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How to improve tracking of Star Adventurer (with/without Guiding)

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#26 Aaron_tragle

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Posted 17 December 2017 - 12:37 PM

Amazing image. Very impressive for 30s subs. Glad that your lens is working well!

#27 mxcoppell

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Posted 17 December 2017 - 01:52 PM

Amazing image. Very impressive for 30s subs. Glad that your lens is working well!

Thanks Aaron! The 70-200mm + TC1.4III worked pretty well - but it's very heavy as well. I am in the process of improving my single-sub exposure time. Just got another counter weight. 



#28 mxcoppell

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Posted 29 December 2017 - 09:19 PM

Finally got some time at the end of the year to test out the polar scope alignment for the Star Adventurer. 

 

Here is the result. I noticed there is a small shift. But not sure if it's big enough that requires adjustment.

 

"Home" position.

IMG_3130.jpg

 

Rotated 180 degrees:

IMG_3131.jpg

 

Any suggestions?



#29 Jim Waters

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Posted 29 December 2017 - 09:44 PM

You are good to go.  There's very little shift.



#30 mxcoppell

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Posted 29 December 2017 - 10:13 PM

Thanks Jim.

 

Also, tested out the extra counter weight. Looks good statically - set all RA clutch loose and the balance can be hold well. But it doesn't mean it could do like this in the field, it will be a challenge to re-balance after pointing the camera to the target - the balance will be changed for sure. So moving the counter weight position can't be avoided - and it will impact the polar alignment more or less. confused1.gif

 

IMG_3133.jpg

 

IMG_3134.jpg

 

IMG_3135.jpg

 

IMG_3136.jpg

 

IMG_3137.jpg



#31 mxcoppell

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Posted 29 December 2017 - 10:30 PM

Jim, one more question for you. 

 

The total weight of everything in the picture that is carried on top of the mount (+DEC bracket and 2 counter weight). It's 15lbs - that exceeds the SA's limitation of 11lbs. 

 

Somewhere I read that the payload capacity in the mount's specification does not include the counter weights (total 2.2 x 2 = 4.4lbs). But even with this assumption, the payload is 10.6lbs and is extremely close the the maximum payload of 11lbs. Could this be an issue? 



#32 GoFish

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Posted 29 December 2017 - 11:10 PM

Granted, I use a little smaller lens than what I see in your photo. But I am able to set up DSLR/lens and guidescope, and balance them, without using ball head(s) or counterweights.

 

How? I bought a second dovetail and bracket assembly, then removed the dec bracket from the spare. I fastened the second dec bracket to the counterweight end of my original dovetail. So now I have a dovetail bar with a dec bracket on each end - perfectly symmetrical. 

 

Then I fastened the guide scope, with Synta-style stem, to the lower dec bracket using the 1/4” screw. I fastened the camera directly to the 1/4” screw mount on the upper bracket.  I can easily balance this configuration about both RA and dec without using counterweights by sliding the dovetail bar along its slot. 

 

This drastically reduces the total weight on the mount. And provides fine control of pointing for both the guidescope and the camera. Works great. 

 

I can still add a counterweight, if needed, but it would take an awfully heavy lens to make this necessary. 



#33 dkeller_nc

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Posted 29 December 2017 - 11:19 PM

Those are actually very nice!  Especially with a telephoto zoom lens that don't normally have a very good reputation for holding still when doing long exposures with temperature swings.

 

While I can't help much with the specific questions about the Star Adventurer's operation, I do have a general observation.  You mention using a guide scope/camera and PHD2.  If that's a correct interpretation, then you can get a total RMS error displayed when you use the "view graph" function in PHD2.  What is this value?  Even if your polar alignment isn't perfect, PHD2 should be able to hold your target fairly well.  Certainly well enough to get 60s or longer subs without obvious star trails.

 

One useful observation to make would be whether the guiding graph stays on the targeted star over a 10 minute period.  You will see a fair amount of bouncing around due to inaccuracies in the internals of the Star Adventurer and the effect of atmospheric seeing, but on average the star's position should always return "home".  If it doesn't, and the "guide East" and/or "guide North" error continues to increase over that ten minute period, that tells you that your polar alignment is far enough off that PHD2 cannot issue large enough corrections to overcome the PA error.

 

In other words, PHD2 itself should be able to tell you whether your PA is good enough for each session.



#34 mxcoppell

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Posted 30 December 2017 - 12:38 AM

Granted, I use a little smaller lens than what I see in your photo. But I am able to set up DSLR/lens and guidescope, and balance them, without using ball head(s) or counterweights.

 

How? I bought a second dovetail and bracket assembly, then removed the dec bracket from the spare. I fastened the second dec bracket to the counterweight end of my original dovetail. So now I have a dovetail bar with a dec bracket on each end - perfectly symmetrical. 

 

Then I fastened the guide scope, with Synta-style stem, to the lower dec bracket using the 1/4” screw. I fastened the camera directly to the 1/4” screw mount on the upper bracket.  I can easily balance this configuration about both RA and dec without using counterweights by sliding the dovetail bar along its slot. 

 

This drastically reduces the total weight on the mount. And provides fine control of pointing for both the guidescope and the camera. Works great. 

 

I can still add a counterweight, if needed, but it would take an awfully heavy lens to make this necessary. 

That's a good idea indeed.  I will find a 40cm light weight dove bar with 3/8 slot in the middle and give it a try. Before that, I will give current setup a shot - I saw some people using Sigma 150-600mm on the SA. Will give some faith to the SA . laugh.gif

 

Update: After I thought about it - the dovetail needs to have a hole to work with the built-in polar scope, that's something extra to worry about. 


Edited by mxcoppell, 30 December 2017 - 01:24 AM.


#35 mxcoppell

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Posted 30 December 2017 - 12:39 AM

Those are actually very nice!  Especially with a telephoto zoom lens that don't normally have a very good reputation for holding still when doing long exposures with temperature swings.

 

While I can't help much with the specific questions about the Star Adventurer's operation, I do have a general observation.  You mention using a guide scope/camera and PHD2.  If that's a correct interpretation, then you can get a total RMS error displayed when you use the "view graph" function in PHD2.  What is this value?  Even if your polar alignment isn't perfect, PHD2 should be able to hold your target fairly well.  Certainly well enough to get 60s or longer subs without obvious star trails.

 

One useful observation to make would be whether the guiding graph stays on the targeted star over a 10 minute period.  You will see a fair amount of bouncing around due to inaccuracies in the internals of the Star Adventurer and the effect of atmospheric seeing, but on average the star's position should always return "home".  If it doesn't, and the "guide East" and/or "guide North" error continues to increase over that ten minute period, that tells you that your polar alignment is far enough off that PHD2 cannot issue large enough corrections to overcome the PA error.

 

In other words, PHD2 itself should be able to tell you whether your PA is good enough for each session.

I did some PHD2 test couple of months ago but it didn't go well (like I described in my original post, the guiding didn't help the exposure time at all). Didn't get a chance to take a screenshot of the guiding graph, will do next time. 



#36 dkeller_nc

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Posted 30 December 2017 - 11:44 AM

What I was getting at (but didn't state explicitly) is that poor star shape could have other causes than poor polar alignment.  Just one would be shifting in the ball head that you have on the camera.  Personally, I'd remove the ball head and mount the camera directly on the star adventurer. Another possibility would be a shift in the lens' zoom position.  Many imagers use "gaffers tape" to lock down the zoom position of the lens while using it for AP.  



#37 mxcoppell

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Posted 30 December 2017 - 12:47 PM

What I was getting at (but didn't state explicitly) is that poor star shape could have other causes than poor polar alignment.  Just one would be shifting in the ball head that you have on the camera.  Personally, I'd remove the ball head and mount the camera directly on the star adventurer. Another possibility would be a shift in the lens' zoom position.  Many imagers use "gaffers tape" to lock down the zoom position of the lens while using it for AP.  It

It's very possible. Removing ball-head has more than one benefits - removing ball-head locking shift (both at base and the ball locking ring), enhancing setup balance and reducing overall payload weight. 

 

My problem without the ball-head is - it's hard to aim the camera to the new target once the PA is done. Normally I tighten the RA clutch firmly after tracking started. Without the ball-head, I need to loose the RA clutch with firm force, positioning the camera to the new target, and tighten the RA clutch again firmly. Most of the time, the PA is off (looking into the polar scope - Polaris is not on the circle anymore. bawling.gif )

 

Didn't find a good practical solution for the above problem yet.


Edited by mxcoppell, 30 December 2017 - 01:21 PM.


#38 Aaron_tragle

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Posted 30 December 2017 - 02:58 PM

 

What I was getting at (but didn't state explicitly) is that poor star shape could have other causes than poor polar alignment.  Just one would be shifting in the ball head that you have on the camera.  Personally, I'd remove the ball head and mount the camera directly on the star adventurer. Another possibility would be a shift in the lens' zoom position.  Many imagers use "gaffers tape" to lock down the zoom position of the lens while using it for AP.  It

It's very possible. Removing ball-head has more than one benefits - removing ball-head locking shift (both at base and the ball locking ring), enhancing setup balance and reducing overall payload weight. 

 

My problem without the ball-head is - it's hard to aim the camera to the new target once the PA is done. Normally I tighten the RA clutch firmly after tracking started. Without the ball-head, I need to loose the RA clutch with firm force, positioning the camera to the new target, and tighten the RA clutch again firmly. Most of the time, the PA is off (looking into the polar scope - Polaris is not on the circle anymore. bawling.gif )

 

Didn't find a good practical solution for the above problem yet.

 

How do you do your PA? I personally use the sharp cap polar alignment tool and get it under half a arc minite



#39 Jim Waters

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Posted 30 December 2017 - 04:27 PM

 

My problem without the ball-head is - it's hard to aim the camera to the new target once the PA is done. Normally I tighten the RA clutch firmly after tracking started. Without the ball-head, I need to loose the RA clutch with firm force, positioning the camera to the new target, and tighten the RA clutch again firmly. Most of the time, the PA is off (looking into the polar scope - Polaris is not on the circle anymore. bawling.gif )

 

Didn't find a good practical solution for the above problem yet.

I use the DEC L Bracket on my setup.   I have my Canon 6D on the DEC L  Bracket axis.  Yes, tightening and loosening the RA and DEC Clutches will cause the mount to shift.  I have found that applying a thin layer of grease to the RA and DEC threads (not the clutch surfaces...) helps with the clutches.  They are easier to tighten and loosen and I do not over tighten...  (your mileage may very)  DEC and RA balance is key.  Try to get as good a balance as you can.  Make sure the RA is balanced to the East or West a little so the RA Worm is engaged.  

 

If you are using a Ball-Head that mounts directly to the RA clutch you will always have problems with PA.



#40 mxcoppell

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Posted 30 December 2017 - 07:51 PM

How do you do your PA? I personally use the sharp cap polar alignment tool and get it under half a arc minite

Aaron, I tried to search SharpCap PA tool. Most of the article on the internet is about doing it with Go-To mount. Not sure if it's easy to do with portable mount like SA (only RA axle could be rotated). Could you share more information about how to do SharpCap with SA? It will be a game-changer if I could use this method to redo the PA in 2-3 minutes. 



#41 mxcoppell

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Posted 30 December 2017 - 07:58 PM

I use the DEC L Bracket on my setup.   I have my Canon 6D on the DEC L  Bracket axis.  Yes, tightening and loosening the RA and DEC Clutches will cause the mount to shift.  I have found that applying a thin layer of grease to the RA and DEC threads (not the clutch surfaces...) helps with the clutches.  They are easier to tighten and loosen and I do not over tighten...  (your mileage may very)  DEC and RA balance is key.  Try to get as good a balance as you can.  Make sure the RA is balanced to the East or West a little so the RA Worm is engaged.  

 

 

 

If you are using a Ball-Head that mounts directly to the RA clutch you will always have problems with PA.

Thanks Jim!

 

I will give it a try tonight to see if it improves balance (and get rid of the extra counter weigh) by removing the ball-head on the DEC L-Bracket. I think my biggest problem is over-tightening the RA clutch. Will try to find the sweet spot of the tightness level. 

 

Need to find a quick way to redo the PA after all the adjustment. 

 

Will report back.



#42 Aaron_tragle

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Posted 30 December 2017 - 08:08 PM

Can do, I will when I get inside after this imaging session

#43 GoFish

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Posted 30 December 2017 - 08:19 PM

I really like the Star Adventurer. But it has some weaknesses. 

 

The altitude adjustment for PA is pretty coarse. Mine has a lot of “stiction” and tends to jump around while turning the adjuster screws. Azimuth is similar but not quite as bad. 

 

It is manageable and I always end up with “good enough” PA. 

 

But the coarseness, jumpy-ness, and stiction make it really hard, for me, to use SharpCap’s fabulous PA tool. SharpCap works well to measure the resulting PA error, but I prefer to use the PA scope to make the adjustments.

 

YMMV. 



#44 Jim Waters

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Posted 30 December 2017 - 08:59 PM

Yes - The Alt Adjustment on the wedge needs to be redesigned.  The gears are way too coarse.  If you have "stiction" make sure the Alt Locking Lever is a little loose or you can try some grease where the Alt portion of the wedge meets the base.   

 

The AZ Adjustments are OK if you take into account that this type of design is used on other mounts.  IMHO the biggest design problem is that the polar scope can't be freely rotated.  I mounted my polar scope off to one side for now.  It can be rotated on the "Mini" mount.  I would also like to see greater magnification in the polar scope and a brass RA gear.



#45 donlism

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Posted 30 December 2017 - 09:01 PM

Oh my gooness.  I'm taking a big chance, here, because it's based on assumptions, but I have to go ahead anyway.  I apologize in advance if I'm way of track.

 

After reading through the thread...

 

Get rid of those ball mounts!  They could very well be at the heart of all your problems.  They're not necessary, for any reason or any purpose.  They do only harm: they increase the level arm, so that more weight is  required to counterbalance and more effort is required by the mount to move everything.   They introduce additional flexure, so that your guide scope and camera are wiggling all over the place and no longer point to the same place in the sky.  They're just bad, bad, bad.  Take them off.  Now.  Go right now, and take them off.  I'll wait.  4.gif

 

(Just kidding about the mood.  grin.gif  I'm actually a very nice, patient, and easy-going person!)   But they really are wrong and bad.  Consider this: each arcsecond of error along a 200mm length represents moving the end of that object by approximately 0.0001mm.  The pixels in your camera are 4.22um, so that's an error of about 40 arcseconds of error along the focal length of your lens to move an image point from one pixel to the next one over.  It's a tiny amount.  I betcha... I just betcha... if you take your rig and just push and pull on the camera a little, you can bend it a lot more than 0.004mm.  The question is how much it will bend on its own, just due to the weight of the camera at the end of a long arm.  Spare no expense in making that arm shorter and stiffer.

 

I'm reading between the lines, and so this is risky, but I think one of the basic gaps in your knowledge so far is understanding how an equatorial mount works.

 

Imagine a rotating spindle in front of you, sticking up out of the desk.  Draw an arrow on the top end of it, to show where's pointing at the walls of your room.  Rotate the spindle counter-clockwise, and notice that it points to different places on the walls.

 

Now...  Introduce another spindle, rotating the opposite direction, and attached to a bracket at the bottom of the first spindle.  Draw an arrow on the end of it,  and notice something very important: when the primary spindle rotates 10 degrees toward the east, the secondary spindle riding along with it rotates 10 degrees toward the west, and so... it remains pointing at the same place on the wall.

 

So far so good.  Now, replace the arrow on top of the second spindle with a little toy horse who's reared up on his hind legs with his body pointed up more toward the ceiling.  You'll notice he keeps pointing to the same place on the upper wall and/or ceiling as the two spindles rotate.  Now twist the horse toward the left or the right, and you'll notice he keeps pointing to the same place on the wall as the spindles rotate.  Now replace him with a turtle and some duct tape so that he's pointing downward, and you'll notice that he points to the same place on the walls as the spindle rotates.

 

(Yes, yes... there is a tiny little offset as one spindle goes around the other.  We could fix that by making the machinery a little more complex, e.g. stacking the second spindle on top of the first... or by making the distance to the walls infinite.)

 

If the spindles were not aligned, and had their axes pointing in two different directions, this wouldn't work.  The horse or turtle would point to different places as the axes turned.

 

When you polar align, you're aligning the spindles -- one through the earth, and the other through the center of the RA axis.  You're not aligning to the position on the wall, in any way shape or form... unless you want to use a spot on the ceiling, with a laser pointer attached to each spindle, to see if they're aligned well with each other.  That spot is near Polaris in our northern sky.

 

Once you have the RA axis parallel to the earth's axis, and rotating at the same speed, you can attach whatever you want to it, and it will continue to point to the same place on the walls of the universe.  Your mount already has factilities for rotating the mount on two axes, which is enough to point anywhere.  In other wise, the rotation around the RA is just an adjustment of where you're pointing.  The Dec axis is also just "pointing."  Think of the RA and Dec axes of your mount as a big ball mount, attached to your RA spindle.

 

Since you can rotate around RA and up and down in Dec as necessary to point anywhere in the sky, there's no need or reason or need to have additional ball mounts just messing up the stiffness and leverage and weight and all that.  And the axes only have to be tight enough that they don't slip, so loosening them shouldn't be too traumatic.  And the balance should be really, really good, so that the RA motor doesn't have to exert more than a few gnat's wings worth of effort to keep the RA axis turning at the right speed.  (The 200" Hale telescope weighs 500 tons and its RA motor is 1/12 horsepower.)

 

Capisce?  Is good, no?



#46 GoFish

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Posted 30 December 2017 - 09:26 PM

Reached the same conclusion. Ball mount(s) banished. 



#47 GoFish

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Posted 30 December 2017 - 09:31 PM

Yes - The Alt Adjustment on the wedge needs to be redesigned.  The gears are way too coarse.  If you have "stiction" make sure the Alt Locking Lever is a little loose or you can try some grease where the Alt portion of the wedge meets the base.   

 

The AZ Adjustments are OK if you take into account that this type of design is used on other mounts.  IMHO the biggest design problem is that the polar scope can't be freely rotated.  I mounted my polar scope off to one side for now.  It can be rotated on the "Mini" mount.  I would also like to see greater magnification in the polar scope and a brass RA gear.

I improved my az performance by replacing the wimpy plastic washers with (somewhat) thicker nylon washers, then carefully adjusted the two HSH screws for smoother operation. 

 

Where are you suggesting the grease?  On the alt pivot?  Between the alt  “clamp” surfaces?  All of the above? wink.gif



#48 Jim Waters

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Posted 31 December 2017 - 12:34 AM

I forgot about those screws and washers.  I replaced the existing washers with larger Nylon washers.  

 

I think we need some pictures.  There's the stationary lower base of the wedge, the upper AZ rotating piece and the Alt piece.  I lubed the place where the Alt and AZ rotating pieces meet.  I also inserted a very "thin" Mylar washer to fill the void between these two pieces.  In general I greased most places where plastic and / or metal rub together.  Except the RA and DEC clutch surfaces.

 

I will try to get some pictures together to show my modifications better.



#49 black metal

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Posted 31 December 2017 - 04:06 AM

Current setup:

  • Sky-Watcher Star Adventurer
  • Nikon D500 (Stock)
  • Nikon 70-200mm f2.8 II
  • Orion 50mm Guiding Scope
  • Orion Starshoot Autoguider
  • Manfrotto Aluminum Tripod (with 20-lbs dumbbell added weight)

Dec bracket and the counter weight kit are deployed. I use 2 ball heads, one for the D500+70-200/2.8 on the rotate-able geared head side, the other ball head installed on the counter weight bar side for the guiding scope. Overall, I don't think this setup exceeds the payload limitation of the Star Adventurer.

For polar alignment, pretty sure I got it very well before the shooting starts. Tested the tracking without guiding with focal length at 200mm, 30-second shot looks pretty good (frame center, stars look round and solid). But for 45-second or 60-second shots, the star trails are very obvious. With PHD2 guiding, the guiding chart looks pretty smooth if I don't touch the setup. But when taking test shots, I still can only get solid stars at 30-seconds - 45-second and 60-second have obvious trails.

After tracking for an hour or so, I went back to check the polar scope - Polaris didn't wander off its path on the circle in the polar scope. So I would assume the PA is still good.

From the PHD2 guiding chart (RA-only), I don't see the guiding adjustment getting worse. It looks pretty smooth. Next time I will capture a guiding chart to post here.

I don't have any ideas about how to improve this other than more carefully checking the tripod level.

Another thing bothered me is that - with guided tracking, isn't it should be much better? I am thinking I should be able to take 120-second sub-shot without guiding and 300-second sub-shot with guiding at 200mm (or 280mm with TC1.4). Am I expecting too much?

My goal is to use my existing photo gears - without using telescopes and big tracking mounts, to see where the limits are.

At last, not many Nikon D500 samples on CN forum, here are a few of mine shot 2017/10 and 2017/11 at Fort Griffin Historical Site (Class-2 dark site).

MX-20171118-233808-20171127232836.jpg
"Orion Rises Above Fort Griffin"

MX-20171127-193436-20171127232859.jpg
M31, 30s/200mm/f2.8/iso3200/64-light/25-dark/25-bias
hi I think these shots are amazing I have just recieved a skywatcher star adventurer and am still learning how to use it, may I ask you on your editing are these cropped shots from using a 200mm lens? and what software do you use to get this result thanks, john

#50 mxcoppell

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Posted 31 December 2017 - 12:16 PM

hi I think these shots are amazing I have just recieved a skywatcher star adventurer and am still learning how to use it, may I ask you on your editing are these cropped shots from using a 200mm lens? and what software do you use to get this result thanks, john

No problem, John!

 

SA is pretty good. But it does take time to dig its full potential. I am still at the beginning of the learning curve here (with all the wonderful help from the forum members, Thank You All!). 

 

The M31 was my first attempt with SA. It was shot at 200mm with Nikon 70-200/2.8 at f2.8. On a cropped sensor of D500 (not astro-modified). The subject M31 is about 1/6 width of the D500 frame - it's a very tight crop. I used Deep Sky Stacker for alignment and stacking, and Adobe Lightroom for post processing. I was not able to pop out the layers and colors of the wonderful M31. Will definitely visit it again later with more experience. 




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