Pole Master on AstroTrac, go/no-go?

[awasen 11]

Cool, Nebula!

That was even better results than I'd have expected!

Looking forward to the autumn now as it is getting too light here in Stockholm for any serious astrophoto...

[shamantanthew 3]

I'm reporting back with bad news... I think I had the best beginner's luck in the world when I posted those screenshots from my first time out using the Polemaster and the Astrotrac because I have not been able to replicate that success. The last 3 times I've set up I've been limited to about 3 minute subs at 400mm with my 6D. I'm pretty confident the problem is the polar alignment. My guess would be too much flexure in the RA axis when the clutch is loosened to move the arm 30*, although when I return it to the "home" position the star I chose is typically on or very close to the circle that's drawn. Another theory is a balance issue, although I take care to balance every time I set up. 

[fireballxl5 393]

for info, I've found that the EQ6 pole master adaptor I'd bought (solely for my NEQ6 surprisingly) also fits in the polar scope hole on the astrotrac. You need to be careful tightening the grubscrews so as not to damage the inner surface of the polararm hole but it seems like it should work a treat. Will try at next opportunity.

 

 

[kriss13 9]

On 5/22/2016 at 22:38, fireballxl5 said:

for info, I've found that the EQ6 pole master adaptor I'd bought (solely for my NEQ6 surprisingly) also fits in the polar scope hole on the astrotrac. You need to be careful tightening the grubscrews so as not to damage the inner surface of the polararm hole but it seems like it should work a treat. Will try at next opportunity.

 

Great neaws, Astrotrac adapter is not that common to find.

Could you post a picture or two how it would look like while fitting to the polar arm?

What grubsrews?

thx

 

Edited November 10, 2016 by kriss13

[kriss13 9]

Well new toy, new clouds

I got my PM from China under a great discount and Fedex-ed for free at my door (240€ including adapter)

I chose the NEQ6 adapter as one fellow astronomer suggested it would fit and.. it does fit indeed

 My AT was "sleeping" in my g'n'g backpack... I woke it up to take the pictures

True about the grub screws tho... they are pressing the edge ot the AT polar arm hole not perfectly on the inside .

 

 

[kriss13 9]

If the polar arm will fail me (I heard some stories...), I am planning to use another adapter, drill 2 holes into my Giro Mini and bolted there near the RA axis. (see my past bad photoshop proposal:).

Hmmm.. this gives me an idea..."fires up CAD software"..

brb

[awasen 11]

It's been constant cloud coverage here in Stockholm since beginning of October (when it is getting dark enough for astrophoto again after the summer). I have gotten enough starlight only to play around with the rig and get to know my new refractor but not been able to do any photo.

I did test to use the PoleMaster on AT polar arm vs. on the head RA (mounted with the adaptor I made) some and there is much more misalignment when on the arm. I'd say that about one third of the times the PM is on the arm I didn't get a good polar-alignment while when mounted on the head I got about three out of four that was really good. The arm does seem to make it a bit unreliable...

Please note that even the not-so-good PA I got with PM on the arm is way better than what I'd get using the polar scope!!!

[kriss13 9]

Well it is good to know there is "plan B", aka PM near the RA axis.

I will test and report back once the clouds are gone.

One thing to keep in mind about polar arm... it has some clicks at different positions.. maybe if the arm is "between clicks" it is pushed out of perfect alignment by the small clicking pin.

I will try to see if there are any differences at the clicks vs the arm somewhere in between them.

[StuartJPP 5,023]

I am sure that the arm in a position between detents would probably not be aligned properly, by how much I am not sure...

The AstroTrac polar scope arm from my experience isn't perfectly aligned but it isn't far off.

The best method is to get the PoleMaster attached to the RA axis if you can as that is what actually counts....though that is a bit trickier.

[kriss13 9]

First test... on the polar arm is unconvincing.

I had a small oval stars, for 2 min exposure with a 80/560 refractor, reduced at f5, prime exposure, not sure if it is from PM, the arm or it's me :).

The align procedure was done 3 times always with the same affect, a bit of oblong stars... but the freezing was too much at 3 am so I gave up 

I used a Mabook pro 15" retina from 2012 with win in virtual machine (Paralles Descktop).

What I don't like about PM:

-Mac version has a problem with retina screens (not with regular ones)... most of Macs are retina and will be retina.. helooo

-Mac version won't show the template circles... WHAT??!!

-Win version has lower fps than Mac, like 5 fps ... figure that! Yes games are working perfect, high fps in WM but apparently not PM software.

-to position the cursor EXACTLY in the center of a star is very hard, I had to enable mouse keys to move it with small increments via keyboard.

The PM is a great tool just because the I reduced the align procedure from 20min to 2-3 min.

So far I managed to get max 3min with the polar scope, but after a lot of time spent in the dreaded "Z position"... and not every time, hit and miss mostly.

Next time I ill report it, the PM will be on the RA axis.

Made a blueprint for an arm that will attach to my MiniGiro (I need to find a shop to CNC it), and I will use the cap of the adapter (NEQ6 adapter) with a center hole drilled for RA locking lever to pass through to lock the new arm to the GiroMini.

This will allow me to rotate the new arm around the RA axis for the align procedure (via a grub screw) without rotating the telescope so the balance will be the same.

I will not use the AZEQ5 because my new arm will give me the freedom of rotation Astroctrac arm does, and because is cheaper (50€ vs 10€ mine)

 

Edited December 1, 2016 by kriss13

[1DegreeN 7]

I have the Polemaster mounted in the Astrotrac's polarscope arm, using the adapter from Cyclops Optics. In the setup phase of the PM's procedure, when you rotate the PM (i.e. the polarscope arm) back to the origin and check that your chosen star follows the green circle, the star clearly deviates from the circle between detents but at the detents it is bang on the circle. I use PHD to guide (and dither) my imaging camera so I can judge the accuracy of the polar alignment from the amount of drift in the declination. On Tuesday night and again on Wednesday I was getting approx 4 arc seconds of dec drift in 10 minutes which is about 2 pixels on my imaging camera. 

If your polarscope arm is not sufficiently accurately aligned with the RA axis, this should become apparent after you do your alignment and then continue monitoring the pole via the PM application.

Edited December 2, 2016 by 1DegreeN

[kriss13 9]

On 12/2/2016 at 15:33, 1DegreeN said:

I have the Polemaster mounted in the Astrotrac's polarscope arm, using the adapter from Cyclops Optics. In the setup phase of the PM's procedure, when you rotate the PM (i.e. the polarscope arm) back to the origin and check that your chosen star follows the green circle, the star clearly deviates from the circle between detents but at the detents it is bang on the circle. I use PHD to guide (and dither) my imaging camera so I can judge the accuracy of the polar alignment from the amount of drift in the declination. On Tuesday night and again on Wednesday I was getting approx 4 arc seconds of dec drift in 10 minutes which is about 2 pixels on my imaging camera. 

If your polarscope arm is not sufficiently accurately aligned with the RA axis, this should become apparent after you do your alignment and then continue monitoring the pole via the PM application.

Are you guiding the Atrotrac?

I always pot the polar arm of Atrotrac in the "click" position, never in between.

[1DegreeN 7]

Yes I am guiding the Astrotrac but only because I want to dither my frames. I'm imaging with a DSLR (modified 700D) and frequently suffered from the dreaded "rain noise" or "walking noise" and dithering is the only way I've found to avoid it. Of course the Astrotrac can only be guided in RA so PHD cannot correct any drift in the declination, and unless your polar alignment error is zero there will always be declination drift. I use BYEOS to manage the imaging session and control the dithering; in PHD I have to periodically reselect the guide star to reset the declination drift to zero which prevents the dither interval extending to BYEOS's 90 second timeout.

[kriss13 9]

On 5/4/2016 at 23:26, kriss13 said:

Or maybe we could mount the polar camera onto a plate near the RA knob, screwed bu the same 3 screws as a member suggested., so we could have both. I did a crude mocap in Photoshop.. you get the idea.

 

 

 

I started a thread based on this idea here.

 

 

Edited September 22, 2017 by kriss13

[shamantanthew 3]

On 5/7/2016 at 18:04, shamantanthew said:

Here's my homemade adapter at the end of the counterweight bar using approximately $5 worth of hardware store goodies:

Astrotrac Polemaster Adapter by Shaman Tanthew, on Flickr

Reviving this thread as I just had a thought... I've always been bothered how the TH3010 head clutches introduce some play/wobble into the system when released to swing the arm the 15-30 degrees required for the PoleMaster routine. It looks like it comes back right where it was, but pixels matter! An alternative for those of us not mounting the PoleMaster in the polar scope holder would be to have the Astrotrac wind itself along the length of its screw to do the swinging for the PoleMaster routine; however, the Astrotrac's too slow to do this in a reasonable amount of time, the fastest it can go is 1.5x sidereal rate (using a switch via RJ45-RJ12 at the autoguide port). But it must be capable of faster speeds (forward and reverse) because it's quite fast to spool through those first 10 seconds after starting the Astrotrac or when it comes time to rewind it. Anyone know if it's possible to make the Astrotrac speed forward the entire way through the length of the screw, not just the first little part?

[1DegreeN 7]

It is possible to wind out the Astrotrac quickly, at its rewind speed. I can't remember where I got this from, probably from SGL, but according to Richard Taylor (Astrotrac founder):

"If you hold down the track button whilst powering up, the TT320 will give 3 beeps in quick sucession BEEP, BEEP-BEEP. If you press track the drive arms will open about an inch, as normal, and stop in the ready to track position. Press track again, and the drive arms will open all the way out at rewind speed with the LED flashing blue. When you have finished cleaning, press the rewind button to close the drive arms"