Will I just have to live with it? Polar scope

[theghettostylus]

Hello! Good afternoon and jazz.

I've calibrated my eq3-2 polar scope a couple of times now and got it as perfect as a human can get it and stopped the focuer from moving by putting a rubber ring inside and made sure everything is right.

My problems is no matter how close to perfect I get the adjustment of the reticle there is still movement of the image when I rotate in Ra while calibrating.

My cross hair does stay centered while rotating though. Is this normal? Is that how it looks when the reticle is in line with the RA axis?

Also when I have done my polar alignment and put on my scope and weights my polar alignment has been shifted of course.

Can I polar align before and after the mount is weighted wih the scope and weights?

Thanks

Jason.

[ronin]

I suspect the actual gears do not mesh perfectly, or as well as they could. They just are not precision equipment at the end of the day, I suspect that you could buy as good or better gears on ebay.

May be worth pulling it apart and cleaning and regereasing and resetting the gears, however that is not a 5 minute exercise, and I still suspect there will be play in the mechanical train.

[Davey-T]

If you're not imaging with it it's good enough as is for visual.

Dave

[jambouk]

I polar align after mounting the kit.

I'm unsure what you mean about the reticle. If you rotate the RA the cross hairs should ideally stay on the target you've aligned the polar scope on, but the rest of the printing on the reticle should rotate.

James

[theghettostylus]

Say I'm calibrating on a TV antenna and I get the reticle spot on the antenna and background rotate in a none perfect circle.

I have regressed the mount, maybe I should spend some time on tweaking the gears.

I am using it for imaging..

I know people say it isn't made for that but I like a challenge and will push the mount until breaking point to get some nice images

[Alien 13]

It should be possible to get the center crosshair spot on, the usual method requires you to set it up at two points 180 degrees apart but it may be necessary to use more points for fine tuning.

Alan

[jambouk]

Right, I think I get you now.

My mount's polar scope reticle does exactly the same thing. I'm unsure if it is an issue with the polar scope reticle manufacture, the milling of the hole the polar scope sits in, or of the RA axis itself, but I wouldn't worry about it.

Polar scope PA is only really the first step towards "perfect" polar alignment anyway. I suspect even if you could achieve "perfect" PA by using the polar scope alone, the imperfections in the rest of the mount would limit your tracking for long unguided subs (>120-240 seconds) anyway; depends also on the focal length of the scope.

If you really want to tighten up your PA, you should be doing something like the synscan handset polar alignment routine, or a drift alignment method, both of which only only need a rough and ready polar alignment to start with.

James

[theghettostylus]

I don't want to get into drift at the moment as it would take far to long every time I take the scope out of the shed, I only have the RA Dec motors but the other night I managed to get a 6 min unguided but now its gone down to about 30 secs when the scope is pointing almost straight up then above the horizon its about 4 mins.

I may save up for a better mount maybe a eq6 synscan or something as I can see this imaging thing taking over my wages aha roll on the darker nights so I get more time but on the plus side I've got plenty of time to get the mount as good as it can be before the dark nights set in.

[jambouk]

What is the focal length of your scope?

Can we see a large file of the 6 minute sub?

I think you have the polar scope as accurate as you can get it. There are drift aligning methods which can be undertaken relatively quickly.

Is your kit perfectly balanced when fully loaded?

I don't want to dampen your efforts, but if you don't want to do any form of drift alignment, and can't guide, i think the possibility of achieving reproducibly perfect PA is low, and that limitations in your mount and motors will also limit the chances of obtaining consistently long exposures.

I'd be tempted to go for lots and lots and lots of 20-60 second exposures rather than aiming for 6 minuters as I suspect you'd end up binning 90% of of the 6 minute subs due to poor tracking, but maybe only 10% of the 20 second ones.

Get saving for an HEQ5 or above.

James

[Gazabone]

You should be able to drift align the polar scope to the mount. You'll need to make sure that the collimation screws on the polar scope are nice and tight though which may explain the problems you're having. It did take me a little while to get it right on my 3-2 but was worth doing

[Alien 13]

I think you are doing well getting subs of 2 mins or over I can usually get 90 seconds reliably with a 135 or 200mm lens but something like 70 seconds with my scope, making sure the gears are in constant mesh by slight overbalancing helps too.

Alan

[glowjet]

If you have obtained just about spot on accuracy with the Polar scope cross hair rotating on centre, and the background is not concentric, when the body is spun through 360°, in other words it spins slightly off centre, then the fault, I am sure will lie with the manufacturer, as the holes in the body castings will not have been bored in line.

This is not the first time this has cropped up, as I seem to recall it has been mentioned in dispatches before. I think this is something you are going to have live with for the time being until you can upgrade to a better mount for your imaging, if you want to go that far.

There is one last thing you might check, if you can, is the Polar scope on centre of the hole it fits into, sometimes the Polar scope thread in the body has also been machined a little off line.

I don`t think adjusting the gearing will have any effect, other than to make the mount run a little smoother.

Good luck with your Photography

[theghettostylus]

I don't have the file I was just testing see how far I could go, I got up 2 siz mins but as the sky isn't that dark it wasn't worth keeping. I don't mind taking lots of 30 second subs or 60 if I can balance the mount better.

I didn't want to go and get a proper imaging set up and then find I didn't enjoy it so went for the eq3-2 and 150p just to get my feet wet as If I do go the serious road I can keep the scope as its fantastic and just upgrade the mount and sell the old one. I can always piggyback as I do like that side of imaging as well but thanks for all the advice!!!!