Starlight Xpress SXV-M25C - Manual (Page 21)

Handbook for the SXV-M25C Issue 1 June 2004
21
at a rate proportional to the square root of the number of summations (summing 4
images will double the signal-to-noise), but different exposures must be used.
Summing an image with itself will not change the S/N ratio! Another recent addition
to the range of highly effective image enhancing software is a program called ‘Neat
Image’. There is a free demo version for download at:
http://www.neatimage.com/download.html
Although I have concentrated on the use of a telescope for deep-sky imaging, do not
forget that you have the option of using an ordinary camera lens for impressive wide-
field shots! A good quality 200mm F3.5 lens with an infrared blocking filter will yield
very nice images of large objects, such as M31, M42, M45 etc. If you cannot obtain a
large IR blocker for the front of the lens, it is quite acceptable to place a small one
behind the lens, inside the adaptor tube. You can even try using a light pollution filter
to bring out nebulae, reduce light pollution and sharpen the star images. The Hutech
IDAS types are particularly effective with a colour camera.
Adjusting the focal plane of the camera:
With a very wide field camera, it is very likely that the CCD will not be accurately
parallel to the telescope focal plane. This may be seen as a variation in the focus
quality from one side of the image to the other, or as distortion of the stars towards
one side. Because of this possibility, we have provided an array of antagonistic screws
around the front plate of the SXV-M25. These may be adjusted with an Allen key and
locked at the correct angle to make the focal surfaces co-planar. To make the
adjustment, first slacken all three of the set screws so that the front plate is free to tilt.
The spring washers behind the plate will resist any movement, but turning the main
fixing screws will tilt the plate and allow you to experiment with the alignment. Once
the focus is equally good across the entire image field, turn the set screws to lock the
plate into the correct position.