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State of the Art, Part III
Richard S. Wright Jr.'s Blog

Paramount Polar Alignment

At the Winter Star party, I had two interesting encounters that, more than anything else, have inspired this post. One was a gentleman who told me that with his brand-x mount, “I only need to sync on two stars, and then whatever I slew to, the object is always in my eyepiece”. “Why can’t the Paramount do that, without having to do all those points?”

On another occasion a gentleman nearby, perhaps trying to goad me, was being very loud and vocal about that fact that it takes forty-one stars to polar align a friends paramount, then another forty-one just to see if he had done it right.

Where do these people get their information?

How many stars does it take to polar align a Paramount? Well, exactly, precisely, and without exception… one. Uno. Eins. Un. Monad. Quote me on that, track me down at a star party and hold me to it if you like. It’s just one. Just like any other German equatorial mount in fact.

Actually, it can also be zero. You could use a planet instead.

The confusion is to some degree understandable. What’s happening is many people are confusing TPoint’s polar alignment feature with other software-assisted polar alignment techniques that can be applied to all mounts. They are different tools, they do different things, but at the same time they can appear similar. Aspirin and a vaccine both have health benefits, but they are not performing the same function.

 We also have the problem that the visual crowd and the imaging crowd each have very different ideas of what polar alignment really is, and how close it needs to be, or even what the term “sync” means. One of the things TPoint can do is refine your alignment much like a drift alignment procedure. Except TPoint is faster, unattended, and does a vastly better job… but it’s not how you do the initial alignment, and it’s not even necessary for visual observing, or even to some extent if you just want to guide your way out of a sloppy polar alignment. (TPoint will be the topic of my next post, but you shouldn’t even start using TPoint until you have a preliminary polar alignment, so that’s where I’m going to focus for now.)

Again with the disclaimer: this is how I do MY polar alignment. I’m portable, in a hurry, and I have my quirks. To start with, I don’t like polar ‘scopes. They are fine, lots of people swear by them, some swear at them, and I am in the latter group. Besides, I like to do my initial alignment in the daytime long before Polaris is visible. I’m also assuming the imaging train is mechanically STRAIGHT and along the axis with the Versa Plate, and not skewed by some number of DEGREES up or down, left or right. TPoint can actually do a really good job of modeling this out later, but your initial alignment is not going to be that great if this is the case. You have been duly warned.

Step 1: Level the mount as best as possible. See my last blog post for how wonderful the Pyramid Portable Pier is for this task. This step used to be very frustrating, but was worth the effort. Now it’s both easy and worth the effort!

Step 2: Loosen the head of the tripod and point the mount north. I use a compass if necessary and just get it as close as I can make it. If you can see Polaris when doing this, that’s a great guidepost, naturally. Assuming you’re not using a polar alignment scope, just get the RA axis pointing more or less at Polaris. If Polaris is behind some trees or a building, don’t fret over this. You really don’t need to sight on Polaris if I the imaging system’s mechanical axes are close to orthogonal (90 degrees of each other) and the optical axis is aligned with the mechanical axis. Also, be sure to carefully set the altitude of the mount’s polar axis to your current latitude. You should have done this already, and it’s easy to do on the Paramount since it has nice tick marks on the altitude adjustment.

Step 3: Plug in your computer, make sure TheSkyX has the correct lat/long for your location and the current time, and slew to a nice bright star. Not too close to the meridian, and a northern declination works best. Alcor and Mizar are my favorites, because it’s easy to know you’re looking at the right star(s) when you see the pair in the finder or on camera.  A well-aligned finder scope is often missing from many an imager’s scope. For a portable imager this is a mistake because the next thing you want to do is center this bright star in the finder. You do this by making adjustments to the mount. It’s best to not even have your hand paddle plugged in at this point! An alternative I sometimes use is one of those green lasers and they work fantastically… but are often banned at star parties. If you don’t have a camera in place, you can then refine this mechanical alignment with an eyepiece. Start with a wider field, and then drop down to a higher power view to center up the star. An eyepiece with an illuminated reticule works great for this. If you’re a DSLR imager (which I frequently am), then great, you can look right through the viewfinder and center up the star there right where it’s going to fall on the chip.

Step 4: For visual work, you’re pretty much done (although we can refine this more later). In TheSkyX, select “Sync” from the telescope menu to sync on the star. The visual gentleman at the WSP will find that he can now slew to any target he likes and with a nice low power eyepiece his target will likely be in view, just like with his other mount. If the Paramount (or any quality German equatorial mount) is “good and level”, and your scope is on “good and straight”, you should be able to slew to any visual object anywhere and find it in a low power or wide field eyepiece. If you’re planning to image, you might as well go for the gold. Take a picture here, Image Link, and sync on the Image-Linked photo.

Didn’t I say I do this in the daytime somewhere? Yep. After getting the mount level and more or less pointing north, I’ll home the mount and slew to the brightest star in the sky…. the sun. Oh, I should mention that you better sure has heck have your scope covered when you do this! Let’s not destroy your optics or camera in the process. If the moon is up, it works just as well, and possibly is a safer target depending on the type of your scope (those big open truss thing-a-ma-bobs can be hard to protect adequately from sunlight). Now, adjust the mount mechanically until the sun or moon is directly in line with your scope’s optical tube. A finder scope really helps , but the aforementioned warning about the sun applies, this time of course, please don’t burn your eyes by looking at the sun through a finder either. For that matter, you should cover the finder if you slew to the sun; you very well might set your shirt on fire even if you don’t plan to look through it!

I do not sync on the sun or the moon however. They are just guideposts. Oh, well actually for solar observing (with adequate filtering), you actually can center the sun and sync, and you’re in great shape all day long. You could also if you’re doing nighttime imaging go ahead and center the moon, but I like to take it a step further.

Now that I’m within a couple degrees of the pole, I can slew to a bright star or planet and they will usually show up in my finder scope. Yes you can see planets and bright stars during the daytime; you just need to know where to look (and TheSkyX makes this easy). The sun and moon make great jumping off points. Now, without using the hand paddle, I tweak the mounts altitude and azimuth to get the planet/star centered in the finder scope. If possible, I put in an eyepiece, one with a reticule is even better, and refine my pointing further just like I would at night.

I could sync at this point, but I like to wait until sunset. It’s amazing, but depending on the optics and camera I can get stars in an image as little as ten minutes after sunset, and almost always by twenty minutes after sunset. I’ll take a picture with the Camera Add On, Image Link, and then sync on the photo.

With some qualification, I can say the mount is now aligned with the pole. For imaging, I’m going to want to refine this considerably, and I usually call this my “initial alignment”. For visual I could stop here, or I could tighten it up just a little more.

Many telescope mounts have both one and two star alignment routines. What they are attempting to do with two stars is model the fact that your ‘scope may not be mounted entirely straight relative to the mechanical axis. The mount may not be perfectly level or pointed North, the mirror may be tilted slightly, etc. All these “misalignments” add up.

Even with a perfect mount, the optics, or the mounting of the optics tends to be a frequent point of failure for perfect alignment. Adding extra pointing samples allows most mount control programs to do a better job of when you slew to a star on the other side of the sky for example. Of course when the object is not in the field of view you still need to hunt around for it, and often you can add a supplementary observation to help improve pointing… in that part of the sky.

This is where TPoint comes in, and it can do this much better, and it only requires six points. Six… not forty-one and you only have to do the procedure once. Six may be more than two or three that other fork-mounted ‘scope guys advertise, but when you consider that you have to keep adding more calibration points when you slew elsewhere… well why not just get the six right off the bat and be done with it? One point and a well-aligned optical train and you can get away with wide fields, or perhaps a little “Star Searching” (a feature of TheSkyX that slews the mount in an outward spiral pattern to quickly locate objects outside the current field) to find what you want. Six samples, no further mount adjustments and TPoint, and your object will always be right in your low powered eyepiece…. every time. For visual, the most you’d ever want is twelve points and even at high magnification and low fields of view, you’ll find the object always dead near in the center of the field every time. No further adjustments to the mount needed either by the way.

What about the needs of the imager? Well, let’s save that for next time when I talk more about T-Point for visual use, and polar alignment fine tuning.

 


Posted 08-14-2012 4:38 PM by Richard Wright

Comments

Ernie wrote re: State of the Art, Part III
on 08-15-2012 1:47 PM

Finally, the new Tom's corner with our new host Richard.  :-)

Richard Wright wrote re: State of the Art, Part III
on 08-16-2012 8:53 PM

Those are some mighty big shoes to fill....

trimil wrote re: State of the Art, Part III
on 08-31-2012 12:53 AM

Richard,

Great primer on daytime alignment. Imaging or viewing near it is unfamiliar territory for most of us and that warning about the sun can't be repeated too often. Earlier this year I was setting up for the partial eclipse with a non-goto Tak EM-10. Got the polar alignment through several iterations and settled down to a long series of subs at a 30 second interval.

After the sun disappeared behind some trees, it was time to quit and put everything away. Out of habit, I retracted the dew cap, the solar filter popped off, and I reached for the lens cap... Then a moment of sheer panic! Did I really do something that stupid?

The tree leaves were thick enough, and the time between the filter coming off and the lens cap going on was only a few seconds, so the attached DSLR lived to tell about it. It could have been ugly if Mr. Sun was a little higher in the sky or if the camera mirror was in the up position.

Richard Wright wrote re: State of the Art, Part III
on 08-31-2012 7:47 AM

Wow great story there too, and a nearly catastrophic one equipment wise! It sounds exactly like the sort of thing I'd do too....

Steve Norvich wrote re: State of the Art, Part III
on 09-13-2012 4:02 PM

Wonderful.  Thanks so much!

   

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