Whats up with the VX goto all of a sudden?

[Kirscovitch]

Ok. When the mount works I love it. However last week when I went out, last night and tonight I am trying real hard not to break it into pieces. All three nights my GOTO has been horrible. I'm not quite sure what the deal is. Had good results the first half dozen times I setup but the last 3 have got me super frustrated.

Tonight I went to a pretty dark spot out in the country. It was dark enough to make out the brighter stars so I set the tripod pointed north, leveled it and put the mount and OTA on. Wanting to save the camera and laptop batteries I put in a 12.5mm reticle EP and started the 2 star alignment. After that did the 4 calibration stars. Moved on to ASPA and it was off by quite a bit. After PA the handheld read that it was off by about 6" both ways. Went back to the align mount option and did it again and then I was 0's across the board.

This has been the routine I have followed the last 3 nights out and same outcome. I punched in Jupiter and it swung over but stopped nowhere close to it. It was about 4 finger widths away from where Jupiter was. Confused I swung to Mars. Same thing. GOTO was way off. So I powered down and tried again. 2 + 4 star alignment and ASPA. Slewed to Jupiter. Not close.

3 hours later and 5 attempts at alignment I gave up and drove home scratching my head at what I was doing wrong. If this was the first or second time I had it out and had problems I would blame myself. It really gets me mad knowing that I had used it 5 or 6 times without an issue and now the last 3 have been total garbage.

[Steve Ward]

I would suggest that it's an inputted time error , four finger-widths is around an hour in angular terms , a Daylight Saving adjustment forgotten ... ?

[Kirscovitch]

Now that you mention it, I do believe I was entering the time as standard. Boy do I feel stupid 

And I did have problems starting around the time the time change went into effect.

Makes me feel worse that I made sure that I had all the time and location accurate. Even went so far as to double and triple check the lat and long. I don't know how I missed the daylight savings setting.

I knew it had to be operator error somewhere. Just needed that extra set of "eyes" to point it out.

Thanks Steve! I owe you one! 

[Steve Ward]

No problem ..... been there , done that ...  

[knobby]

And another one in the daylight saving time club here !

Did it last year and fully expected to do it again this year ...

Thanks for the inadvertant heads up chaps

[Kirscovitch]

Well with this bit of advice I hauled everything back out to the yard. Setup and changed the standard to daylight savings. Did the 2 star align and 2 quick calibration stars. ASPA and slewed over to Mars. Still off!

Not as much but it was about a finger width off to the left and slightly lower. Slewed to Vega. Low and left. 

It is way closer than it was before so I know that was part of it. Don't know what else is going on.

How close do you have to be time wise? I am within a minute according to my phone. It shouldn't throw it that far off should it?

[Kirscovitch]

Or what about location? Come to think of it I never changed my lat an long but would a 15 mile drive put it that far out of whack?

I'm pretty sure I'm using the correct alignment stars. Use a skymap on my phone to figure out what they are. A new one I used for calibration was Alberio. I knew it had to be it. A double star on orange and a smaller blue one. I'm just at a loss as to why it's still off. Thought the time change would be the answer.

[ronin]

A 15 mile change should not really cause it, the purpose of an alignment is to work out the errors to adjust for and I would have thought that this was compensated for. Equally I sometimes use mine 23 miles away and I do use a seperate location

It is however one of those things that the better you set it then the greater the accuracy, or the lower the errors that the scope has to compensate for.

What alignment stars are you using?

Just wondering if you have mixed up 2 of them - thinking Castor and Pollux here.

If any are around I tend to use the big red ones, they are a good colour and are usually seperate to others in the sky.

It is not always possible however.

It maybe worth searching out the Meade alignment stars, they have a list of bright ones that sit somewhat alone. Their idea is the scope aims at the big bright single one and you centre it. So even if you have no idea what it is you should just stuff the big bright one in the middle of the view . But it is a useful list.

[Kirscovitch]

I usually use the stars that first pop up on the list. Earlier tonight was Capella and Procyon. 

I originally was thinking that maybe a different set would be better so I tried different alignment stars. Arcturus and Spica. Capella and Spica. Pollux and Arcturus. I am not the most familiar with the spring stars as I have been with the winter ones so I tried to keep the alignment to stars I could easily recognize. And I was using a reticule EP so centering was not a problem. 

I just don't see what I'm doing wrong as a few weeks ago GOTO was spot on. I was amazed at the accuracy. So it has to be an error somewhere on my part.

[Steve Ward]

It's a cumulative thing , 1 minute out time-wise is 1/4 degree out , not starting from exactly Home parked position , different location etc , etc , all add up ... 

[ronin]

The only other thing I can think of - and I have no idea what it is called on the VX mount or even if it exists - is what Meade refer to as training the drives.

Done during the day and you centre something stationary and the scope moves off a set amount and you recentre the target. In effect the software measures movement and sort of recalibrates itself.

Never actually bothered on any of the Meades I have however a friend with the ETX-90 says it is worthwhile. The movement accuracy is supposed to be better.

The other option or thing to try, not a fix, would be to just do the alignment, then tell the mount to goto a suitable star, centre it and perform the PAE action. Thoughts being it might (just a might) then centre things better afterwards.

The other idea is press the Reset button and start all over again and see if that reverts back to the better accuracy.

[Dsidote]

The VX has something similar. Look in Utilities -> calibration.

I've had my AVX go a little crazy sometimes too.  When you use the ASPA it adds error to your GOTO alignment so you have to unsync from your 2 star alignment star and then repeat the GOTO calibration. There is a section in the manual about this.

I do a 2 star alignment followed by 2 calibration stars and then ASPA. I then return the mount to the home position, turn off the mount, and repeat the 2 + 2 alignment and ASPA 2 more times. It takes about 10-15 minutes and I can get very accurate PA. I don't usually bother with unsyncing, instead I use plate solving to let the mount know where its pointing. My GOTOs are usually spot on after that.

[Owmuchonomy]

I'm not familiar with that mount system but for my SW mount the star choice is quite critical. After much trial and error the key lies in the local meridian. For good polar alignment a 3 star alignment won't work for me (it's primary purpose appears to be to map the sky for GoTo and to take out cone error). I find the trick is to use a two star alignment using two stars on the same side of the local meridian that you want to image or observe and more than 30 deg of dec apart. Then perform the PA. Works every time for me. The issue of poor GoTo then only arises when a meridian flip occurs. Just a thought from personal trial and error on many a cold night.

[Dsidote]

Good point! I usually just let the mount software pick the calibration stars for me and it does just that.

[Owmuchonomy]

I keep a shortlist of 4 or 5 suitable stars listed by season and RA/Dec coords. I then make sure I only choose from those for the alignment process. The software usually picks similar ones but after all it doesn't know which side of the meridian you want to play! Therefore you may have to intervene.

[Kirscovitch]

Thanks for the tips guys. I will try them all out next time out. Way the weather looks it will be Saturday. 

[Kirscovitch]

I can't find the manual for the scope so I downloaded it and just spent the last half hour or so reading it cover to cover.

Lots of good info for un-syncing alignment stars after the polar alignment as well as choosing calibration stars on the opposite side of the meridian. Also I was using some stars near the zenith which sounds like a no no lol.

So this gives me a question though. If I plan on imaging something in the east, say M13, should I use eastern alignment stars and western calib stars or align in the west and calibrate in the east?

[Steve Ward]

If you're imaging you need to forget about fine tuning the Go-To and concentrate your efforts on Polar/Drift Aligning your mount , and think about getting a guiding system sorted out.

The Go-To will just get you pointing at your target , PA/DA and guiding will let you stay pointing at it for long exposures. 

[Owmuchonomy]

I can't find the manual for the scope so I downloaded it and just spent the last half hour or so reading it cover to cover.

Lots of good info for un-syncing alignment stars after the polar alignment as well as choosing calibration stars on the opposite side of the meridian. Also I was using some stars near the zenith which sounds like a no no lol.

So this gives me a question though. If I plan on imaging something in the east, say M13, should I use eastern alignment stars and western calib stars or align in the west and calibrate in the east?

Post 13. Same side of the meridian.

[PeterCPC]

To save time or location errors you might want to consider getting the Skysync accessory - I picked up a second hand one for £100 ($160) and it works fine.

Peter

[knobby]

Doesn't the skysync stop the aspa working?

[PeterCPC]

Don't see why it would.The Skysync will tell the mount exactly where it is and current time before alignment. Then align in the normal way.

Peter

[knobby]

Just something I heard... Did seem strange at the time.

[dobbie]

Try this first align the mount with the star it says on your hand set then press align then undo the alt/az locks then manually move your scope using your finder and align second star then press enter ,, don't know how but its works on the eq5 GOTO .

[Kirscovitch]

I think my biggest problem was the whole daylight savings time debacle. And then thinking back to when I set it up the second time that night I never powered down to realign after the ASPA. I just did the polar align and then slewed over to Mars. Weather is supposed to be fairly crummy for the next week or so and it is still eating me up not knowing if I have the problem figured out. I'll keep you all posted if and when I can get back out.