Re: [APML]: Re: 201xt

["David B. Toth" <ve3gyq@amsat.org>]

At 01:16 PM 9/26/96 -0400, Gary Holland wrote:
>
>Since we were discussing the 201xt vs st4 (for guiding) and the differences
>I decided to email John Hoot and ask him how important that the guider be
>cooled.
>
>Below is his reply.
>

< deleted stuff >


Gary: I really don't buy all of this. 
Cooling the chip WILL allow you to get down to fainter stars. I wouldn't
agree with his assumptions as to what are the significant contributors to
the noise in the guider mode.

He thinks you can take 20 second exposures to guide with. That is NONSENSE.
The best guiding occurs with 1 sec. or less exposures ... I think Brad
Wallis and Benoit Schillings showed this in graphic detail at the SBIG
conference. If you believe you can get by with 20 sec. exposures, then go
for the cheaper guider. But why do you think it is easier to find guide
stars with the ST7 than the ST4? It is because :
1) the guider chip in the ST7 is regulated as opposed to the same chip in
the ST4;
2) it is a 14 bit setup with greated dynamic range and lower noise


Dave