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A cheap Dobsonian push-to method

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#1 electropop999

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Posted 06 July 2020 - 01:34 AM

Hi, I recently got an 8 inch Apertura Dobsonian telescope. Then I made a simple method for pointing Dobsonian telescope to astronomical objects. For Altitude I use the digital angle gauge, for azimuth I use tape measure in metric system + I made a mobile site for converting from azimuth to tape measure scale. More detail is shared at http://trinkc.blogsp...-telescope.html

I hope this could be useful for Dobsonian telescope users. .

 

Thank you!


Edited by electropop999, 06 July 2020 - 01:34 AM.

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#2 Anony

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Posted 06 July 2020 - 03:01 AM

You might prefer using regular setting circles. I know there are some templates out there, or you can just make your own here: https://www.blocklay...r-printeng.aspx

 

Although you can make them tape measure style, it's a lot easier to view with a dob if printed out in a proper circle -- can do the top or underneath with cutout method.

 

Then use sky safari/stellarium/whatever to get the coordinates, no need for conversion to tape measure scale.



#3 GeneT

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Posted 06 July 2020 - 06:01 PM

You might prefer using regular setting circles. I know there are some templates out there, or you can just make your own here: https://www.blocklay...r-printeng.aspx

 

Although you can make them tape measure style, it's a lot easier to view with a dob if printed out in a proper circle -- can do the top or underneath with cutout method.

 

Then use sky safari/stellarium/whatever to get the coordinates, no need for conversion to tape measure scale.

Many years ago, telescopes came with setting circles. They worked great. I found them reasonably accurate.


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#4 smiles233

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Posted 07 July 2020 - 10:45 AM

How do I get the coordinates in sky Safari. Thanks

#5 Xeroid

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Posted 07 July 2020 - 11:19 AM

Use the Search icon and enter the object name your interested...



#6 aeajr

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Posted 05 August 2020 - 08:21 AM

Hi, I recently got an 8 inch Apertura Dobsonian telescope. Then I made a simple method for pointing Dobsonian telescope to astronomical objects. For Altitude I use the digital angle gauge, for azimuth I use tape measure in metric system + I made a mobile site for converting from azimuth to tape measure scale. More detail is shared at http://trinkc.blogsp...-telescope.html

I hope this could be useful for Dobsonian telescope users. .

 

Thank you!

Very nice job on the blog spot article.   Enjoyed reading it.

 

You may wish to post the link into this discussion.

 

Using an angle gauge to help find targets – AltAz coordinates
https://www.cloudyni...y/#entry8120838

 

 

I have an Apertura AD12.  I added the AZ scale into the mount.

 

Printable Setting circles
https://www.cloudyni...ntable circles

Attached Thumbnails

  • Apertura AZ scale close (640x480).jpg
  • Apertura AZ scale mounted on plate with 3M77 contact glue (640x480).jpg

Edited by aeajr, 05 August 2020 - 08:30 AM.

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#7 Beeham

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Posted 05 August 2020 - 09:09 PM

A good azimuth ring and an accurately-adjusted digital angle-finder are, in my opinion, just as good as go-to but without the need for batteries.

 

Make sure the scope is level - errors in the horizontal plane become more evident at high altitude angles.

 

You can make a "fine-tune" device for your angle-finder with a few hardware-store bits as well...this lets you dial in your altitude angle to eliminate any error from the optical axis being non-parallel to the physical OTA body.  One of mine is shown below...

 

inclinometer holder

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#8 stargazer193857

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Posted 06 August 2020 - 08:12 PM

A good azimuth ring and an accurately-adjusted digital angle-finder are, in my opinion, just as good as go-to but without the need for batteries.

Make sure the scope is level - errors in the horizontal plane become more evident at high altitude angles.

You can make a "fine-tune" device for your angle-finder with a few hardware-store bits as well...this lets you dial in your altitude angle to eliminate any error from the optical axis being non-parallel to the physical OTA body. One of mine is shown below...


No batteries...
How do you get the coordinates that change each minute? Or do you base it on degrees from a known star?

I don't know how angle readers work, but wouldn't they work the same even if the scope is not level? I'm guessing they work off of gravity.

Now an EQ mount with angles on it sounds great, except for the big newt issue.

#9 stargazer193857

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Posted 06 August 2020 - 08:18 PM

Why do people use degrees azimuth instead of 24 hours, which many catalogs use?

Converting degrees from the north star to degrees above the ground also sounds like it needs some math before one leaves. A very interesting math problem indeed.

#10 Tom Stock

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Posted 06 August 2020 - 11:15 PM

A good azimuth ring and an accurately-adjusted digital angle-finder are, in my opinion, just as good as go-to but without the need for batteries.

 

I have never heard of a digital angle finder without batteries.

 

Is it solar powered? Nice classic C8


Edited by Tom Stock, 06 August 2020 - 11:17 PM.

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#11 aeajr

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Posted 07 August 2020 - 12:03 AM

I have never heard of a digital angle finder without batteries.
 
Is it solar powered? Nice classic C8

I have a very nice analog angle gauge that requires no batteries.  It works just fine.  Cost $5

 

But I do prefer the digital type. One cost $11, one $26 and one $33.   I like to have several because I loan them to friends to try the system.  They try it, they like it, get their own and return mine so I can loan it out again. 

 

The batteries are small so I keep spare ones in the box.  Same battery that I use for the RDFs.


 

Why do people use degrees azimuth instead of 24 hours, which many catalogs use?

Converting degrees from the north star to degrees above the ground also sounds like it needs some math before one leaves. A very interesting math problem indeed.

You have taken something simple and easy and tried to make it hard.   Clearly you don't understand the process.

 

You just read the AltAz degrees off of Stellarium or SkEye or some other readily available app.  So very easy. Works day or night. Unaffected by light pollution. Just use the AltAz coordinates to go right to the target.  Works great!

 

I never use paper charts.  I have them, but they gather dust. 

 

No need to memorize the sky or understand RA/DEC.  No need to memorize constellations or struggle because light pollution robs you of stars to hop by.   Just go right to the target.  Sweep a little left or right and there it is.  

 

Oh, I am learning the sky as I go, but my lack of depth of memorization has not held me back one bit. 


Edited by aeajr, 07 August 2020 - 12:10 AM.

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#12 stargazer193857

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Posted 07 August 2020 - 01:37 AM

Ok, you have your phone and Stellarium with you, and it does degrees.

Does the alt angle gauge measure the tube relative to the base or relative to gravity?

Does the azimuth angle get alined with a compass, and does Stellarium go by magnetic north?


I'm just trying to understand how this works.

#13 aeajr

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Posted 07 August 2020 - 06:49 AM

electropop999 is the OP, so he may do something differently. Here is how I use this system. Whole process typically takes less than a minute.

Angle gauge measures tube absolute angle. This is a carpenter's level. Angle is not relative to mount.

I set my azimuth scale to zero on Polaris at the start of the evening and I am good for the night.

If I want to find M31, I find it on Stellarium which gives me the realtime AltAz coordinates.

I move the tube to the Az using that scale on my mount. Then I raise the OTA to the Alt angle using the angle gauge.

Using my finder scope or low power eyepiece I sweep a little left and right till I have the target. It takes a few seconds typically.

This is so easy. Don't over complicate it.

I will actually be giving a workshop on this method for the club.

Edited by aeajr, 07 August 2020 - 06:51 AM.

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#14 Beeham

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Posted 07 August 2020 - 07:57 AM

No batteries...
How do you get the coordinates that change each minute? Or do you base it on degrees from a known star?

I don't know how angle readers work, but wouldn't they work the same even if the scope is not level? I'm guessing they work off of gravity.

Now an EQ mount with angles on it sounds great, except for the big newt issue.

I use Stellarium or SkiSafari on my phone for real-time alt/az coordinates.  (OK, yes the phone has batteries, but it's not in the same category as dragging around a car battery to provide power for a goto rig.)

 

There are both digital and analog angle finders - I have used both.  The one shown is digital, but again, the battery is inside the unit and self-contained.

 

You need to level the mount, because if your horizontal plane of azimuth rotation is off, when you go to a given set of coordinates, even though the angle-finder is based on gravity, you'll end up looking at the wrong place in the sky due to the error in the horizontal plane - you'll get the right alt but the wrong az location.

 

The big advantage to this system is the relative simplicity - mount, scope, and box of eyepieces/gadgets is all you need to move.  Level the mount, stick the scope on it, and calibrate off a known star, and you're ready to go.  No polar alignment, multi-star calibration, battery cables, computer hookups, etc.

 

If the scope is level I typically find I get the desired object in view of my 15mm eyepiece on the first shot.  

 

I hope this is helpful - cheers!


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#15 clearwaterdave

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Posted 07 August 2020 - 08:30 AM

The circles are a very good way to locate stuff.,I made angle gauges for nothing and they are pretty accurate.,Here is my first hi-tech system.,and my OneSky's.,.

Attached Thumbnails

  • 20140116_152851.jpg.jpg
  • 20180825_172109..jpg.jpg


#16 stargazer193857

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Posted 07 August 2020 - 08:58 AM

I'm really liking this.
To keep the phone dim enough before you can toggle over to Stellarium, do you just keep it inside a red bag big enough to stick your hand in?

I prefer to pan a bit rather than level a scope, unless there is a simple way to do that or there is a noticeable slant. I'd use shims to get close. I doubt twist feet would be as steady.

#17 BrettG

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Posted 07 August 2020 - 09:03 AM

Does there have to be an accounting for true north vs magnetic north when setting up the azimuth circles?  I've had them on my AD10 since I bought it (6+ years ago), but have never really used them, as the few times I've tried - they were always off some.



#18 aeajr

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Posted 07 August 2020 - 09:06 AM

Leveling the mount is always a good idea but if it is off a bit it is not a problem. I use my scopes on my sidewalk and my side yard, neither of which is level. I level by eye and that seems good enough. It just needs to be level enough to use the scope safely.

The method still works.

My finder has a 5.5 degree FOV. My max FOV of my low power eyepieces for my various scopes have a  .8 to 4 degree FOV, depending on which scope I use. The larger the FOV the less critical the level.  

 

The angle gauge will give you the correct angle regardless of the level of the mount.  Where the error will occur will be in the left right sweep as you spot the target.  If the mount is not exactly level the sweep left and right will not be level.  I have not found this to be a problem.


Edited by aeajr, 07 August 2020 - 09:39 AM.

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#19 stargazer193857

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Posted 07 August 2020 - 09:29 AM

My plan is a linear tap around the bottom circle.
Move the pointer above zero.
Tilt on a foot and look up the tube till aimed at Polaris. Use 1x finder to get close. Only shim if on a hill.
Altitude angle finder stays on UTA.
Get out phone in red bag. Look up DSO coordinates.
Slew AZ. Slew alt. Pan side to side in low power eyepiece.

Sounds like a cheap plan.


But how do I print the right size accurately? Just ask a professional to do it, I guess. Will they print on plastic? Do you contact cement it on?

#20 stargazer193857

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Posted 07 August 2020 - 09:32 AM

And does Stellarium need constant internet connection, or does it download or calculate the next 72 hours?

#21 Beeham

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Posted 07 August 2020 - 09:35 AM

Does there have to be an accounting for true north vs magnetic north when setting up the azimuth circles?  I've had them on my AD10 since I bought it (6+ years ago), but have never really used them, as the few times I've tried - they were always off some.

I don't use anything beyond a known target to calibrate, so magnetic vs. true North doesn't matter.

 

Example: Jupiter is easy to find right now; I point to that with my Telrad and get it in view, then I look it up on Stellarium to see it's current coordinates.  I rotate my azimuth ring until Jupiter's azimuth is right under the pointer.  I check altitude coordinate, too, just to be sure, and if it's off (usually just a fraction of a degree) I tweak the angle-finder until it too reads correctly.

 

Now everything's set to go - no compass bearing or other alignment necessary.


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#22 BrettG

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Posted 07 August 2020 - 09:44 AM

I don't use anything beyond a known target to calibrate, so magnetic vs. true North doesn't matter.

 

Example: Jupiter is easy to find right now; I point to that with my Telrad and get it in view, then I look it up on Stellarium to see it's current coordinates.  I rotate my azimuth ring until Jupiter's azimuth is right under the pointer.  I check altitude coordinate, too, just to be sure, and if it's off (usually just a fraction of a degree) I tweak the angle-finder until it too reads correctly.

 

Now everything's set to go - no compass bearing or other alignment necessary.

Ahhh... I see I would have to do something closer to 0 to do that - the circle does not rotate - the piece above with the pointer does, so short of trying to lift the whole thing for a target like that (not happening :)

 

Of course, I have a Nexus II on the way, but I am sure that there will be nights I want to use the circles on the scope, rather than the DSC.



#23 aeajr

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Posted 07 August 2020 - 09:45 AM

My AZ circles are not adjustable.I have to move the mount to do the alignment at the beginning of the night. Only takes a minute or so.

 

Below I show my AD12, XT8 (sold) and 80 mm mounts.  I also have an ES Twilight that just got its AZ scale.   

 

I originally had a round plastic protractor on the GSkyer mount, as shown in one photo but it interfered with the OTA above 60 degrees and was prone to damage.  I transferred the markings to the mount with a sharpie.  Not perfectly accurate but it has proven to be close enough to be effective.  Absolute accuracy is not required. 

 

 

If you want to use a compass as your AZ circle then you need to be aware of your local declination.

https://www.usgs.gov...cience_products

 

In NY, I believe the difference between true north and magnetic north is about 13 degrees.  But since I don't use a compass I don't worry about it. 

https://www.ngdc.noa...s/magcalc.shtml

 

Keep the compass away from from a large steel tube or it may throw things off.   And there are local anomalies.  When using the compass on my phone I get a "strange anomalies" message. 

 

Better to align on a celestial object with Polaris being the best choice.

Attached Thumbnails

  • Gskyer AZ circle.jpg
  • XT8 Degree Wheel (320x240).jpg
  • Apertura AZ scale close (320x240).jpg
  • Gskyer mount with degree markings (320x240).jpg

Edited by aeajr, 07 August 2020 - 10:05 AM.

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#24 BrettG

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Posted 07 August 2020 - 09:45 AM

And does Stellarium need constant internet connection, or does it download or calculate the next 72 hours?

I cannot answer for Stallarium, but I know SkySafari does not need the internet connection for coordinates.  I assume Stellarium would be the same though. I am sure others here know though for sure.



#25 BrettG

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Posted 07 August 2020 - 09:48 AM

My AZ circles are not adjustable. I have to move the mount to do the alignment at the begining of the night.  I use Polaris if I can see it.  If not, then I use something else.   

 

If you want to use a compass as you AZ circle then you need to be aware of your local declination.

https://www.usgs.gov...cience_products

 

In NY, the difference between true north and magnetic north is about 13 degrees.  But since I don't use a compass I don't worry about it. 

https://www.ngdc.noa...s/magcalc.shtml

The base has a compass built in - I suppose I trust it enough :)

 

I cannot see Polaris, ever, from my normal observing location - tree in the way.  Would roughly aligning the base north, and setting the pointer to 0 work at that point?  E.g., Do that, then say, look up Jupiter, rotate to the Az coordinates (for the sake of argument, we will assume the Altitude is correct) and it would be there?  Or do I have to account for the 13 degrees as well?  I am in Mass, so I assume it's similar.




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