Celestron's AVX default accuracy.

[newbie alert]

newbie alert. I was going to PA on Regulus but could see some kind of flashing warning but couldn't read what it said. So i chickened out and pressed back and manually slewed to Arcturus instead. I got the flashing warning again and again hit back. So i manually slewed to Denebola and got the same warning again...I kept thinking i had done something wrong so i'd power down and power up again and restart right from scratch.
So yes...going to have to look in the settings and see how i can change that scrolling flashing text

I'm sure there's a setting to either increase or decrease the brightness on the handset but can't remember  what and yes I agree that sometimes it's hard to read..just a red blurb... I'm using Capella at the moment..seems to work on that..but if you get the warning again don't power down as it's just saying it's either too  near the zenith,pole or I think western horizon..

[newbie alert]

Mathmog,I'd like to know what scope you're using to be able to use a 6mm plus 2.25 Barlow as unless I have hugely transparent skies I can't use a 7mm on mine..

[Olsin]

Cheers guys ... I've now tried the new power supply and adjusted the scrolling text settings on the handset. Now i can read what it says. Strange that by default it should be set so high.

So i started out by levelling the base. Once done i attached the mount, tube and other bits and bobs and balanced it out. Using my polar scope and the app "Polar Align" i PA'd the mount spot on - i aligned the polar scope to the mount a few days ago.
I then powered up and entered all correct parameters and selected 2 star alignment.
The 1st star, Capella was about half a tubes (8") width from the edge of my FOV.

Does this mean, despite being careful and thorough with the initial levelling, PA and entering of parameters, i hadn't been accurate enough?

The next star was a bit closer and the last 2 remaining stars of a complete 2+4 alignment, were both almost spot on.
I then slewed to Denebola and started the ASPA. I could now read what was on screen and simply followed the instructions. It was a bit tricky using the altitude nob's to get Denebola smack on as tightening them introduced small movement in the other axis.
I have replaced the large bolt that sits under the polar scope with a smaller one so that i can use the polar scope. The tip of that bolt is not as round as the default one so i suspect that's introducing inaccuracies. Still, after a lot of messing about i got it tightened down with Denebola dead on the cross hairs and finished the procedure.
Powered down, set to index and powered up again.
Same run through using 2+4 and display align showed .. alt 3min 32sec, az 2min 27sec.
I understand that's not a particularly good alignment although i don't know how i could have been more accurate during setup and alignment.

Although cloud came in ended the session, if instead of selecting display alignment i had done another ASPA, powered down and 2+4 calibration, (so, 2+4 + ASPA + 2+4 + ASPA + 2+4) should i have expected to see the accuracy increase?

[The-MathMog]

12 minutes ago, Olsin said:

Cheers guys ... I've now tried the new power supply and adjusted the scrolling text settings on the handset...

It is a decent alignment. Not good, but decent. Getting a better one than that takes precision, either centering every star in a very high magnification eye-piece, and making sure you slew to it from the same side each time (as slop in the gears can also produce errors). That or you simply have to do "drift aligning". It is often easier to do than one might think, but it takes some testing and practise.

Regarding the slew to your first star, this sounds perfectly normal. You have to remember, that when you polar align, you don't polar align your scope, but your mount. There will almost always be a small difference between your scope and your mount, and this error is partly what shows up when you do your first slews. When you star-align, you then actually align your telescope, and the mount can then calculate what I believe is known as "cone error" which is the error between the mount and the telescope. 

My scope does the same. Even with a pretty good initial PA, it will still miss the first star a bit because of this and is perfectly normal.

Depending on how accurate you were, then I'd say yes, you should expect an increased accuracy in PA. There are of course some limiting factors as to how accurate the mount can calculate it, but a lot closer or even under 1 arc minute should be possible, and then drift align is your only option.

 

4 hours ago, newbie alert said:

Mathmog,I'd like to know what scope you're using to be able to use a 6mm plus 2.25 Barlow as unless I have hugely transparent skies I can't use a 7mm on mine..

I am using a Celestron 130 SLT OTA. But I am only using the 6mm + 2.25x Barlow combination for alignment, as it is indeed a bit too much magnification for most circumstances.

[Filroden]

After you ran the first 2+4 star alignment did you check the PA alignment?

I ask, because you'd normally either polar align with the polar scope or with the ASPA routine. There should be no need to do both. If the PA alignment error after the first star align is the same order of magnitude as what you've achieved with ASPA then no need to do ASPA. If there is a difference then you're not getting your PA quite right with the polarscope and you probably need to look again at this. I'd decide which routine you prefer (which is easiest or which gives best results) and really work on improving that process rather than trying to do both.

FWIW, I personally use ASPA + drift.

[newbie alert]

Sounds like you're doing it right apart from the bit  when you say..

Powered down, set to index and powered up again.

are you telling it to go to home position and then adjusting to set to index marks? If yes then you are undoing all the work you have just done..

slew it to home..power down and then start again (Don't move to index marks) although I've never redone it before..only ever done it once but makes sense if you have the time and have clear skies

[Olsin]

Thanks MathMog, as i mentioned before i use my DSLR for centering. It has a flip out and turn around live view screen that can have a grid projected on it. The grid intersects in the middle of screen giving me cross hairs. I can zoom in on the star and get it absolutely dead on.
However you are correct, I don't use the zoom in feature everytime, inaccuracies could be creeping in there. I'll tighten up my act and see if i can improve those align numbers.
I've read posts of people saying they get 90 sec subs just by doing a 2+4 then ASPA and another 2+4. I can see i've got a way to go before i can match that.

@Filroden .. No i didn't check PA alignment there, i went straight into the ASPA routine.
I realise it shouldn't be necessary to do both analogue and ASPA but i wanted to see if they matched up. My thoughts were that if ASPS slewed right back on the star and there was no need to adjust then the analogue PA routine would suffice in the future.
I should have done it the way you mentioned though. My way leaves me in doubt as to which of the 2 routines was inaccurate. I'm none the wiser. So yes, maybe i should concentrate on one method. ASPA and drift you say. I'll have to look into that.

@newbie alert .. Hm, no, what i done was powered down (leaving the scope pointing at Arcturus i think) and then manually reset the mount to the index position before powering up again. I didn't select goto home on the handset and i didn't set home position before i started. I've somehow changed my default home setting position and can't get it back.
When i first got the mount, selecting goto home on the handset would send it back to the index position. Then i accidentally clicked "set" one night when i meant to select "goto home". Since then the mount doesn't associate home with the index position. I've tried restoring factory defaults but it doesn't change anything. If i want it to goto the home/index position now i have to set it at power up and then reset it if i power down and power up again.

Are you then saying that by manually setting the mount to the index position after i powered down, i ruined my alignment?

[iapa]

If you manually aligns the index marks before you next power on, you can go to telescope / home / set

it should retain that in future- as long as you do not "set" when it's in a different positin

[newbie alert]

Are you then saying that by manually setting the mount to the index position after i powered down, i ruined my alignment?

Probably yes..are you selecting home position in utilities?  

I've never redone the align mount before,I might try it as sounds logical but as I can do 2min exposures with a sct to push it higher I'd be guiding.. unless you can select home I wouldn't do it manually unless you can put your own index marks and be confident that it's in exactly the same place any alignment is going to be spoiled..

[PeterCPC]

I don't know why you are powering down. I never powered down when completing the ASPA routine. Rather than powering down you just need to update the star alignment by using the Undo that I listed.

Peter

[Olsin]

@ Peter ..

4 hours ago, PeterCPC said:

I don't know why you are powering down. I never powered down when completing the ASPA routine. Rather than powering down you just need to update the star alignment by using the Undo that I listed.

Peter

I rebooted the mount simply because i've read a few places that rebooting and doing another 2+4 should be better than unsyncing through the handset and re-aligning ... although it's all still very new to me. I don't know if one way is actually better than the other. However, now that i can read what is scrolling across the screen on my handset (which in turn now makes the manual much easier to follow), i'm sure it's only a matter of time before i've settled into a good routine.

[MattJenko]

There are one or two items that are getting a little confused at times here, so worth restating clearly, just to reinforce this rather useful discussion.

Polar alignment and star alignment are two very different things. ASPA or polar alignment through the polar scope aligns the mount with the Earths rotational axis. You can power off as many times as you want once this is done, it is physically aligned with the rotation of the Earth, end of. It won't need doing again until the mount is physically moved.

Once polar aligned, then the star alignment tells the mount where the telescope on it is actually pointing. This should be done through the telescope, because even if the mount is in a known 'home' position (mine never is), the scope is not necessarily perfectly aimed in the saddle/rings etc. The first star can be waaay off and that has no relation to how well the setup is polar aligned, it is a function of where the mount thinks the scope is currently pointing in RA/DEC. Once you have done a couple (or more) of star syncs in various parts of the sky, then the mount has a good understanding of where it is pointing and gotos start to actually work well.

All the other comments about balance, power and the like are all valid for the tracking side of things, just remember the distinction between polar and star alignment.

[MattJenko]

I'd also be rather surprised if an AVX could do 60 seconds unguided with an 8" SCT and not noticeably trail to be honest.

[Olsin]

57 minutes ago, MattJenko said:

I'd also be rather surprised if an AVX could do 60 seconds unguided with an 8" SCT and not noticeably trail to be honest.

Now that's the sort of honest opinion i was looking for when i first started this thread.
All things being equal, just what is the AVX capable of?
I don't really want to keep wasting my time chasing accuracy if that accuracy is not to be had.
I've already considered polemaster and a guide scope/cam configuration but that would just be introducing even more complexity into an already challenging exercise.
I'll go that route if i have to, however if the AVX is capable of comfortably giving 60-90 second subs though a manual alignment and maybe a touch more if i perfected drift aligning, then i'd certainly be happy with that for now.

[The-MathMog]

7 minutes ago, Olsin said:

Now that's the sort of honest opinion i was looking for when i first started this thread.
All things being equal, just what is the AVX capable of?
I don't really want to keep wasting my time chasing accuracy if that accuracy is not to be had.
I've already considered polemaster and a guide scope/cam configuration but that would just be introducing even more complexity into an already challenging exercise.
I'll go that route if i have to, however if the AVX is capable of comfortably giving 60-90 second subs though a manual alignment and maybe a touch more if i perfected drift aligning, then i'd certainly be happy with that for now.

As mentioned, I have been capable of getting unguided subs of 180s with it (possibly more, haven't tested yet, as I can guide now), which was using a 2.25x barlow effectively giving my newtonian a focal length of 1450~. Not quite the 8'' cassegrain FL, but up there so 90 should indeed be possible. Though I have to mention, that that was after I PEC trained it. At that focal length or more, tiny periodic errors in gears become quite noticeable, and before doing the "training" I had to throw away half of my subs of 120 secs, as periodic errors would return every 8-9 minutes or however long it takes. That PEC training worked wonders though, for what I initially thought was star trails. You can do manual training (though a bit tedious to do for 8 minutes), or you need a camera to make the adjustments, and by then you are pretty much guide-capable anyway.

But to be honest, I think a lot of mounts would struggle to not get star-trails at that focal length, as the PA really needs to be incredibly precise. Then it also comes, not only to how accurately the mount can be PA'd, but also how capable you are yourself  

[newbie alert]

1 hour ago, MattJenko said:

I'd also be rather surprised if an AVX could do 60 seconds unguided with an 8" SCT and not noticeably trail to be honest.

120 sec subs

[newbie alert]

2 hours ago, MattJenko said:

I'd also be rather surprised if an AVX could do 60 seconds unguided with an 8" SCT and not noticeably trail to be honest.

If you can't do more than a min with a avx and sct then if look at your polar alignment.

[MattJenko]

That is a nice individual sub. Do they all look like that in a session?

[Olsin]

After 4 complete routine run through's last night i've given up trying to get my AVX accurate. I think i've been unlucky and brought the worst one of the batch. I've also located the problem which is the altitude knobs.
On top of the 4 run through's i tried an ASPA and got the star dead on. I then unsynced and immediately ran through another ASPA on an adjacent star. It should have been spot on considering the mount had just been polar aligned but it was half way across the FOV..hm, I finished the routine and again tried another ASPA on another star. Again it was way out!.
I think the problem is tensions in the alt bolts, there is to much play in them. Trying to tighten them just introduces movement on the az axis....loosening and redoing the az axis also affects the alt axis. It takes a long time to align the star dead center and often i have to settle for one of the axis's (or both) not being absolutely tightened right down. I have to compromise if i want a dead center alignment. As soon as i slew the mount again it seems to release small tensions in the alt/az knobs. I noticed to that the merest brush against the weight bar was also enough to knocked it out of alignment.
I'm a bit saddened by the realisation that i may have brought a lemon, especially considering the amount it cost ... a definite under the belt blow to my enthusiasm.
So yes, 4 complete run through's and every run through was double minutes out of alignment when checked!

I have been as precise as i can at every step of the set up, i can't do it any better than that. You can't make something more level than level, you can't point it more north than north. Double checking and then re-checking every entry into the handset and spending time to precisely get the alignment stars to end dead middle of viewfinder using the correct down and right buttons on the handset to finish off.

Ok...writing that down helped a bit. There's still enthusiasm there.

I guess a polemaster won't help that much if the mount itself can't stay where it's put. Would a guide scope/cam/PHD be able to soak up those inaccuracies?

[newbie alert]

Revert to polar align and 2 star +4 calibration stars and then a ASPA.. .then do your imaging...think you trying to get it more than precise is taking the edge off what you're there to do.. the bolts should be tight enough to hold on position..and yes don't even breathe near the scope once it's imaging..let alone knock it

[The-MathMog]

1 hour ago, Olsin said:

After 4 complete routine run through's last night i've given up trying to get my AVX accurate. I think i've been unlucky and brought the worst one of the batch. I've also located the problem which is the altitude knobs.
On top of the 4 run through's i tried an ASPA and got the star dead on. I then unsynced and immediately ran through another ASPA on an adjacent star. It should have been spot on considering the mount had just been polar aligned but it was half way across the FOV..hm, I finished the routine and again tried another ASPA on another star. Again it was way out!.
I think the problem is tensions in the alt bolts, there is to much play in them. Trying to tighten them just introduces movement on the az axis....loosening and redoing the az axis also affects the alt axis. It takes a long time to align the star dead center and often i have to settle for one of the axis's (or both) not being absolutely tightened right down. I have to compromise if i want a dead center alignment. As soon as i slew the mount again it seems to release small tensions in the alt/az knobs. I noticed to that the merest brush against the weight bar was also enough to knocked it out of alignment.
I'm a bit saddened by the realisation that i may have brought a lemon, especially considering the amount it cost ... a definite under the belt blow to my enthusiasm.
So yes, 4 complete run through's and every run through was double minutes out of alignment when checked!

I have been as precise as i can at every step of the set up, i can't do it any better than that. You can't make something more level than level, you can't point it more north than north. Double checking and then re-checking every entry into the handset and spending time to precisely get the alignment stars to end dead middle of viewfinder using the correct down and right buttons on the handset to finish off.

Ok...writing that down helped a bit. There's still enthusiasm there.

I guess a polemaster won't help that much if the mount itself can't stay where it's put. Would a guide scope/cam/PHD be able to soak up those inaccuracies?

Did you ASPA RIGHT after you did the first one? Not refreshing all the star-aligns first? If so, then it would always miss, if you adjusted the PA. Or by unsync do you mean doing the star-aligns again? Just asking to clear up any confusion for me  And how long can your mount keep a star centered during an exposure?

Hmm. A few last questions too, before running conclusions. Simple of course, but important nonetheless. Have you tightened the bolt underneath the mount head into the stand properly? Tightening it up a bit after doing the last Az adjustments can help a bit too. It should be tight enough for the mount not to easily move, but loose enough for those last Az-adjustments.
Also, you should be able to tighten both Az bolts properly. It takes a bit of practise to do that properly, as you mentioned, it can move a bit in the last adjustment, but by that point, you should predict what the final movement would be, so that it ends up centered and also tight. Sure it can't stay completely centered if you bump into it, but it shouldn't move a lot either. You are not by any chance on soft ground either? 

If it still doesn't work out for you, then the best you can do is simply to contact the place you bought the mount and get a replacement (or even refund if that is what you want) while you still can. Errors do happen from time to time, either under development or during rough shipping (though it would have to be veeery rough, for a mount to be faulty).

But do check those last things beforehand. Everything should be tightened down firmly for the mount to work at its optimum

[Olsin]

Chuckles ... I've just deleted a long winded explanation explaining why i did what i did, how i did what i did and the circumstances i was working under but at the end of the day, i'm only kidding myself.
Yes i blundered. I hadn't tightened down the bolt holding the mount to base. That explains the consistently high figured align errors, despite all other parameters being on track.
As soon as i read that line in your post, i remembered that i had only tightened it sufficiently to hold the mount while i attached the leg plate. I didn't get back to it.
Visually observing the play on screen in the alt/az bolts lead me to conclude 2+2=3.

The good thing is though, i now know the whole handset routine pretty well.

With clear skies forecast for this evening/night i'm now itching to put it all together and see if i can't achieve a decent PA and star alignment.

Thank you everybody for your help and encouragement.