VintageBigBlue.org

 

Re: Please Help : G11 not holding polar alignment


May 10, 2005

 


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

#25429 May 10, 2005

My new NON- GOTO G11 (March of 2005) does not seem to be holding its

polar alignment.



I do a drift alignment of 5 minutes or more. I move the scope around

to point at something like m101 and then come back and check the

alignment. Usually it will drift about 10 arc seconds in about 5

minutes in altitude or azimuth.



. The tripod is on asphalt.

. The lock bolts for altitude and azimuth have been replaced with

hex bolts so I can use a wrench.

. The clutches are tight and left at the same tension.

. 8 inch Newtonian + guide scope + camera = 30 lbs.



There was about .005 of play in the RA and DEC axis, so I added a 3rd

shaft bearing to both. The RA now has .0025 and the DEC still

has .005. (I think this may have helped some.)



What prompted this investigation were two 1-hour exposures of m81 and

m82 that had horrendous rotation. I was making a lot of DEC

corrections, but it was a new mount and I just wasn't sure.



I do not think the altitude or azimuth or the tripod are moving.



Is this normal?



Any help would be deeply appreciated. I have been playing with

telescopes and taking pictures for only a year and a half, so my

education is bound to have some holes in it.



Thanks,

Will Sater



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

#25430 May 10, 2005

Hi Will,



That doesn't sound normal, but there are some normal reasons why

this might happen. My G11 holds polar alignment for about a month,

but it is mounted on a permanent pier. I expect that in my case the

primary cause is shifting of earth and thermal expansion/contraction

around the pier.



Sounds like you've taken care of most mount-related slippage that

can occur, but flexing can happen in the telescope itself and in its

mounting and support. It can also happen in the focuser, camera

mount, or in the spider/secondary support. All of these can easily

masquerade as a drift, even if you are perfectly polar aligned.

Sometimes, this can be very difficult to diagnose, but you can go a

long way by tightening everything down, locking focusers, and using

screw-in adapters as much as possible.



Secondly, tightening El & Az axis after polar alignment almost

inevitably moves them, altering the alignment. For this reason, I

always keep the axis locking bolts tightened very snug, and adjust

the axis without loosening them.



Regards,



-Paul







--- In Losmandy_users@yahoogroups.com, "Will Sater" wsater@c...>

wrote: > My new NON- GOTO G11 (March of 2005) does not seem to be holding

its > polar alignment.

>

> I do a drift alignment of 5 minutes or more. I move the scope

around > to point at something like m101 and then come back and check the

> alignment. Usually it will drift about 10 arc seconds in about 5

> minutes in altitude or azimuth.

>

> . The tripod is on asphalt.

> . The lock bolts for altitude and azimuth have been replaced with

> hex bolts so I can use a wrench.

> . The clutches are tight and left at the same tension.

> . 8 inch Newtonian + guide scope + camera = 30 lbs.

>

> There was about .005 of play in the RA and DEC axis, so I added a

3rd > shaft bearing to both. The RA now has .0025 and the DEC still

> has .005. (I think this may have helped some.)

>

> What prompted this investigation were two 1-hour exposures of m81

and > m82 that had horrendous rotation. I was making a lot of DEC

> corrections, but it was a new mount and I just wasn't sure.

>

> I do not think the altitude or azimuth or the tripod are moving.

>

> Is this normal?

>

> Any help would be deeply appreciated. I have been playing with

> telescopes and taking pictures for only a year and a half, so my

> education is bound to have some holes in it.

>

> Thanks,

> Will Sater



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

#25431 May 10, 2005

Hi Paul,



You are right about the flexure. I did notice that it took as much as

2 or 3 minutes for everything to settle and then the DEC movement

seemed to stop. I thought I had found the problem. This is probably

most of it.



When I realized this I tried again and this time it took about 20

minutes for it to move about 15 arc seconds and was still moving.



I read somewhere that this equates to about 2.5 arc minutes off polar

alignment which is not quite as good as I was hoping for.



Heck, is it possible the setup is still flexing after 20 minutes?



Also, you said

> Secondly, tightening El & Az axis after polar alignment almost

> inevitably moves them, altering the alignment. For this reason, I

> always keep the axis locking bolts tightened very snug, and adjust

> the axis without loosening them.



I always tighten the bolts before I check the drift.

I have tried making adjustments with the bolts tight and with them

loose and it's much easier the way you do it. Good to know this is

the way to go.



Thanks for help,



Will







--- In Losmandy_users@yahoogroups.com, "Paul K" pkane2001@h...>

wrote: > Hi Will,

>

> That doesn't sound normal, but there are some normal reasons why

> this might happen. My G11 holds polar alignment for about a month,

> but it is mounted on a permanent pier. I expect that in my case the

> primary cause is shifting of earth and thermal

expansion/contraction > around the pier.

>

> Sounds like you've taken care of most mount-related slippage that

> can occur, but flexing can happen in the telescope itself and in

its > mounting and support. It can also happen in the focuser, camera

> mount, or in the spider/secondary support. All of these can easily

> masquerade as a drift, even if you are perfectly polar aligned.

> Sometimes, this can be very difficult to diagnose, but you can go a

> long way by tightening everything down, locking focusers, and using

> screw-in adapters as much as possible.

>

> Secondly, tightening El & Az axis after polar alignment almost

> inevitably moves them, altering the alignment. For this reason, I

> always keep the axis locking bolts tightened very snug, and adjust

> the axis without loosening them.

>

> Regards,

>

> -Paul

>

>

>

> --- In Losmandy_users@yahoogroups.com, "Will Sater" wsater@c...>

> wrote:

> > My new NON- GOTO G11 (March of 2005) does not seem to be holding

> its

> > polar alignment.

> >

> > I do a drift alignment of 5 minutes or more. I move the scope

> around

> > to point at something like m101 and then come back and check the

> > alignment. Usually it will drift about 10 arc seconds in about 5

> > minutes in altitude or azimuth.

> >

> > . The tripod is on asphalt.

> > . The lock bolts for altitude and azimuth have been replaced

with > > hex bolts so I can use a wrench.

> > . The clutches are tight and left at the same tension.

> > . 8 inch Newtonian + guide scope + camera = 30 lbs.

> >

> > There was about .005 of play in the RA and DEC axis, so I added a

> 3rd

> > shaft bearing to both. The RA now has .0025 and the DEC still

> > has .005. (I think this may have helped some.)

> >

> > What prompted this investigation were two 1-hour exposures of m81

> and

> > m82 that had horrendous rotation. I was making a lot of DEC

> > corrections, but it was a new mount and I just wasn't sure.

> >

> > I do not think the altitude or azimuth or the tripod are moving.

> >

> > Is this normal?

> >

> > Any help would be deeply appreciated. I have been playing with

> > telescopes and taking pictures for only a year and a half, so my

> > education is bound to have some holes in it.

> >

> > Thanks,

> > Will Sater







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

#25432 May 11, 2005

Will;



With the mount tracking an object the optical tube with attached

camera is continuously changing it's orientation so any flexure in

the system could be ongoing, no settling down. What is your tube

material and the make of the telescope. I have heard of scope tube

flexing and differential flexing between the tube and guide scope.

I have even heard of flimsy tube rings causing problems due to

flex. No fun to try and track down.



Rich Wood





--- In Losmandy_users@yahoogroups.com, "Will Sater" wsater@c...>

wrote: > Hi Paul,

>

> You are right about the flexure. I did notice that it took as much

as > 2 or 3 minutes for everything to settle and then the DEC movement

> seemed to stop. I thought I had found the problem. This is

probably > most of it.

>

> When I realized this I tried again and this time it took about 20

> minutes for it to move about 15 arc seconds and was still moving.

>

> I read somewhere that this equates to about 2.5 arc minutes off

polar > alignment which is not quite as good as I was hoping for.

>

> Heck, is it possible the setup is still flexing after 20 minutes?

>

> Also, you said

>

> > Secondly, tightening El & Az axis after polar alignment almost

> > inevitably moves them, altering the alignment. For this reason,

I > > always keep the axis locking bolts tightened very snug, and

adjust > > the axis without loosening them.

>

> I always tighten the bolts before I check the drift.

> I have tried making adjustments with the bolts tight and with them

> loose and it's much easier the way you do it. Good to know this is

> the way to go.

>

> Thanks for help,

>

> Will

>

>

>

> --- In Losmandy_users@yahoogroups.com, "Paul K" pkane2001@h...>

> wrote:

> > Hi Will,

> >

> > That doesn't sound normal, but there are some normal reasons why

> > this might happen. My G11 holds polar alignment for about a

month, > > but it is mounted on a permanent pier. I expect that in my case

the > > primary cause is shifting of earth and thermal

> expansion/contraction

> > around the pier.

> >

> > Sounds like you've taken care of most mount-related slippage

that > > can occur, but flexing can happen in the telescope itself and in

> its

> > mounting and support. It can also happen in the focuser, camera

> > mount, or in the spider/secondary support. All of these can

easily > > masquerade as a drift, even if you are perfectly polar aligned.

> > Sometimes, this can be very difficult to diagnose, but you can

go a > > long way by tightening everything down, locking focusers, and

using > > screw-in adapters as much as possible.

> >

> > Secondly, tightening El & Az axis after polar alignment almost

> > inevitably moves them, altering the alignment. For this reason,

I > > always keep the axis locking bolts tightened very snug, and

adjust > > the axis without loosening them.

> >

> > Regards,

> >

> > -Paul

> >

> >

> >

> > --- In Losmandy_users@yahoogroups.com, "Will Sater"

wsater@c...> > > wrote:

> > > My new NON- GOTO G11 (March of 2005) does not seem to be

holding > > its

> > > polar alignment.

> > >

> > > I do a drift alignment of 5 minutes or more. I move the scope

> > around

> > > to point at something like m101 and then come back and check

the > > > alignment. Usually it will drift about 10 arc seconds in about

5 > > > minutes in altitude or azimuth.

> > >

> > > . The tripod is on asphalt.

> > > . The lock bolts for altitude and azimuth have been replaced

> with

> > > hex bolts so I can use a wrench.

> > > . The clutches are tight and left at the same tension.

> > > . 8 inch Newtonian + guide scope + camera = 30 lbs.

> > >

> > > There was about .005 of play in the RA and DEC axis, so I

added a > > 3rd

> > > shaft bearing to both. The RA now has .0025 and the DEC still

> > > has .005. (I think this may have helped some.)

> > >

> > > What prompted this investigation were two 1-hour exposures of

m81 > > and

> > > m82 that had horrendous rotation. I was making a lot of DEC

> > > corrections, but it was a new mount and I just wasn't sure.

> > >

> > > I do not think the altitude or azimuth or the tripod are

moving. > > >

> > > Is this normal?

> > >

> > > Any help would be deeply appreciated. I have been playing with

> > > telescopes and taking pictures for only a year and a half, so

my > > > education is bound to have some holes in it.

> > >

> > > Thanks,

> > > Will Sater



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

#25436 May 11, 2005

Will;



When you Drift Polar Align is your AZ bolts tight or loose? If they're

loose and you tighten them after achieving a good Drift Align sometimes

tightening the bolds shift the axis. Try doing your Drift Align with your

bolts fairly tight and don't tighten them when you're done. Or do one final

drift check after tightening them to make sure the alignment isn't

shifted...joe :)



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

From: "Will Sater" wsater@...>

To: Losmandy_users@yahoogroups.com>

Sent: Tuesday, May 10, 2005 11:07 PM

Subject: [Losmandy_users] Please Help : G11 not holding polar alignment





My new NON- GOTO G11 (March of 2005) does not seem to be holding its

polar alignment.



I do a drift alignment of 5 minutes or more. I move the scope around

to point at something like m101 and then come back and check the

alignment. Usually it will drift about 10 arc seconds in about 5

minutes in altitude or azimuth.



. The tripod is on asphalt.

. The lock bolts for altitude and azimuth have been replaced with

hex bolts so I can use a wrench.

. The clutches are tight and left at the same tension.

. 8 inch Newtonian + guide scope + camera = 30 lbs.



There was about .005 of play in the RA and DEC axis, so I added a 3rd

shaft bearing to both. The RA now has .0025 and the DEC still

has .005. (I think this may have helped some.)



What prompted this investigation were two 1-hour exposures of m81 and

m82 that had horrendous rotation. I was making a lot of DEC

corrections, but it was a new mount and I just wasn't sure.



I do not think the altitude or azimuth or the tripod are moving.



Is this normal?



Any help would be deeply appreciated. I have been playing with

telescopes and taking pictures for only a year and a half, so my

education is bound to have some holes in it.



Thanks,

Will Sater















Yahoo! Groups Links







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

#25454 May 11, 2005

Thanks for the input everyone.



Now that flexure seems to be most of the problem, I am hoping the

remainder will resolve its' self as I work with the mount a

little more.



If there still is an alignment problem, I'm guessing it will only

be an issue when I'm shooting pictures close to the pole.



Clear skies,



Will







--- In Losmandy_users@yahoogroups.com, "Will Sater" wsater@c...>

wrote: > My new NON- GOTO G11 (March of 2005) does not seem to be holding

its > polar alignment.

>

> I do a drift alignment of 5 minutes or more. I move the scope

around > to point at something like m101 and then come back and check the

> alignment. Usually it will drift about 10 arc seconds in about 5

> minutes in altitude or azimuth.

>

> . The tripod is on asphalt.

> . The lock bolts for altitude and azimuth have been replaced

with > hex bolts so I can use a wrench.

> . The clutches are tight and left at the same tension.

> . 8 inch Newtonian + guide scope + camera = 30 lbs.

>

> There was about .005 of play in the RA and DEC axis, so I added a

3rd > shaft bearing to both. The RA now has .0025 and the DEC still

> has .005. (I think this may have helped some.)

>

> What prompted this investigation were two 1-hour exposures of m81

and > m82 that had horrendous rotation. I was making a lot of DEC

> corrections, but it was a new mount and I just wasn't sure.

>

> I do not think the altitude or azimuth or the tripod are moving.

>

> Is this normal?

>

> Any help would be deeply appreciated. I have been playing with

> telescopes and taking pictures for only a year and a half, so my

> education is bound to have some holes in it.

>

> Thanks,

> Will Sater



Contact Us
This Site's Privacy Policy
Google's privacy policies

S
e
n
i
o
r
T
u
b
e
.
o
r
g