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Prime Focus Imaging

In prime focus imaging the optical path contains the fewest possible elements . Ideally it consists of a single mirror or lens . In practise a second mirror is usually added to the first mirror ,as in SCT or Newtonian telescopes . Often a Barlow lens is added to the path in order to increase the magnoification as is usual for visual observations as well . The optical system projects the image on the CCD-chip or the photographic film . Prime focus imaging provides for the same magnification , or more precisely , field of view (FOV) given the same optical path . The camera is fixed to the telescope with a camera adapter or , in some cases it is mounted in place pf an eyepiece using an eyepiece adapter .
The advantage of using this technique is the easily reproducable mechanical arrangement providing for more reproducible results . Compared to the afocal method the prime focus technique has less problems since the camera optics are often of a lower quality than we would like for astronomical use .
Prime focus imaging has until now been my primary method of astroimaging .

Eyepiece Projection

This uses a camera adapter with an eyepiece mounted in front of the imaging surface . In other respects the technique is like prime focus imaging , however , much higher magnification is possible - provided the aperture of the telescope allows it .

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Last update 21 January 2006 by Jan Andersen.
Background image : Video image of the Pleiades
Top caption : Lunar Eclipse 21-01-2000