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Datalord

Polar alignment woes

28 posts in this topic

It couldn't be, since yesterday was 20th.

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I'm sure someone with same mount will be able to pinpoint your problem 

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Posted (edited)

OK, Datalord - here are some even more refined instructiions!

1.       Setting up the telescope

The telescope needs to initially be set up like this. If a dual fork telescope (like a CPC) take careful note of how the single arm of the Evolution is being manoeuvred during this process. On an Evolution, it will start on the left of the Tube like this.

 Wedgediagram.jpg.571ef0b7cc9c6fb78da45f55c6ff8c55.jpg

Note that here it is assumed that the StarSense camera has been prior calibrated and any Finderscope (or RDF) also properly aligned with the Tube.  

The wedge altitude adjustment knob should be pointing accurately south; the tube also pointing south; the ORIGINAL check marks on the telescope are aligned; the wedge set at your correct latitude (51° for London). The mount arm is leaning north. .

2.       How do I know if I am sufficiently accurately pointing south?

To succeed with a StarSense Polar Align, my experience suggests that your Tube at its NORMAL check marks should be aiming south with less than a two degree error from the S Meridien. If not, the later physical alignment process will dump your Cal Star outside of your FOV and it is then very difficult to complete a polar align. I believe that on a GEM it is desirable to strive towards this same ‘rough’ accuracy (albeit that the set up procedure and orientation is different).

Do note that it takes a full turn of the Alt knob to adjust by 0.45°. So if your initial PAE is 5° start again with a better tripod position.  One way to achieve this (due south) is to use a compass or ‘phone APP. Here, do remember to adjust for magnetic north deviation. If you are confident that you are aligned along the southern meridian with less than a 2° error; skip to step 3.  If not, read on to learn how to get past this tricky first hurdle. There is a crude, but effective ‘old fashioned’ way, and I think that the first time you attempt a polar align on wedge with StarSense it is well worth trying this route to get the best first result.

After setting up as above and getting as close to being aligned along the south meridian as possible; unlock the Evolution’s Azimuth clutch (the lower) and rotate the mount arm 180° so it is now pointing north like this. Note how the Tube is now facing down and the SINGLE mount arm is on the other side of the Tripod when compared to the first image. Do note that your telescope is still NOT switched on (oh what joy to have 'free 'clutches!).

Wedge2.JPG.e3b5e1f9752f9fc3aee4feaa8a860bbf.JPG

Now bring the Tube up parallel with the Mount Arm like this;

IMG_0651.JPG.407a02bd24c11799cf96dd933407b1c4.JPG

 

With the telescope now LOCKED in this position with both arm and tube parallel to each other (at your latitude wedge setting) and pointing north (n.b. lock clutches and wedge etc.), move the entire telescope until Polaris is in your Finderscope (and eyepiece); whilst adjusting only the wedge altitude knob. This isn’t easy with a heavy telescope! But it is well worth the struggle just to get your FIRST ever visual Polar Align highly accurate. I believe that GEM users do something very similar, and this step is undoubtable easier with a GEM! You only need to do this once! Here, you will probably need a decent quality RACI Finderscope and Reticle eyepiece for best results.

When Polaris is in the cross hairs of both Finderscope and a reticle eyepiece, mark your exact Tripod leg positions on your patio for future reference.

Notice that your usual mount/tube check marks are no longer aligned. So with a blob of Tippex ('liquid paper'), mark their NEW position. 

Then next time you set up all you need do is use these tripod leg marks and these NEW check marks and you should quickly have Polaris in your FOV. Indeed, if you do this very accurately you should never need to see Polaris again. Just use your tripod leg marks and NEW check marks. You might ask, why don't Celestron add these marks? It is because Meade hold the patent (so make your own!). You might want to try with a wax crayon or something until sure you have these exactly right.

Your tripod and wedge are now fairly close to polar alignment. Now carefully (so not to move tripod or wedge) unlock the azimuth clutch; rotate the mount 180° and put the tube back to its original check marks position aligned along the South Meridian like this next image; which is the same as figure 1.

Wedgediagram.jpg.571ef0b7cc9c6fb78da45f55c6ff8c55.jpg

Step 3 Setting tracking (wedge = yes).

Your telescope is in its correct start position.

a)       Turn on the telescope. Wait for its boot up process to complete. DON’T press Align!

B) Press <menu>; select <telescope>; select ‘wedge = yes’.

Note that this step isn’t described in any StarSense instruction manual. However it does appear in the ‘Menu Tree’ of the latest manual. After setting this, go <Back>; <Back> to the H.C’s post boot up status (scrolling “press align”).

This step must be accomplished using the StarSense Hand Controller (HC). You CANNOT do a polar align in either SkyPortal or SkySafari APP as although these APPs might suggest you can set 'Starsense on a wedge;'  and that might possibly make it track in RA only there is NO polar align roiutine in the APPs.

c)       Now turn the telescope OFF and then ON.

This step might not be strictly necessary. However, some users have reported strange issues with the wedge = command. As the H.C. remembers the wedge= <setting>, I decided to reboot the scope here so that it wakes up in ‘wedge mode’. Of course, if you have set this during a prior use it will then always wake up in wedge mode; hence you can omit this step for future use with a wedge (but you need to turn it back to ‘wedge = no’ for Alt-Az mode).

You obviously must ensure that <location><time><date><Zone><DST> are inserted correctly.

Step 4; Auto-Align (prior to Polar Align).

d)       After booting up your telescope now in what I call “wedge mode” (see step 3); using the H.C. press <Align>; <Enter> and proceed with a standard Auto-align.

e)       During the process, you should perform a <calibration> of the OTA/camera if you have not ALREADY done so. As I had previously been using my StarSense in Alt-Az mode (e.g. with no wedge), my Tube/Camera was already calibrated. BTW, I suggest it is best to first master a routine StarSense Auto-Align without wedge before adding the extra gizmo complexities!

 Users familiar with a normal StarSense Alt-Az Auto-Align will be amazed here that despite the mount arm leaning over alarmingly and the tube gyrating in a strange fashion a perfect StarSense Auto-Align will be achieved. Your GoTos will also be good, but the telescope is NOT yet Polar Aligned. It just proves how fantastic StarSense is on a wonky mount or upon uneven ground! It’s a fantastic tool if you generally struggle with alignments and huge a time saver if you don’t.

Step 5: Polar Align.

f)        Now press <Align>; scroll up/down (using 6 & 9 buttons); select <Polar Align>.

g)       Your screen will display the Polar Alignment Error of your mount. Take great care here.

This is displayed for {N-S} and {W-E} as EITHER;

DD.DD° or MM.MM’ or SS.SS” which reflects the PAE error expressed degrees OR minutes OR arc-seconds.

It is very difficult to read the symbol that identifies the ‘currency.’ Hence you might see an error of 0.98° (degrees), but if the error was 0.54° it is instead expressed as 32.2’ (arcminutes).  It is hence the easiest user error in the world to think that your error is 32 degrees when it is actually 32 arcminutes (or even 32 arc-seconds).

h)       The H.C screen will then offer you a star (usually ‘Archid’; which might not be in your vision due to obstructions!). Scroll (using up/down) to a star in the H.C screen that you know is in your vision. Then press <enter> to GoTo that star. The Tube will move to that star; then it will move again to reflect the Polar Error.

If your initial starting position was less than 2° from the south meridian, your Cal Star should remain in the FOV of your least powerful eyepiece (40mm). If not, it is very tricky to complete the next step. You almost certainly need (say) a RACI Finderscope and reticle eyepiece.

i)         Centre it in your eyepiece by physically adjusting the wedge using the (wedge) Alt-Az adjustments. The HC buttons are locked out to prevent movement of the motor. Do not move tripod etc.

j)         Press <enter> to accept the new Cal Star. You have now completed and ASPA (All Star Polar Alignment)

Then, you will be returned to the ‘align’ menu. You need to scroll to StarSense Auto-Align.

k)       Do note that contrary to earlier guidance you should do NOT need to reboot at this stage. See “big ifs”  below

Step 6; perform another StarSense Auto-Align.

Step 7 Repeat ASPAS (steps 5 & 6) and you should then see a progressive convergence towards ever improved results.

What I did here was do each succesive ASPA using a different Cal star. Each time I would <GoTo> then add it as an alignment reference. The more aligment references (that act like SYNC) the more accurate this process will become.  After each ASPA you do a fresh auto-align (no need to more the scope back to its check marks).

Now here are some big ifs…..

If after a subsequent ASPA (7) you see a worsening of the reported PAE results in the hand controller (step 5) that means one of three things. Either the fabled StarSense on a wedge ‘bug’ has struck; or you have misread an improved PAE which is now expressed in arc-minutes (or arc-seconds) rather than degrees or you have made a user error. It is easy to screw up here, notably by nudging tripod or it sinking into grass. You really need to be on hardstanding. There is no doubt that an intermittent ‘bug’ does exist, but how many reports are due to user error is questionable. It has been suggested to Celestron that they should change this format to DD°, MM’,SS” to avoid future confusion. But it is really hard to read the HC screen with impaired vision.

If when performing the final auto-align you get a “failed align” don’t panic.

I have deduced here that the choice of Cal Star (step 5) can be crucial. For example; I was picking Arcturus which was very high in the sky what was happening was that the natural routine sequence of StarSense motion then had the camera looking for stars that are low and very close to the horizon. In an urban back yard this inevitable increases the likelihood of StarSense failing due to local obstructions such as walls trees and fences.

If this happens; don’t panic; remember that you have already completed the physical Polar Align and your wedge and tripod are hence already set. Go back to step 4 and start again from the ‘home’ position. Here do reboot.

Next time in step 5 select a Cal Star in a different part of the sky. I suggest you try a star at a mid R.A and in whichever direction you have the MOST low level obstructions. The reason being that StarSense will always move the Tube away from its start point (which will be your Cal Star) hence I believe this increases your chances that StarSense will move and seek its alignment in your least obstructed part of the sky (so is less likely to fail). Starsense ALWAYS moves in the same motion, so a bit of trial and error will identify the best region of the sky (by compass point/altitude) to select your Cal star.

There is no hard and fast rule about this as whatever Cal Star is right in winter won’t be the same as in summer.  So what you are looking for is the zone of the sky where StarSense has least trouble avoiding local obstructions. Of course, your local obstructions will differ from mine. But I am confident that if you carefully watch the movement of the Tube during the final auto-align you will determine the sky zone your Cal Star should sit to work best for you.

In the above, one assumes that you have correctly set location/date/time/zone/dst (remember UK clocks change this Sunday!).

I will be honest and say it has taken me a month to master this, and until I discovered the Tippex and tripod leg tips I struggled to get my initial polar align under 3° on either axis. Now I enjoy an inital  sub 1° PAE in both axis (note I do leave my telescope assembed and carry it from my conservatory with the wedge Alt unchanged) and can get down to a few arc-minutes by repeating the ASPAs, but it isnt easy. For example, the slightest nudge/tilt on the tripod when adjusting the knobs can throw you out by 3°.  But I was a decent pin-ball player and could flip my flippers without nudge or tilt!

My advice to those who DON'T own a wedge is buy a GEM instead. But it can be tamed.

Hope this helps, shoult if you want more assistance, but it takes a lot of skill.

Noah

ADDED

Datalord; just realised that I didn't cover your Regulus question. The PAE doesn't reflect the error from your Cal Star Regulus. It is the polar error of wedge/mount.  Celestial geometry might mean it is a small number as regards Polar alignment but might be  huge when compared to the location of you chosen Cal star. All your result means is your tripod wasn't as close to the Meridian as you hoped. Try the Tippex route.

Edited by noah4x4
Afterthought

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