Need help with Drift alignment

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  • Member since
    April, 2012
  • From: North Carolina east coast USA
Need help with Drift alignment
Posted by stepping beyond on Friday, October 04, 2013 9:28 AM

I just don't know if I'm doing everything correct . I still am working my manual controls a whole lot with the motor running. I even switched from N to S on the Hemisphere control switch to see if that would improve , does anyone have an equatorial mount that can take me by the hand through this process. I've tried to read up on it and tried diferent things and still I'm manually having to do everything "FRUSTRATION" I'm not dumb but, I am a bit thick sometimes. The answer could be right in front of me and I wouldn't see it.

  • Member since
    November, 2009
Posted by Poppa Chris on Friday, October 04, 2013 10:10 AM

If you are going through all of the trouble of doing a drift alignment, I'm assuming that it is for photography as it wouldn't really be needed for visual observing.

The whole concept is to adjust your mount's attitude towards the sky, not the scope's.  If an object is centered in the crosshairs of a reticle eyepiece and while the mount's tracking is on it slowly drifts away from center, then the mount (not the scope) is not aligned with celestial north.  Think Alt-Az and not RA-Dec when adjusting the mount.  If the drift is to the right or left then you must adjust the Alt of the mount.  If the drift is up or down you  must adust the Azimuth of the mount.  If drift is a combination of both, pick one and work on it until you can isolate it down to just one remaining error.  If you get that worked out as close as possible, then you are probably facing either periodic error or backlash or some other motor drive error.  This is where an autoguider comes into the picture to constantly correct the mounts drive speed to deal with these raher small but contunuous errors.

If you are doing visual observing and the object remains in view for a reasonable amount of time after some drift alignment before you need to manually adjust, I would just live with it.  It's not worth all of the setup and guidiing equipment, etc. for visual work.      

---Poppa Chris---

Denham Springs, Louisiana USA

"Second star to the right - Then straight on until morning!" - Peter Pan

Celestron CPC1100GPS (XLT) - 279mm aperature, 2800mm Focal length. (f10) Celestron Ultima LX (70deg AFOV) Eyepieces 32mm thru 5mm, Canon EOS Rebel T2i DSLR, Backyard EOS imaging software, Orion Star Shoot Planetary Imager IV, Celestron Skymaster 15x70 binoculars

 

  • Member since
    April, 2012
  • From: North Carolina east coast USA
Posted by stepping beyond on Friday, October 04, 2013 10:56 AM

Yes Chris, I'm getting myself prepared for Jupiters rising in my backyard sky. I really would like to video  our largest gas giant, I attempted to try Saturn but, proved to be too much -- to do it manually. The motor works I had Saturn tracking from the driveway in front last year. I've had some great moments videoing but, I got my parents  coming down later this month and I really want to "SHINE" like Vega. They've seen my moon progress and are really impressed that I can do something like that and are very happy that I'm still into the AP Loving all the captures I post to Facebook.

  • Member since
    November, 2012
Posted by MooseMan01 on Saturday, October 05, 2013 3:38 PM

I got out my EQ mount and took a few pictures this morning. This is very basic stuff but I hope it will be helpful.

You must get THIS axis of the mount pointed to Polaris:

The EQ mount has 4 separate controls. The two "manual controls" which you referred to, are the ones which are attached by flexible cables. These are the ones which you adjust while observing. Note that they move the telescope position. They do not have anything to do with the alignment. It's the other two controls you use for alignment. As I think Poppa Chris pointed out, these alignment controls are actually Alt-Az controls.

Here is the altitude control. It changes the angle of the mount:

The correct angle is in fact the same as your geographic latitude. If you are located in Kings Mountain NC then your latitude is 35 degrees. Begin by setting the altitude to this value using the scale shown on the mount.

As you see, mine is actually quite close to 45 degrees, because I am in Canada.

Next there is the azimuth adjustment:

On mine you just swivel and pan the head around by loosening the locking thumbscrew, grab the mount by the base and rotate it.

The tricky part is getting it pointed right at Polaris. As I said in your location Polaris will be at an altitude of 35 degrees, due north. If you've set the alt adjustment to 35, it should be just about right (as long as the scope is on reasonably level ground). Use a compass to verify north and identify which one it is, if you are not sure.

In my case I look along the axis by eye, try to aim it towards Polaris kind of like looking down a gun barrel. I have to crouch down a bit to get my head in the right spot. Then look with one eye along the edge of the mount, and adjust the alt-az controls until it's real close. At that point you will have a rough alignment, probably good enough for observing and ok for imaging with a web cam. Once you have it set right don't adjust those controls any more. To look at targets you must only use the RA/ Dec controls to move the telescope.

This will work ok, for a crude adjustment. You will occasionally need to make a slight adjustment of declination once in a while due to drift. The amount required depends on how close you are aligned to the celestial pole, and how much magnification you are using. Also, the further away your targets are from Polaris makes a difference. Targets near polaris will not drift as much, because the sky is like a wheel and you are pointing toward the center, the "hub", which does not have as high angular velocity as at the "rim".

Here's a picture showing the general concept, from the Royal Astronomical Society of Canada:

For more precision, you need to fine-tune using drift techniques. But they are only needed when doing long-exposure photography where it needs to be bang-on the whole time. So if I were you I'd not worry about that until later.

  • Member since
    April, 2012
  • From: North Carolina east coast USA
Posted by stepping beyond on Saturday, October 05, 2013 6:47 PM

Thank you Mooseman, I had my scope aligned I thought. But how much does it matter that the driveway is up and the backyard is 20' down a hill? Does that make my alignment void? I'm getting better at the moon but, those planets are really difficult to get and keep in view. I practice a lot and read the instruction booklet while I was doing and I still would like very much to be able to relax a little while videoing but, as of now I'm constantly checking adjusting and I'm really worn out after one moon video. Should this AP stuff really be that hard? I do get very excited when I keep the moon in my fov, just letting it drift , then adjust drift so on and so on.The stars do drift down to the left or it may be right, I've already forgot. I'm trying to deal with this on my own but, there comes a time when my head just hurts from beating it with my good hand. I really had 1 time when I first got my SSUE ll and kept Saturn in the field but, I couldn't get it focused while looking at the laptop screen. I was aligning from the driveway but, I curse the lights and cars too much to keep focused on the task at hand.

  • Member since
    November, 2009
Posted by Poppa Chris on Saturday, October 05, 2013 8:55 PM

If you are videoing the Moon and planets you rarely need more than a minute or two to collect more than enough frames to stack in Registax or AVIStack2. So if the image doesn't drift out of the field of view in say 3 minutes,you should be good to go. Let the software take care of alignment during the stacking process. In fact, I usually don,t even bother with setting up my fork-mount SCT on its wedge when doing planets. I just use Alt-Az for these short videos.

Now if you are going for DSOs that are much dimmer and require much longer exposures, then I would worry more over the drift alignment and probably add autoguiding too.

---Poppa Chris---

Denham Springs, Louisiana USA

"Second star to the right - Then straight on until morning!" - Peter Pan

Celestron CPC1100GPS (XLT) - 279mm aperature, 2800mm Focal length. (f10) Celestron Ultima LX (70deg AFOV) Eyepieces 32mm thru 5mm, Canon EOS Rebel T2i DSLR, Backyard EOS imaging software, Orion Star Shoot Planetary Imager IV, Celestron Skymaster 15x70 binoculars

 

  • Member since
    November, 2012
Posted by MooseMan01 on Saturday, October 05, 2013 9:47 PM

Stepping Beyond, don't get frustrated! Nothing is easy until we know how. After all this is high tech stuff.

First of all, you must be certain it's polaris. Or else it simply won't work. Not sure how familiar you are with the night sky, but knowing where polaris is, is essential to doing astronomy. Polaris is always in the same spot on the sky, night after night and it is a useful star to use for doing tests on your equipment. Now here is something you can do- any scope looking at Polaris will always keep it in the field of view, all night long. It requires no motors or special alignment. So I suggest you point your scope at polaris first, without the motor. Crank up the magnification and take a look. Then go inside and have a cup of tea. Come out and check it 15 minutes later- if no change, star still in the same spot- you know it's polaris.

Not sure about the effect of the hill in your yard. Perhaps other experienced astronomers can comment. Have fun!

  • Member since
    April, 2012
  • From: North Carolina east coast USA
Posted by stepping beyond on Sunday, October 06, 2013 5:04 PM

Thank you Chris, I do want to be able to view the planets from my laptop , That's really why Alanna bought the SSUE ll for, she got so upset when all I would do after viewing is complain about my neck. Care and concern is her main priority, when it comes to my health . One day I just may surprise the World with a processed capture of a Planet. That would really be exciting and a "WOOHOO MOMENT", but I don't want to get ahead of myself. I gotta take my time and do it right "with help from the forum"

  • Member since
    November, 2012
Posted by MooseMan01 on Monday, October 07, 2013 8:14 PM

Well I was thinking about the hill question, and the basic instructions of using the EQ mount is that it must be leveled first. It won't work on a hill. But depends on how steep, and for how long you need to keep the object in view.

Here is why. I drew this picture to explain it. As you see, when on a hill the axis of rotation of the mount will not be the same as the axis of rotation of planet earth. This despite the fact you're pointed at the star.

 

  • Member since
    April, 2012
  • From: North Carolina east coast USA
Posted by stepping beyond on Tuesday, October 08, 2013 9:06 AM

Mooseman, thank you for taking the time to draw that for me but, I didn't explain fully correct. I view sometimes from my driveway level and I can see Polaris, I also view from all over my backyard darker site on a mound like , that looks level . My backyard is pretty wavy like the ocean but, it's what I've got and I have to deal with it. There 3 places where the scopes are set up and I would say they're not perfectly level but, I took my 4 ft. level out to survey before I even set the tripod and stick the feet in the ground. I will get another smaller level ,  while I'm out seeing the Doc.

  • Member since
    November, 2012
Posted by MooseMan01 on Tuesday, October 08, 2013 3:04 PM

Ok Stepping Beyond, so now we have Polaris, we have the mount angled at 32 degrees, plus or minus a tiny bit, and the scope is on reasonably level ground. Make sure the counterweight is not too heavy, causing the mount to drift. Also, check that the motor is in fact properly attached and working. On my EQ I have a nagging problem that once in a while the worm gear connecting the RA drive keeps loosening off. When this happens I can't drive the mount, because the worm gear is disconnected. Then it spins freely, but the mount does not move.

There's so many little things that can go wrong, it's hard to diagnose through the internet. Sorry I can't come over to help out! :)

Is there an astronomy club in your area? Check it out. If so, how about you go to one of their meetings, and ask some questions. An experienced person looking at the problem directly with you would probably be able to get this going. Plus, it's nice to talk to other people in your town who share the same hobby as you. When I go to visit the astronomy club here, they give presentations once a month on some topic of interest. Last month the talk was about Saturn. This month, Andromeda.

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