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Re: [Losmandy_users] Re: polar alignment/pointing protocol


Apr 11, 2001

 


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

#3642 Apr 11, 2001

Hi Greg



further to your last,I met Eddie T because we both had the same magnitude of

problems with the G-11 but we pretty much worked them out.



Hopefully,my findings will help you out.



First,there is a lot of "techie" stuff that people do,mostly because they

can and then others follow suit who can't...that causes problems.

I'm not saying this is you but sometimes reading these posts,I've got to

shake my head as to why intuition is sometimes so askew.I've been guilty of

the same and when taking a "backward" step have found I was the problem.(but

don't admit this to my wife eh!)



But lets go back to the fundamentals and perhaps something might result that

can help you....plain and simple,the G-11 right out of the box will track

visually and pretty damn near perfectly.You cannot assemble it wrong as long

as the ra DSC moves when the ra axis does and ditto for dec.

Thousands are using these well and I for one have never monkeyed with the

secondary system alignment but my LXD 500 8" AND c-11" all caught

the objects within a 40mm meade EP and now 31mm nagler.



A couple things about the dsc's is to make certain they are programmed at

the proper tics (4096 I think it is).The manual is confusing because

it more or less implies 9000 setting can be used and would be more accurate

but that is only if you use an aftermarket encoder of that value.

Next,pull your polar scope and dump that skinny little flex washer.

Instead I use a rubber O ring that fits snug over the end.(O rings are made

to very accurate tolerances)Now when I snug it up,I can just turn it for

alignment but it does not move laterally or longitudinally.

While the polar scope is out,mount it on something like a camera tripod

or sawhorse.Focus and sight it in just like a rifle scope.Centre the

furthest object you can.If at twighlight use a star.

The next part is not meant to be condescending,but I'll go over polar

alignment just so there is a check list.

First,spot and confirm polaris.

Look thru the ra polar axis hole and centre the star.

Level your mount

Ensure polaris is recentered

Install polar scope.

Align polaris.

***the value of the Losmandy polar scope is really the orientation of

inscribed constellations.If you cannot see the other 2 guide stars

because of seeing conditions and only see polaris,you will always be at

least .75 degrees away from alignment.You will also have to calculate in

what direction "off" is.

Assuming though that all three are visible in the polar scope,I find that

their proper alignment is in the middle of the 3 tic marks for each star.

Having done this and I can do it in about 2 minutes,you are polar aligned

period!Any finer is purely drift method and for long exposure

photography.You should not notice dec drift for hours.



So what else can go wrong?One thing is the DSC cpu.It operates in UT time.

I have tried everything but what works for me is the following protocol.

Set up the DSC with the current date in your local time.(don't go forward

just because its another day in England or change it after midnight)Enter

and then pick a locational star in the area of sky you want to view.Verify

its identity and then centre it in reticle ep under hi mag.(You cannot be

accurate in a normal viewing ep.)

Now,turn the scope to a close easy to find M object.Use the DSC to do this

because when you "zero" out and the object is not centered you'll understand

by how much.This is a timing issue between the algorithms in the DSC and

your actual location/time.This variance however should only be in RA and

pretty consistant.Centre the object.Then hit

MENU and REALIGN ON OBJECT.

Now all your objects should be much closer.

BY THE WAY....use 1 star alignment.(not 2 star)

Intuition tells you that 2 stars would be more accurate than 1 but thats not

true in this case.The accuracy comes from polar alignment and 1 star.

(using 2 throws eveything off)

I'm certain the Above will put you an object in a 9.25FOV using a 35mm

almost everytime.

Now you can concentrate on the other big alignment factors of

diffraction,mirror flop and mirror slop.The other issue in setting this up

is to view with the ep straight thru if you can.This will ease your mind as

to the diagonal.The diaonal or oag can cause some big issues so do straight

thru first...be happy then try with the diagonal.Once happy,don't change its

orientation or you may have to realign on a new object.When you swing more

than 15 degrees or cross the meridian you may have to realign.

After getting this to a level where you are happy and you notice you are off

more than the "standard" when going to farther parts of the sky,try

orthogonting your axis.

The method in the Losmandy DSC manual works well,Just remember to move the

scope,physically (not the alt/az fine controls).Be patient and iterrate

until polaris is centred.Once done then recheck you scope for level and

polar align again.





Now there is one last consideration of pointing accuracy with the G-11.

The RA shaft/needle bearing connection.

Without a doubt,when you clutch,align then swing the scope,unclutch to

center and the reclutch you are going to have error.

The bearing/shaft machining tolerances and/or wear due to loading weight

play a big factor...not so much in guiding but in pointing for sure.

I ahve found there are shafts like mine that are really good..1.249"

Some though go down to 1.247.Thats a lot and it is magnified by as much as

double because being suspended at either end the load will pull to one side

at the top and force the shaft to the far side at the bottom.

This eccentricity is a big problem with pointing.

Good news though is its easy to fix most of it.Add the third bearing.

Do it in DEC and RA because the smae thing happens in both axis but is more

noticable in the DEC.



Good luck...I went thru all this stuff,2 stars etc and now I do the above

and after my first setting and realign I use only the DSC's.

To tell you how accurate,I have my f6.8pronto loaded with an st-7e.It is

side saddle with a TV 101.I centre my star in a TELRAD.The guide star

usually shows up in the focus mode of the st-7e.I centre it in the screen

and hit ENTER on my DSC.Then I use my tv 101 with a 31mm Nagler5

to finf an M class cluster.Centre it.It usually comes onscreen

somewhere.Centre it on the computer.Hit REALIGN ON OBJECT and for the rest

of the nite,never look into the TV101 again to realign.

I'm sure the fov on the st-7e is close or less than the 9.25.

let me know how it works out



JImmy











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

#3643 Apr 13, 2001

Thank you for this excellent review. I have a few questions and

coments below.



--- In Losmandy_users@y..., "James A. Thibert" thibertj@h...> wrote:

> Hi Greg

>

> further to your last,I met Eddie T because we both had the same

magnitude of

> problems with the G-11 but we pretty much worked them out.

>

> Hopefully,my findings will help you out.

>

> First,there is a lot of "techie" stuff that people do,mostly because

they

> can and then others follow suit who can't...that causes problems.

> I'm not saying this is you but sometimes reading these posts,I've

got to

> shake my head as to why intuition is sometimes so askew.I've been

guilty of

> the same and when taking a "backward" step have found I was the

problem.(but

> don't admit this to my wife eh!)



The saying is, a wise man learns from others, a fool learns from

experience. In amateur astronomy, I'm learning a lot from experience.





>

> But lets go back to the fundamentals and perhaps something might

result that

> can help you....plain and simple,the G-11 right out of the box will

track

> visually and pretty damn near perfectly.You cannot assemble it wrong

as long

> as the ra DSC moves when the ra axis does and ditto for dec.



This is one of my first "doublechecks" because even on the Super

Polaris silly mistakes were possible, like sticking the computer wires

into the dual axis drives, etc.



> Thousands are using these well and I for one have never monkeyed

with the

> secondary system alignment but my LXD 500 8" AND c-11" all caught

> the objects within a 40mm meade EP and now 31mm nagler.

>

> A couple things about the dsc's is to make certain they are

programmed at

> the proper tics (4096 I think it is).



Yes, 4096. The NGC Max encoder test wouldn't give you a 360 degree

readout for a 360 degree turn otherwise. It also pays to make sure

that Dec increases as you go N and the value for RA increases as you

head "down" into the E. Otherwise there are + and - thingies in the

computer that need to be changed.



The manual is confusing because

> it more or less implies 9000 setting can be used and would be more

accurate

> but that is only if you use an aftermarket encoder of that value.

> Next,pull your polar scope and dump that skinny little flex washer.



??? Sitting here at the computer I can't remember which washer we're

talking about. Also where do I buy these O rings (I know, I know,

Mcmaster Carr probably) but can you give me the specs so I know

exactly what to ask/look for. Is the flex washer the one that looks

warped?



> Instead I use a rubber O ring that fits snug over the end.(O rings

are made

> to very accurate tolerances)Now when I snug it up,I can just turn it

for

> alignment but it does not move laterally or longitudinally.



I like this idea better than filing away at the "run out" of some

other washer.



> While the polar scope is out,mount it on something like a camera

tripod

> or sawhorse.Focus and sight it in just like a rifle scope.Centre the

> furthest object you can.If at twighlight use a star.



I'm a little dubious about this. As someone else posted, these

reticles are extremely easy to break. Let's just say that what seems

like very gentle turns are sufficient. This is "learning from

experience." My inclination, these days, is to think that the

designers were trying to tell us something by making those screws hard

to get 0.035". I'm also wondering whether the "New" polar scopes

might be easier to break than the old ones, accounting for some of the

discrepant experiences on this list.



> The next part is not meant to be condescending,but I'll go over

polar

> alignment just so there is a check list.

> First,spot and confirm polaris.

> Look thru the ra polar axis hole and centre the star.

> Level your mount

> Ensure polaris is recentered

> Install polar scope.

> Align polaris.

> ***the value of the Losmandy polar scope is really the orientation

of

> inscribed constellations.If you cannot see the other 2 guide stars

> because of seeing conditions and only see polaris,you will always be

at

> least .75 degrees away from alignment.You will also have to

calculate in

> what direction "off" is.



Well, I think it's more a matter of chance than anything else. I

mean, if you align DEAD ON polaris you are only off by .86 degree. By

looking at the sky you can offset into the right quadrant. But .4,

.75, what's to argue?



> Assuming though that all three are visible in the polar scope,I find

that

> their proper alignment is in the middle of the 3 tic marks for each

star.

> Having done this and I can do it in about 2 minutes,you are polar

aligned

> period!Any finer is purely drift method and for long exposure

> photography.You should not notice dec drift for hours.

>

> So what else can go wrong?One thing is the DSC cpu.It operates in UT

time.

> I have tried everything but what works for me is the following

protocol.

> Set up the DSC with the current date in your local time.(don't go

forward



??? Sky commander instructions do say to go forward. They say that

the computer counts from the BEGINNING of the calendar day UT. So if

it's 10 o'clock at night and I set tomorrow's date I'm only two hours

off. If I set today's date I'm 22 hours off. This only matters for

planet position in any case.



> just because its another day in England or change it after

midnight)Enter

> and then pick a locational star in the area of sky you want to

view.Verify

> its identity and then centre it in reticle ep under hi mag.(You

cannot be

> accurate in a normal viewing ep.)



Yes.



> Now,turn the scope to a close easy to find M object.Use the DSC to

do this

> because when you "zero" out and the object is not centered you'll

understand

> by how much.This is a timing issue between the algorithms in the DSC

and

> your actual location/time.This variance however should only be in RA

and

> pretty consistant.Centre the object.Then hit

> MENU and REALIGN ON OBJECT.

> Now all your objects should be much closer.

> BY THE WAY....use 1 star alignment.(not 2 star)



OK, but this is something mysterious I want to check out. Sky

commander instructions on how to reach "dec 90" are: set your scope so

that Polaris swings through center of FOV on E side, W side, and then

set it up so that you have Polaris in FOV, altitude w/in fov doesn't

matter (they say). Then 2 star align. I've never done it but I'd

like to try. Sky commander dec 90 may be easier than NGC Max dec 0.



> Intuition tells you that 2 stars would be more accurate than 1 but

thats not

> true in this case.The accuracy comes from polar alignment and 1

star.

> (using 2 throws eveything off)



Well, I want to experiment on this one.



> I'm certain the Above will put you an object in a 9.25FOV using a

35mm

> almost everytime.

> Now you can concentrate on the other big alignment factors of

> diffraction,mirror flop and mirror slop.



I haven't found side to side mirror flop to be a big deal (yet,

anyhow). Maybe I'm just lucky. There's some focusing flop at high

power, maybe 3 arc minutes.



The other issue in setting

this up

> is to view with the ep straight thru if you can.This will ease your

mind as

> to the diagonal.The diaonal or oag can cause some big issues so do

straight

> thru first...be happy then try with the diagonal.Once happy,don't

change its

> orientation or you may have to realign on a new object.When you

swing more

> than 15 degrees or cross the meridian you may have to realign.



It seems to me better performance than 15 degrees is possible. I did

swing from Capella (setting in W) to M3 to m13 (in E) with no

realignment in my testing phase before clouds ended the exercise. I

think more accuracy in the OTA alignment (in my case) is possible. I

also think the accuracy of the NGC Max procedure is ENTIRELY dependent

on minimal OTA offset. It is possible that with more attention to OTA

optical alignment the NGC Max procedure would eliminate the need for

everything else. Don't know. But right now I'm hanging on to both

computers, on the thought that the NGC Max is useful for alignment and

diagnostics and the Sky Comm is most useful because of the way its

database is organized and other features, like a built in heater.



> After getting this to a level where you are happy and you notice you

are off

> more than the "standard" when going to farther parts of the sky,try

> orthogonting your axis.

> The method in the Losmandy DSC manual works well,Just remember to

move the

> scope,physically (not the alt/az fine controls).Be patient and

iterrate

> until polaris is centred.Once done then recheck you scope for level

and

> polar align again.



This is more easily said than done. It's a real hassle and shimming

stuffing pieces of flotsam between a $1k OTA and $2k mount is a real

tribute to incomplete design thinking somehwere. Either the mount

head or the dovetail rails should have some kind of adjustment for

this stuff, it would be much easier. I mean, here I am, out in the

dark, looking at these pieces of plastic to see which one will move

the OTA 6 arc minutes???



>

>

> Now there is one last consideration of pointing accuracy with the

G-11.

> The RA shaft/needle bearing connection.



Yeah, I'm gong to look into this.



> Without a doubt,when you clutch,align then swing the scope,unclutch

to

> center and the reclutch you are going to have error.

> The bearing/shaft machining tolerances and/or wear due to loading

weight

> play a big factor...not so much in guiding but in pointing for sure.

> I ahve found there are shafts like mine that are really good..1.249"

> Some though go down to 1.247.Thats a lot and it is magnified by as

much as

> double because being suspended at either end the load will pull to

one side

> at the top and force the shaft to the far side at the bottom.

> This eccentricity is a big problem with pointing.

> Good news though is its easy to fix most of it.Add the third

bearing.



OK



> Do it in DEC and RA because the smae thing happens in both axis but

is more

> noticable in the DEC.



OK



> Good luck...I went thru all this stuff,2 stars etc and now I do the

above

> and after my first setting and realign I use only the DSC's.

> To tell you how accurate,I have my f6.8pronto loaded with an

st-7e.It is

> side saddle with a TV 101.I centre my star in a TELRAD.The guide

star

> usually shows up in the focus mode of the st-7e.I centre it in the

screen

> and hit ENTER on my DSC.Then I use my tv 101 with a 31mm Nagler5

> to finf an M class cluster.Centre it.It usually comes onscreen

> somewhere.Centre it on the computer.Hit REALIGN ON OBJECT and for

the rest

> of the nite,never look into the TV101 again to realign.

> I'm sure the fov on the st-7e is close or less than the 9.25.

> let me know how it works out



I anticipate success. But I started with an OTA that was really off,

and didn't have it working for more than 10 minutes before clouds

killed any additional confirmation.



>

> JImmy



Thanks for taking the time to write this all out, it will be useful to

refer people to it in the archives. Please don't forget to post

additional informatin on the O ring. -gn.



>

>

>

>

>

>

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

___

> Get Your Private, Free E-mail from MSN Hotmail at

www.hotmail.com







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

#3673 Apr 17, 2001

Hi Greg



re:my last and your questions....



The O ring is one that you can get at an auto store.I don't have my mount

with me right now (I'm 350kms away) but you can bring the polar scope with

you and get a nice fit right there (then buy 2)



The alignment screws are a problem because all you want to do is center the

target. An artificial star or pinhole light worked well.Just use the force

of your thumb and index finger "rolling" the hex wrench.Using any more could

decrease sensitivity and increase torque which ='s broken scope.



I think a 2 star algorithm is a throwback to early "goto" days...you

know..."last year".It was intended to accomodate non- polar aligned

scopes.It is not as accurate and I don't think it takes scope orientation

into account.The 1 star does.

Perhaps the best would be a 2 star "polar aligned" setting.



The shimming should not take place between the scope and the mount.

Orthogonality on the G-11 is pretty good if not superb.Then entire "losmandy

secondary system"relies on it being good. The shimming is done between the

OTA and its mounting bracket screws.(usually only on 1 side is necessary and

metal is need for shim.I used tinfoil which is a known dimension and can be

doubled or quadrupled jsut by folding it.It won't change over time or with

the weather either)



good luck



JImmy





----Original Message Follows----

From: gnowell@...

Reply-To: Losmandy_users@yahoogroups.com

To: Losmandy_users@yahoogroups.com

Subject: [Losmandy_users] Re: polar alignment/pointing protocol

Date: Fri, 13 Apr 2001 16:16:03 -0000



Thank you for this excellent review. I have a few questions and

coments below.







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