Re: Stopping down the I-band camera

["Tom Droege" <droege@snapmail.us>]

Michael and all,

Thank you for the suggestions. I am presently fussing with the apertures. 
Michael, on a "good" night I get a fwhm number (near the end in
make_list.out) of 3.5 for V and 4.0 for I +/- 0.1.  Given these numbers,
where should I set the aperture?  General rule? Where should the aperture
be set in relation to the observed fwhm?

My current problem is getting some "good" nights.  At the moment all data
has had a very high sky brightness.  I seem to recall that that is typical
of this time of year here.  When we go out at night to see meteors all we
see is skuz even though the weather forcast is "clear".  Can anyone
comment on this?

Tom Droege

>
>> 6) Stop down the I telescopes.
>>
>> I have not settled this for sure yet.  The I cameras see about twice the
>> sky background as the V cameras.  Stopping down to a 3 inch aperture
>> makes
>> the sky background about equal.  I have tried this and the I focus is
>> clearly better.  Possibly I will cut masks at 3.5" and compromise.  Get
>> a
>> little better focus and a reduced sky background.  Still testing.
>
>   It would be interesting to take and compare two datasets on
> two different nights:
>
>       a) aperture wide open -- look at several tiles repeatedly.
>               Reduce the data with the standard synthetic aperture
>               size in the pipeline.
>
>       b) aperture stopped down -- look at the SAME tiles repeatedly.
>               Reduce the data with a smaller synthetic aperture
>               size in the pipeline.
>
>   If the focus is improved by stopping down the aperture, it may
> be possibly to dig down almost as far into the noise in both
> sets of exposures.  Using a smaller synthetic aperture in the
> measuring procedure will include a smaller amount of sky background,
> and the sky background will be smaller, too.
>
>   So, Tom, if you were to look at the same regions of the sky
> on two nights, then compare the "sigma-versus-mag" plot
> for each night, you might have a quantitative basis for
> making the decision to go with or without an aperture mask.
>
>                                 Michael
>
>
>