Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

The reflector limbo: how low do you go?

  • Please log in to reply
42 replies to this topic

#26 stargazer193857

stargazer193857

    Cosmos

  • *****
  • Posts: 7750
  • Joined: 01 Dec 2013
  • Loc: Southern Idaho

Posted 08 November 2019 - 07:30 PM

waytogo.gif

That's a good workaround with a smaller scope.

With a 24 inch, it would probably take a 5 inch lift to achieve10 degrees and it getting the piece in place is probably difficult to the weight. One also has to preplan this since the foot should pointed more or less south (for someone in Australia.) And it will mess up DSC alignment.

But for a one time observation, it is workable.

I observe at 10 degrees and below on a regular basis so I modified my 16 inch so it would go below the horizon. My 22 inch stops at about 8 degrees but since it has a horizontal focuser, it's very uncomfortable trying to view even at 8 degrees.

I don't consider a refractor a workaround since it requires giving up so much aperture.

Jon


Use thy wheelbarrow handles, and slide the block under with one foot, after using that foot to tap the foot board.

Yes, should confuse electronics, if they sense and anticipate an alt AZ mount.

#27 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 79455
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 08 November 2019 - 09:10 PM

Use thy wheelbarrow handles, and slide the block under with one foot, after using that foot to tap the foot board.

Yes, should confuse electronics, if they sense and anticipate an alt AZ mount.

waytogo.gif

 

With many scopes, that should work. Putting the handles on and taking them off is something I dislike but it should work, particularly with 2 people.  Another similar trick would be to position the scope vertically and then rotate it so is aligned east-west and push on it up high sideways to lift the north side free of the ground. Then one could push a board under the pad with a foot.

 

I might just try this the next time I have someone to help me. One way or another, your puck idea seems like it should work and would avoid having to cut the front cross board just for that once a year view. 

 

Jon



#28 a__l

a__l

    Apollo

  • -----
  • Posts: 1122
  • Joined: 24 Nov 2007

Posted 08 November 2019 - 10:41 PM

If you want to install encoders in the future. Encoders >10K can be very moody. For different reasons. For example, I bought 2 of 40K US digital (for experiment) and regulated them for several days. Do it at night on a polaris star hmm ...
Therefore, make 0 deg necessary (and use eyepiece with a cross).

 

Photo of my 24" - no problem.

Attached Thumbnails

  • horizon.jpg

Edited by a__l, 08 November 2019 - 11:04 PM.


#29 dave brock

dave brock

    Surveyor 1

  • -----
  • Posts: 1833
  • Joined: 06 Jun 2008
  • Loc: Hamilton, New Zealand

Posted 08 November 2019 - 11:16 PM

Sure, they are not what they could be if I were further south but I am not further south and the likelihood of being further south is about zero since I am about 3 miles from the US Mexico border.

I do have a clear view of the southern horizon, that enters into the equation. The hills in the background are in Mexico.

Jon


I hope that wall that's going to be built doesn't get in the way.😁
  • Jon Isaacs likes this

#30 dave brock

dave brock

    Surveyor 1

  • -----
  • Posts: 1833
  • Joined: 06 Jun 2008
  • Loc: Hamilton, New Zealand

Posted 08 November 2019 - 11:21 PM

You're lucky Jon, you get to challenge yourself viewing O Cent.... we have to contend with it being an easy naked eye sight at 77º....... undecided.gif


Yes, close to the zenith as does most of the good stuff from down here.😉
  • Kunama likes this

#31 dave brock

dave brock

    Surveyor 1

  • -----
  • Posts: 1833
  • Joined: 06 Jun 2008
  • Loc: Hamilton, New Zealand

Posted 08 November 2019 - 11:26 PM

Build it so you can point it down a hill at buildings below.


Hmmmm! 😠

#32 Napp

Napp

    Surveyor 1

  • *****
  • Posts: 1618
  • Joined: 26 Jul 2015
  • Loc: Florida, USA

Posted 09 November 2019 - 12:10 AM

I made some simple modifications to my Explore Scientific 16" DOB specifically for observing down to the horizon at the Winter Star Party in the Florida Keys.  There you are looking straight out over the Florida Straits.  It's far enough south that Eta Carina, the Jewel Box and other gems clear the horizon.  The skies can be steady enough to observe almost right down to the water.  I had to twist the slack out of the mirror straps and add bungees to provide necessary tension to make up for the counterweights no longer working at almost horizontal.  Looking forward to February for another chance to observe those southern beauties.


  • cloudypatio likes this

#33 Aperturefever

Aperturefever

    Mariner 2

  • -----
  • topic starter
  • Posts: 275
  • Joined: 12 Dec 2010
  • Loc: Lake Macquarie, Australia

Posted 09 November 2019 - 05:48 AM

It's interesting how a small consideration can have knock-on effects you wouldn't have thought of. I will have Nexus digital setting circles and a Stellarcat system, so perhaps I need to think this through.

Discussion on mirror support is especially interesting. I have a JP Astrocraft cell, so no sling, but whiffle trees. This means the mirror is clipped in and cannot fall forward. But I am curious as to how close to the horizon you get before the flotation points start to have a lesser effect, and the whiffle tree/sling considerations take over? Is it very late in the game? And when this happens, what goes on with your mirror face as the flotation starts to have a diminishing influence?

My biggest concern, however, is the balloon attached to Jon's scope. If things go pear-shaped, I imagine him disappearing in the distance, clinging onto said balloon, Mary Poppins style. Mind you ... he would get a decent view down low!


Edited by Aperturefever, 09 November 2019 - 05:48 AM.

  • Jon Isaacs likes this

#34 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 79455
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 09 November 2019 - 06:04 AM

But I am curious as to how close to the horizon you get before the flotation points start to have a lesser effect, and the whiffle tree/sling considerations take over? Is it very late in the game? And when this happens, what goes on with your mirror face as the flotation starts to have a diminishing influence?

 

 

My thinking is this: 

 

When objects are low on the horizon, I am looking through so much atmosphere and the image is sufficiently degraded by the low elevation seeing that the optical quality is no longer important, or at least as important. As long as the mirror is safe from damage, you're fine. You won't be splitting close doubles or viewing the planet's 10 degrees above the horizon.

 

My biggest concern, however, is the balloon attached to Jon's scope. If things go pear-shaped, I imagine him disappearing in the distance, clinging onto said balloon, Mary Poppins style. Mind you ... he would get a decent view down low!

 

 

Thank you for your concern.  The balloon I use is a hot air balloon and like most Cloudy Nights members, I produce large quantities of hot air. It is generally well controlled so there are very few problems. 

 

:lol:

 

Jon


  • Aperturefever, havasman, airbleeder and 1 other like this

#35 ed_turco

ed_turco

    Vanguard

  • *****
  • Posts: 2435
  • Joined: 29 Aug 2009
  • Loc: Lincoln, RI

Posted 10 November 2019 - 11:31 AM

I consider myself an "experienced observer."  These days I spend about 500 hours a year out under the night sky with a telescope and I have been doing for quite a few years.. 

 

Jumping on a plane?  That's easier than making some cuts on my rocker box? It doesn't seem that way to me. 

 

I know that observers who have limited observing opportunities/time seem to not be interested in observing near the horizon but that's not me, I have plenty of time and so I will go as low a 5 degrees, even lower.  There's interesting stuff down there.  Sure, they are not what they could be if I were further south but I am not further south and the likelihood of being further south is about zero since I am about 3 miles from the US Mexico border.  

 

I do have a clear view of the southern horizon, that enters into the equation The hills in the background are in Mexico.

 

 

Jon

That horizon doesn't look so hot.  There's a guy with a big telescope in the way!jump.gif


Edited by ed_turco, 10 November 2019 - 11:33 AM.

  • Jon Isaacs likes this

#36 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 79455
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 10 November 2019 - 12:35 PM

That horizon doesn't look so hot.  There's a guy with a big telescope in the way!jump.gif

 

roflmao.gif  

 

Ed.

 

Thanks for the laugh.  My wife got good laugh out that too.

 

 goodjob.gif

 

It took me a moment to realize it was joke, you almost got me.

 

Jon


  • 25585 likes this

#37 havasman

havasman

    Cosmos

  • ****-
  • Posts: 9946
  • Joined: 04 Aug 2013
  • Loc: Dallas, Texas

Posted 10 November 2019 - 01:19 PM

I'm pretty fanatical about observing along the meridian and as near zenith as possible. But I sit on the ground at the dark site and point the scope between the trees (not really tall) @ 400 meters away along the south end of the observing field to see NGC5128 and 5139. Though the view is compromised by the atmosphere and the inspection time is limited by the width of the clearings, the view of the giant globular and exotic galaxy is still pretty dang exciting. I've seen 'em from NSW too and that's a whole different experience. But that's only going to happen rarely.

 

I'm generally not in favor of self limiting options. I want my gear to allow the widest capabilities.

 

​It's a valid consideration but I doubt the Pratt mirror cell fails to provide effective support to a thin modern mirror for which it is designed for the amount of time you're likely to view near the horizon.



#38 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 42915
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 10 November 2019 - 05:09 PM

I'm cobbling together a 24" build and have reached the stage where I have to cut out some of my front rocker board to accommodate the lower struts at an almost horizontal angle. I was considering it this afternoon with the struts hard down against the front rocker board, and thinking - hang on ... I never observe that low with my 16". Why would I bother with a 24? I've been around the block at this point and tried to nab the stuff down low north like notherners have done the same down south. OK, so maybe you do it on a whim and on the odd occasion ... but really ... the experienced observers know not to bother looking through pea soup. It's easier to jump on a plane and fly up (down?!) to an accommodating reflector owner in a better location.

So my question is this: at what latitude do you pull the pin for observing? And I'm not talking the bragging rights stuff where you saw something famous, but the working observing area where you hit the point of diminishing gains?

I have pretty clear skies where I am ... but geez ... not sure if I would bother at an attitude that warrant cuts in this rocker board at this point in my observing career.

Thoughts?

I have a physical stop on my scope at +10°.

I rarely go below -35° declination, which is 20° above my horizon (I observe at 35°N), except for a few objects in the -35° to -40° band.

And most of the time I try to not view anything below 30° from the horizon, where the atmosphere is twice as thick as the zenith.

Reasons?

--the muck is too thick--water vapor, dust, light, air refraction, et.al. (seeing, transparency, and darkness are all poorer at very low altitudes.)

--I've seen the targets I'd seek from Australia, where they all had dramatically better appearances

--there are uncounted thousands of objects at higher declinations I have not seen in my scope.  I'll start worrying about those close to my

southern horizon when I have exhausted the list of possibles that are farther north.

--My main targets are faint galaxies and planetaries, both of which are much better when high in the sky.

 

If I built myself an observatory, it would have a roll-off roof.  I would position the walls so the scope could not see below 20° at least.


Edited by Starman1, 10 November 2019 - 05:19 PM.


#39 a__l

a__l

    Apollo

  • -----
  • Posts: 1122
  • Joined: 24 Nov 2007

Posted Yesterday, 05:10 AM

Probably everything went smoothly with your encoders. They are very sensitive to pinch, bend, not sufficient hold, noise from motors Servocat, etc. I spent a lot of time eliminating these causes. Therefore, I see no reason why I should limit my telescopes. That I could in a comfortable environment to look for problems and fix them.

 

Ps. Alternatively, if there is such a desire, you can install a limiter that can be installed or removed. In case of repair or replacement of equipment on your telescope.


Edited by a__l, Yesterday, 09:21 AM.


#40 a__l

a__l

    Apollo

  • -----
  • Posts: 1122
  • Joined: 24 Nov 2007

Posted Yesterday, 09:23 AM

Borisov is looking for comets near the horizon. Including galactic comet and several others. Where professional observatories do not work, which have a 20 degree limit :)


  • Jon Isaacs likes this

#41 25585

25585

    Fly Me to the Moon

  • *****
  • Posts: 5843
  • Joined: 29 Aug 2017
  • Loc: In a valley, in the UK.

Posted Yesterday, 12:18 PM

How low do GOTOs go to, and still work?



#42 GShaffer

GShaffer

    Knight of Ni

  • *****
  • Moderators
  • Posts: 6458
  • Joined: 28 Feb 2009
  • Loc: Bogart, Ga USA

Posted Yesterday, 12:50 PM

It is pretty rare that I view below 18/20 degrees with any scope much less a reflector......I do occasionally need to remind myself what things look like viewed underwater though :)


  • Asbytec, Aperturefever and Kunama like this

#43 a__l

a__l

    Apollo

  • -----
  • Posts: 1122
  • Joined: 24 Nov 2007

Posted Yesterday, 05:23 PM

How low do GOTOs go to, and still work?

For example, Nexus DSC has a limit that you set.

In the general case, this depends on the accuracy of setting the center of the encoder Alt. The so-called error of the sines-cosines.

Besides. You may have a bend of the arm and the encoder will freeze. You can loosen the arm fixation (on rocker), but the sinus-cosine error will remain.

 

The author of the topic recommendation. If you will use US Digital Optical Encoders. Follow the correct installation sequence for the 2 washers (supplied with the encoder kit) and arm. Otherwise, you will always have a pinch and incorrect operation of the encoder.


Edited by a__l, Yesterday, 05:32 PM.



CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics