Astrograph?

[stefski]

What's the difference between an astrograph and a telescope? BTW, this is not the first line of a joke! :-)

stef

[Ben Ritchie]

In theory, at least, an astrograph is a telescope with the sole purpose of astrophotography, typically including wide, distortion-free fields of view for astrometry (i.e. position-finding)

The term's been rather diluted to mean a telescope that's well-suited to imaging

[stefski]

Cheers! :-)

[Ben Ritchie]

now what's the real punchline

[Doc]

Some astrographs are F2.8 so let in loads of light great for astrophotography. But a PITA to collimate I bet.

[Ben Ritchie]

There are a number of designs quicker than f/2.8 - I think Mersenne-Schmidts are around f/1.25 and the Baker-Nunn design is f/0.75, classical Schmidt cameras are faster than f/2

The LSST is a Mersenne-Schmidt design, with an 8m mirror giving a 3.5-degree field of viwe