Starlight Xpress SXVF-H36 - Manual (Page 8)

Handbook for the SXVF-H36 Issue 1 August 2007
8
Astronomical Imaging with the SXVF-H36
1) Getting the image onto the CCD:
It is essential to set up a good optical match between your H36 and your telescope.
The H36 has a very large CCD area and so many of the popular ‘SCT’ ‘scopes are
unable to provide good quality star images over the large chip. Because of this
limitation, the H36 was designed for use with a wide field highly corrected refractor,
such as the Takahashi FSQ106 or similar, and is supplied with an M72 spacer ring to
screw into the FSQ106 focus assembly. Here is a view of an SXVF-H36 attached to
the author’s FSQ, via the adaptor ring.
As a general guide, most CCD astronomers try to maintain an image scale of about 2
arc seconds per pixel for deep sky images. This matches the telescope resolution to
the CCD resolution and avoids ‘undersampling’ the image, which can result in square
stars and other unwanted effects. To calculate the optimum focal length required for
this condition to exist, you can use the following simple equation:
F = Pixel size * 205920 / Resolution (in arc seconds)
In the case of the SXVF-H36 and a 2 arc seconds per pixel resolution, we get
F = 0.0074 * 205920 / 2 = 762mm