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#1 alan01346

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Posted 15 August 2019 - 02:13 PM

I've known what an equatorial mount was since the 1980s but I never owned one before.

 

east.jpg

 

The bulk of sky is to the left, about opposite the counterweights.  North is to the right.  The north star is about off the end of the polar axis.  But My RA and Dec adjustment handles don't point the scope anywhere near where I want it to point.  If you turned the scope CCW 90 degrees in the picture it would be close, about at the upper left corner.  I've been trying to figure this out for a couple days.

 

 



#2 siriusandthepup

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Posted 15 August 2019 - 02:25 PM

Loosen up the locks on both axis - the two conical knobs near the setting circles - NOT the lock for the dovetail plate.

 

You can now point your scope where ever you want. Retighten the axis locks. Use the RA axis flex cable knob to track and the Dec axis flex cable to position.


Edited by siriusandthepup, 15 August 2019 - 02:26 PM.


#3 photoracer18

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Posted 15 August 2019 - 02:31 PM

OK I am figuring you are over thinking this. On an average un-powered GEM mount you roughly line the polar axis up on Polaris by adjusting latitude and rotate the mount head by loosening the lower knob and tighten both back up, then just loosen both of the RA and DEC locks, move the tube to point at the part of the sky you want to be in and lock them back down, then use the slow- motion cable handles to refine the thing you want to see (or scan the area or star-hop or whatever method you used in the past. Once you have the object in the field you just need to "chase" the object with the RA slow-motion cable to keep it in the field. I can't tell you which direction to turn the handle because it depends on which side of the mount you have it mounted on. Normally you put the slow-motion cables on the side that is easiest to use while still looking thru the eyepiece.


Edited by photoracer18, 15 August 2019 - 02:32 PM.


#4 alan01346

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Posted 15 August 2019 - 02:53 PM

Turning the handles moves the scope in the wrong planes.  The only thing I've seen work is if I  loosen the clamp bolt to the tripod and spin that 180 degrees.  But that points the RA axis at the south sky.

 

When I put it together the only thing I noticed where there were 2 possible places to put it on was one of the knobs for the slow motion cables.



#5 Barlowbill

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Posted 15 August 2019 - 03:09 PM

That scope is sitting in my closet.  It belongs to my son-in-law and I despise it.    My pea brain does not get along with equatorial mounts.  Besides, the red dot finder must be the worst ever devised.  I would love to have the scope on a little Dob mount.  Best of luck



#6 vtornado

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Posted 15 August 2019 - 03:10 PM

Hello Alan, welcome to the forum.

 

When the axis of the scope is aligned with  the RA axis of the mount, and the scope axis points upward,

(just like in your picture) what does your declination axis read? 

 

It should read 90.

I have seen some mounts where the declination circle is way off.


Edited by vtornado, 15 August 2019 - 03:23 PM.


#7 Astrojensen

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Posted 15 August 2019 - 03:22 PM

 

Turning the handles moves the scope in the wrong planes.

No, they don't. You have to forget the up-down and sideways movements you're used to from altaz mounts. The scope moves in the equatorial coordinate system now, not in the horizontal, altaz coordinate system. 

 

I tried to find a decent video on youtube that could explain it, but failed. Here's a picture of one of my own telescopes on an equatorial mount, pointed towards the southeast. I hope this can explain the function of a german equatorial mount.

 

gallery_55742_4772_118707.jpg

 

 

Clear skies!
Thomas, Denmark


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#8 Redbetter

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Posted 15 August 2019 - 03:40 PM

Where is the RDF?  It should go in the spot that is turned down and looks like a handle.  (I don't see it in the image so I am wondering how you are pointing the scope.)  First step will probably be to install the RDF and rotate the tube in the rings so that the RDF and focuser are both positioned in usable way.  Second step will be to roughly sight in the RDF in daylight on something in the distance you can point the scope at and get centered in the eyepiece. The RDF has to be adjusted to match where the eyepiece is pointing.

 

You need to get a feel for how this OTA will move about when pointing at things.  To do that, point the RA axis roughly due north (as it will be at night in the northern hemisphere), loosen the clutches on both axes while holding the tube.  Then point the scope toward where Saturn/Jupiter/Moon etc. will be. Then point to where something near zenith will be, something fairly far north, something about 45 degrees off the horizon to the east, and the same to the west.  After doing that you will start to have an idea of what it takes to point the tube.  

 

Typically you will loosen a single clutch at a time to get the OTA pointing in roughly the desired direction before tightening the clutches and using the slow motion knobs to better position and track.  Balance can be important to allowing the knobs and clutches to work properly.  If the balance is poor it will likely slip or fail to move when you turn the knobs.

 

Now for the bad news:  this is a Jones-Bird (often called "Bird-Jones") system with a cheap corrector built into the focuser.  Unfortunately, these rarely work well and are considered somewhat of an abomination to foist on newbies.  Don't expect to get decent collimation of it or particularly sharp images.   Hopefully it will work well enough to give you an introduction to actually observing and learning how this sort of mount system works. 



#9 alan01346

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Posted 15 August 2019 - 03:46 PM

No, they don't. You have to forget the up-down and sideways movements you're used to from altaz mounts. The scope moves in the equatorial coordinate system now, not in the horizontal, altaz coordinate system. 

 

Wrong planes in the sense that I won't go where I want.  My understanding of equatorial is that one pivot is aligned with the earth's axis, and the declination axis moves essentially north and south.  Time as the earth rotates is marked off on the RA axis instead of degrees, this is what a simple tracking motor drives.

 

But I can't get to any south sky at all.  My axes are pointing wrong somehow.



#10 alan01346

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Posted 15 August 2019 - 04:12 PM

Off on a tangent of sorts, we're expecting showers so I put the telescope under cover.

 

I bought this as a telephoto lens for terrestrial stuff like butterflies, I wanted a lens about 1000 mm focal length.  Which this might work at but the equatorial mount is clumsy and not appropriate for.  My photo tripod is a Manfroto 055CX3 with an Oben BE-117 ball head.  The ball head has this quick release on it:

th_02-oben_be_117_ball_head_1396973133000_887592.jpg

 

On the top is a quick release with, guess what, a dovetail.  The clamp on the quick release doesn't open quite far enough for the telescope's dovetail.  I wonder if there are dovetail adapters, I haven't found anything so far.  The clamp bolt is captive (doesn't fall out) so an adapter would probably have something on top to fit the telescope's dovetail and a smaller dovetail on the bottom to fit the Oben quick release.

 

The telescope's dovetail has 2 drilled and tapped holes in the bottom (1/4-20?).  Might be able to put a qr-020 onto it.


Edited by alan01346, 15 August 2019 - 04:23 PM.


#11 Redbetter

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Posted 15 August 2019 - 04:22 PM

Wrong planes in the sense that I won't go where I want.  My understanding of equatorial is that one pivot is aligned with the earth's axis, and the declination axis moves essentially north and south.  Time as the earth rotates is marked off on the RA axis instead of degrees, this is what a simple tracking motor drives.

 

But I can't get to any south sky at all.  My axes are pointing wrong somehow.

You just haven't learned how to maneuver it yet.  To point due south on the meridian that counterweight will be sticking out horizontal on one side or the other just like Thomas shows in the image above.  It is counterintuitive until you understand how the motions work with the GEM.  You will have to play with awhile until you figure out how to get it to point where you want.  

 

Tube rotation to be able to use focusers and finders is something that one has to keep in mind with these equatorial mounts.   Alt azimuth mounts are a lot easier to understand in this regard and don't have the tube rotation problem--instead the rotation is of the axes in the sky as view through the eyepiece which adds a different element to potential confusion with orientation.



#12 aa5te

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Posted 15 August 2019 - 04:27 PM

The 14th and 15th picture down on this page show an EQ mounted scope pointed South:

https://themcdonalds...th-an-eq-mount/


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#13 S.Boerner

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Posted 15 August 2019 - 04:32 PM

This video might help...

https://www.youtube....h?v=F7HVDKAZ6eM


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#14 SteveG

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Posted 15 August 2019 - 05:00 PM

This video might help...

https://www.youtube....h?v=F7HVDKAZ6eM

Perfect explanation, and he includes the "meridian flip".



#15 tomykay12

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Posted 15 August 2019 - 05:08 PM

Try looking thru the other end; that should reverse things


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#16 Sketcher

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Posted 15 August 2019 - 05:12 PM

HI Alan, and welcome to CloudyNights! banjodance.gif bounce.gif

 

If we start with your telescope and mount oriented as shown in your picture, with the telescope pointed toward Polaris.  And if you want to point the telescope at something above your southern horizon, the following is one way of getting there:

 

Lock the Declination axis.  Then, gently holding the telescope tube, loosen the RA axis lock just enough to permit the telescope to move in RA.  Now move the telescope in RA either toward or away from the camera (based on your photo), until the counterweight shaft is parallel to the ground.  Now lock the RA axis and while holding the telescope tube, loosen the Declination axis enough to permit movement in Declination.  Now move the telescope in Declination, through your zenith, toward your southern horizon.  Tighten the Declination axis once the telescope is pointed as high as you want it to be pointed above your south horizon.

 

Now you may have noticed that your eyepiece and/or finder are in awkward positions to use.  That can be remedied by loosening the cradle around the telescope and rotating the telescope within it, then tightening it down again.

 

To point the telescope at specific objects above your southern horizon, you'll want to make further adjustments in RA and Declination.  Just keep in mind that movements in Declination move the telescope toward or away from the north celestial pole, while movements in RA will move the telescope east or west along a curved line of constant Declination.

 

It will help to use star charts that show lines of RA and Declination, preferrably on a fairly large scale (showing large areas of sky) until you get the hang of how an equatorial mount works.

 

An equatorial mount takes time to learn, but once one fully adjusts to them, they become very easy, natural, and convenient to use.  It's this initial learning phase where all the problems lie!

 

Different explanations work better for different people, so I would suggest reading as much as you can about the function and use of an equatorial mount -- and of course, practice a lot with the one you have.  Don't be too concerned if some of the explanations don't make sense.  At some point everything will "click" into place -- all will make sense -- and you might even end up wondering how something so easy (once you've learned it) seemed to be so complicated (prior to learning it).


Edited by Sketcher, 15 August 2019 - 05:55 PM.


#17 alan01346

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Posted 15 August 2019 - 07:30 PM

Try looking thru the other end; that should reverse things

I like that answer.  I looked to see if I could have put something on upside down, like the whole equatorial mount was upside down on the tripod but I don't think so.  I'll look at it more tomorrow but it's like getting to parts of the sky are trying to pull sideways on the pivots, not the way they're designed to go.

 

This was from the other side at the same time, didn't post it before.  Much background clutter.  And the parts show better from the other side.

 

west.jpg

 

Right now it's on the porch with the tube and counterweights off, I'm thinking of taking it back apart and reassembling it, watching for places in the directions where I could have made a wrong choice.


Edited by alan01346, 15 August 2019 - 08:40 PM.


#18 bunyon

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Posted 15 August 2019 - 08:42 PM

Yes, that's it. You're still thinking in alt-az. Thinking that way, yes, an EQ feels wrong. 

 

To point your scope to the SE from where it is shown in the original photo, you want to loosen the RA axis and push the scope away from you about 45 degrees (assuming you're standing where you were when you took the picture). Lock the RA axis down, loosen the Dec axis and turn the scope toward you about 135 degrees.

 

You should now be pointed SE. From there, use both axes to get to where you want to go. 

 

There is no longer an up/down or left/right. For awhile that will be a pain but what you gain is an east/west and north/south and the relative position of two objects in those coordinates never changes (well, assuming one isn't a planet).

 

 

Now, for the bad, but possibly good, news. Bad: If you bought this scope to use as a terrestial telephoto lens, the mount is completely wrong. On Earth, we definitely have an up/down, left/right system. If you want to use it for terrestial photography, you should replace the mount with an alt-az.

 

Possibly good news: Alternatively, you can just point the polar axis at the horizon and, voila, your mount is an alt-az. 

 

Good luck.



#19 alan01346

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Posted 15 August 2019 - 09:44 PM

When I put it together it was in the garage at night and I couldn't find the garage light in it.  Next day I took it outdoors and just parked the tripod so the scope was pointed at some trees about 40-50 feet away.  So the first thing I saw in it was some leaves.  I'll probably want an extension to focus closer but I don't have my t-mount yet.

 

Yes, since the dovetail came with 2 tapped holes I can make something to bolt on without even modifying anything else.  Take the scope and dovetail from one mount and put it on the other, best if I can make a quick release on the alt-az too.

 

Downloaded the video so I could watch it eventually.  I don't have things balanced anywhere near that well yet, I was saving it for later.



#20 lphilpot

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Posted 15 August 2019 - 09:53 PM

Equatorial and alt-azimuth mounts both have two axes of movement at right angles to each other. An alt-az has a horizontal (azimuth) rotation with a vertical axis, and a vertical (altitude) rotation with a horizontal axis. With any equatorial mount (including your GEM), both of those axes are the same relative relationship, but they're tilted so that one of them is coincident with the earth's axis (the RA axis). It just takes a bit of acclimation before you lose the tendency to lift one leg of the tripod off the ground when trying to position it. I spent years with a GEM and still do that when I have to use a fork mount.  :)



#21 EJN

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Posted 15 August 2019 - 10:02 PM

Right now it's on the porch with the tube and counterweights off, I'm thinking of taking it back apart and reassembling it, watching for places in the directions where I could have made a wrong choice.

 

That would be a waste of time, from the picture it looks assembled properly.

 

You just have to get used to a different coordinate system and a different way

of pointing.

 

It's not hard. I learned to use a German equatorial mount when I was 12.


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#22 Napp

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Posted 15 August 2019 - 10:39 PM

I like that answer.  I looked to see if I could have put something on upside down, like the whole equatorial mount was upside down on the tripod but I don't think so.  I'll look at it more tomorrow but it's like getting to parts of the sky are trying to pull sideways on the pivots, not the way they're designed to go.

 

This was from the other side at the same time, didn't post it before.  Much background clutter.  And the parts show better from the other side.

 

attachicon.gif west.jpg

 

Right now it's on the porch with the tube and counterweights off, I'm thinking of taking it back apart and reassembling it, watching for places in the directions where I could have made a wrong choice.

 

As others have pointed out you appear to have correctly assembled the mount.  When I got back into the hobby a few years back it was with a scope on an alt-az mount.  Alt-az mounts are very intuitive - they move as you would expect them to.  When I bought an equatorial mount I discovered they were anything but intuitive in how they move.  Be patient and don’t give up.  I finally got used to the equatorial mount but I often chose the wrong movement still.  No big deal - it’s easy to reverse what I did.  Stick with it and you’ll figure it out.  When you want to point south just loosen both the RA and the Dec clutches and move the scope around.  In fact just play with that movement and explore what happens.



#23 alan01346

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Posted 16 August 2019 - 10:42 AM

Thanks, I guess I was mostly looking to find out if I had it put together right.  So something changes when the counterweight arm is level, reminds me of the catches on my Chinese garden cart.  I managed to point it at ground level to the south.

 

My T-mount showed up in the mail while I was out there so I got to play with that.  Haven't looked at the pictures yet, this was a cell phone picture.  I can shoot RAW files so I have some leeway on exposure.  And looking through the camera's viewfinders works reasonably well.  Using my IR remote as a cable release as usual.

 

IMG_20190816_103801_cr_1024.jpg

 

Everything is so wobbly.

 

For terrestrial, az-el stuff, I could use the declination for elevation and loosen the clamp where the mount hitches to the tripod and pivot there for azimuth.



#24 lphilpot

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Posted 16 August 2019 - 11:00 AM

Yep - That's correct for looking south with a GEM. Virtually every type of mount has its 'dead zone(s)'. For a GEM, it's straight south. For a fork, it can be weird straight north if you're using a less-than large SCT and your head won't fit well in the little "hole" between the eyepiece, fork tines and motor. A horseshoe mount isn't all that popular these days, but it possibly has fewer dead zones. For an alt-az, it's straight overhead. For a ball mount, it's ... well, it's fine-tuning the balance. smile.gif

 

Wobby? That can be largely fixed with good design, common sense and $$$ (in varying amounts). But a GEM, for all its advantages, does carry the built-in disadvantage of multiple masses hanging on moment arms, so the way to fix the wobbles is some ratio of lighter weight, less moment-arm and better (i.e., more $$$$) construction. It just is what it is. Your camera is probably contributing significantly to the wobbles.


Edited by lphilpot, 16 August 2019 - 11:02 AM.


#25 alan01346

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Posted 16 August 2019 - 11:36 AM

For a first scope I'll live with wobbly I guess, it just surprised me for some reason.  I only paid $169 for the scope.  Everything should be several times bigger/heavier, but not everything was tightened down either, there was some ability to just nudge it where I wanted.

 

DSC_6767_rot_ri_cur_shp25_1024.jpg

 

So, cows 1/4 mile away as a first test.  I wasn't sure how the f-stop of the scope would work out, it's not in your favor.  I usually use about an f/9 with aperture priority for maximum depth of field.  There isn't much depth of field here, the center cow is almost in focus but that's about it.  Could be some vignetting too, this is the full frame, not cropped.  ISO was set to 400, shutter speed 1/200.




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