VintageBigBlue.org

 

Periodic error on a G11


Dec 2, 2002

 


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

#12981 Dec 2, 2002

Hello,



I have been doing CCD imaging with my Losmandy G11 and an

SBIG ST2000XM camera. After much work with backlash adjustments, tuning

the TVC, and debugging, repairing and installing an SBIG relay box,

I can finally say that I can actually guide my C11 on a star with decent

results. Now, I discover that my star images are still elliptical,

rather than round. I am guessing that this is due to periodic error

from the G11 worm gear. Am I correct in this assumption? Do any of you

have experience with programming the PEC correction on the G11 stepper

motor drive? Do you have to reprogram this every night you go out?



Thanks in advance,



Laurel O. Sillerud





[Non-text portions of this message have been removed]



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

#12982 Dec 2, 2002

Laurel,



A little more info is needed. It sounds like you're using the standard Losmandy drive (non-Gemini version)? If so, as I recall, PEC has to be retrained each time you start up. (The Gemini retains PEC data in memory.)



Also, do you have the newer worm on the mount? My experience with the old worm (from a 1997 vintage G-11) was that it had sharply abrupt periodic error which was difficult (if next to impossible) to guide out. The new worm still has periodic error (just about all mounts that don't require taking out a second mortgage do.) It's just that the 'error' is a lot smoother and the SBIG self guider can correct it out easily, even without PEC.



Also, what focal length are you attempting to image at? If you're attempting to image at f/10, you'll be pushing the limits of the G-11, and may never be successful. The only decent results I'd ever had with my old SCT were when I used the .33 focal reducer (Optec.)



Finally determine if it really is periodic error, and not SCT collimation problems. I've tried using my 10" Meade SCT for imaging and kept getting elongated images despite adding the new worm, Gemini, etc. I tried shooting a ten second test shot, and found I was getting the same elongation. Turns out it was the OTA, not the mount. There are some inherent problems with imaging with an SCT that the manufacturers would just as soon you not know about g>.



Jim Girard ----- Original Message -----

From: Laurel O. Sillerud

Subject: [Losmandy_users] Periodic error on a G11?





I have been doing CCD imaging with my Losmandy G11 and an

SBIG ST2000XM camera. After much work with backlash adjustments, tuning

the TVC, and debugging, repairing and installing an SBIG relay box,

I can finally say that I can actually guide my C11 on a star with decent

results. Now, I discover that my star images are still elliptical,

rather than round. I am guessing that this is due to periodic error

from the G11 worm gear. Am I correct in this assumption? Do any of you

have experience with programming the PEC correction on the G11 stepper

motor drive? Do you have to reprogram this every night you go out?





[Non-text portions of this message have been removed]



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

#12985 Dec 2, 2002

Laurel;



Check your documentation. A lot of people forget some PEC's only allow a certain number of corrections in one training session or cycle of the worm (4mins?). If you 'over' train the PEC by making to many corrections in the training period you over write the beginning corrections making the whole training session usless. Limit yourself to less than the number of corrections allowed and see if that helps...joe :)





"May You Go Among The Imperishable Stars"



Joe Mize :)

www.svic.net/jmize

Moon Phase:

tycho.usno.navy.mil/cgi-bin/phase.gif ----- Original Message -----

From: Laurel O. Sillerud

To: Losmandy_users@yahoogroups.com

Sent: Monday, December 02, 2002 12:40 PM

Subject: [Losmandy_users] Periodic error on a G11?





Hello,



I have been doing CCD imaging with my Losmandy G11 and an

SBIG ST2000XM camera. After much work with backlash adjustments, tuning

the TVC, and debugging, repairing and installing an SBIG relay box,

I can finally say that I can actually guide my C11 on a star with decent

results. Now, I discover that my star images are still elliptical,

rather than round. I am guessing that this is due to periodic error

from the G11 worm gear. Am I correct in this assumption? Do any of you

have experience with programming the PEC correction on the G11 stepper

motor drive? Do you have to reprogram this every night you go out?



Thanks in advance,



Laurel O. Sillerud





[Non-text portions of this message have been removed]





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[Non-text portions of this message have been removed]



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

#12986 Dec 2, 2002

Laurel:

As Jim stated there are problems inherant in STC's. Besides Coma out not to far from center, (corrected with a field flattener), there is mirror shift, and on some models big time. I have an 8" Celestron that is very bad. Except for the 16' Meade, non of the SCT's that I am aware of have a mirror lockdown feature. It is possible to rework your scope to add a locking device, but I am not the one to tell you how to do it. You may try some testing to see if it is Mirror shift (and all SCT.s have it), and check Doc G's info site ( www.mailbag.com/users/ragreiner ) for posssible further help on the subject.

Harry L. Juday



---- Original Message -----

From: Jim Girard

To: Losmandy_users@yahoogroups.com

Sent: Monday, December 02, 2002 1:15 PM

Subject: Re: [Losmandy_users] Periodic error on a G11?





Laurel,



A little more info is needed. It sounds like you're using the standard Losmandy drive (non-Gemini version)? If so, as I recall, PEC has to be retrained each time you start up. (The Gemini retains PEC data in memory.)



Also, do you have the newer worm on the mount? My experience with the old worm (from a 1997 vintage G-11) was that it had sharply abrupt periodic error which was difficult (if next to impossible) to guide out. The new worm still has periodic error (just about all mounts that don't require taking out a second mortgage do.) It's just that the 'error' is a lot smoother and the SBIG self guider can correct it out easily, even without PEC.



Also, what focal length are you attempting to image at? If you're attempting to image at f/10, you'll be pushing the limits of the G-11, and may never be successful. The only decent results I'd ever had with my old SCT were when I used the .33 focal reducer (Optec.)



Finally determine if it really is periodic error, and not SCT collimation problems. I've tried using my 10" Meade SCT for imaging and kept getting elongated images despite adding the new worm, Gemini, etc. I tried shooting a ten second test shot, and found I was getting the same elongation. Turns out it was the OTA, not the mount. There are some inherent problems with imaging with an SCT that the manufacturers would just as soon you not know about g>.



Jim Girard ----- Original Message -----

From: Laurel O. Sillerud

Subject: [Losmandy_users] Periodic error on a G11?





I have been doing CCD imaging with my Losmandy G11 and an

SBIG ST2000XM camera. After much work with backlash adjustments, tuning

the TVC, and debugging, repairing and installing an SBIG relay box,

I can finally say that I can actually guide my C11 on a star with decent

results. Now, I discover that my star images are still elliptical,

rather than round. I am guessing that this is due to periodic error

from the G11 worm gear. Am I correct in this assumption? Do any of you

have experience with programming the PEC correction on the G11 stepper

motor drive? Do you have to reprogram this every night you go out?





[Non-text portions of this message have been removed]





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ADVERTISEMENT









To unsubscribe from this group, send an email to:

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[Non-text portions of this message have been removed]







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

#12988 Dec 2, 2002

hard to say, are the stars elongated in the RA direction?.. if so then you

do have some sort of tracking or guiding error. If the elongations is in

some random direction (other than east-west direction) then you are most

likely suffering from flexure. Compare several trailed images from

different directions in the sky to be sure you did not get flexure in the

East-West direction by pure bad luck.



Could also be STV setting problems, adjust the agressivity setting on your

STV. Contact other users with your setup and compare notes on STV settings

to use.



Most people do not use PEC with an autoguider.. how are you guiding?,

guidescope or off-axis guider?..



"Laurel O. Sillerud" laurel@...> wrote:

> Now, I discover that my star images are still elliptical,

>rather than round. I am guessing that this is due to periodic error

>from the G11 worm gear. Am I correct in this assumption?



Herm

Astropics home.att.net/~hermperez



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

#12989 Dec 2, 2002

Laurel,



What software are you using with your camera?



This is really important, since the stepper drive system you have

cannot react to simultaneous corrections in the X and Y axis at the

same time. If simultaneous corrections are sent, they are simply

ignored by the mount.



If you are using CCDSoft make sure you have the latest update

available from Bisque installed. In it there is an option to send

correction commands sequentially rather than simultaneously.



Other software like CCDOps works fine with the stepper.



This plauged me for months a year or so ago until I finally figured

out what it was with a little help from my friends here of course :)



Regards,

--- In Losmandy_users@y..., "Laurel O. Sillerud" laurel@u...> wrote:

> Hello,

>

> I have been doing CCD imaging with my Losmandy G11 and an

> SBIG ST2000XM camera. After much work with backlash adjustments,

tuning

> the TVC, and debugging, repairing and installing an SBIG relay box,

> I can finally say that I can actually guide my C11 on a star with

decent

> results. Now, I discover that my star images are still elliptical,

> rather than round. I am guessing that this is due to periodic error

> from the G11 worm gear. Am I correct in this assumption? Do any

of you

> have experience with programming the PEC correction on the G11

stepper

> motor drive? Do you have to reprogram this every night you go out?

>

> Thanks in advance,

>

> Laurel O. Sillerud

>

>

> [Non-text portions of this message have been removed]



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

#12996 Dec 3, 2002

I think that all of the new Meade GPS models have mirror locks.

Not that I recommend them, but this capability has been added.



Mark ----- Original Message -----

From: Harry L. Juday

To: Losmandy_users@yahoogroups.com

Sent: Monday, December 02, 2002 2:10 PM

Subject: Re: [Losmandy_users] Periodic error on a G11?





Laurel:

As Jim stated there are problems inherant in STC's. Besides Coma out not to far from center, (corrected with a field flattener), there is mirror shift, and on some models big time. I have an 8" Celestron that is very bad. Except for the 16' Meade, non of the SCT's that I am aware of have a mirror lockdown feature. It is possible to rework your scope to add a locking device, but I am not the one to tell you how to do it. You may try some testing to see if it is Mirror shift (and all SCT.s have it), and check Doc G's info site ( www.mailbag.com/users/ragreiner ) for posssible further help on the subject.

Harry L. Juday



---- Original Message -----

From: Jim Girard

To: Losmandy_users@yahoogroups.com

Sent: Monday, December 02, 2002 1:15 PM

Subject: Re: [Losmandy_users] Periodic error on a G11?





Laurel,



A little more info is needed. It sounds like you're using the standard Losmandy drive (non-Gemini version)? If so, as I recall, PEC has to be retrained each time you start up. (The Gemini retains PEC data in memory.)



Also, do you have the newer worm on the mount? My experience with the old worm (from a 1997 vintage G-11) was that it had sharply abrupt periodic error which was difficult (if next to impossible) to guide out. The new worm still has periodic error (just about all mounts that don't require taking out a second mortgage do.) It's just that the 'error' is a lot smoother and the SBIG self guider can correct it out easily, even without PEC.



Also, what focal length are you attempting to image at? If you're attempting to image at f/10, you'll be pushing the limits of the G-11, and may never be successful. The only decent results I'd ever had with my old SCT were when I used the .33 focal reducer (Optec.)



Finally determine if it really is periodic error, and not SCT collimation problems. I've tried using my 10" Meade SCT for imaging and kept getting elongated images despite adding the new worm, Gemini, etc. I tried shooting a ten second test shot, and found I was getting the same elongation. Turns out it was the OTA, not the mount. There are some inherent problems with imaging with an SCT that the manufacturers would just as soon you not know about g>.



Jim Girard

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

From: Laurel O. Sillerud

Subject: [Losmandy_users] Periodic error on a G11?





I have been doing CCD imaging with my Losmandy G11 and an

SBIG ST2000XM camera. After much work with backlash adjustments, tuning

the TVC, and debugging, repairing and installing an SBIG relay box,

I can finally say that I can actually guide my C11 on a star with decent

results. Now, I discover that my star images are still elliptical,

rather than round. I am guessing that this is due to periodic error

from the G11 worm gear. Am I correct in this assumption? Do any of you

have experience with programming the PEC correction on the G11 stepper

motor drive? Do you have to reprogram this every night you go out?





[Non-text portions of this message have been removed]





Yahoo! Groups Sponsor

ADVERTISEMENT









To unsubscribe from this group, send an email to:

Losmandy_users-unsubscribe@egroups.com







Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.





[Non-text portions of this message have been removed]





Yahoo! Groups Sponsor

ADVERTISEMENT









To unsubscribe from this group, send an email to:

Losmandy_users-unsubscribe@egroups.com







Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.







[Non-text portions of this message have been removed]







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

#40444 Nov 2, 2008

I posted the negative scans in the photos section in Dr G.s Losmandy

images. (Also put a photo of "my telescope stuff" I hate to say it but

I have accumulated several more scopes and mounts since!) Will get

around to doing a Pempro run eventually. Charles



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