Re: [APML] Beep on ST4

[Matt BenDaniel <matt@starmatt.com>]

At 12:20 PM 6/20/2002, Gene Horr wrote:
>> Massimo Costa wrote:
>
>> from ST4 manuals I read that a beep during tracking means that the guide star drops in
>> luminosity half value. Have I to consider it a fatal error?
>
>Well, generally yes.  9 times out of 10 (guesstimate) something bad is happening
>that will ruin the shot anyway (it is clouding up, optics are dewing, dessicant
>has gone bad, it is flipping between guide stars, etc).
>
>Occassionally you do get cases where the initial exposure was at a moment of
>great seeing and the energy was focused on one/fewer pixels.  But in my 
>experience this is rarely the case.
>
>I just always restart in this case.

Gene,

Restarting the ST-4 tracking during an exposure can create a problem if you don't do it exactly right. The guide star may jump to another position on the ST-4 chip. That can lead to oval stars.

The way to do it is to hold the MODE button down when you restart tracking (which AFAIK is an undocumented feature). This tells the ST-4 to replace the guide star exactly back where it started. But you have to do just right. I think you release the MODE button once you see the little red dot on the LED display. It's so tricky that I'm reluctant to do it, even though I've done it successfully on several occasions.

--
Matt BenDaniel
matt@starmatt.com
http://starmatt.com


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