Re: Stopping down the I-band camera

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

Thank you Michael,

>   If you have a good set of data from one nice night, you might
> run the pipeline two or three times from the "stars" step onwards,
> changing the aperture size each time and seeing which value gives
> the best sigma-versus-mag plot.

This is sort of what I have been doing.  Just looking for guidance.  Sigh!
 At this stage multiple things are going wrong and the sky is not so good
so it is hard to sort things out.

I have problems like the same code (I think) works on one computer but
quit working on another after running several days.  Just the normal start
up problems with new things everywhere.

I am very optimistic about the coming season.  I don't really get a lot of
good data until August or so.  So there is time to debug everything.

This season I want to set up good procedures everywhere so the data is as
consistent as it can be.

Tom Droege



>
>   Tom wrote:
>
>> 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?
>
>   Advantage of using large aperture: you get a more equal fraction
> of the stellar light from stars all over the field if the PSF changes
> shape or size from corner to corner.  Advantage of using a small
> aperture: you add less background noise to the stellar signal.
>
>   A decent general rule for relative photometry on a single
> frame is to use an aperture radius of about 1-3 FWHM.  So,
> given the numbers Tom quotes above, I'd say that an aperture
> radius of around 4-7 pixels would be fine.
>
>   If you have a good set of data from one nice night, you might
> run the pipeline two or three times from the "stars" step onwards,
> changing the aperture size each time and seeing which value gives
> the best sigma-versus-mag plot.
>
>                                      Michael
>
>
>