48 replies to this topic

[Domer]

I have an iOptron SkyTracker Pro.  With my Canon 6D Mark Ii and a "nominal" lens (either 14mm or a 24-105mm), I have no problem adjusting the counterweight to achieve a good balance in any position. 

 

However, I just purchased a Sigma 150-600mm lens that is rather long and hefty.  When the lens pointed off at an odd angle (e.g., perpendicular to the polar axis, upward, and back), it doesn't seem possible to achieve a good balance in all rotated positions.  I believe this is because the heavy lens moves the center of mass away from the counterweight axis.  So in one position (say, 45 degrees), the camera side is heavier.  But in another position (say, -45 degrees), the counterweight side is heavier.

 

Am I missing something or is this normal?  I suspect that if it were possible to place a counterweight such that the center of mass was opposite the camera/lens center of mass, this wouldn't be a problem.  But I don't think that's possible with the iOptron tracker.

 

Is the answer to just point the camera at the subject and then adjust the counterweight to achieve the best possible balance and hope for the best as the tracker moves during the shoot?

[Ishtim]

I have one of these, but have yet to mount a "long" lens on it.  It sounds like you understand the problem well and your solution may work, but I'd like to offer another potential solution based on my experience with long lens mountings.  Consider using a long(er) dovetail that fits your ball head to allow adjustment of the axis along the length of the lens so that the CG of the camera lens combo is centered over the counterweight axis.  How long of a dovetail will be determined by the amount of balance compensation needed.  An example of a long dovetail is a Manfrotto 393 at about 4-5 in. long.  I know its an alt/az mount and you wouldn't want this on top of you SkyTracker, but the principle to balance the long lenses on it are the same.

 

What type of ball head are you currently using?    

[Domer]

Ishtim,

 

I have a Manfrotto Ball Head (MK190XPRO4-BHQ2).  Since I have to have a solution that works with the SkyTracker Pro, I'm not sure what other dovetail options are viable.

[Domer]

The rig looks sorta like the image shown in this review:  https://astrobackyar...der-pro-review/

 

I'm using a different lens but the length is comparable.  And instead of a flat mount (the red one in the photo), I'm using the Manfrotto ball head so I can point the camera wherever I need it.

[Ishtim]

It looks like the MHXPRO4-BHQ2 uses a "fixed" position, quick release plate and doesn't allow any lateral adjustment.

 

What I was attempting to describe is shown on the MHXPRO4-BHQ6.  It looks like it has some, albeit limited travel for this type of adjustment.

Here's a side-by-side of the BHQ2 and BHQ6... 

https://www.manfrott..._pro_ball_head/

 

You may have heard of the adjustable plates using the name "Arca-Swiss" to describe the mount standard.

Here's a nice intro...

https://photographyl...-release-system

 

Let us know what you come up with as I am sure you aren't the first nr the last one to encounter this.

Edited by Ishtim, 21 November 2019 - 01:05 PM.

[scadvice]

Maybe I'm missing the problem your talking about but I seem to get the best balance using a little longer Vixen rail so I can slid the camera and lens to the fore and aft balance point. I use a pencil to find the balance then mount it and RA balance. 

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[Domer]

It looks like the MHXPRO4-BHQ2 uses a "fixed" position, quick release plate and doesn't allow any lateral adjustment.

 

What I was attempting to describe is shown on the MHXPRO4-BHQ6.  It looks like it has some, albeit limited travel for this type of adjustment.

Here's a side-by-side of the BHQ2 and BHQ6... 

https://www.manfrott..._pro_ball_head/

 

You may have heard of the adjustable plates using the name "Arca-Swiss" to describe the mount standard.

Here's a nice intro...

https://photographyl...-release-system

 

Let us know what you come up with as I am sure you aren't the first nr the last one to encounter this.

Interesting - I'll have to look into a ball head like that.  But I'm not sure there is enough travel to achieve the balance I need.  Thanks for the info!

[Domer]

Maybe I'm missing the problem your talking about but I seem to get the best balance using a little longer Vixen rail so I can slid the camera and lens to the fore and aft balance point. I use a pencil to find the balance then mount it and RA balance. 

That's quite a setup!  Does this mount allow the camera to be tilted up?  I assume that it can rotate around the counterweight axis, but it's not obvious if the upward tilt is possible.

 

Where did you get that rig?

[scadvice]

Once I mount the camera on the Vixen rail I keep it pointed parallel to the rail. The rail is just a 8 inch I happen to have. I bought this SkyTracker used and it came with the Neewer Panaramic  tripod head bought by the previous owner.

 

https://www.amazon.c...74370609&sr=8-3

 

The rest is this:

 

https://www.adorama....hUaApZeEALw_wcB

 

I think the counter weight  extension was from William Optics it also came with the mount when I bought it.

I built an adapter for the PoleMaster myself but I think you can buy them. Finally, I already had the tripod and made the tripod plate.

[Domer]

That slide mount might help a bit, but I would still need the ball head in order to point the camera upward to get shots of specific nebulae, galaxies, etc.  I guess I'll have to get creative and see if I can rig something up that will allow me to align the center of gravity for the camera/lens combination with the counterweight axis.

[scadvice]

The Neewer Panaramic  tripod head is mounted on the counterweight axis just above the Vixen bar and can be unlocked and rotated. A ball head would work also but I got the Neewer with the setup so I used it. It will align to your specific desired object just like the GEM does. I considered a ball head but felt that I may be unbalancing the setup each time I moved it around. Food for thought...

[Domer]

scadvice, I looked at that Neewer mount and it doesn't appear to have a tile capability - it looks like it rotates only.  I would need to rotate and tilt to point at specific objects after aligning the star tracker.  Am I not looking at it correctly?

[scadvice]

No, Your seeing it correctly. It doesn't tilt. You don't need it to. It will position just like a German Equatorial Mount. The RA axis rotates on that balance point swinging the counterweight. This is your guiding axis when the mount is polar aligned.  

 

The DEC axis(Declination) by using and releasing the rotary clamp, the Neewer Panaramic  tripod head rotates on the counterweight shaft axis for positioning only to your object then you lock back down.

 

https://www.youtube....?v=CpSzVe1unsI 

[Domer]

Hmmm...  I think I get it now.  I was thinking you needed the ability to rotate AND tilt in order to point the camera at any position in the sky, but I now see you can accomplish the tilt by freeing the clutch and spinning the counterweight mechanism.  I haven't done it that way before - I've always used the ball head.  But this approach makes sense.  I'll need to play with it, then maybe buy a mount with a slide rail to see if I can achieve a good balance.

 

Thanks, everyone.

[Domer]

I drove out to the desert last night to get some shots with my Canon 6D Mk II and the Sigma 150-600mm lens mounted on the iOptron Skytracker Pro.  I balanced it the best I could, but it wasn't perfect.  Could a counterweight imbalance result in minor star trails?  In every single shot I took at 600 mm, the stars had a slight motion blur.  I checked and double-checked my polar alignment, using the Polar Finder app to ensure I had it dialed in perfectly.

 

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Edited by Domer, 24 November 2019 - 04:41 PM.

[scadvice]

I'm guessing that your having flexture problems. As the mount moves the mounting screw is not enough to hold a steady position and it is flexing as it tracks. You may need a double support bracket.

 

Example:

 

https://www.amazon.c...t_top?ie=UTF8  

 

I suspect I may be getting some with my setup though it's only 135mm.

Edited by scadvice, 24 November 2019 - 07:58 PM.

[NGC 2419]

Shooting at 600mm is asking a lot from a Skytracker. Your lens and camera weigh 87% of the rated payload.

I've found balance to be important on my Skyguider Pro, but I don't think it's going to get you untrailed stars at 600mm on the Skytracker.

Clear skies!

Edit to fix percentage. Still think 600mm is too much for that mount.

Edited by NGC 2419, 24 November 2019 - 08:11 PM.

[Cfreerksen]

Best we could get out of my friends Sky guider pro was 60 sec at 360mm focal length.

 

It does really well at 60 seconds with WO Z61 and EOSrp. 90 seconds result in trails.

 

Chris

 

60 sec exposures:

 

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Edited by Cfreerksen, 24 November 2019 - 08:50 PM.

[Domer]

Sorry, I actually have the SkyGuider Pro, not the SkyTracker Pro.  It has a max weight capacity of 11 lbs.  My camera is 1.7 lbs, the Sigma lens + mounting bracket weigh 4.25 lbs, and the Manfrotto ball head weighs 1.1 lbs for a total of 7 lbs, so about 65% of the max.  That should be fine.

 

Scadvice - That bracket is probably exactly what I need to get the center of mass aligned with the counterweight axis.  Too bad they are out of stock... I'll have to keep shopping.

[Domer]

Cfreerksen - great shot and excellent colors!

[Cfreerksen]

Sorry, I actually have the SkyGuider Pro, not the SkyTracker Pro.  It has a max weight capacity of 11 lbs.  My camera is 1.7 lbs, the Sigma lens + mounting bracket weigh 4.25 lbs, and the Manfrotto ball head weighs 1.1 lbs for a total of 7 lbs, so about 65% of the max.  That should be fine.

 

Scadvice - That bracket is probably exactly what I need to get the center of mass aligned with the counterweight axis.  Too bad they are out of stock... I'll have to keep shopping.

Does yours have the Arca Swiss mount. this one came with a vixen mount.

 

Here is how I configured my friends Sky Guider Pro. Used a rail I had from my Edge8 and attached a laser to assist with pointing to targets. Later found out that the carrier bracket was on upside down. After that correction it balanced out nicely with no extra weights.

 

Chris

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Edited by Cfreerksen, 24 November 2019 - 08:58 PM.

[Domer]

Very nice.  I need to do this as well.

 

Funny - I was using a laser last night to assist in pointing as well and trying to think of a way to attach and align it.

[Cfreerksen]

Very nice.  I need to do this as well.

 

Funny - I was using a laser last night to assist in pointing as well and trying to think of a way to attach and align it.

I would think at 600mm you are going to have a tough time finding your target. We had a tough time on targets at 360mm. i mean Orion is easy, lots of landmarks. Finding the Veil Nebula a bit more difficult. 

 

What F is the 600mm lens? At f5.9 it's tough getting enough signal at exposures no longer than 60 seconds. At 600mm i would guess you will have issues with exposures over 30-40 seconds.

 

Chris

[NGC 2419]

I finally got tired of short exposures and star trails and bought a guider. But since I hate the thought of dragging a laptop outside, I'm using a Raspberry Pi with Astroberry and a small tablet for control. Easy 3 minute subs up to 400mm, all keepers.

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[Domer]

I concur.  What I usually do is start at 150mm (f5.0), shoot a 30-45 second exposure, find the object I want, then center the target and zoom in, rinse and repeat until I get to 600mm (f6.3) and then start shooting 120 second exposures.  But the laser was helpful for setting the starting point.

 

Edited by Domer, 24 November 2019 - 09:47 PM.