Pole Master on AstroTrac, go/no-go?

[awasen]

I am looking into the Pole Master to use with my AstroTrac Pier/Wedge/Head.

I have gotten a promise by the Pole Master people that they will create an adapter for the AstroTrac Polar Arm. So, the question being since the Polar Arm is not in center of the polar axis of the AstroTrac head would that cause problems?

The Pole Master is designed to sit in the RA/Polar axis but with the AstroTrac it will be about 20 cm (8") to the side of the axis...

Thoughts?

[awasen]

Attached picture to clarify my concern...

[StuartJPP]

I'd say the ideal place would be on the DEC clutch as shown in green, however anywhere in DEC would be appropriate as long as it is roughly facing north. The PoleMaster doesn't have to be perfectly aligned/parallel with RA, it just has to be able to see Polaris and the surrounding alignment stars during it's rotation.

The reason I'd choose DEC and not the polar scope arm is that it eliminates any misalignment of the polarscope arm with the actual RA, which most AstroTracs suffer from (though can be fixed relatively easily). The polar alignment  procedure would be to release RA, rotate ~30 degrees, lock it down, rotate it again ~30 degrees, lock it down, rotate back.

The polar scope arm should provide a similar ride and in fact with its detent click when rotating it might be easier to move it from one click to the next , but only if it is well collimated/parallel with the actual RA rotation of the mount.

 

[StuartJPP]

I forgot to mention that for QHYCCD to make the most sales for the AstroTrac user base it is obvious that the polar scope arm is the preferred choice for them as every AstroTrac has got that arm...only a small percentage has got the TH3010 head...

[awasen]

True, most would not have the AT head... Didn't really consider that...

As for the rotating of the Pole Master when aligning, wouldn't rotate the actual Pole Master in the adapter do instead of moving the whole arm?

 

[StuartJPP]

You have to rotate the polarscope arm as that is representative of the rotation of the RA axis (if it is well aligned). 

Rotating just the PoleMaster in the polarscope arm won't do anything except show errors in the arm to PoleMaster coupling (which could be useful to ensure it is true). But it won't show any errors of RA to the celestial pole.

[Jim Waters]

Ideally the Pole Master should be mounted on the RA axis of the Astrotrac.  IMO the polar scope arm has too much variation from position to position and is likely not at right angles to the RA axis.  My Astrotrac was not at right angles in any of the positions and each position was different.

Jim

[1DegreeN]

I noticed that the Polemaster Astrotrac adapter is already listed for sale on Aliexpress: http://www.aliexpress.com/item/PolarScope-adapter/32597284685.html

I haven't seen it on other vendors' sites yet but they may just be slower to update. From the photographs it looks like it is designed to fit to the polarscope arm. I'm very interested but from my latitude Polaris is only 14 degrees above the horizon and usually buried in haze and I'm not at all sure that the Polemaster could detect all the stars required for alignment. If there is positive feedback from other Astrotrac users then I'll buy it - even if I can't make good use if it locally it will still be a very useful tool if I travel to higher latitudes or ever manage a trip down under to photograph the southern sky.

John

[StuartJPP]

The PoleMaster is designed to work at altitudes down to 30 degrees, beyond that atmospheric refraction correction needs to be used which the software supports. But I am not sure how accurate it will be at 14 degrees...have a look here:

http://qhyccd.com/ManualPoleMaster1.html

When using atmospheric correction the PoleMaster camera needs to be orientated correctly with the horizon.

You will also need to ensure that the polar scope arm is true to the RA axis...sometimes it needs tweaking which also applies to the regular polar scope.

I haven't tried it on mine yet...will do eventually if the weather ever clears...

[cygnux1]

On 23/03/2016 at 06:37, Jim Waters said:

Ideally the Pole Master should be mounted on the RA axis of the Astrotrac.  IMO the polar scope arm has too much variation from position to position and is likely not at right angles to the RA axis.  My Astrotrac was not at right angles in any of the positions and each position was different.

Jim

Exactly..and perhaps for some the modification to align the PS arm with RA axis is simple,but for others not so DIY inclined..definitely NOT!

One only needs to visit the AT yahoo forum to gauge the level of frustration of the AT's weakest link..it's inability without much additional laborious and often costly customization to accurately PA for longer f/l - exposure AP.

 

[StuartJPP]

18 hours ago, cygnux1 said:

Exactly..and perhaps for some the modification to align the PS arm with RA axis is simple,but for others not so DIY inclined..definitely NOT!

One only needs to visit the AT yahoo forum to gauge the level of frustration of the AT's weakest link..it's inability without much additional laborious and often costly customization to accurately PA for longer f/l - exposure AP.

 

I keep hearing this and can't disagree more. There are some issues with the AstroTrac, it isn't perfect, and there are no doubt some issues with specific AstroTracs. However I have had great success with both of mine. Each has performed well beyond my expectations, both the TT320X non-guided model as well at the TT320X-AG guided model (I don't use guiding on the AT though).

I ended up with the AstroTrac TW3100 wedge, which also gets a slating, and the TH3010 AstroTrac head, which also gets a slating as well as the AstroTrac Polar Scope, which gets a massive slating. I also mount it on a rigid Gitzo GT5541LS tripod which luckily doesn't get a slating. (Initially I used the Manfrotto 410 Junior Geared head on a cheap Giottos tripod and 300mm f/4 L IS lens which was pretty good, but I wanted to use my 500mm lens instead.)

The total cost of modifications I did to both my units amounted to approximately £0.02 worth of copper tape which I already owned, this was used to shim the polar scope arm. Time was spent collimating everything, but I don't charge my time to hobbies so the total cost is still £0.02.

I am not disputing the fact that people are having difficulties, but I am disputing that they can't be remedied without requiring costly customisation. Astrophotography is a hobby that is more than just plug and play or point-and-shoot. A bit of DIY of some description is almost always mandatory. There are plenty of cloudy nights to get familiar with the kit, if people aren't prepared to do so then perhaps it is better for them to stick to 50mm widefield imaging.

 

[1DegreeN]

Just to note that Robin Lee at Cyclops Optics now has the Polemaster adapter for Astrotrac in stock.

[awasen]

Ok, so I finally got the chance to test out the PoleMaster on my AstroTrac!

It's been overcast, cloudy and raing for the past few weeks so when I finally got a clear sky I got in a hurry! There was some haze coming in so I rushed out just after sunset and set my AstroTrac Pier up and prepared everything as far as I could.

The haze was holding off until dark and I had no problem at all to get Polaris into view in the PoleMaster software. The English in the software is much better in the latest version and I had no issues at all with the driver installation.

I have to say that not having to bend down and try to find Polaris through the Polar Scope is a HUGE relief!
Only that made the $198 worth it!

I had the PoleMaster mounted in the Polar finder arm with the supplied adapter for AstroTrac. I started with the polar arm in the lowest right position (seen from the "front") as I know the right side on my AstroTrac is much more attuned to the RA axis than the left side. I started with it at about 5 o'clock (closest to the AstroTrac arm) and then rotated it up to 3 o'clock and finally to 12 o'clock for the alignment. I tested some more and at 11 o'clock I could clearly see that it drifted off in setting from the axis. At 9 o'clock position it was horribly off axis so I would concur with Jim from previous e-mails here that if you are running the AstroTrac Head (which I am) you would really benefit from getting the PoleMaster on the head axis directly!

The whole process of aligning is SO simple and quick though. I had not looked at the software or the manual before going out and in less than 10 minutes the first try I had it aligned!
I'd do it in about 3-5 minutes without the experimenting would be my guess...

I removed the PoleMaster carefully from the Polar arm and inserted the AstroTrac polar scope and it showed a bit off NCP so with the AstroTrac polar scope I would have adjusted somewhat on the "DEC" axis (sideways) but I decided to trust the PoleMaster.

I put the PoleMaster back again and verified the alignment and could see it was a little off again so I fine tuned it. With the PoleMaster in place I could conclude that the lever for locking the height adjustment on the wedge pushes the alignment off quite a bit. The three sideways knobs did not affect the alignment at all but I am always very careful when tightening them. The height locking screw is a problem though, I had to redo it four times before I managed to get it spot on in the PoleMaster software with all knobs fully tightened.

I then mounted my camera with my Tamron 150-600 mm lens and could se that it was a whole bit of shaking in the PoleMaster but after it had settled down (which took much longer than I had expected) I started a 3 minute exposure at 300 mm and got nice and round stars. I then tried 400 mm for 3 minutes, perfect again!
Unfortunately the haze and clouds came pouring in fast so my 5 minute test never run complete before the clouds messed it up...

I have never gotten 3 minutes at 400 mm before so clearly I got a much better alignment than ever before!
And I didn't have to neither kneel nor break my neck to get it done!

I also can conclude that a lot of my previous issues must have been from misaligning when tightening the height locking knob on the wedge.
I have not waited long enough for the mount to settle down after framing or mounting accessories so the first frame has been "fuzzed" up a bit.
I have NEVER realized just how much the mount is moved around (and becoming misaligned) when moving, framing an focusing!

I now selected a frame so I could keep the PoleMaster mounted in the Polar arm all the time but being able to mount the PoleMaster on the head RA axis directly would mean that I can keep it there running and re-align whenever I see it trading off the NCP.

I am very, very satisfied with the PoleMaster and now I only need to find a workshop that can help me with getting it mounted on the AstroTrac head...

Anyone have any suggestions for the RA locking knob?

Take care!

Regards,
Anders
Stockholm, Sweden 

 

[awasen]

I looked into mounting the PoleMaster on the AstroTrac head and that would be very easy as the big "washer nut" fits perfectly on the top of the AT head. Just drilling three holes and thread them for M3 and fasten the washer so I can screw the PoleMaster AstroTrac mount into the "washer nut" would work perfectly.

The problem lies in that i would then have to move the locking knob for the DEC to the side of the AstroTrac head. Not a huge undertaking but drilling a 5 mm hole straight in would require tools I don't have...

Also it would seem the original locking screw on top of the head is not standard mm thread (can someone confirm that?). I would most likely aim for buying a clamping handle instead of the original "dial knob" and place it on the opposite side of the DEC handle and thread it to standard M6.

 

[StuartJPP]

The thread on the DEC locking screw is BSF/UNF...I can't remember the exact size, I wrote it down somewhere but can't find it, would have to measure again.

BSF/UNF = British Standard Fine / American Unified Fine.

 

I also had a play with my PoleMaster on the AT. I had it on the mount head on a dovetail. The problem I found was that when releasing the RA clutch there is a fair bit of shift and wobble until you tighten it up again...Once locked again it seemed to go back to the same place and it did form a "circle". And tracing the star back did follow that circle and ended up where it started.

I checked against the polar scope and there was certainly a difference between them but I didn't get a chance to see which one was better due to clouds coming in.

Will try again whe the weather is a bit more tolerant 

[awasen]

Well, come to think about it it doesn't really matter what the thread is in the current knob as I will drill a new hole in the side of the head and make it M6 and buy a M6 clamping handle. The original round clamping knob pretty much sucks anyway...

Figured to just drill holes and add three M3 screws in the top to keep the washer in place and screw the PoleMaster into that.

I noticed there are some small brass(?) inlays in the holes so I will add those back so the new screw is not pushing directly against the shaft.

[Kbklarry]

On 3/29/2016 at 15:29, StuartJPP said:

I keep hearing this and can't disagree more. There are some issues with the AstroTrac, it isn't perfect, and there are no doubt some issues with specific AstroTracs. However I have had great success with both of mine. Each has performed well beyond my expectations, both the TT320X non-guided model as well at the TT320X-AG guided model (I don't use guiding on the AT though).

I ended up with the AstroTrac TW3100 wedge, which also gets a slating, and the TH3010 AstroTrac head, which also gets a slating as well as the AstroTrac Polar Scope, which gets a massive slating. I also mount it on a rigid Gitzo GT5541LS tripod which luckily doesn't get a slating. (Initially I used the Manfrotto 410 Junior Geared head on a cheap Giottos tripod and 300mm f/4 L IS lens which was pretty good, but I wanted to use my 500mm lens instead.)

The total cost of modifications I did to both my units amounted to approximately £0.02 worth of copper tape which I already owned, this was used to shim the polar scope arm. Time was spent collimating everything, but I don't charge my time to hobbies so the total cost is still £0.02.

I am not disputing the fact that people are having difficulties, but I am disputing that they can't be remedied without requiring costly customisation. Astrophotography is a hobby that is more than just plug and play or point-and-shoot. A bit of DIY of some description is almost always mandatory. There are plenty of cloudy nights to get familiar with the kit, if people aren't prepared to do so then perhaps it is better for them to stick to 50mm widefield imaging.

 

Hello,

Would you please explain to me how you shimmed the polar scope arm and exactly what type of copper tape you used? I am also using a Gitzo tripod, but the smaller GT3530LS. For an alt-az mount, I'm using my Really Right Stuff full gimbal mount. I also have a Gitzo leveler on my tripod. I use a smartphone inclinometer on my astrotrac, to which I've attached an Arca Swiss plate, to set the latitude for my gimbal mount. I think my system should work really well. I'm just getting started.

 

Thanks,

Larry

[StuartJPP]

Hi Larry,

The copper tape I used was some RF screening tape that I had laying around. I am sure that the copper tape you can get for slug/snail control is the same. I used it as it is a bit thicker than regular tape and a bit more robust.

Regarding your gimbal head, they work well except that it gets difficult to frame objects facing towards the NCP...well mine did.

Good luck...

[awasen]

Ok, so modification is complete!

As I said I also drilled the corresponding holes in the big "washer-nut" so I can use it as a "quick connect" without having to fumble with the small M3 screws and instead just simply screw/unscrew the PoleMaster if I need to pack the head.

If I am at home I can attach the PoleMaster directly to the head with the three screws to get a tighter fit although there is NO wobble with the "quick connect" either.

I drilled and threaded a M6 into the side of the head instead of the original knob that was on the top.

Regards,
Anders

 

 

 

[Kbklarry]

1 hour ago, StuartJPP said:

Hi Larry,

The copper tape I used was some RF screening tape that I had laying around. I am sure that the copper tape you can get for slug/snail control is the same. I used it as it is a bit thicker than regular tape and a bit more robust.

Regarding your gimbal head, they work well except that it gets difficult to frame objects facing towards the NCP...well mine did.

Good luck...

Thanks for your quick reply explaining the copper tape I can use. So, now where do I apply it exactly?

I was looking at your flickr account astro photos. I'm blown away at what you are able to do! You are amazing! I was once an astronomy and astrophysics major - a long time ago - and your photos look like what one used to need the Hubble telescope to capture.

Thanks again,

Larry

[shamantanthew]

Very cool! I'd love to figure out a way to fashion an adapter to mount the Polemaster to the counterweight bar or at the end of the counterweight bar... I'm not looking to modify my TH3010 head yet!

With the Polemaster I've been reading that you need to rotate along the RA axis and then eventually return it to where you started... how precise do you have to be when you return it? Does it have to go exactly back to where you started or just somewhere in the neighborhood?

[ajk]

5 minutes ago, shamantanthew said:

Very cool! I'd love to figure out a way to fashion an adapter to mount the Polemaster to the counterweight bar or at the end of the counterweight bar... I'm not looking to modify my TH3010 head yet!

With the Polemaster I've been reading that you need to rotate along the RA axis and then eventually return it to where you started... how precise do you have to be when you return it? Does it have to go exactly back to where you started or just somewhere in the neighborhood?

Somewhere close-by seems to work fine for me.

[kriss13]

On 3/3/2016 at 20:30, awasen said:

Attached picture to clarify my concern...

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.

 

[1DegreeN]

I used the Polemaster on my Astrotrac for the first time a couple of nights ago. I had it attached to the polarscope arm with the PM-ST adapter made by Cyclops Optics. The PM software appears to compensate accurately for atmospheric refraction (Polaris is shifted by nearly 4 arc minutes at my latitude of 14 degrees) and after alignment I ran PHD’s drift alignment tool which reported a PAE of 1.07 arc minutes. I went on to do some imaging and my PHD logs show that my PA was at least as good as I’ve achieved previously via drift alignment. I was a little impatient with the PM alignment and I'm sure I can do better if I spend more time on it but the PM promises to give me a consistently good PA after just 10 minutes effort vs a protracted drift alignment that could take an hour or more. I do use the TH3010 head but I’ll stick with the polarscope arm mount for now and see how far I can push this. I was doing 5 minute subs with a 200mm lens and they were all good, so a very encouraging first outing for the Polemaster.

John

[shamantanthew]

I also used the PoleMaster on my Astrotrac and it worked great. I managed a 6 minute exposure at 400mm on my Canon 6D without significant trailing after my very first time using the PoleMaster... that's twice as long as I managed prior to the PoleMaster and using the polar scope (fairly well collimated polar scope but not collimated polar scope arm). I did start to see trailing at 7 minutes.

This is an image from the handle of the Big Dipper at 54.8 degrees of DEC. Here's 100% crops from the center and the very corners:

400mm 6 min Astrotrac Polemaster by Shaman Tanthew, on Flickr

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

As Stuart mentions, yes, loosening the RA clutch induces some tilt/instability while swinging the camera, but fortunately the TH3010 head seems machined well enough that tightening it back down brings it back to where it started.