Re: TOM2

[Chris Albertson <chrisalbertson90278@yahoo.com>]

Tom,

Just a guess.  If the rings are present even after changing out
the optics maybe they are there on TOM1 also only hidden by the
extra reflected light?  In other words rings are caused by
darkening the sky.  I don't know where the rings are or the
percent of light in the ring vs. the core but if your optics
were perfect and the PSF well sampled theory says you should
see defraction rings.  What do out of focus stars look like on
both sides of best focus?  In the ideal case the rings will be
brighter on either side of best focus.  At best focus how 
"tall" is the ring as a fraction of the central peak?


--- Tom Droege <tdroege@veriomail.com> wrote:
> Slowly I am getting TOM2 running.
> 
> While the change of lens back to the old chipped elements greatly
> reduced 
> "ring around bright stars" problem, I now see that it did not cure it
> 
> completely.  I can really see nothing wrong with the lenses.
> 
> I put a long lens shield on the I camera and this seemed to help the
> "ring" 
> problem a little.  Still, I can see rings around the bright stars
> with TOM2 
> and they are not visible on TOM1.
> 
> If anything, TOM2 is in a better position with respect to reflected
> light 
> than TOM1.  There is nothing above TOM2.  It is in the top of the
> dome and 
> looks down in all directions.  TOM1 sits sticking out over a porch
> and has 
> white reflecting doors on each side.  It also sees light reflecting
> off the 
> shed roof that houses the dome.  So I would think that TOM1 is in a
> worse 
> situation for reflected light.
> 
> These rings have persisted for several different lenses and several
> cameras.
> 
> The bright star rings thus remain a mystery for TOM2.
> 
> I spent some time moving TOM2 around to get it aligned to north.  The
> way I 
> do it is to use "follow" fields and measure star movement on
> successive 
> fields.  I can then rotate the dome platform for N-S drift and adjust
> the 
> RA DAC for E-W drift.  They do not affect each other very much.
> 
> TOM1 continues to take pretty good looking data (to me).  I collected
> 56 
> images in V and I each for five different fields last night.  Unusual
> 
> weather for December when the moon is dark, but I am enjoying it and 
> getting a lot of images on disk.   As I recall, last year I never got
> a run 
> that was even close to the longest night of the year.  This year I
> have 
> several.
> 
> Tom Droege
> 
> 
> 


=====
Chris Albertson 
  Home:   310-376-1029  chrisalbertson90278@yahoo.com
  Cell:   310-990-7550
  Office: 310-336-5189  Christopher.J.Albertson@aero.org

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