[M]: re: 201XT question
| Subject: | [M]: re: 201XT question |
| From: | Guido Pasi |
| Date: | Mon Jun 05 13:03:39 2000 |
At 05.16 05/06/00 -0400, Alan wrote:
>Ive noticed when centering a guide star in the reticle eyepiece prior to
>autoguider insertion, stars that appear to be the same brightness are
>perceived to be quite different by the 201. Ive had stars I thought would
>need only a 1 or 2 second exposure by the 201 end up with 6,8 or 10 second
>exposure. Then Ive had what I thought was a star of equal brightness, end
>up using 1 or 2 second exposures when it should have been 6 or 8 seconds. It
>doesnt make sense. Can anyone shed any light on this subject?
I too have noticed that thing and I have made two hypothesis.
Excuse my terrible English, I hope I will explain my ideas in a
understandable way!
I presume your focus is good.
1) dont rely on what you see, check the real brightness with a catalog.
Take care that star catalogues show a lot of differences, in particular for
stars about mag.8-10. I have the SAO and the GSC and they never agree! In
some occasions the difference is remarkable, more than one mag. and this
means that someone is wrong. On the whole the GSC seems to be more
reliable, but check every time the star you chose, by any catalog you can!
2) the TC255 chip of the camera has not the same efficiecy for every
wavelength: this means that different stars, with different spectrum might
expose the CCD in a different measure.
Certainly someone here in Mapug could explain this in a more precise way.
Hi all
Guido Pasi
Genova - Italy
>Ive noticed when centering a guide star in the reticle eyepiece prior to
>autoguider insertion, stars that appear to be the same brightness are
>perceived to be quite different by the 201. Ive had stars I thought would
>need only a 1 or 2 second exposure by the 201 end up with 6,8 or 10 second
>exposure. Then Ive had what I thought was a star of equal brightness, end
>up using 1 or 2 second exposures when it should have been 6 or 8 seconds. It
>doesnt make sense. Can anyone shed any light on this subject?
I too have noticed that thing and I have made two hypothesis.
Excuse my terrible English, I hope I will explain my ideas in a
understandable way!
I presume your focus is good.
1) dont rely on what you see, check the real brightness with a catalog.
Take care that star catalogues show a lot of differences, in particular for
stars about mag.8-10. I have the SAO and the GSC and they never agree! In
some occasions the difference is remarkable, more than one mag. and this
means that someone is wrong. On the whole the GSC seems to be more
reliable, but check every time the star you chose, by any catalog you can!
2) the TC255 chip of the camera has not the same efficiecy for every
wavelength: this means that different stars, with different spectrum might
expose the CCD in a different measure.
Certainly someone here in Mapug could explain this in a more precise way.
Hi all
Guido Pasi
Genova - Italy
