength in diopters, that is given by:
diopters = 1000 / (focal length in mm)

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Canon PowerShot SX30 IS +3 more
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