Can anyone help with accurate Polar Alignment Meade LX90

[Ryan_86]

Hi all, I am desperately trying to figure out how to polar align to true north, using a fork mount on an EQ wedge. I'm debating whether to purchase an explore scientific polar/finder scope from FLO. I'm thinking the finder needs to be mounted to the wedge and not the scope for accurate pa?

If anybody has any experience/knowledge with this or a similar set up, I would be forever thankful.

Thanks

Ryan 

[Freddie]

Have a look at the DARV method for PA. No need for a polar scope.

[Ryan_86]

Will have a look now, cheers pal.

[Ryan_86]

Fantastic thank you Freddie. It seems straight forward. So once I have done this, is it still worth aiming to true north via a polar finder so I can take images?

Thanks

Ryan

[Davey-T]

Dunno about true north but if you point the forks at Polaris with the scope aligned to the forks, get Polaris in view with a wide angle eyepiece 26/30 mm by adjusting the bolts and then spin in RA and adjust so that Polaris stays tracking around the eyepiece when spinning, if that makes sense.

This will get you pretty close and you can the refine it using DARV as Freddie said.

https://www.cloudynights.com/articles/cat/articles/darv-drift-alignment-by-robert-vice-r2760

Dave

[Freddie]

As Dave says, get close and then DARV to fine tune or just go with DARV as it is pretty quick once you get used to it. I think it is best to stop thinking in terms of "true north" as that doesn't get you properly polar aligned.

[michael8554]

Hi Ryan

The  polar scope is an expensive option that will only get you roughly polar aligned, you'll still need to drift align if you're going to image.

You could use Polaris and your existing finder, offsetting Polaris roughly to the hour angle, then drift aligning.

You could take a jpg after guesstimating, and use PlateSolve2 to calculate the RA and Dec of the centre of the frame, then adjust accordingly.

If you're serious about imaging you should consider guiding, you can then use PHD2's polar align features.

Michael

[Ryan_86]

Wow it's amazing what can be learnt from you guys here fairplay??

Ok I will ignore true north  and go for the Michaels suggestion of offsetting Polaris to the hour angle then use the DARV method as me tiones by Davey-T and Freddie. Would you guys be kind enough to check my steps and correct me if I have anything incorrect.

Set tripod and wedge in home position

Level mount and arms

Attach scope equipment camera etc.

Set latitude

Balance scope on both axis to set scope at 90 degrees so it's inline with fork arms. Using the raci finder place Polaris on the hour mark using polar finder app

Locate Polaris using widefield ep and adjust using lat adjuster then spin ra to ensure Polaris completes an accurate rotstion around the ep

Perform DARV drift alignment using DSLR with atleast a 2 min exposure and adjust until the trail overlaps one another

Make sure the handset is setto.pilar mode before I begin.

Do you guys think  I would benefit from using an illuminated 9mm crosshair eye piece in any way? I have ordered a 0.63 focal reducer for later on. If i still cant achieve accurate tracking i will get stuck into the platesolve2 programme.

Thanks again all??

Ryan

 

 

Set latitude and point scope at 90degrees so inli

[Davey-T]

16 minutes ago, Ryan_86 said:

 

Do you guys think  I would benefit from using an illuminated 9mm crosshair eye piece in any way? I have ordered a 0.63 focal reducer for later on. If i still cant achieve accurate tracking i will get stuck into the platesolve2 programme.

Thanks again all??

Ryan

Not really needed nowadays, it's easier to drift align using a camera

I find a right angled finder a worthwhile upgrade with illuminated crosshairs, once aligned properly with the scope it helps get targets into the comparatively small field of view of the SCT.

You can see mine on the left in the picture, it's an Antares one, not particularly well made but it works OK.

Dave

 

[Freddie]

In terms of your set-up routine I wouldn't bother with the two finding polaris steps. I would just get it pointed roughly in the right direction and then DARV. The DARV method will quickly get you set correctly once you have had a couple of nights practice. If you are a long way out, the V will be very wide so you need a reasonably big adjustment and the return line will indicate in which direction to make that adjustment.

[Ryan_86]

Ok so if i perform the DARV method after levelling and balancing it should be accurately aligned when I point the telescope back up at Polaris is it? 

DARV says to Set Dec of scope to 0 degrees due south for altitude axis, and again 0 degrees pointing at eastern or western for the azimuth axis. Am I setting the dec on the wedge or the dial near the top of the fork? Please excuse this last question, when it says point scope due south at 0 degrees dec, is that simply pointing south?

Thanks again guys

Ryan

 

 

[Freddie]

It means to slew the scope using the controls so that the scope is pointing in the directions you have described. You then adjust the mount (not the pointing position of the scope) until you have the flat lines and not the Vs as described in the method.

Once complete, the mount is polar aligned. I would forget about thinking in terms of pointing at polaris as that is slightly offset from the true polar alignment position.

[Davey-T]

Forget Polaris, a GoTo to Polaris will not end up with the scope and forks pointing to it.

Do the DARV and adjust the bolts to see whether it gets better or worse and find the right direction to nudge it into line.

Try not to aim exactly South try a little one side or t'other of the meridian, with scope aimed south, forks aimed north the dec should read 0

Dave

[Ryan_86]

Right ok, I understand the method now. I must remember to ignore Polaris haha. 

Again thank you both, without yiur help I'm sure my setup woukd be finding its way on ebay. I have a star adventurer also so I thibk because that relies on a Polar scope and true north, I thought that was the only possible way to aligning this set up.

Thanks both, I will let you know how I get on if the chance comes

All the best.

Ryan 

[Ryan_86]

Hi all, I'm eagerly awaiting an opportunity hopefully this weekend to try out the DARV method. Once aligned do I need to perform a 2/3 star alignment? I don't fancy doing all that work then messing it up shortly after?

Thanks again.

Ryan