38
3 The Telescope
Fig. 3.9 Diagram showing chromatic aberration. Note how red, green, and blue light splits to arrive
at different focal points
Fig. 3.10 Diagram showing
coma in a refracting
telescope, but the same effect
applies to reflecting
telescopes
frame may appear out of focus. This is generally not a problem for cameras with
small chips, but it becomes increasingly problematic for those with large ones. This
effect is illustrated in Fig. 3.11.
The sudden onset of coma could be a tracking error, especially for long exposure images. If the mount is tracking too fast, too slow, or not at all, then the stars
will appear to trail and become elongated. If you suspect a tracking error, park the
telescope and go through the startup procedure again. If the coma persists and it
3 The Telescope
Fig. 3.9 Diagram showing chromatic aberration. Note how red, green, and blue light splits to arrive
at different focal points
Fig. 3.10 Diagram showing
coma in a refracting
telescope, but the same effect
applies to reflecting
telescopes
frame may appear out of focus. This is generally not a problem for cameras with
small chips, but it becomes increasingly problematic for those with large ones. This
effect is illustrated in Fig. 3.11.
The sudden onset of coma could be a tracking error, especially for long exposure images. If the mount is tracking too fast, too slow, or not at all, then the stars
will appear to trail and become elongated. If you suspect a tracking error, park the
telescope and go through the startup procedure again. If the coma persists and it