LX200 drive training

[peter brown]

G'day,
Thanks for your time. I have mounted my LX200GPS on a pier and ultrawedge and am trying to get my autoguider working. Think I need to train my drives and PEC etc.
Could any one tell me if I can do all this with it in polar mode or do I have to take the whole thing down and do it ALT AS?
Thanks in anticipation
Peter B

[AndrewJ]

Gday Peter

The following answers assume you are running the latest firmware 4.2g

You can do drive training in polar using a star, but the RA results aren't very accurate/repeatable.
As long as you can see a reasonable terrestrial target, you can do drive training on the wedge. To get the best results in RA, you need to have the OTA as close to DEC=0 as possible.
Assuming you have a target that matches these requirements
just tell the scope it is Alt/Az ( via the handbox ) and do a drive train as per normal. When done, tell it its Polar again.
For PEC, the only gotcha is it plays back inverted in the Sth hemi
Thus after training ( using Meades mechanisms), you need to invert it

Andrew

[bmitchell82]

Save yourself the hassle do not use PEC if you are autoguiding they only end up fighting each other! and PEC is a arse you have to keep on renewing the data. guiding will work to sub pixel at speeds hence you wont have drift (if your setup is working nicely).

[AndrewJ]

Gday Brendan



Not true in an LX200GPS, ( if done correctly )
PEC is applied proactively as a fundamental speed adjust
It only gets updated once every 2.4 seconds.
Thus, if properly done, it can result in much lower guide adjusts being required for scopes with bad underlying PE.



Dunno where that comes from????
For 497 Austostars, if you dont park, yes, it has to be redone
but the LX200GPS uses sensors to resynchronise the worm each boot
This mechanism works quite well, and has been proven in practice.

Andrew

[bmitchell82]

like i said you have to lay down the pec and in the case like i said before if your using sub pixel guiding then it doesn't matter that much. instruments such as meade where you do pay a premium price shouldn't be that out of whack if it is ide be taking it back!

my logic behind this is if i can hold round stars with a overloaded eq6 for 20min + with a $16.95 DSE scope and a $100 DSI all with rough polar alignment then why bother? guiding is so much faster to set up! :) thats my 2 bobs worth

[AndrewJ]

Gday Brendan



You may also just have a very good worm, many others dont,
and for them a good PEC model "helps".
It doesn't eliminate the need to guide, but it does reduce it.
And, assuming a Meade 10" its going to be twice your focal length
which also adds problems if imaging without a reducer.

Also, ref the EQMod site and see the efforts some people are going to to reduce the PE in their EQ6 mounts.
If you got a good worm, be happy :)

Andrew

[bmitchell82]

I must have a decent worm as with polar alignment i can hold round stars for close to 3 min and out of 10 shots i keep 7-8 of them. But still if your PE is that bad that you need an PE program to give the guider a chance, take it back or upgrade the worm gears.

You are right with the Meade 10" but then again im running 25kg of telescope optice/gear on a EQ 6 with a 2x 2" barlow putting the F# at 9.2 and still get round stars with a rough polar align. When guiding came to sub pixel then as long as it was close enough aka polar and PE, it negated most of it. Im not saying that with the incresed accuracy (minimized) of PE and 10 min no drift Polar your guider would be doing little work, but once again if your cam can do .5 second iterations and shoot the guiding command though eqmod/ST4 port in less than a second you will always get round stars :)

As with everything there is a limit to accuracy with atmospheric turbulence, light pollution, and pollution in general if your looking for that Nth degree of accuracy go into the darkest spot you can find, and wait for that perfect night where the atmosphere is still :) then all the fine fine adjustments and perfect PE will make the difference between a good shot and a unreal shot:thumbsup:

(don't miss understand me i just love debating and will push my point till somebody can prove to me without a doubt that their way is better for me than my way ;) as everybodys way works best for them as it is what they are used to)

[AndrewJ]

Gday Brendan



Ahh but PE is like religion
There are no Specs to define whats good:thumbsup:
50arcsec pk-pk with a pure sinusoidal error is easier to work with than say a high freq sawtooth at only 10sec pk-pk
Its all relative



Understood, and its always an interesting debate, as it depends on many things, including your actual equipment, which can be quite variable.
Ie there is no "correct way" that suits all.

The question was asked re a Meade LX200GPS scope.
For these Meades, there is no overhead in PEC playback
( ie guide commands dont fight PEC for the right to play with the motors )
As such a good PEC model will help, as any good proactive corrections will be better than reactive ones.

Andrew

[bmitchell82]

hehehe yes you are quite right there, i was looking though the Synta EQ6 manual, and though basic says not to run a PE model when guiding as it does fight for motor time.

Im still unsure how meade does it though because the PE model basically tells the motors to speed up slow down, and the guiding does the same one has to yeild and to my train of thought if one motor is speeding up and the guide camera needs to slow down then the guiding is going to be skewed as when you first pick a guide star it does a initiation proceedure (basically finding out what pulses do what to guide accurately) then instead of a 30ms pulse it will only be say 10ms worth because of the PE working.

With PE being mainly mechanical based and not reliant on Atmosphere and Local weather the guiding star is a much better measure of accuracy as the earth is moving the atmosphere is moving and for all intents and reason the object you are observing is moving. with that in mind the only way is to have a live input into your mount then everything is aligned accordingly.

hehehe :)