Test with Star Adventurer Tracking Mount

[W5JCK]

A bit windy tonight with 5 mph wind and some gusts over 10 mph. But I think I can still draw a few conclusions.

I set up the mount and aligned it to Polaris with the knowledge that the Sky-Watcher Star Adventurer's polar alignment scope shows an image rotated 180°. When I aligned the mount Polaris was in the 11:30 position, so I placed Polaris on the scope ring at the 5:30 mark, as that is rotated 180°.

I was shooting with the Sony a6000 and an old 200mm f/4 Nikon (film era non-AI lens.) It is not that big nor that heavy since it is only f/4.

My test included 30 subs at 30 sec, ISO 800, f/8. The individual subs look okay. See sample single image below. However, after I finished I used an app called StarStaX to quickly stack the 30 subs. StarStaX does not do any alignment, so my thought is that this should show any drift in the mount over the 25 minutes I was shooting the 30 subs. It showed a lot of drift and a lot of jumping around. See image below.

Finally I put Jupiter and its moons in the view, and following SwimsWT's suggestion I took a 4 minute sub with the RA purposely moved off alignment by about 25° to see if it tracked in a straight line. See image below.


1 x 30 sec, f/8, ISO 800 using a6000 and Nikon 200mm f/4 non-AI lens


100% crop of 30 x 30 sec subs stacked but not aligned (lot of drift and a lot of movement)


100% crop of 1 x 240 sec with RA purposely moved 25° off (not straight at all)

Okay I realize the wind could have been a factor, but I'm thinking even calm conditions would have not given much better results. I'm thinking this mount is not very good at 200mm at even just 30 seconds. Hopefully it will do better at 85mm and wider. I will try to test that in the near future when the winds are calm.

--
Jack Swinden
An astrophotography hobbyist and amateur radio instructor and examiner. Sony a7 and Sony a6000. https://www.flickr.com/photos/jackswinden/

 

[W5JCK]

As you can see the lens is not that big or heavy.




a6000 with Nikon 200mm f/4 non-AI lens



--
Jack Swinden
An astrophotography hobbyist and amateur radio instructor and examiner. Sony a7 and Sony a6000. https://www.flickr.com/photos/jackswinden/

 

[Rutgerbus]

Hmmm, that are some interesting findings. What kind of tripod are you using? Could be that that's the part of your setup which causes the problems (Maybe it is just not sturdy enough).

I also have a not so sturdy Manfrotto tripod (which I was able to get from a dumpster since someone threw it away because the fluid head was broken....just bought myself a new actiongrip ball head for that)

Below you can see my setup before purchase of the Star Adventurer with my "home build Barndoor". As you can see, tripod is not that big and causes a lot of frustration due to fibration which I tried to reduce with rubber bands around the lens and barndoor (off course this didn't help allot ;-)). Luckely, it has a long center column where you can hang some weights to. I just put some (4x2kg) old dumble weight-disks around it which are beeing held in place by a metal pin. works wonders for me.

I just shot this M42 lately 420mm, 12x100sec @ ISO800, stacked in DSS.....DSS took all 12 single shots with a treshold set to 85% of the best images to stack.









--
www.rutgerbus.nl
Photographic Moments
A photon only stops "existing" when it is captured by your sensor.

 

[W5JCK]

I don't remember the brand of the tripod I'm using as I've had it for many years, but it was not a professional one. I have a professional Manfrotto heavier tripod but there is no way to easily hang weights under it, so I'm using the other one. The one I'm using with the Star Adventurer is carbon fibre or some other polymer. I've hung about 4 pounds of weight under it and that helped a lot with vibrations. But yes I definitely need to get a better tripod.

I am new to tracking, so I have no idea of what is typical and what is not. I assumed good tracking mounts would not have so much drift over time. Maybe they do. I just don't know. Hopefully the wobbling part is correctable too. I get some good single images at 200-400mm at 30 to 60 sec, but a lot of them are throw-aways. I does a lot better at shorter FL like 85mm and shorter.

My other issue is that no matter where I place Polaris on the polar alignment scope ring the tracked images look about the same. I've tried flipping just one axis, rotating 180°, and no flip or rotation, but they all look a bit elongated on longer exposures. I think the proper alignment is to rotate 180° so that is what I'm currently doing. I am having to struggle a bit to align it as I have to view Polaris about 2° or 3° above a nearby three story apartment building which is lit up at night. The glare makes it difficult to see through the scope, but I can just barely see through it. I checked the calibration of the mount as per the manual and it seems well calibrated.

Oh well, it does produce better images than using no tracker at all, but I was hoping to get 2 to 4 minute exposures at mid to longer telephoto. That won't be possible though since it struggles at 60 sec at even 200mm.

--
Jack Swinden
An astrophotography hobbyist and amateur radio instructor and examiner. Sony a7 and Sony a6000. https://www.flickr.com/photos/jackswinden/

 

[W5JCK]

I just read this good review of the Star Adventurer that was in the Nov/Dec 2014 issue of SkyNews. (The link is to a PDF file.) He thinks anything above a lightweight 300mm lens is too much for the mount, and shots above 135mm started giving trails in some images. So I guess he is confirming what I'm seeing. A decent mount up to about 100mm or so of FL, but pushing your luck beyond that FL.

 

[Trollmann]

100% crop of 30 x 30 sec subs stacked but not aligned (lot of drift and a lot of movement)

Looks like plain good old fashioned periodic error!

Astronomical mountings all have some periodic error - if not the gears would mesh and the mount would stall. So periodic error is a necessary evil with geared mounts.

Cheap mounts usually have more - and more also erratic - periodic error than more expensive mounts. As we pay the periodic error gets more even and also shrink.

The amount of periodic error shown here is as expected given the price point of the mount (some might be a bit more lucky and get a slightly smoorther mount while others will fare a bit worse because rather wide production tolerances). Erratic periodic error is harder to guide out than a smoother mount.

Cheap mounts usually have periodic errors in the 30-arcsecond ballpark (a bit more than one Jupiter diameter) - and a smooth mount with 4 arcsecond periodic error cost a small fortune.

Looks s bit worse in this test than what the actual error might imply. Guess you have a lot of good images waiting for us in the future!

 

[Lyle Aldridge]

I hope I'm not raising the obvious, Jack, but since you're new at this, and since you're not seeing a difference when setting Polaris at different spots, is the polar scope aligned with the polar axis? You can't really do polar alignment without first aligning the scope to the axis. This means pointing the scope at a distant terrestrial object, and adjusting it so its view remains the same when the RA axis is rotated. Don't ask how I know this.

 

[W5JCK]

I hope I'm not raising the obvious, Jack, but since you're new at this, and since you're not seeing a difference when setting Polaris at different spots, is the polar scope aligned with the polar axis? You can't really do polar alignment without first aligning the scope to the axis. This means pointing the scope at a distant terrestrial object, and adjusting it so its view remains the same when the RA axis is rotated. Don't ask how I know this.

Yes I checked the calibration using the method you mentioned and it was already well calibrated.

 

[swimswithtrout]

I was very specific that you need to shoot 1-10min long exposure. No stacking etc. That's why I emphasized stopping down to f16; your stars won't be effected at all, since they're point sources, but it will tame the sky background.

Shooting just ONE, very long shot, covering at least one full worm gear cycle, will help you sort out short period vibrations like shutter slap, concrete vibrations etc , from the long period PE.


I'm a bit concerned with the PA offset Jupiter image ! It clearly shows the long period oscillation due to PE, but at an incredibly short frequency. The iOptron SkyTrackers worm gear has a period of 10 minutes, during which there's a totally flat segment of ~ 3 min, then a slow rise for ~ 2 min, then a much sharper curve to it's max, then back in reverse.


I have shot many photos with SkyTracker using my 200mm lens, @ 120", tossing out the worst, and usually get ~ 50-60% usable subs, but looking at your short 4 min grab, I wonder how small the worm gear is in the Adventurer.

 

[RustierOne]

I don't remember the brand of the tripod I'm using as I've had it for many years, but it was not a professional one. I have a professional Manfrotto heavier tripod but there is no way to easily hang weights under it, so I'm using the other one. The one I'm using with the Star Adventurer is carbon fibre or some other polymer. I've hung about 4 pounds of weight under it and that helped a lot with vibrations. But yes I definitely need to get a better tripod.

I am new to tracking, so I have no idea of what is typical and what is not. I assumed good tracking mounts would not have so much drift over time. Maybe they do. I just don't know. Hopefully the wobbling part is correctable too. I get some good single images at 200-400mm at 30 to 60 sec, but a lot of them are throw-aways. I does a lot better at shorter FL like 85mm and shorter.

My other issue is that no matter where I place Polaris on the polar alignment scope ring the tracked images look about the same. I've tried flipping just one axis, rotating 180°, and no flip or rotation, but they all look a bit elongated on longer exposures. I think the proper alignment is to rotate 180° so that is what I'm currently doing. I am having to struggle a bit to align it as I have to view Polaris about 2° or 3° above a nearby three story apartment building which is lit up at night. The glare makes it difficult to see through the scope, but I can just barely see through it. I checked the calibration of the mount as per the manual and it seems well calibrated.

Oh well, it does produce better images than using no tracker at all, but I was hoping to get 2 to 4 minute exposures at mid to longer telephoto. That won't be possible though since it struggles at 60 sec at even 200mm.

 

[W5JCK]

I was very specific that you need to shoot 1-10min long exposure. No stacking etc. That's why I emphasized stopping down to f16; your stars won't be effected at all, since they're point sources, but it will tame the sky background.

Shooting just ONE, very long shot, covering at least one full worm gear cycle, will help you sort out short period vibrations like shutter slap, concrete vibrations etc , from the long period PE.

I'm a bit concerned with the PA offset Jupiter image ! It clearly shows the long period oscillation due to PE, but at an incredibly short frequency. The iOptron SkyTrackers worm gear has a period of 10 minutes, during which there's a totally flat segment of ~ 3 min, then a slow rise for ~ 2 min, then a much sharper curve to it's max, then back in reverse.

I have shot many photos with SkyTracker using my 200mm lens, @ 120", tossing out the worst, and usually get ~ 50-60% usable subs, but looking at your short 4 min grab, I wonder how small the worm gear is in the Adventurer.

Here is a post full of images where a guy took apart his Star Adventurer to look at the gears.

 

[W5JCK]

I'm confident you will continue to make improvements in handling your equipment. You have been experimenting and have an analytic mind. There are limits to what can be accomplished with any equipment. But I don't think you've reach that point yet.

 

[shenango]

Hi Jack;

I am having the same problems as you have with my Ioptron smart EQ. The test I designed can be done in the house and although it will not pinpoint very miniscule events it will be of value to show stability and wind driven effects. First, set up your equipment in a room where you have 15 or so feet of open space, an open basement is perfect. Tape a laser pointer to your lens hood so it points to an open wall and turn your tracker on. The dot will move in relationship to the movement of the tracker. The further away your wall is from the camera the more pronounced any movement will be. Tape an 8.5x11 piece of graph paper to the wall so the dot will track across the wide length of the paper. If you have access to a video set up you can record the movement of the red dot while doing various things to try to upset the dot . IE: turn a fan on and off directed at the lens hood, set your intervalometer to actuate the shutter to see if mirror slap might be a problem. There are many things you can emulate to see if a problem can be eliminated from your equipment use your imagination. Audio is a plus as you can announce when and what you are doing to interfere with your setup. If you play the video back in slow motion you can actually see a nervous dot or small fluctuations in the movement across the graph.

I found that even the slightest vibration ( my 10 pound dog running down the hallway) will be evident on the graph. My testing might not be the answer to your problems but it was a good way to waste an afternoon of snow and icy conditions. The only thing I need now is for the clouds to go away and the temp to stay above zero so I can get back out.

Jerry

 

[W5JCK]

Hi Jack;

I am having the same problems as you have with my Ioptron smart EQ. The test I designed can be done in the house and although it will not pinpoint very miniscule events it will be of value to show stability and wind driven effects. First, set up your equipment in a room where you have 15 or so feet of open space, an open basement is perfect. Tape a laser pointer to your lens hood so it points to an open wall and turn your tracker on. The dot will move in relationship to the movement of the tracker. The further away your wall is from the camera the more pronounced any movement will be. Tape an 8.5x11 piece of graph paper to the wall so the dot will track across the wide length of the paper. If you have access to a video set up you can record the movement of the red dot while doing various things to try to upset the dot . IE: turn a fan on and off directed at the lens hood, set your intervalometer to actuate the shutter to see if mirror slap might be a problem. There are many things you can emulate to see if a problem can be eliminated from your equipment use your imagination. Audio is a plus as you can announce when and what you are doing to interfere with your setup. If you play the video back in slow motion you can actually see a nervous dot or small fluctuations in the movement across the graph.

I found that even the slightest vibration ( my 10 pound dog running down the hallway) will be evident on the graph. My testing might not be the answer to your problems but it was a good way to waste an afternoon of snow and icy conditions. The only thing I need now is for the clouds to go away and the temp to stay above zero so I can get back out.

Jerry

 

[rokaroka]

Hi Jack;

I am having the same problems as you have with my Ioptron smart EQ. The test I designed can be done in the house and although it will not pinpoint very miniscule events it will be of value to show stability and wind driven effects. First, set up your equipment in a room where you have 15 or so feet of open space, an open basement is perfect. Tape a laser pointer to your lens hood so it points to an open wall and turn your tracker on. The dot will move in relationship to the movement of the tracker. The further away your wall is from the camera the more pronounced any movement will be. Tape an 8.5x11 piece of graph paper to the wall so the dot will track across the wide length of the paper. If you have access to a video set up you can record the movement of the red dot while doing various things to try to upset the dot . IE: turn a fan on and off directed at the lens hood, set your intervalometer to actuate the shutter to see if mirror slap might be a problem. There are many things you can emulate to see if a problem can be eliminated from your equipment use your imagination. Audio is a plus as you can announce when and what you are doing to interfere with your setup. If you play the video back in slow motion you can actually see a nervous dot or small fluctuations in the movement across the graph.

I found that even the slightest vibration ( my 10 pound dog running down the hallway) will be evident on the graph. My testing might not be the answer to your problems but it was a good way to waste an afternoon of snow and icy conditions. The only thing I need now is for the clouds to go away and the temp to stay above zero so I can get back out.

Jerry

 

[Lyle Aldridge]

I also ordered the counterweight kit for the Star Adventurer to help balance the load. Slowly but surely I should start to make improvements.

I think you'll find the counterweight kit goes a long way toward correcting the problems you've encountered. I don't have experience with the SSA, but even my larger mount's DC motors can create error and vibration all by themselves unless they're turning against a certain amount of counter-force. This shows up worst on targets east of the meridian, when the mass of the camera-side is "assisting" the motor, rather than resisting it. The effect is best controlled by "east-weighting" with the counterweight, rather than truly balancing the load.

 

[JPatrick]

Jack,

As one of the other posters comment, I believe most of what you're seeing is periodic error in the gear set. I noticed that the Star Adventurer has an autoguider port. Have you tried or thought about trying adding a small guide scope to your setup? A 6x30 finder plus guide cam should be sufficient with a 200mm lens. I know autoguiding can be a pain, but it might also be an option. Anytime you get above a couple hundred mm of focal length, guiding or a very precision gear set becomes important.

Patrick