Mesu 200 Polar Alignment with PHD (and SiTech)

[pubquiz]

Over the past week or so in gaps in the clouds I have been setting the PA on my Mesu

I found this a good method.I realise most of this is well documented on many sites but thought I would repeat here with reference to SciTech and PHD. So appologies if you have heard it all before

1) In SiTech exe click 'Config' then 'Change Config' then the 'Freeze Declination' box on the Mount Parms tab in SciTech

2) Open up PHD and connect camera and mount and bring up the 'Bullseye' overlay under the 'Tools' tab

3) Orientate your guide scope so that vertical and horizontal movement are indeed vertical and horizontal (when using the guide function of PHD this doesn't matter but at this stage it does)

4) To set the RA point your scope at a star near to where the Meridian and Celestial Equator cross.

5) Don't use the guide function yet but just start taking pics with a 1 to 2 sec exposure of a brightish star.

6) With the movement controls in SiTech exe position the star on a horizontal line of the bullseye...it doesnt have to be on a vertical line as we are only checking for vertical movement.

7) Sit and watch the star for any vertical movement.

8) Adjust the RA knob on the mount a couple of turns in one direction ....the star will have moved so reposition it on a vertical line.

9) Watch the star again and see if it is moving faster or slower than before so you now know which way to turn the knob...the idea is to get it to stay vertically on the horizontal line of the bullseye for as long as poss (don't worry about any horizontal movement). Just getting it to stay pretty much on the line for a couple of minutes with no vertical movement is ok at this stage as we will be doing it more accurately with PHD guiding soon.

Tighten up the RA adjusting nuts/clamp bolt.

10) Now we will set the DEC axis...slew the mount with the handbox/or on screen buttons so it is now pointing at a star as near to the Eastern or Western (doesn't matter which) horizon as poss so basically as low as you can get to the horizon. Again position a star on a horizontal line.

11) This time adjust the DEC adjustment knobs on the mount ....again we are looking for no vetical movement of the star for a couple of minutes.

The above method gets an approx Polar alignment so we will now use the guiding function of PHD to get it spot on....the reason I did it this way 1st was that if the alignment is quite a way off the red trace of PHD (explained soon) just shoots off the graph immediately and you are not sure which way and how much to adjust things.

12) Go back into 'Change Config' and 'Mount Parms' in SiTech and untick the 'Freeze Declination' box that you ticked earlier ...this will turn the dec motor of the mount back on.

13) Leave the scope pointing where it is and in PHD turn off the bullsey overlay.

14) Select a star and start the calibration process as normal in PHD and start guiding.

15) While still guiding we now need to turn off the DEC Guiding in PHD so you can either stop guiding and click the 'Brain' and select it at the top right ('Dec Guide Mode' and select 'Off') OR even easier click 'Enable Graph' in Tools (since we need the graph anyway) then select 'off' in the bottom right hand selection box on the graph screen (there is 'Off' 'Auto' 'North' and 'South' in this box we need to select off...this is only refering to the DEC part of guiding)

16) Now on the graph click the 'RA/DEC' button so the display changes to show a blue and red 'dx' and 'dy'

17) Now look at the red 'dy' line ...if we have got the polar alignment (PA) pretty good in the first steps as above the line should only be rising or falling slowly...if it shoots up or down very quickly we are still a way off ...the idea is to get the red line as flat as poss by adjusting the knobs on the DEC axis (remember the scope is still pointing at the E or W horizon)

18) This is good to do now as you get a real time indication of which way and how much to turn the knob.

19) After adjusting the star will have moved again so click 'Stop' in PHD re click the star then click the 'PHD button next to stop to recommence guiding.....it doesn't go through calibration again as it is the same piece of sky ...just start guiding again and watch the red trace on the graph (I usually click the 'Clear' box on the graph to start it afresh) ...keep doing this till the line is as flat as you can get it ...it will wobble slightly but we are loooing for it to stay as level as poss.....tighten up the DEC adjustment knobs on the mount when done.

20) Now we are ready to go back and fine tune the RA alignment

So using the motors position the scope so it is pointing at a star as near as poss to the Meridian and Celestial Equator.

21) Since we are now in a different piece of sky we will have to recalibrate PHD guiding so after clicking the 'Stop' button in PHD go into the 'Brain' and tick the 'Force Calibration' box at bottom left and on the graph select the DEC guiding box at bottom right to 'Auto' again.

22) Select a star and click the PHD button again and it will start its guiding calibraton.

23) Once the guide lines are green indicating guiding has commenced click the bottom right button on the graph again to select DEC guiding to 'Off'

24) As before look at the red 'dy' line and adjust the RA KNOBS on the mount to get a flat line again.

The PA is now pretty much spot on...after adjusting the RA it does affect the DEC a bit so you may want to go back and forth a couple of times refining it

Also the longer the focal length of the scope used the more accurate it will be .......it doesn't matter about it being ABSOLUTELY bang on if you are guiding but if the scope is permanently mounted in an observatory, like mine , it is worth doing to improve gotos etc.

I have attached 2 screen grabs one shows that alignment is still slightly off with the red line going up (the full graph left to right is 10 mins). The other is with PHD during guiding so it is correcting for this.

These were done last night and I ran out of time to get spot on but will do next time.

I realise this has been a long drawn out explanation but hope it helps as there must be others like me who need their hands holding throughout the whole process

Tom

[themos]

Hello, I think you may confuse readers with steps 8, 11 and similar. It's not the "RA" or "DEC" directions that need adjusting, it's the altitude and azimuth directions of the polar axis. Also, I am not convinced that you must look at dx/dy graphs in PHD. I think you need to be looking at RA/DEC graphs as polar misalignment results in declination drift (to first order)

[pubquiz]

Hi Themos

On a GEM mount though RA is the Az and DEC is the ALT ...on a fork mount you refer to them as ALT AZ ..on a GEM as RA and DEC

Either way I think people will know that AZ or RA is the right and left movement of the mount to adjust and DEC or ALT (or even Elevation) is the up and down

In PHD you DO select the dx/dy graph when using this method ...see here for the same explanation in another thread http://njstargazer.org/PolarAlignment.asp

I tried to make it as easy as poss to follow without getting too technical re alt/az/dec/ra /elevation etc but am more of a tutorial follower than writer

Tom

[themos]

The New Jersey Stargazer site is wrong on this. All dx and dy information tells you is how you've oriented your camera relative to the mount. And it's wrong to confuse two different notions such as Declination and Elevation/Altitude.

[perfrej]

Jeez!

i do not mean to be rude, but is this a procedure that you HAVE to go through? It seems a bit overly elaborated and kind of complicated.

/per

[vdb]

How Olly and I did it.

-Setup Mesu, make sure it's level

-Look through finder and put polaris at 2/3 off center

-Guide without dec corrections for 5 minutes in East, adlust altitude, recheck ...

-Guide without dec corrections for 5 minutes close to meridian adjust Azimuth, recheck ...

We take 30 minute subs since then without any rotation ...

I've done this 2 times and it never took more than 20 minutes in total (actually last time I spent less then 10 minutes, must have been lucky with the finder scope), easiest mount to polar align ... and that with 50 KG of total weight.

The adjustment screws are just stellar.

/Yves

[pubquiz]

No you don't HAVE to do it it's not compulsory...use any method you like!

[perfrej]

Gotcha!

/p

[pubquiz]

Hi Yves

Yes the method I posted looks long and drawn out....takes longer to read than actually do though

The using PHD method though is quite quick and easy ...it's just the way I described it goes into every little stage and ....when I read tutorials I quite like the ones that go into great detail and don't assume any previous knowledge but it looks like I am alone in that.

Obviously it hasn't gone down well so would delete but I am not allowed to edit yet .

I agree the Mesu's adjustments are great.

Since you are a Mesu user Yves what do you think of the RA trace on the graph in a post I posted (haven't had any replies yet) should I expect a smoother line?...would appreciate your expertise on it

Post is here:

Thanks

Tom

[pubquiz]

The New Jersey Stargazer site is wrong on this. All dx and dy information tells you is how you've oriented your camera relative to the mount.

And it's wrong to confuse two different notions such as Declination and Elevation/Altitude.

Although it does tell you how your camera is oriented relative to the mount in this procedure IT DOES show the PA error.

During PHD's calibration process is doesn't matter how the guide cam is oriented ...PHD allows for this in the process.

I tried it last night to prove this.... after lining the cam up so it follows inputs on the hand pad going vertically up and down and horizontally left and right I did a calibration in PHD then selected Dec guiding off and watched the red line move up showing PA to be a slight bit off

I then stopped PHD, physically turned the guide cam 45 degrees in the guide scope, re calibrated, turned off Dec guiding and watched the red line again.

It drifted again IN THE SAME DIRECTION AT THE SAME RATE showing that guide cam orientation doesn't matter when doing this procedure as long as you don't alter it's orientation after PHD does it's calibration

After moving it 45 degrees and selecting dx/dy the blue RA graph did of course move downwards but this doesn't matter as we are only interested in the red Dec graph.

I always position the guide cam in line with the axes anyway as its easier to position a star (as mentioned in step 3).

As stated dx/dy MUST be selected as if you leave it on RA/DEC then the red line never moves (Dec guiding is selected off remember) and remains perfectly level whatever your PA is.

Tom

[themos]

Thank you for taking the time to test this and the clarification. It seems that PHD plots deviation of star image when in dx/dy mode and size of correction when in RA/DEC mode. Which would explain why you get a flat DEC graph when you turn DEC guiding off. Or maybe it does plot Ra/Dec deviations but flatlines the Dec if it's turned off. An alternative, if your ASCOM Telescope driver supports it, is to allow DEC guiding in PHD but forbid it in the Telescope driver. EQMOD, for instance, allows this, I think, so you can still get a Dec graph out of PHD. I still have a hard time believing that dx/dy plot will reliably tell you about Declination excursions. I know you investigated it for a 45-degree rotation relative to the ideal camera orientation but if some poor unlucky person placed their camera at 90-degrees to the ideal I think they would end up confused about the meaning of the dx/dy graph.

Actually, I had a look at the log file that PHD produces when Dec guiding is turned off and both DecDuration and DecDistance are set to zero. That's just silly and explains why you can't get a Dec graph out of PHD when you turn Dec guiding off.

[themos]

Here's another easier solution: Leave Dec guiding to Auto but in the "brain" dialog, look for "Disable guide output" checkbox and tick it! You then get a DEC graph when you use the RA/DEC option in the graph window.

.

[pubquiz]

Wouldn't diasabling guide output also disable the RA guiding as well though?

It's just that it is pretty easy to disable the Dec guiding from the button on the actual graph 'on the fly' so to speak and also to experiment with just giving North or South corrections etc.

Probably quite a few ways to do it just that the PHD method does seem nice watching how TINY mount alterations effect the trace in real time.

It was something to do over these past few nights betwen flippin clouds keep coming and going

Re the poor unlucky person placing the cam 90 degres to the ideal ...again it doesn't matter how you place the cam anywhere round a full 360 degrees as once PHD has done its calibration the red trace always goes the same way.

I agree though that the left and right buttons would move the star up and down though ....did this a few times with my basic G11 ...just held handbox sideways

If guiding, just the initial polar align in stage one or Yves method will be ok of course ....just thought I would get it absolutely spot on with PHD as mount will now never be moved and I had nothing else to do over the past few days of changeable skies ....I do admit I get too obsessed with things sometimes though

I also admit (as Per pointed out )that my description is a bit long winded (and the RA/AZ reference not fully correct)

Basically though it's just a usual drift align then a more accurate version in PHD.

Don't mind how the skies are tonight...off to the pub quiz later....jackpot's up to £1000

Tom

[themos]

Yes, you'd lose the RA guiding as well but that's not important for polar alignment. I used this method but with a piece of software called EQAlign and it's nicer than PHD because it annotates the camera image with targets for where a particular star should end up after you correct the polar axis. I'll make a test of what happens to dx/dy when you rotate the camera and report back because I'm really curious now!

[pubquiz]

There is a PA routine in the controller the Mesu uses (SiTech) as well...sounds similar to the EQ Align you describe.

Not tried it yet though as only just got the mount and still learning it....will definitely give it a go sometime though see if it agrees with the other method.

Tom