Question re Polarscope Fitting from a Newbie

[Johnny666666]

Hi to everyone on the forum :-)

My very first question regards the fitting and rotation of a polarscope. I'm completely new to astronomy and I've recently purchased a Skywatcher 150P on an EQ-3.2 mount, and had enough cash left over for a Polarscope and twin motor drives. I spent an enjoyable day putting it all together but a frustrating evening trying to sort out the polarscope. Once I'd found out I needed to remove the existing polarscope holder and day/date circle from the mount and replace it with the optional one, I couldn't find any information whatsoever regarding it's rotation.

I found the polarscope just screwed in until it stopped dead, but when I did so, with the mount at 'home' (I believe it is called) the polarscope diagram was about 135 degrees from horizontal - by that I mean the writing etched into the diagrams was 'almost' upside down. I then removed the polarscope and fitted some of the thin plastic shims I found behind the holder I had taken out, and managed to get the polarscope diagrams and writing 'the right way up' when the mount is at 'home'. Sort of. If I fully tighten the polarscope it does still misalign (with the mount at 'home').

My question is this - is the angle of rotation of the polarscope within the mount totally irrelevent? If I rotate the RA axis to so that the polarscope shows Polaris in transit, and then tighten the polarscope fully, I then need to adjust the rotation of the RA axis to put Polaris back in transit. Is this normal? Do I just need to tighten it completely and leave it there?

I have some further questions regarding the setting circles but for the moment I just want to find out about the polarscope fitting. There is absolutely zero information out there about its fitting, but a plethora of info about aligning it, which is irrelevent if it's not fitted correctly

Be kind...! (and apologies for any incorrect terminology)

John

[jambouk]

Hi john .

Your polarscope should sit firmly in its hole, so screw it in nice and tight (not overly so though). The position of the polaris circle is irrelevant, as you will rotate the RA to get it to where you want it (and where polaris needs to be) in order to polar align the scope. In the home position, all of out small polaris circles will be at different positions; this is fine.

I'm not sure that answers your question though.

Once the polar scope is fitted, you do need to align the reticle within it to the RA axis of the mount. There are threads on here about that and online tutorials.

Good luck.

James

[Johnny666666]

Hi James, thank for the information.

Yes, that answers my question perfectly, thank you! It's not mentioned anywhere that I've found, and a concise "screw the polarscope fully home - it doesn't matter where polaris is because the it is aligned by rotating the RA axis" wording would be useful in the (non-existent) instruction manual for complete novices like me. It always seemed odd that amongst all the detail of aligning this, that and the other no mention was made of actually fitting the polarscope!

I did align the reticule after fitting it, though I am tempted to unscrew it, remove the thin shim washer and re-fit it, because it's not a 'firm' fit and I can squash the washer to different degrees by further tightening the polarscope. What do you think? I also had a similar issue to another member, whereby the crosshairs were aligned correctly at either extreme of the 180 degree rotation of the RA axis, but they appeared to drift out of alignment and back in again during rotation. I'm not sure what would cause this and how much it would affect aligning...?

John

[jambouk]

You want there to be as little, ideally none , movement of the polar scope s possible. Take it out and refit it, the. Realign the reticle. A tedious hob but better to have it correct.

Are you aligning the reticle in the day time using a distant object on the horizon? This is much easier than trying to do it on polaris at night.

With regards the cross hairs moving out of a perfect arc during a 180 rotation, make sure the counterweight bar or counterweight (if attached) isn't knocking against the body of the mount or a tripod leg as you rotate which i've seen happen when the mount is pointed to a low elevation (7 degrees above the horizon). The other thing might be that there is some lateral play in the RA axis or that it just can't do a perfect circle so when you rotate it with the clutches off it either drops/sags in it's way around, or that it just rotates in a slightly elliptical way. Whatever causes it, it happens everso slightly on my mount too, but the cross hairs are pretty much bang on at either end of the 180, and my polar alignments seem to be reasonably accurate for my needs.

Is the polar scope protected on your mount? On the heq5 and neq6 it has a screw on cap to stop the polar scope being bashed during transport from one place to another; there is no such protect on my azeq6 and i wish there was something more protective than a dust cap. If you are going to transport it, just have a think about if thee would be a simple modification you could do to protect it, or just take care with it. You should be able to find pictures of how the heq5 and neq6 deal with this.

James

[StevieDvd]

If you want to be exact with the fitting then it is possible to align the polarscope with the setting circles. This means that you can dial the setting circles to the date & time (by rotating the RA) and it sets the small bubble in the right position ready for you to align.

Basically, you set the RA position to a set date/time and by unscrewing the holding allen screws the polarscope is moved till the bubble sits in the position for that date/time combo.

All of which is only of use if you have no other way of knowing the polar transit position when setting up - if you are observing visually the centre cross is a good enough point to line up with polaris.

[Tonys]

James makes a good point about using a distant target in the daytime to centre the reticule as having done it at night I can confirm it's a pain, especially those tiny grub screws. I didn't do it by choice though, it's just that I couldn't get my eq5 to go below 30 degree latitude setting and so it couldn't be pointed at a daytime target. I don't know if this is just a loveable foible of my mount or common to all eq5's, or if I missed something.

[Johnny666666]

Thank you - I did wonder about the slightly 'squashy' nature of the washer behind the polarscope, so I'll remove that tonight and re-fit it without the washer.

I also aligned the polarscope during the day using a distant object as per the instructions and online guides and managed to get it pretty much spot on. When I check the alignment again I might look at the method found on the 'astronomy shed' of using the straight line of a TV aerial and also imagining that one part of the aerial is Polaris and rotating the RA axis to simulate its orbit. My initial alignment did show that the cross hairs moved ever so slightly out of arc, but were bang on at either end of the 180 degree rotation. I didn't notice any play whatsoever in the mount and I didn't have the counterweight bar fitted as far as I can remember - the online guides suggested to have the scope and counterweights removed simply for ease of rotation.

As soon as I've done that I'll post again with my findings, then move onto the next question

Many thanks - John

[oldpink]

James makes a good point about using a distant target in the daytime to centre the reticule as having done it at night I can confirm it's a pain, especially those tiny grub screws. I didn't do it by choice though, it's just that I couldn't get my eq5 to go below 30 degree latitude setting and so it couldn't be pointed at a daytime target. I don't know if this is just a loveable foible of my mount or common to all eq5's, or if I missed something.

when I did mine I got my EQ5 down to about 10 deg, but that wasn't enough I needed it down further to get to my target

so I adjusted my tripod leg's to raise the back end  so pointing the polar scope lower down to where I needed it