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New to using equatorial mount

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#1 Mr Oldschool

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Posted 14 October 2021 - 03:39 PM

Hi all,

 

I've used altazimuth mounts for all my life, and as a gift for my 17 year old daughter, I just got a couple higher power telescopes for her (than what we previously had been using), but I am struggling to understand how to use the older of the two that has an equatorial mount.  When I align the azimuth with north and set the altitude to my local latitude, the right ascension is able to swing in an arc from horizon to horizon if I am viewing to the southern sky.  But to view the northern sky, suck as Polaris, or the Big Dipper, do I loose the declination lock and "flip" the scope upside down to view the other direction?  The RA doesn't swing in the right manner to go horizon to horizon when doing this, so I'm not sure how to point it to NW or NE directions.  I can tell it isn't reversing the azimuth to point south instead of north, because then the altitude will be dead opposite where it is supposed to be.  I would very much appreciate someone making this clear for me.  With my old scopes, it was always just point and shoot, so to speak, so this is just very confusing for my middle aged mind...


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#2 Mr Oldschool

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Posted 14 October 2021 - 03:55 PM

Here are some pictures of the mount in question...

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#3 Mr Oldschool

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Posted 14 October 2021 - 04:00 PM

I'm also curious if anyone knows what this dohickey does.  It seems to rotate freely from sitting on top of the silver spinny gear-like thing to touching the same spot on the bottom of the same thingy.  I can't find a function for either of them, as nothing seems to happen when I twist or turn them.

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#4 photoracer18

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Posted 14 October 2021 - 04:07 PM

That dohickey disengages the optional RA drive so you can move it manually. Nice thing about those old Nihon Seiko mounts is you can move the RA axis to point straight up and use it as an Alt-Az mount if you wish.


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#5 P_Myers

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Posted 14 October 2021 - 04:34 PM

Isn't it called a.... "thing a ma jig" 


Edited by P_Myers, 14 October 2021 - 04:34 PM.

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#6 Mr Oldschool

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Posted 14 October 2021 - 04:36 PM

That dohickey disengages the optional RA drive so you can move it manually. Nice thing about those old Nihon Seiko mounts is you can move the RA axis to point straight up and use it as an Alt-Az mount if you wish.

Do you mean the slow move knob at the end of the flexible shaft?  It doesn't seem to affect the function of that knob in any position.  As far as I can tell, it is a piece of metal loosely held to a shaft by a screw, and nothing more.



#7 JamesMStephens

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Posted 14 October 2021 - 04:42 PM

Do you mean the slow move knob at the end of the flexible shaft?  It doesn't seem to affect the function of that knob in any position.  As far as I can tell, it is a piece of metal loosely held to a shaft by a screw, and nothing more.

I think what photoracer is telling you is that it would engage/disengage the drive motor, but since you don't have the motor installed it won't do anything.

 

Jim


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#8 Steve C.

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Posted 14 October 2021 - 04:43 PM

Here's a video that runs through the basics.  https://youtu.be/RFCreX1x4_s

 

If you've never used a GEM before, I agree, it can seem convoluted. But it soon becomes second nature.

 

Good luck.


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#9 Mr Oldschool

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Posted 14 October 2021 - 04:52 PM

I think what photoracer is telling you is that it would engage/disengage the drive motor, but since you don't have the motor installed it won't do anything.

 

Jim

Ah, got it.  Thanks for the clarification!


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#10 Mr Oldschool

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Posted 14 October 2021 - 04:55 PM

Here's a video that runs through the basics.  https://youtu.be/RFCreX1x4_s

 

If you've never used a GEM before, I agree, it can seem convoluted. But it soon becomes second nature.

 

Good luck.

Thanks for the link.  I hadn't been able to find much to help explain things, so it is much appreciated!  Yes indeed, convoluted is a good word for it.  At least the most basic operation makes sense, and I find it quite cool.  I just need to get through the bootstrap loader...



#11 GoFish

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Posted 14 October 2021 - 04:55 PM

When manually pointing a GEM, I just loosen both clutches and let my hands move the tube however they decide is best. Once pointed, I couldn’t possibly tell you which axis I moved or how much. 
 

The exception to that purely “zen” technique is that I know to put the counterweights on the same side of the meridian as the object I want to view. 



#12 JamesMStephens

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Posted 14 October 2021 - 05:16 PM

Ye olde meridian flip https://www.youtube....h?v=-9q3Ft8TCoU

 

Was the tube bumping in to the tripod?

 

Jim


Edited by JamesMStephens, 14 October 2021 - 05:17 PM.


#13 Mr Oldschool

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Posted 14 October 2021 - 05:17 PM

Here's a video that runs through the basics.  https://youtu.be/RFCreX1x4_s

 

If you've never used a GEM before, I agree, it can seem convoluted. But it soon becomes second nature.

 

Good luck.

Just finished watching the video, and it makes much more sense now, thank you!

 

The way the scope pivots around on the  mount actually kind of reminds me of the heavy machine gun rig they were using in Aliens, but I digress...



#14 Mr Oldschool

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Posted 14 October 2021 - 05:33 PM

Ye olde meridian flip https://www.youtube....h?v=-9q3Ft8TCoU

 

Was the tube bumping in to the tripod?

 

Jim

I don't think the tube was hitting that I can recall.  I think I didn't have both axes unlocked to move it, so I couldn't figure out how to direct it.  I was just afraid to mess something up in the fixed positioning, so I couldn't visualize how to move it left to right in the northward direction.  I had the counterweight parallel to the side (level with the tube), and loosed the declination to flip the tube in the opposite direction, but that didn't work...  Seeing someone demonstrate the motion makes it much clearer.


Edited by Mr Oldschool, 14 October 2021 - 05:37 PM.

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#15 JamesMStephens

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Posted 14 October 2021 - 06:33 PM

Now that the mount is working for you maybe you can tell us a little more about that old scope.  Four inch Newt?  How do the mirrors look?  How is the image?

 

Jim



#16 Mr Oldschool

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Posted 14 October 2021 - 07:06 PM

I'm just getting it sorted out.  It is a Tasco 11T.  The guy I bought it from was the original owner, who bought it from Macy's in the mid 80's.

 

The plate on the side says:

tasco

Reg. No. 511300

450 Power

Astronomical

Reflector Telescope

D=4 1/2" F=900MM

Coated Optics

Model No. 11T

Made in Japan

 

It came with two eyepieces, H20mm and SR4mm, and a 2x Barlow.  The H20mm has a plastic piece on the down side that says "Moon".

Also, the body of the scope has a white circle with the letters "JT" on it near the front end.

 

When I was trying it out before buying I determined that the 5x finder scope was useless.  It has no focus adjustment.  Unscrewing the eyepiece from the body reveals a metal piece threaded into the inside of the eyepiece that has the crosshairs attached.  Unscrewing that piece released the two lenses and a fixed spacer that fits between them.  So, out of focus and staying that way...  At least finder scopes are pretty cheap.

 

The image quality looking at trees on a mountain about 5 or 6 miles distant was not stellar.  I could tell that they were trees, but the details were a bit blurry no matter where I racked the focus to.  The previous owner said he had never collimated the mirrors, so, ever hopeful, I'm chalking it up to that in the absence of further problems.  The eyepieces definitely need cleaning.  Pretty sure the mirrors need cleaning, even though he was storing it with the lens cap on.  Then I get to try to figure out how to collimate without the aid of a lens alignment laser.  I've seen that there are tutorials, but I haven't watched them yet.


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#17 Mr Oldschool

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Posted 14 October 2021 - 07:13 PM

I'm just getting it sorted out.  It is a Tasco 11T.  The guy I bought it from was the original owner, who bought it from Macy's in the mid 80's.

 

The plate on the side says:

tasco

Reg. No. 511300

450 Power

Astronomical

Reflector Telescope

D=4 1/2" F=900MM

Coated Optics

Model No. 11T

Made in Japan

 

It came with two eyepieces, H20mm and SR4mm, and a 2x Barlow.  The H20mm has a plastic piece on the down side that says "Moon".

Also, the body of the scope has a white circle with the letters "JT" on it near the front end.

 

When I was trying it out before buying I determined that the 5x finder scope was useless.  It has no focus adjustment.  Unscrewing the eyepiece from the body reveals a metal piece threaded into the inside of the eyepiece that has the crosshairs attached.  Unscrewing that piece released the two lenses and a fixed spacer that fits between them.  So, out of focus and staying that way...  At least finder scopes are pretty cheap.

 

The image quality looking at trees on a mountain about 5 or 6 miles distant was not stellar.  I could tell that they were trees, but the details were a bit blurry no matter where I racked the focus to.  The previous owner said he had never collimated the mirrors, so, ever hopeful, I'm chalking it up to that in the absence of further problems.  The eyepieces definitely need cleaning.  Pretty sure the mirrors need cleaning, even though he was storing it with the lens cap on.  Then I get to try to figure out how to collimate without the aid of a lens alignment laser.  I've seen that there are tutorials, but I haven't watched them yet.

Okay, so that was a "Moon filter"...  Taking it out of the eyepiece makes the image much nicer.  Still seems slightly "hazy" but I think I can clear that up (I hope).


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#18 JamesMStephens

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Posted 14 October 2021 - 07:20 PM

I imagine you already own an eyepiece or two, maybe try a different one than the Huygens or Ramsden that came with the scope (unless these are 0.965").  I suspect that a 2X Barlow came with the set, which would give you the advertised 450X with that 4-mm eyepiece (which isn't advisable).

 

Jim



#19 Mr Oldschool

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Posted 15 October 2021 - 02:30 AM

Are you saying using the 4mm eyepiece with the 2x Barlow isn't advisable? If so, why?

I have a couple eyepieces that go to the Mesixi telescope we had been using, but I think they are a different diameter and likely won't fit. I don't know what the number you mentioned means.

I've been stargazing for a long time, but I know very little about telescopes. The ones I've used have been low power and lower quality, so they taught me pretty much nothing but frustration.

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#20 JamesMStephens

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Posted 15 October 2021 - 08:49 AM

Are you saying using the 4mm eyepiece with the 2x Barlow isn't advisable? If so, why?

I have a couple eyepieces that go to the Mesixi telescope we had been using, but I think they are a different diameter and likely won't fit. I don't know what the number you mentioned means.

I've been stargazing for a long time, but I know very little about telescopes. The ones I've used have been low power and lower quality, so they taught me pretty much nothing but frustration.

Sent from my SM-G781U using Tapatalk

I'm saying 100X per inch on that telescope is pushing it.  Especially with that Ramsden eyepiece.  Magnification isn't fixed for a telescope, it's the scope's FL divided by the FL of the eyepiece.  I think it's conventional wisdom that if there's an advertised magnification for the scope it indicates low quality, but I don't entirely buy that.  If you bought a scope 50 years ago the manufacturer might have reasonably assumed you would stick with the eyepieces provided with it.  There's no such thing as a 450X telescope, per se.  

 

The 0.965" is the barrel diameter of the eyepiece, and I'm guessing that this is the size of those two eyepieces.  The US standard is 1.25", or 2" barrel diameter.  

 

I'll bet the primary/secondary mirrors are pretty decent, so a good upgrade would be to replace the focuser with a 1.25" model and get a couple of nicer eyepieces.

 

Jim


Edited by JamesMStephens, 15 October 2021 - 08:53 AM.


#21 Mr Oldschool

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Posted 15 October 2021 - 11:30 AM

Yes, these eyepieces are 0.965".  Looking at the other thread from ten years ago where someone had an identical telescope, these appear to be the standard eyepieces that came with it.

 

I do understand the concept (now) that the magnification is calculated by focal length of telescope and focal length of eyepiece.  I'm still struggling to understand why setting up higher magnification has the limitations you mention.  Why is it that 100x per inch, as you say, is pushing it?

 

Perhaps a better way to approach the whole subject is to start with my objective.  I want to give my daughter a telescope that can reliably provide large, clear views of Mars, Jupiter, Saturn, and potentially Venus, although I know there isn't much to look at there, and it's brightness can make it harder to view.  I want to be able to see the bands and Big Red Spot on Jupiter.  I want to look at Saturn and see distinct rings.  What do I need to do to be able to get these kind of observations?  What is needed to be able to view a nebula and actually see a distinct gaseous shape, rather than just a nice spray of light around some stars?  Someone on here in another thread mentioned that you will never be able to make observations like what they show in photos.  Is that because the photos are using the giant telescopes of observatories?  What are the obstacles that I'm facing, so I can work with them to get my best results?

 

Thanks for all the guiding by the hand here.



#22 JamesMStephens

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Posted 15 October 2021 - 12:18 PM

Yes, these eyepieces are 0.965".  Looking at the other thread from ten years ago where someone had an identical telescope, these appear to be the standard eyepieces that came with it.

 

I do understand the concept (now) that the magnification is calculated by focal length of telescope and focal length of eyepiece.  I'm still struggling to understand why setting up higher magnification has the limitations you mention.  Why is it that 100x per inch, as you say, is pushing it?

 

Perhaps a better way to approach the whole subject is to start with my objective.  I want to give my daughter a telescope that can reliably provide large, clear views of Mars, Jupiter, Saturn, and potentially Venus, although I know there isn't much to look at there, and it's brightness can make it harder to view.  I want to be able to see the bands and Big Red Spot on Jupiter.  I want to look at Saturn and see distinct rings.  What do I need to do to be able to get these kind of observations?  What is needed to be able to view a nebula and actually see a distinct gaseous shape, rather than just a nice spray of light around some stars?  Someone on here in another thread mentioned that you will never be able to make observations like what they show in photos.  Is that because the photos are using the giant telescopes of observatories?  What are the obstacles that I'm facing, so I can work with them to get my best results?

 

Thanks for all the guiding by the hand here.

 

 

There's only so much detail present in an image (resolving power is inversely proportional to aperture--the bigger the objective lens or mirror, the higher the resolving power), so magnifying past a certain point doesn't gain anything, and the larger the scope, the higher that maximum useful magnification might be.  That said, 4.5" is (in my book) respectable, but 450X would be a lot.  Optical quality also comes into play, increasing the magnification of a bad image doesn't do any good.  Also, for a given aperture higher power means smaller exit pupil, which exacerbates the effect of "floaters" in the eye.  There's some wiggle room here, but take a look at this for starters

 

https://www.astronom...-magnification/

 

As far as imaging, a small diameter scope can take incredible images, but they're the result of stacking multiple images, something possible with electronic cameras and computer processing.  This is effectively the same as taking a long time exposure, bringing out detail in faint objects.  Stacking separate images also reduces the effect of random noise.)

 

Jim



#23 Mr Oldschool

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Posted 15 October 2021 - 02:15 PM

Here are a few other pictures of the bits of the scope. 

 

I took apart the finder and took some pictures to show its guts.  Not much to see.  Two convex lenses held at a fixed distance from each other by a sleeve of black plastic.  Copper wire reticle in the threaded part that holds the lenses into the eyepiece.  Black plastic pinhole part the fits into the other end, and threaded parts to hold the whole thing together...20211015_090711.jpg



#24 Mr Oldschool

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Posted 15 October 2021 - 02:16 PM

20211015_090739.jpg



#25 Mr Oldschool

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Posted 15 October 2021 - 02:23 PM

...And some more views of the eyepieces:

20211015_091205.jpg




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