Re: It's The Optics Stupid!

["Robert Creager" <robert_creager@logicalchaos.org>]

This might be an easy question for someone in the know.

Any reason the exposures could not be different for the two camera's, by using the shutters at different times?  It wouldn't be to difficult to have both exposures centered at the same time in the software.  This could blur some variablility, but I wouldn't think too much.

What might be the pro's/con's of each method?

Thanks,
Rob

Tom Droege <tdroege2@earthlink.net> wrote ..
> It has been a struggle, but I have finally found something that changes
> (improves) the error.
> 
> Yesterday I had Dan make aperture masks for the I lenses.  These have a
> center hole of 3 inch diameter, so it cuts out nearly half the light. 
> I 
> did this because the I cameras see many more stars than the V cameras,
> so 
> the sensitivity is wasted when we require V and I detections.  If the 
> exposure is increased, then the I stars are lost due to saturation.
> 
> This mask pretty well balances the two cameras.  The I camera still sees
> a 
> little more sky.
> 
> I then made a run with 200 second exposures instead of the usual 100 
> seconds.  This required a little work to get the RA drive timed right,
> but 
> now the largest error is due to TOM1 misalignment.  This is not easy to
> fix 
> with the coo coo clock mount.
> 
> A run was made (in spite of all that moonlight) where the telescope is
> returned to home after each exposure.  With the longer exposure, the 
> brighter stars appeared on four frames.
> 
> In the past, the V camera has always had significantly less spread in 
> errors than the I camera.  See for example, Figure 3 and 4 from TN-88.
> 
>  From this short run, the I data has less spread than the V data, and is
> about half the value of similar runs taken earlier this month.
> 
> Is this a scatter problem???  The flat field should correct for optical
> gain unless light from a point source produces a different flat than one
> from a diffuse source.  Optical experts might comment.  Is this a standard
> problem?  Is there a standard solution?
> 
> I do remember that Arne Henden wanted to cut down the aperture.
> 
> Tom Droege