Doh, guiding issues tonight !!!

[kirkster501]

Got the new rig running outside at F5.  The first few subs are stunningly sharp!  For some reason though I am getting guiding issues with guidsecope.  Typical!!  All starts off OK then Dec just goes haywire.  The scope is perfectly balanced in Dec.  I have done this a million times.  In the end, rather than stop the whole thing, rebalnce etc I have just turned off dec guiding tonight and left RA only.  Lets hope for the best!

Any thoughts please??  Could I have Cone error maybe?  

Thanks, Steve

[jambouk]

I know nothing about guiding, but i can't see how cone error would cause this problem.

I hope you get it resolved quickly.

James

[kirkster501]

Well the five min M33 luminance subs are coming in lovely.  So seems to be OK with just RA guiding.

Maybe my polar alignment could be out a bit in my eagerness to get going with the new scope.

[jambouk]

Yes, i suspect it is a polar alignment issue. But glad it's working without the dec adjustment anyway.

Looking forward to seeing the image.

James

[Daniel-K]

i agree PA, i dont know what your setup routine is but i usually PA with scope off then mount everything then PA again as mounting the gear normally knocks it out a tad. or you could have knocked your polar scope and its not calibrated correctly. i wouldnt worry to much as long as your subs look good  thats all that matters

Dan

[kirkster501]

Hmm, I have just realised that one leg of the tripod is just very slightly touching the side of the concrete path.  And despite my tiptoeing, the slightest move, even if I do not move my feet and they are planted to the spot, any shifting of my weight or move of my upper body and I get a peak in the guide graph!!!  Boy is it sensitive!  It must still transfer through to the mount and be detected by the guiding gear!  I am not re-enabling DEC now though lets get the subs in and learn the lesson (if indeed that is the root cause of tonight's issue).

[Freddie]

Not so sure it's PA as getting good results with DEC turned off implies the PA is spot on.

[jambouk]

Lol. It was the operator walking around that was causing the trouble!!!!! Let's hope a hedgehog doesn't start using the tripod as a scratching post whilst you are inside

Glad you've identified the issue and worked a solution out for next time.

James

[kirkster501]

Lol. It was the operator walking around that was causing the trouble!!!!! Let's hope a hedgehog doesn't start using the tripod as a scratching post whilst you are inside

Glad you've identified the issue and worked a solution out for next time.

James

Well James, lets hope that was indeed the issue.

As a side note, its my understanding that the "weights" side of the scope should always be slightly heavier than the "scope" side so that the motor always has to be driving the gears and no backlash will develop.  What about DEC?  Should the camera side or the lens side be "heavier" ??  Not so sure about that one tbh....

[jambouk]

Again, this is something i don't know as i don't [yet] do any long exposure DSO imaging or guiding. But there have been lots of threads about this on the forum so have a search for 'unbalanced' or similar terms in the relevant sections of the forum and i'm sure you'll find lots of differing opinions.

James

[Gina]

I thought it was the scope side that should be slightly heavier.  Maybe someone who knows for sure could answer this?

[todd8137]

I know nothing about guiding, but i can't see how cone error would cause this problem.

I hope you get it resolved quickly.

James

Lol do you no what cone error is ?

Pat

[jambouk]

Ish. But if he's never encountered this problem before it would seem odd for cone error to appear out of no where would it not? And if there was new cone error, surely it would result in a gradual drift of the imaging scope away from the target and result in corrections needed in both RA and Dec?

James

[swag72]

......As a side note, its my understanding that the "weights" side of the scope should always be slightly heavier than the "scope" side so that the motor always has to be driving the gears and no backlash will develop.  What about DEC?  Should the camera side or the lens side be "heavier" ??  Not so sure about that one tbh....

Here's my understanding of weights.

If the weights are pointing towards the East and you are imaging an object that is rising towards the meridian, then you have the weights slightly heavy. If you have crossed the meridian and the weights are now pointing towards the west and you are therefore imaging a target on it's drop from the meridian towards the west, then you have the scope side heavy, so move the weights up.

Regarding the DEC, you should have the camera end slightly heavy.

[Freddie]

Agree with Sara. Another way to look at it is to always have the weights moved slightly to the east. ie when weight bar is pointed east move the weights towards the end, when bar is pointed west, move the weights away from the end.

[Gina]

Thanks

[todd8137]

Here's my understanding of weights.

If the weights are pointing towards the East and you are imaging an object that is rising towards the meridian, then you have the weights slightly heavy. If you have crossed the meridian and the weights are now pointing towards the west and you are therefore imaging a target on it's drop from the meridian towards the west, then you have the scope side heavy, so move the weights up.

Regarding the DEC, you should have the camera end slightly heavy.

I use lead fro this the stuff that you put on windows cost me about 6 quid ,and when it flips I just take it of and put it back on works. A treat

[todd8137]

Ish. But if he's never encountered this problem before it would seem odd for cone error to appear out of no where would it not? And if there was new cone error, surely it would result in a gradual drift of the imaging scope away from the target and result in corrections needed in both RA and Dec?

James

May be

Pat

[kirkster501]

Cone error is when the scope is not "true" with respect to the mount when it is pointed in different areas of the sky. 

I have not had to deal with cone error before since I have never built a scope from the OTA and dovetails from scratch before - my other scopes have all had cone error accounted for by the various washers etc you see on the dovetails.

Great description from Sara about the weights and which end they should be on.

[ollypenrice]

Rather than turning off Dec altogether it can often be productive to turn it off in the direction that isn't doing anything other than overshoot. This means trying both Dec+ and Dec- and ditching the one you don't need.

I do this on one of the Tak mounts here. Rather than re polar align it I'm going to leave it because, guided only in one dec direction, its guide trace is, absolutely, to die for. If it ain't broke...

Olly

[steppenwolf]

On the subject of adjusting the balance, the mantra I work to is 'make the rising side heavier' - simples!

[kirkster501]

On the subject of adjusting the balance, the mantra I work to is 'make the rising side heavier' - simples!

I like....

[russellhq]

On the subject of adjusting the balance, the mantra I work to is 'make the rising side heavier' - simples!

The way it was explained to me was "Keep the east side heavy". But when it comes to doing it, all I can remember is that I need to keep one side heavy and forget which! I might write something on the mount or weights to remind me...

[kirkster501]

Well, all going very well tonight!

[jambouk]

Bonus