| Gene Baraff |
| (sage) |
| 06/23/09 08:23 AM |
Re: what's up with SHS yahoo group?
|
Quote:
That is the idea but I am too tired to consider if you have it right or backwards ( you seem like you think these things out so I bet you have it right). I know many of the early SHSs were built backwards and had to be fixed later in the large observatories.
No. This was one from the top of the head, so it is 50-50 that I got it wrong. The purpose of my post was to clarify the idea - not the details.
In either case - right or wrong - the effect on the image would be, I think, no different from what observers used to the view through a Newt encounter upon their first view through a refractor with a diagonal ahead of the eyepiece.
The information about an SHG (not an SHS) that I found to be most fascinating was the description of a computer algorithm which is able to remove the effects of both a less than perfect scanning mechanism, and less than perfectly dust-free slits. In spirit, it was related to what the astrophotographers do when they use flats to subtract out noise from their shots. In this case, the "flat" is produced by an averaging algorithm, first in the x direction and then, separately, in the y direction.
The one handles non uniformities in the x direction due to unsteady drive speed. The other handles non uniformities in the y direction due to dust on the slits.
Gene