Re: TASS - PSFs

[Michael Gutzwiller <deepsky@fuse.net>]

droege@wwa.com wrote:
> 
> I have been focusing and adjusting the VCO.  The best I can do is:
>   Camera                      PSF
> V  (Camera O)                 3X9
> R  (Camera 1)                 5x7
> I  (Camera 2)                 7x7
> 
> The PSF seems to stretch out much more than can be explained by the
> VCO setting.  I can get numbers like 3x5 for V with the optimum VCO
> setting for V, but then the R and I numbers get much worse.  I assume
> that the minimum area for all three is what I want to work for??  What
> say Mike?

Minimal area is correct.  The smaller the area of the PSF the better the
separation from other stars and the better the statistics.
> 
> The PSF above is what comes out of Star in the star list.
> 
> How do these numbers compare with what the rest of you are seeing?
>

They arre comparable.  I have had great difficulty getting the I
filtered PSFs to be smaller than 7x7 though I usually can get V to 5x5
at the same time.  I don't seem to be seeing as much disparity in focal
length between the two as you are getting.
 
> It seems to me that I could attempt to improve the focal length for V by
> adding some glass.  This would add two surfaces with the resultant light
> loss.  It would also require a lot of fussing.  I figure it is not worth
> it.
> 
> BTW, now that I have three cameras all looking at the same spot, I can
> compare stars found.  It is roughly what I would expect.  The I camera
> finds more stars.  The I filter has roughly twice the bandwidth of the
> V and R.  But it also sees more background light.  This is a tough game.
> With the sky background limit, twice the light only gets you Sqrt(2)
> more S/N.  This holds true for larger diameter lenses.  S/N goes up
> with the diameter, so it is just not worth the effort to go to more
> expensive lenses.
> 
> Tom Droege