Telecentricity in Micro Four Thirds.

Started Oct 30, 2013 | Discussions thread
Tom Axford Veteran Member • Posts: 4,433
Re: Telecentricity in Micro Four Third

The MFT manufacturers claim that their lenses are near telecentric and I see no reason to disbelieve them.

In discussing this it is important to understand what telecentric means.

For a telecentric lens the principal light rays forming the image are parallel to the optic axis (a line through the centre of the lens) when they leave the back of the lens, even at the edges of the image. See this article  for a fuller explanation.

It has nothing whatever to do with the distance between the back of the lens and the sensor. But the back element of the lens must be at least as large as the sensor itself for a fully telecentric lens.

The main industrial use of telecentric lenses is in measuring the size of objects with camera systems - again see the article I referenced above for more explanation. This is so because of the property of telecentric lenses that the size of an object in the image does not change as the focus changes, so the accuracy of measurement is not affected by the accuracy of focus.

You can use this property to check for yourself whether or not your lenses are telecentric. Put your camera on a tripod and switch to manual focus. Then change from focus at infinity to focus at the closest point possible and see what happens to objects at the edge of the image frame. If they just go in and out of focus without changing position, then your lens is telecentric or nearly so.

I have done this with only a couple of my lenses and they certainly are near telecentric.

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