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Re: [Losmandy_users] Re: PEC & Backlash


Oct 14, 2005

 


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#27429 Oct 14, 2005

I have a used GM8 (non-Gemini). I know there's supposed to be ways to

measure and reduce P.E. and Backlash, but don't know how. Would

appreciate whatever direction anyone could provide. In case it matters,

I'm using the mount with a SV102 refractor and an old ST8, and using

CCDSoft for camera control software.

Thanks,

JDBraddy



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#27510 Oct 20, 2005

Well, guess I was mistaken, it's been a week since I posted this

question, and haven't gotten a single reply from anyone. I figured some

of you astrophotography guy's would point me toward a tutorial or

someting. Oh well, hope you have better luck with your question Tom!

JDBraddy



--- In Losmandy_users@yahoogroups.com, "James Braddy" JDBraddy@s...>

wrote: >

> I have a used GM8 (non-Gemini). I know there's supposed to be ways to

> measure and reduce P.E. and Backlash, but don't know how. Would

> appreciate whatever direction anyone could provide. In case it

matters, > I'm using the mount with a SV102 refractor and an old ST8, and using

> CCDSoft for camera control software.

> Thanks,

> JDBraddy

>



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#27511 Oct 20, 2005

I use a G11/Gemini for astrophotography with an ST2000XM CCD (self

guiding). I'm assuming you are self-guiding with the ST8? I don't use

PEC or the the DEC backlash feature. Rather I slightly overweight the

scope on the East side of the RA and and introduce a "delay after

correction" in CCDSoft. The slight overweighting helps tracking a great

deal by "climbing up" the gear instead of falling down on the other

side. This can be accomplished by moving the counterweights down the

shaft a bit, or up, depending on which side of the meridian you're on at

the time. The overweighting also effectively reduces all backlash in RA.

You can test your overweighting by making small RA corrections with the

hand controller while viewing at high power and see the affect before

and after adjusting the weight positions. You'll see the difference and

get a feeling for the right amount of counterweight movement. I think

many mounts are the same way (for example, I've heard of people using

this technique on even the AP900 and AP1200 mounts).



The delay after correction in CCDSoft lets the scope settle out after

each correction, finishing it's movement and damping out any vibration,

before starting imaging for the next guide exposure and correcting

again. This eliminated an oscillation in guiding that affecting my

images. I use a delay of 1-3 seconds, depending on what works best on

that night.



I experimented with PEC and TVC (DEC backlash correction) on the

G11/Gemini but found them unnecessary. I did find that careful

adjustment of the worm spacing for both axis and proper lubrication of

the bearings made a tremendous difference and that these adjustments

were essential for good tracking and guiding.



Are you experiencing any specific problems with tracking, like losing

the guide star suddenly or "jumps" reflected in double (or more) star

images or shadows? Let me know...I've worked through many of these as

well.



Clear Skies-



Craig

On Thu, 2005-10-20 at 08:43 +0000, James Braddy wrote:

> Well, guess I was mistaken, it's been a week since I posted this

> question, and haven't gotten a single reply from anyone. I figured some

> of you astrophotography guy's would point me toward a tutorial or

> someting. Oh well, hope you have better luck with your question Tom!

> JDBraddy

>

> --- In Losmandy_users@yahoogroups.com, "James Braddy" JDBraddy@s...>

> wrote:

> >

> > I have a used GM8 (non-Gemini). I know there's supposed to be ways to

> > measure and reduce P.E. and Backlash, but don't know how. Would

> > appreciate whatever direction anyone could provide. In case it

> matters,

> > I'm using the mount with a SV102 refractor and an old ST8, and using

> > CCDSoft for camera control software.

> > Thanks,

> > JDBraddy

> >

>

>

>

>

>

>

>

>

> Yahoo! Groups Links

>

>

>

>

>

>

>

>



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