Q:
Auto Aperture gives inconsistent result.
For Btarg1 the old HOU program auto aperture would get 131801
value pretty consistently. With the new program the values are
all over tha place and none are close to what we get with the
old one. Maybe I did something wrong but if you can't get some
consistency in the readings it makes the lab useless. Have you
any ideas as to what I'm doing or did I miss something here? |
A:
There is a problem with "auto aperture" [with
HOU IP 2.0 release Aug 2008].
It often does not use a star radius and sky radius that
is large enough, especially for a bright star like in Btarg1.
I suggest you stick with "aperture" and set
the star radius and sky radius manually.
You can tell instantly if you're in the right ballpark
by the red circle that gets drawn on the image. It's
got to fully contain the star and then some. I find that
a nominal value of 10 star radius and 20 sky radius will
give good results most of the time, if star field is
not too dense with stars.
As an interesting exercise, to see the effect of star/sky
radius in the "Aperture" function, try doing
a series of increasing values, e.g. (3,8); (5,10); (8,16);
(10,20); (20,30) on the same star. The good news is that
it will give result immediately for each new pair of
values entered. The counts result for each will increase
for each one, but the successive deviation decreases
once you get to a large enough threshold to fully enclose
the star. |
