Re: [MaxImDL] Question about DEC compensation


Apr 29, 2010

 


----------------------------

#40957 Apr 29, 2010

Hi,



I'm sorry if this may have been covered before, but searching the archives didn't seem to answer it.



I've been reading Jim McMillan's treatise on autoguiding, in particular the section on DEC compensation. He says that, in his opinion, it is unnecessary and may cause the autoguider to chase the seeing to the detriment of the guiding. I would like to know if: 1: Anyone can bear this out, and 2: Using MaximDL 5, how do you turn off DEC compensation if I'm attaching to my mount and the DEC box is greyed out?



Thanks,



-Jim



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#40958 Apr 29, 2010

I guide with several different setups, and in each case the guiding is poor

(sometimes, extremely poor) if I don't use declination compensation. There

may be special cases where you don't need it, but my experience is that it's

essential.



That is also consistent with all the analytical work I've done with respect

to guiding theory. Guiding is pretty crude: the only control signal normally

available is a timed correction at a fixed rate. While the guider is a

feedback controlled system, it isn't very stable. That's why the control

loop gain (which just defines the relationship between correction time and

the correction angle) needs to be fairly accurately established. You can do

that by calibrating for each declination, or by calibrating once and then

correcting for declination. Those approaches produce identical results. But

operating at a different declination than you calibrated to, without

compensation, just means you are operating uncalibrated. It means your loop

gain is in error, and you are prone to severe under- or overcorrection.



Chris



*****************************************

Chris L Peterson

Cloudbait Observatory

www.cloudbait.com



----- Original Message -----

From: "Jim McKay" astroguy67@...>

To: MaxImDL@yahoogroups.com>

Sent: Thursday, April 29, 2010 12:13 PM

Subject: [MaxImDL] Question about DEC compensation





> Hi,

>

> I'm sorry if this may have been covered before, but searching the archives

> didn't seem to answer it.

>

> I've been reading Jim McMillan's treatise on autoguiding, in particular

> the section on DEC compensation. He says that, in his opinion, it is

> unnecessary and may cause the autoguider to chase the seeing to the

> detriment of the guiding. I would like to know if: 1: Anyone can bear

> this out, and 2: Using MaximDL 5, how do you turn off DEC compensation if

> I'm attaching to my mount and the DEC box is greyed out?

>

> Thanks,

>

> -Jim



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