"Home" position - how important is it?

[PJR]

Hi guys

This is probably a silly question, but as the title says, just how important is the home position and how accurate should it be?

I have a SW EQ5 Pro SynScan.  Occasionally on switch-on, it asks if it starting up from the home position.  I haven't yet figured out the reasoning as to when this question appears, but with use, I hope it will become obvious.

Does this mount have sensors so it knows where its alignment on the RA/Dec axes (had to look that plural up!), or does it rely on this home position being an accurate starting point?

Many thanks in advance

Peter

[oldpink]

normally it remembers where the park position is  (90 deg) and rotates to it
it will ask if it wasn't closed down correctly the last time out

I have 2 marks I made to align home in case of accidental power off
or if something messes up so I can set it back quite accurately

[lensman57]

Hi guys

This is probably a silly question, but as the title says, just how important is the home position and how accurate should it be?

I have a SW EQ5 Pro SynScan.  Occasionally on switch-on, it asks if it starting up from the home position.  I haven't yet figured out the reasoning as to when this question appears, but with use, I hope it will become obvious.

Does this mount have sensors so it knows where its alignment on the RA/Dec axes (had to look that plural up!), or does it rely on this home position being an accurate starting point?

Many thanks in advance

Peter

It is not important at all and only meaningful if your mount is set up in an observatory in which case after having parked it in the home position upon the next start up it may accurately align itself to the sky with star alignment. If like most of us you need to move your mount and scope in and out, the home position is less than useless.

A.G

PS: None of SW hobby mounts have encoders on either the RA or DEC axis so the position of mount shown by the handset is at best  a guess and not strictly accurate.

[Cornelius Varley]

Hi guys

This is probably a silly question, but as the title says, just how important is the home position and how accurate should it be?

I have a SW EQ5 Pro SynScan.  Occasionally on switch-on, it asks if it starting up from the home position.  I haven't yet figured out the reasoning as to when this question appears, but with use, I hope it will become obvious.

Does this mount have sensors so it knows where its alignment on the RA/Dec axes (had to look that plural up!), or does it rely on this home position being an accurate starting point?

Many thanks in advance

Peter

I always say No to the question, but the handset expects the mount to start in the normal parked position ie counterweight pointing straight down the telescope pointing at the North celestial pole. From this position the handset can map the approximate location of the first alignment star.

[PJR]

OK Guys

Thanks for the responses.

I think what you are sayng is that following a reasonably accurate polar alignment, in order for the GoTo to operate relatively accurately, the home position also has to be accurate, which is fairly impossible due to the small size of the scales (at best half a degree out) and that the SynScan requires at least a 2-star alignment in order for the GoTo to function well.

In which case, I don't see the point in the accuracy of the polar alignment.  A rough approximation should suffice, followed by Alt/Az adjustments to bring the first alignment start into EP centre.

Peter

[oldpink]

general rule

for visual, rough polar align is fine
for Astro Photography PA is critical regardless of the goto alignment

[lensman57]

OK Guys

Thanks for the responses.

I think what you are sayng is that following a reasonably accurate polar alignment, in order for the GoTo to operate relatively accurately, the home position also has to be accurate, which is fairly impossible due to the small size of the scales (at best half a degree out) and that the SynScan requires at least a 2-star alignment in order for the GoTo to function well.

In which case, I don't see the point in the accuracy of the polar alignment.  A rough approximation should suffice, followed by Alt/Az adjustments to bring the first alignment start into EP centre.

Peter

Hi Peter,

No the alignment of the mount has nothing to do with polar alignment. By aligning the mount what you are doing is mapping your sky to the data base of the mount so the mount knows where it is. I do 2 or 3 cycles of 3 star align and the mount finds the targets pretty well every time, an HEQ5 Pro. Polar alignment is to do with accuracy in tracking a target in the sky and to get rid of the effects of " rotation ". Accurate polar alignment is only required if you use the mount for long exposure DSO imaging. For observation polar aligning the mount using a well calibrated polar scope is more than adequate, for imaging the PA has to be very accurate.

A.G

[IanL]

in order for the GoTo to operate relatively accurately, the home position also has to be accurate, which is fairly impossible due to the small size of the scales (at best half a degree out) 

Read this for getting an accurate home position - more accurate than using the setting circles (actually is it a necessary step, since the setting circles may not be accurately aligned anyway - you follow this procedure and then zero the circles):

http://eq-mod.sourceforge.net/tutindex.html

Once you have the home position, you can mark it on the RA and Dec axes (I use some small stickers and a thin pen line to avoid having to permanently mark the mount).  Bear in mind that you have to level the tripod each time if you want to use home position marks (if you can't level the tripod consistently, you would just follow the 'find the home position' process each time you set up as the home position will vary).

[ronin]

I would guess thast people with a pillar and observatory have said why do I need go through the aligment when the scope hasn't, in effect, moved. And someone added the option to the firmware. The purpose being if you start in an accurately known location and known orientation then the last set of calculated parameters can be reused.

If the system is on a tripod that you carry in and out forget it., or build a pier.

You will get asked it first so that you can skip part of the full alignment.

[Owmuchonomy]

Recently I have started using the option to start from home position. It works very well when I'm solar observing. I can carry out my tripod, plonk it down on my markers (quarry tiles) buried in the lawn, level it and then set up. Yesterday I started from home and with my 40mm EP the sun appeared in the field of view after setting the appropriate RA/Dec coordinates. Then I had time to open a beer. Sorted. So don't underestimate it's usefulness.

[Bizibilder]

The home position can be any position you like.  When the mount asks "Are you starting from the home position?" it is simply asking "Are you starting from the position you last parked the mount without having released the clutches or moved the mount in any way?".  Even if you "plonk the mount down" as long as you are reasonably "accurate" the mount will probably find an object in the field of view when you slew to it but it won't necessarily be bang in the middle of the fov unless you are lucky.  For a pier mounted and well adjusted scope it should be bang in the middle every time!