EQ MOD polar alignment

[malc-c]

OK, I've been preaching about how to polar align EQ mounts using the clock position that the handset gives, but now I'm confused. I'm intending to control my scope using EQMOD with a home made EQDIR cable, and I've been watching the tutorials on youtube, this one in particular

However in the video it shows Polaris at approx 2:30pm position with a clock time shown as 7:17 OK I thought, maybe this is because the polar scope inverts the image ?? - but then the position would be more like 8:30 and not 7:17.

Can someone clarify what orientation is seen through the polar scope. Is it right way up and left/right, inverted but correct left/right, or inverted and flipped ?? I've been assuming that you set the position as a normal clock face when viewed, ie with 12:00 at the top, so for example if the hour value was 6:00 for Polaris, then looking through the polar scope the bubble in which Polaris would be placed is at the bottom of the circle, with the graphics for the constellations in the corresponding places. If this is wrong then that would explain some of the tracking issues I used to experience.

[themos]

The constellations are put in the way you would see them with the naked eye. If Cas W is overhead, then it should be overhead in the reticle.

The polarscope is a standard refractor so if Polaris is above the NCP, it will look to be under the NCP in the reticle (and left will be right).

For EQMOD, I put Polaris in the central cross of the reticle, then adjust elevation of mount until polaris crosses the reticle circle at its top. I then rotate in RA to bring the little circle around Polaris. I then select "12 o'clock" and hit "Set PolarScope Home".

Once that's done, I hit "Align PolarScope", EQMOD turns the scope in RA, the little circle moves off somewhere new and I then use elevation/azimuth of mount to put Polaris in the new position of the little circle.

I hope that's clear enough (and correct!).

[RogerTheDodger]

Dunno whether this helps, but I've only recently been using this method. I started with the little circle at the 12 o'clock position, hit the align polarscope button which moved it round to the same places as depicted in the graphic, aligned and then re-parked. Last time out as I was putting the scope away (after 4 hours out) I repeated this and Polaris was still in the circle.

roger

[chrisshillito]

However in the video it shows Polaris at approx 2:30pm position with a clock time shown as 7:17 OK I thought, maybe this is because the polar scope inverts the image ?? - but then the position would be more like 8:30 and not 7:17.

7:17 is the Polaris Hour Angle not a clock position. Hour angle 0:00 is at the 6 o clock position, hour angle 06:00 is at the 3 o clock position etc.

The graphic shows what you see if looking through the polar scope. You don't need to menatlly flip anything - just get polaris appearing in the position displayed (either manually of using EQASCOM's automated move) and your done.

Chris.

[malc-c]

The constellations are put in the way you would see them with the naked eye. If Cas W is overhead, then it should be overhead in the reticle.

The polarscope is a standard refractor so if Polaris is above the NCP, it will look to be under the NCP in the reticle (and left will be right).

For EQMOD, I put Polaris in the central cross of the reticle, then adjust elevation of mount until polaris crosses the reticle circle at its top. I then rotate in RA to bring the little circle around Polaris. I then select "12 o'clock" and hit "Set PolarScope Home".

Once that's done, I hit "Align PolarScope", EQMOD turns the scope in RA, the little circle moves off somewhere new and I then use elevation/azimuth of mount to put Polaris in the new position of the little circle.

I hope that's clear enough (and correct!).

Thanks for clarifying the way the polar scope displays an image. I watched the rest of the video on how to have EQMOD rotate the RA to the correct position... seems the ideal way to remove any conversion. If I follow that tutorial correctly you could also position polaris at the bottom of the circle and select "6 O'clock" button before hitting the set polarscope home button ?

[chrisshillito]

For EQMOD, I put Polaris in the central cross of the reticle, then adjust elevation of mount until polaris crosses the reticle circle at its top. I then rotate in RA to bring the little circle around Polaris. I then select "12 o'clock" and hit "Set PolarScope Home".

Once that's done, I hit "Align PolarScope", EQMOD turns the scope in RA, the little circle moves off somewhere new and I then use elevation/azimuth of mount to put Polaris in the new position of the little circle.

I hope that's clear enough (and correct!).

Spot on!

Chris.

[malc-c]

Hi Chris,

Thanks for joining this thread. To answer one of my questions, could you explain the relationship between the time of 7:17 and the position of Polaris as indicated in the tutorial video ?

[chrisshillito]

If I follow that tutorial correctly you could also position polaris at the bottom of the circle and select "6 O'clock" button before hitting the set polarscope home button ?

Yes, so long as EQASCOM knows where your starting from (3,6,9 or 12 o'clock) then it will rotate the mount to the correct position. Some starting positions are more friendly than others - particularly if doing this with all the kit in place.

Whatever the starting postion you choose the procedure is essentially the same. Put Polaris on the centre cross then adjust the Alt bolts (for 6/12 o'clock), or Az bolts (for 3/9 o'clock), until Polaris intersects the reticule circle. Rotate the mount in RA until the Polaris circle is over Polaris and then hit the align polar scope. When the mount stops moving put Polaris in the Polaris circle using the Alt/Az bolts.

You only need to set hit the polar scope home button if you want to save that position for future use. So if you can start your mount in a known position (i.e. have marked off the home/Park position in some way that you can return to accurately) then on subsequent setups you don't have to bother with finding the start position manually but can instead just tell EQASCOM to move directly there before hitting the align polar scope button (so a two button solution!)

Chris.

[themos]

I'll have a stab:

Hour angle 0:00 is at the 6 o clock position, hour angle 06:00 is at the 3 o clock position etc.

Therefore Hour Angle 7:17 would appear "earlier" than 3 o'clock and it does!

[chrisshillito]

Hi Chris,

Thanks for joining this thread. To answer one of my questions, could you explain the relationship between the time of 7:17 and the position of Polaris as indicated in the tutorial video ?

I have - see above

7:17 is not a time but is an hour angle. The display is not a clock unless you want to think of it as an upside down 24 hour clock that runs backwards! . Each segment of the display represents 1 hour. Count up the segments anticlockwise from hour angle 0 (which is at the 6 o' clock position of a normal 12 hour clock) and you'll see that the Polaris dot is indeed at a position corresponding to 7:17

Chris.

[jnc71106]

Think I will have a go at doing it this way when the skies clear

Jake

[malc-c]

Chris, thank for the explanation. It has now become very clear.

I have one further question. I'm setting my scope up in an observatory, so am I right that having polar aligned using the method you describe, and saved the position I wouldn't need to repeat this on subsequent nights as the scope would not have been moved between observing sessions ?

[chrisshillito]

I have one further question. I'm setting my scope up in an observatory, so am I right that having polar aligned using the method you describe, and saved the position I wouldn't need to repeat this on subsequent nights as the scope would not have been moved between observing sessions ?

If your mount is observatory based there shouldn't be any need to repeat polar alignment every night. Once set it isn't going to change unless you move the mount (or your pier has moved/sunk etc).

The eqascom method provides a quick way to get pretty close although those into long exposure photography would most likely want to refine the alignment further by drift alignment (again you wouldn't need to do this every night with an observatory mount) .

Chris.

[malc-c]

Thank you Chris.

Looking forward to the next clear night to try this out