Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Equipment Discussions >> Mounts

Pages: 1
Stargazer78
professor emeritus
*****

Reged: 03/05/13

Loc: Susanville California
Drift aligning using PHD guide
      #6067199 - 09/07/13 02:30 AM

Tonight was a little frustrating. For some reason probably me lol..... I cannot seem to get the red DEC line to smooth out on the center of the graph. I start in the east about 40 degrees up my western view is blocked by my house and calibrate PHD. Once done I turn it off and open the brain. I disable the guide output and restart PHD. I adjust for altitude but I cannot seem to get the red DEC line to smooth out. Once I believe I am close but no where near smooth. It just goes back and forth between the center line on the graph. I slew to the south and adjust for my azimuth. Again no luck smoothing out the red DEC line and the blue RA line is all over the place too. The instructions I have read said that once this is done these two should be centered in the graph and running smooth. Can any one give me some advice or a better tutorial?

Post Extras: Print Post   Remind Me!   Notify Moderator  
Stargazer78
professor emeritus
*****

Reged: 03/05/13

Loc: Susanville California
Re: Drift aligning using PHD guide new [Re: Stargazer78]
      #6072232 - 09/09/13 10:20 PM

I have just read that you swith to DX / Dy while doing this. Is this correct?

Post Extras: Print Post   Remind Me!   Notify Moderator  
Phil Sherman
Pooh-Bah


Reged: 12/07/10

Loc: Cleveland, Ohio
Re: Drift aligning using PHD guide new [Re: Stargazer78]
      #6076296 - 09/12/13 02:59 AM

Why not just do a drift alignment using your Canon camera? Your limit on how accurate the alignment will be is controlled by how fine an adjustment you can make in your mount's position. I've been using my imaging camera to drift align for years and have been very successful with it. I assume you're using a computer to control the mount in addition to running your camera.

Set your slew rate to 1x sidereal. This should stop the mount's tracking when slewing E. Set the camera for a 70 second exposure. Start the exposure while tracking at sidereal rate and do the following for the indicated time periods.

time action
00-05 track normally
05-35 slew E
35-70 slew W

Look at your image. The tracked portion will generate a star while the slews will create two tails forming a V shape, with the return tail passing through the star. The width of the opening of the V at the star is the drift that occurred during 1 minute of slews while the relationship between the trails is an indication of which way the mount needs to be adjusted. If your first adjustment increases the size of the V, adjust the mount the other way.

When I do this at the meridian and as close to either horizon as I can get (the same points to measure as other drift alignment techniques), I always find some stars in the image. At one minute per measurement, it doesn't take long to drift align. You can double the sensitivity of this test by increasing the exposure time to 130 seconds and slewing for 60 seconds in each direction.

Phil


Post Extras: Print Post   Remind Me!   Notify Moderator  
Stargazer78
professor emeritus
*****

Reged: 03/05/13

Loc: Susanville California
Re: Drift aligning using PHD guide new [Re: Phil Sherman]
      #6076366 - 09/12/13 05:17 AM

What about adjusting for azimuth? Isn't east and west longitude? A friend of mine was explaining this v method of drift align and it sounds similar to yours you just described.

Post Extras: Print Post   Remind Me!   Notify Moderator  
pubquiz
scholastic sledgehammer


Reged: 10/07/04

Loc: Lancashire England
Re: Drift aligning using PHD guide new [Re: Stargazer78]
      #6094082 - 09/21/13 08:46 PM Attachment (19 downloads)

I posted this (rather long) walk-through of the method I used on the SGL forum so have put it here as well in case it helps.

I did a rough polar alignment first using the standard drift align method then got it spot on using PHD as described below

1)First of all position the scope so it is 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


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

3) 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 referring to the DEC part of guiding)

5) Now on the graph click the 'RA/DEC' button so the display changes to show a blue and red 'dx' and 'dy' (You MUST do this or the red line will not move whatever you adjust once the Dec guiding is turned off)

6) Now look at the red 'dy' line ...if we have got the polar alignment (PA) pretty good 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 Alt axis (remember the scope is pointing at the E or W horizon)

7) After adjusting the knob a very small amount the star will have moved again so click 'Stop' in PHD re centre the star with the scope motors and re click the star then click the 'PHD' button 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 again (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, if it is rising or falling more than before you have turned the knob the wrong way...the line will wobble slightly but we are looking for it to stay as level as poss.....tighten up the ALT adjustment knobs on the mount when done.

8) Now we are ready to 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.

9) 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.

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

11) 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'

12) As before look at the red 'dy' line but this time adjust the AZ 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 a screen grabs showing that alignment is still slightly off with the red line going up (the full graph left to right is 10 mins). After aligning this line will stay level.

ignore the 'peaky' blue AZ line ....that was a tracking problem since rectified

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

Edited by pubquiz (09/21/13 08:55 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
bretm
member


Reged: 12/27/09

Re: Drift aligning using PHD guide new [Re: pubquiz]
      #6094257 - 09/21/13 11:17 PM

I'm a bit confused about how you can use dx/dy mode unless your camera x/y axes are pretty precisely aligned to the mount's ra/dec axes.

PHD2 has some features that make it easier to use as a polar alignment tool

It has a declination trendline graph option that will show the declination line without the need to to stop declination corrections, and if you do stop declination guiding it still graphs the declination line (this eliminates step 3 and 5, as well as 11). For ASCOM mounts, it also changes calibration based on your declination (so no step 9)

PHD2 Beta 2 was just released yesterday at http://www.daddog.com/phd2

Bret


Post Extras: Print Post   Remind Me!   Notify Moderator  
SMigol
sage


Reged: 07/30/10

Loc: California, USA
Re: Drift aligning using PHD guide new [Re: bretm]
      #6094468 - 09/22/13 03:02 AM

Quote:

I'm a bit confused about how you can use dx/dy mode unless your camera x/y axes are pretty precisely aligned to the mount's ra/dec axes.




Displaying the bullseye and doing slow slews is a quick and easy way to align the camera with the mount axes. Just keep a bright star on the lines and you're set.

I agree that PHD2 has some great polar alignment tools that makes PHD1 less desirable for the exercise.


Post Extras: Print Post   Remind Me!   Notify Moderator  
pubquiz
scholastic sledgehammer


Reged: 10/07/04

Loc: Lancashire England
Re: Drift aligning using PHD guide new [Re: SMigol]
      #6094530 - 09/22/13 04:52 AM

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 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..But it DOESN'T HAVE to be for it to work.

Tom

P.S. don't know why I jumped from 3) to 5) above
P.P.S. Interesting about PHD2 ...wasn't aware there was one ...will check it out in that link thanks for that

Edited by pubquiz (09/22/13 04:57 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1


Extra information
9 registered and 32 anonymous users are browsing this forum.

Moderator:  Dave M, richard7, bilgebay 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 633

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics