Home Position

[bmontalto]

Hi guys,

sorry... Newbie here and rather new to astronomy.  I have purchased a Skywatcher 200/1000 with an NEQ5 SyncScan mount and have done quite a bit of reading and research in the Internet.  However there is one thing that I cannot understand at this point in time...  Sorry if it's a very stupid question (as I'm guessing it definitely is).

What is the Home Position and WHY do I need it before/after I polar align my mount?

I have searched high and low on the internet and could not find any answers to why I need the home position (or mount park).  The only piece of information I found is that the Home Position is the position telescopes are set to put on display in shops.  This lack of information makes me guess that the answer is really obvious and I'm missing something.  I know (more or less) what I have to do to get to the home position (with a spirit level and measuring along the RA and Dec axes)... but WHY do I need this position???

Cheers!

[Steve Ward]

Welcome to the forum ... 

The Home position gives the mount a consistent starting point for the Go-To alignment , when you enter the location , time , date etc it knows where it is pointing to to start with and hence where it is in relation to the sky.

[Cornelius Varley]

Hello and welcome to SGL. The home position for the mount (counterweight pointing straight down and the telescope pointing at the North Celestial Pole) is the normal starting position for star alignment. The handset requires a known starting position (home) before it can slew the mount to the first alignment star. The handset knows where this star is based upon the home position. Think of it like giving someone directions to your house without telling them where the starting point is.

[bmontalto]

Thanks for the ultra quick reply!  I thought the go-to would know of the mounts' position by utilising the alignment application it has inbuilt (2 star alignment or 3 star alignment).  Would it need to know the physical position of the mount is in the home position - counterweight shaft pointing down and telescope mount pointing to polaris?

[Steve Ward]

Think of it as Peter suggested , if I give you directions to the pub from here it's ...1st right , 1st right , second left , straight on , 2nd right ..... now if you go out of your door and follow my directions you are not going to end up at my nearest pub .... unless you're my new next door neighbour ... 

The mount contains a very detailed map of the sky in its computer but unless it knows where it is in relation to that map it's basically lost.

[gkec]

Like this

http://www.harrisontelescopes.co.uk/acatalog/939886.jpg

so that it is pointing at Polaris (the north star, technically it should be the North Celestial pole but Polaris is good to get started with).  

RA should be fixed at 0 and Dec 90 -- this is the home position.

You will then need to adjust the Alt-Az bolts to get Polaris in view.  Once you have done this leave the Alt-Az adjustment alone.

[Tinker1947]

Point your scope at polaris, select 2 star alignment, pick a bright star from the list that's in a good position for your filed of view, when the scopae has slewed towards the star and stopped, release the clutches and align by hand, use a low power EP (high MM) then a high power to get the star centred, then tighten the clutches and select the 2nd star, this time when its finished slewing use the hand set to move the star to the centre of your EP,,,,Job done....good luck.... 

[Steve Ward]

Try this full set-up tutorial ... http://www.astronomyshed.co.uk/forum/viewtopic.php?f=19&t=1893

[jambouk]

The mount likes to know that is has a relatively fixed and known starting position before doing a star alignment. So booting the mount in the home position achieves this. It just makes life easier as when you tell it the first alignment star, it will slew roughly to it, else it will slew and look at the neighbors apple tree (or pointing into the lawn) and then will moan and do a rubbish star alignment.

James

[brantuk]

Perhaps the most obvious analogy is if I give you a compass and tell you to go west. You wouldn't know which way is west till you line the compass scale up with the magnetic pointer so you are facing north. Now you can easily determine which direction is west from your "home position".

With a map aligned to the compass you can plot a route in any direction to a chosen spot on the map. Again - a "home position". Well it's just the same with goto mounts and the sky.

[bmontalto]

Wonderful!!!!!!!!!!!!

Thanks for all the great replies  I got it now, it's obvious once it's explained like this.  I can already tell that this is going to be an excellent forum!

Cheers

[Tinker1947]

Wonderful!!!!!!!!!!!!

Thanks for all the great replies  I got it now, it's obvious once it's explained like this.  I can already tell that this is going to be an excellent forum!

Cheers

The regulars like it...

[Steve Ward]

And the more Irregulars .... 

[jambouk]

And us inbetweeners

[kirkster501]

The perfect home position would be pointing directly at the NCP.  In reality it will be a degree or two, often more, out.  But when you do your first slew it assumes this is where the scope is pointing and then goes off towards the star you told it to.  You then centre on this star and then calibrate the scope so it knows exactly where it is pointing.  Do that with a few stars and you have a perfect pointing model.

[Phil Fargaze]

Sometimes the home position can be lost either due to de clutching or loss of power. So a good tip is to put some marks on the 

mount  when it is in the correct home position. Then, select to park in home position, re align the marks, and star alignment should 

proceed without any problems. 

[LunaSwift]

There is a complete series of videos on U-Tube made by Astronomy Shed that cover everything from setting up and Polar Aligning  HEQ5 and 6 mounts . Just type in Astronomy Shed videos  sit back and learn

[hobsey]

There is a complete series of videos on U-Tube made by Astronomy Shed that cover everything from setting up and Polar Aligning HEQ5 and 6 mounts . Just type in Astronomy Shed videos sit back and learn

I may have to have a look at these. Had my cg-5 gt delivered today and im really confused by it all.

[Steve Ward]

There is a complete series of videos on U-Tube made by Astronomy Shed that cover everything from setting up and Polar Aligning  HEQ5 and 6 mounts . Just type in Astronomy Shed videos  sit back and learn

The more observant amongst you would have seen the link to it I posted at the start of the thread ....    

And with regards to Alignment from the Home Position ...

If you go to the trouble of accurately setting up the "Home Position" and intend keeping it , so that you can "Park" the scope at the end of the session and therefore start again next time with everything as was  ....   Do NOT undo the clutches and slew to the align stars by hand as you will undo the home position that you've lovingly set up , but use the handset controls to slew to and centre target.

[Tinker1947]

The more observant amongst you would have seen the link to it I posted at the start of the thread ....  

And with regards to Alignment from the Home Position ...

If you go to the trouble of accurately setting up the "Home Position" and intend keeping it , so that you can "Park" the scope at the end of the session and therefore start again next time with everything as was  ....   Do NOT undo the clutches and slew to the align stars by hand as you will undo the home position that you've lovingly set up , but use the handset controls to slew to and centre target.

I will agree with this for a pier mounted Scope, where the mount is set-up permanently, but for a scope that is set-up on the patio and taken down every time the home position will never be exact so i would still undo the clutches in this instant...

[Steve Ward]

True enough ...  

That's why I carefully marked the footmarks of my tripod in the patio , small holes drilled for secure locating , carefully leveled the mount base , drift-aligned the mount ( no view North ) etc , etc , and set up an accurate home position.

I now just carry the rig out of the patio door in one piece , mount , scope , camera , PSU's , focusers  et al , carefully plonk the legs in the holes and power up.

Provided I set the time accurately , i.e. to the second , the mount puts the alignment stars in the FOV  of the 1000D / ED80Pro everytime , from the Park position.

Obviously this is irrelevant for anyone using a GEM on the hoof out in the field , but highly recommended if you have a consistent viewing location at home but no pier or observatory.

[gkec]

I will agree with this for a pier mounted Scope, where the mount is set-up permanently, but for a scope that is set-up on the patio and taken down every time the home position will never be exact so i would still undo the clutches in this instant...

This has been discussed before but I still really don't get why releasing the clutches is a good idea rather than using the handset as per the user manual. Especially when the OP is new to the procedure.

[Steve Ward]

It's only a good idea if you've no Home position set and inaccurate details inputted to the mount so as to put the first alignment star way off target , in which case it's a little quicker to de-clutch to get a bit closer to start with before centering.

If the mount knows where it is , and what time it is , and where its home position is it will put the alignment star in the EP.

[gkec]

It's only a good idea if you've no Home position set and inaccurate details inputted to the mount so as to put the first alignment star way off target , in which case it's a little quicker to de-clutch to get a bit closer to start with before centering.

If the mount knows where it is , and what time it is , and where its home position is it will put the alignment star in the EP.

I see,  I have a CG5 with the indexes marked and aligning to NCP the target stars are usually in the eyepiece.  I can see if you have no index marks it could be a bit off.  That's the best explanation I have read.

[jambouk]

I don't see the need for knowing the exact home position / parking the scope, for my own set up as i don't have a pier and set up each night. In my situation i just want the mount roughly in the home position to help with the star alignment; again for me (and many others i suspect) having the home position accurate to half a degree or so in both axes is unnecessary as it doesn't confer any advantages as far as i can tell.

James