Advanced VX + polar scope = DEC knob issue?

[Zadoq]

We bought a polar scope for our Celestron Advanced VX mount to speed up the polar alignment process.

As a side line, I find it quite funny that many quite technical items we bought recently just don't come with any instructions. The polar scope was one of them. Still, let's soldier on...

Fitting it to the mount was straight forward. Right, it's in, so now let's look at this baby and let's look for Polaris...

Hang on, I can't quite get to it. Do I really have such a big head? I feel like I'm inside the mount now, yet I can't get a good viewing angle.

The problem is that at the UK latitude, the mount is quite enclined, so the polar axis now decisively points at the south declination knob instead of being parallel to it. That leaves a tiny gap between the polar scope eyepiece and the declination knob to put your head in. I had to twist and contort to try to get one eye in a decent position.

However much I tried, I could not see all the polar scope had to offer.

So the following day, we tried the following:

* as the north declination knob is smaller and T-shaped, we swapped it with the southern huge one

* we changed the mount so that instead of it pointing at the north celestial pole between 2 legs, it had one northern leg (we had to do that because the T-shaped knob would not completely thread in and hit its closest leg past 40 deg latitude)

That worked quite well as access is much better than it was. It isn't perfect though as the T-shaped knob that is now in place is threatening to gouge an eye out of anyone who didn't treat it with the respect it deserves.

So, here it is: has anyone else had that issue and have they found a better way of dealing with it?

Is there a better after-market declination knob? We would prefer one of those star-shaped knobs; one with a bigger diamater but with not such a long handle.

Thanks

Nico & Carly

[Alien 13]

I can understand your problem mine is not quite so bad but the bolt is very close when trying to adjust it.

My solution is to use one of these a right angled camera viewfinder it doesnt need fixing you just hold it in place.

Alan

[jambouk]

I don't have your mount, but to save my neck i use this:

http://www.eastmidlandsstargazers.org.uk/topic/5751-right-angle-polar-scope-viewer/?fromsearch=1

What latitude do you live at?

Have you tried to use the All Star Pole Alignment routine and get away from using a polar scope? What have been your experiences with it?

If you are only ever going to use the mount at roughly your latitude, could you get replacement bolts and cut the excess off so the bolt handle is pretty much flush with the mount body; would that help to make more room?

Jd

[jambouk]

The other thing i just though about whilst waiting for the kettle to boil is.... Have you spent tine centring the polar scope [reticle] with the axis of the mount? If you do this you will get really accurate polar alignments [assuming to subsequently do polar alignment well].

I just found a short but clearly written article on how to do this:

http://www.ioptron.com/Supports/iEQ45_Polarscope_1110.pdf

It's a pain staking thing to do, but get the mount in a position where you can sit comfortably behind it for an hour, and only make small adjustments to the grub screws around the reticle, like an eighth of a turn or less, before rightening up the other two. And make sure you do them up tight each time as once it is aligned you can't go back and retighten them for good luck as you will know the alignment out again. It will take an age to get it perfect, but is quite a rewarding job.

Jd

[Zadoq]

Thanks for the ingenious suggestions

Nico & Carly

[genrege]

Does anyone have a pic of a polar scope fitted to a VX mount?  I just can't see where it goes.  I can unscrew the cap at the back of the mount, and pull the plastic cover thing off the front of the mount, but the hole is obstructed with bits of metal (at the north end).  Just cannot see where I'd fit the scope.

And the reason for that question is this - using ASPA, 2 alignment stars, 1 calib star, I did the mount align, error was fairly close to zero.  I then did a goto Polaris, and the star just wasn't even in the view finder!  Prior to mount align, goto's were pretty much dead centre.  Argghh!  Spending my limited time getting nowhere at the minute!!!

[allcart]

Just slacken the clutch lever on the dec axis and rotate it 90 degress. The bits of metal bits rotate out of the way and give a clear unobstructed view through the hole.

[idigitize]

Does anyone have a pic of a polar scope fitted to a VX mount?  I just can't see where it goes.  I can unscrew the cap at the back of the mount, and pull the plastic cover thing off the front of the mount, but the hole is obstructed with bits of metal (at the north end).  Just cannot see where I'd fit the scope.

And the reason for that question is this - using ASPA, 2 alignment stars, 1 calib star, I did the mount align, error was fairly close to zero.  I then did a goto Polaris, and the star just wasn't even in the view finder!  Prior to mount align, goto's were pretty much dead centre.  Argghh!  Spending my limited time getting nowhere at the minute!!!

are you re-doing the 2 star alignment after the mount align?  I had the same issue on the second time out with my avx. Thought I must be doing something wrong. The instructions say about un-syncing, others say just turn the mount off and on again and re-align.

[knobby]

You need to re do the goto alignment after the aspa as Idigitize said... Sad but true

[genrege]

Got you.  Darn that Celestron manual!  Will take a look tonight when I get home - looks like clear skies and a bright moon.  Ah well, at least the moon will outshine the LP ;-)

As for the ASPA, I did the 2-star align + 1 calib star first, then the polar alignment.  Makes sense to have to redo the goto align; didn't think  of that whilst shivering in the dark!  Off & on will be the way to go for me, not really sure exactly what it's unsyncing.  At the moment it's taking all my available time just messing about with alignment, let alone doing some AP!  Looking forward to the day in become second nature and I do all this in 5 minutes...will report back sometime next year...

[idigitize]

The manual does state that you may need to un sync and realign, and it's a good idea to use 4 stars. 2 stars, and 2 more calibration stars, It doesn't say you have to. And it says that on page 30.

Off to look for a confused smiley....

[knobby]

http://www.celestron.com/support/knowledgebase?article=http%3A%2F%2Fwww.celestron.com%2Fc3%2Fsupport3%2Findex.php%3F_m%3Dknowledgebase%26_a%3Dviewarticle%26kbarticleid%3D2494%26group%3Diframe&title=What+is+a+quick+summary+of+how+to+do+All-Star+polar+alignment+with+CGEM%2C+CGEM+DX%2C+CGE%2C+CGE+Pro+and+Advanced+VX+and+Advanced+GT+Series+mounts%3F

[genrege]

The manual does state that you may need to un sync and realign, and it's a good idea to use 4 stars. 2 stars, and 2 more calibration stars, It doesn't say you have to. And it says that on page 30.

Off to look for a confused smiley....

I see! 

   

[idigitize]

Sorry, my 3rd word 'does' was more in reference to a post that has been removed. It's makes it read a little odd. ... But in a nice way.... It does say that...

[mickjackson]

Also just found this problem.

Any1 know the thread size so I can look for an alternative please ??

[Shelster1973]

Same problem for me.......but now resolved.

Replace the DEC knob with an M12 bolt and all is good.  You need a fairly long one though.  An M12 x 100 should do you good.

The one I have just fitted is a standard bolt head, but am going to look at replacing it with a socket head in the future

[drjamesr]

I changed the bolt for a shorter one, about 4" I think. By the time you are up to latitude 55 degrees no amount of contortion works. It is a poor design.

The bolt thread that matched my original was a US half inch unc, bought from a local steel stockist, who much to my amazement asked me how many I wanted rather than told me they were like hen's teeth.

I found that a short piece of 25mm blue hdpe pipe fits over the bolt head very snugly and with some tape for grip makes it easy to turn.

The down side is that a standard bolt does not have a rounded end and may damage the internals. I have had no problems though.

[drjamesr]

.

The bolt thread that matched my original was a US half inch unc

Having checked what I actually used I was getting confused with a bolt upgrade on something else. The AVX altitude bolt is M12 and 75mm long works fine unless you are in Scotland where it might need to be a couple of centimetres longer.