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What is the magnification?

November 24, 2014

Alternative-Photonics

The PiKon telescope has a magnification factor of about x160.

Slide26

We’ve worked that out based on a standard 35mm film camera. A 50mm lens there gives a x1 magnification. A 100mm lens gives a x2 magnification. The focal length of the objective mirror in the PiKon is 800mm. So, for 35mm film that would give a magnification of x16. But the Raspberry Pi Camera sensor is just one tenth the size of a 35mm film frame. So effectively the magnification is increased by a factor 10 to x160.

Slide27

Another way of thinking about the power of the telescope is the angle of field of view. If we place a 3.6mm wide sensor at the focal point of an 800mm lens, it subtends and angle of view of about a quarter of a degree. The moon subtends an angle of about half a degree at your eye ball, so we’d expect the PiKon to have a field of view that could capture about half of the moon. And that’s just what we get:

moon2-500x375

What is the limit of magnification?

The ultimate magnification of the PiKon is limited by something called Airy Disks. These are circular halos of light which surround a point image in the telescope. They are caused by defraction effects which depend on the size of the objective mirror and limit the ultimate useful magnification.

http://en.wikipedia.org/wiki/Airy_disk

The rule of thumb is that maximum useful magnification is 60 times the size of the mirror (in inches) or 2.2 times (in mm). The PiKon prototype has a mirror diameter of 4.5 inches or 113mm, which means its maximum useful magnification is x270.

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