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Re-positioning polarscope reticule

PostPosted: Wed Sep 28, 2011 8:44 am
by worcspaul
When I first got my EQ5 earlier this year I noticed the position of the polaris indicator in the reticule was such that for it to be at the correct position for polaris transit the counterweight bar would have to be vertically UP. Whilst fitting replacing the adjusting grub screws with thumbscrews (see Polarscope Reticule centering and mods ) I thought I'd take the opportunity to re-position the reticule. This work is probably best done on a clear flat surface with the mount removed from its tripod and counterweight bar removed:

  • Unscrew and completely remove the lens from the rear of the polarscope
  • Holding a soft (microfibre for preference) cloth over the rear of the polarscope, loosen the three grubscrews and then carefully tilt the mount back so the reticule drops into the cloth.
  • Place the reticule on a clean sheet if paper and put a marker on the metal ring to indicate where the polaris circle is. I used a pointer cut from a sticky label. A spot of tippex (dries quicker than paint) would probably suffice :

Image

(This is to make it easier to position the reticule when placed back in the polarscope)

  • Make sure the mount is in the HOME position
  • Taking care not to drop the reticule or get fingerprints on it (been there, done that :sad: ), tilt the mount forward and replace the reticule in the polarscope with the marker at the top.
  • Re-insert the three grubscrews and slowly adjust each one a half turn at a time until the reticule is just held by them
  • If the marker is n't quite at the top, loosen the grub screws a fraction and use a cocktail stick or similar to rotate the reticule (there are a couple of slots in the inner ring of the reticule.
  • Your polarscope reticule should now be in the correct position:

Image

In this image you'll see the three grubscrews have been replace by M3x10 thumbscrews which make life a LOT easier!

  • Finally, replace the lens (fitting an O-ring if you choose to do so, following Dion's tutorial) and screw back in until at the desired focus point

Re: Re-positioning polarscope reticule

PostPosted: Thu Sep 29, 2011 7:36 am
by worcspaul
D'OH!!

I forgot about the inverted image through the polarscope. The polaris indicator should be at the 6 O'Clock position, not the 12 O'Clock shown in the pic. :oops:

Re: Re-positioning polarscope reticule

PostPosted: Mon Oct 17, 2011 1:30 pm
by guyroch
Paul,

This is great... however... it is not enough to say that the polaris indicator should be at 6 O'clock ~ sorry ;)

Polaris is not at 6 O'clock when your mount is in "home" position.

Polaris is at 6 O'clock at specific dates and time throughout the year. One known fact is that Polaris indicator is at the 6 o'clock position at midnight on November 1st. I find the combination of midnight and the 1st day of the month easier to work with.

1. Park your scope; I do this because I like to start from a known _dead_ position. Once your mount is parked, your counter weight bar should be pointing down.
2. Set your RA setting circle to 0 hours.
3. Set the RA date scale to January 1st (see image #1)
4. Loosen the RA clutch and rotate the RA axis until it shows November 1st on the RA date scale (see image #2). Your scope should look something like image #3.
5. Lock the RA clutch
6. THE POLARIS LOCATOR (LITTLE CIRCLE) SHOULD BE POINTING DOWN AT 6 O’CLOCK NOW. IF IT DOES GOTO STEP #10. IF IT DOES NOT, FOLLOW THESE NEXT STEPS.
7. Loosen the polar scope a tad bit (3 hex screws holding the polar scope in place)
8. Rotate the polar scope so Polaris locator (little circle) is at the 6 o'clock position.
9. Tighten the 3 hex screws carefully.
10. Congratulation, you’re polar scope is now properly oriented.
11. Unlock the RA clutch and rotate the RA axis back to its original position, lock the RA clutch. The RA setting circle should show 0 again (as per step #2)

Hope this helps :)

Guylain

Re-positioning polarscope reticule

PostPosted: Mon Oct 17, 2011 4:45 pm
by Shorty73
Guy, I think Paul is just trying to get the Polaris Indicator at 6 o'clock as it justs make life a bit easier and neater when Polar aligning.

If Paul aligns like myself ( and correct me if I'm wrong)

1. Set Polaris indicator at 6 o'clock position by rotating RA.

2. Set RA indicator ring to zero

3. Enter all details into Synscan handset and read off Hour Angle.

4. Rotate RA to this time ( top scale)

5.Align Polaris in indicator in reticule.

I never use the slide rules as with the Synscan these are not required. I've not had the mount that long but I can polar align in minutes that way and take pretty good exposures.

Again I think its neat and tidy to have polaris indicator at 6 when at home position but not mandatory!

Re: Re-positioning polarscope reticule

PostPosted: Mon Oct 17, 2011 10:30 pm
by worcspaul
Shorty's correct in his assumption. Having the circle at 6 o'clock when the mount is in the home position makes life easier. I use a little app I wrote to convert the HA into a position to rotate RA axis to to put circle in right position. It's pretty much how polar alignment works in EQMOD I believe.

Re: Re-positioning polarscope reticule

PostPosted: Tue Oct 18, 2011 9:09 am
by worcspaul
Following on from what I said last night...

In Dion's tutorial he shows the process of placing the indicator at 6 O'Clock by rotating the RA axis then setting the RA clock to 0 before rotating to the relevant Hour Angle. I found that as originally supplied, my reticule had the indicator more or less at the 12 O'Clock postition so that I ended up with weights UP when following the tutorial. As the setting circles on the EQ5 aren't exactly precision made, I hit upon the idea of using the Show Position function of the handset to determine when I'd got the indicator at the right location for the Hour Angle.

The app I wrote takes the HA as entered by the user and converts it into clock minutes then arcminutes (15 arc minutes to one clock minute) then degrees/minutes. Initially this resulted on a figure between 0 degrees 0 mintues and 359 degrees 59 minutes...until I realised that the AX2 (which corresponds to the RA axis) axis position is shown as being between -180 degrees 0 minutes and +180 degrees 0 minutes so I had to modify the app to cater for that. It's then a question of reading the angle displayed by the app then rotating the RA axis until AX2 reaches the given angle

Image

As EQMOD knows the HA all it needs is a known starting point for the indicator, which can be either 3, 6, 9 or 12 O'Clock. Chris Shillito's tutorial Here shows what I mean.

Re: Re-positioning polarscope reticule

PostPosted: Fri Oct 21, 2011 12:23 pm
by themos
Haven't you forgotten to make sure that the central cross of the reticule is placed right on top of your mount's polar axis? That usually means adjusting the 3 grub screws so that, if you center a star on the cross, the star does not drift off the cross when you rotate in RA.

Re: Re-positioning polarscope reticule

PostPosted: Fri Oct 21, 2011 3:28 pm
by worcspaul
Sorry. All of the above makes the assumption that you have previously collimated your polarscope (as per Dion's tutorial) so that the centre of the reticule is aligned with the RA axis.

Having taken a further look at EQMOD it makes life a helluva lot easier. If, for instance, your polarscope reticule happens to be positioned such that the polaris indicator is approximately at the 9 O'Clock position when the mount is in the HOME/PARKED position, for example, you would manually move RA until it is at 9 O'Clock then tell EQMOD that 9 O'Clock was the polarscope's home position before clicking on "Align polarscope" which will rotate the mount in RA until the polaris indicator is in the right position, which will be more accurate than the human eye will manage.

I've yet to try it myself, but I think the combination of EQMOD's polar alignment and "alignmaster" will possibly yield the best polar alignment - especially in a situation where you don't necessarily have a decent view of E or W or S horizons to utilize drift alignment.

That said, with a little care and patience it's possible to achieve a half decent alignment, as I managed to do a few weeks ago when I was able to take a 6+ minute sub of M31 with little trailing. Not that I'm prepared to settle for that, of course. As a "benchmark" I'd like (with guiding) to get images from 5 to 10 min exposure without any trailing/distortion.