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Fun with a classic reflector design


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#1 MistrBadgr

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Posted 22 June 2018 - 08:15 AM

I have really been enjoying the Polaris 114 I bought, the last few nights, mostly looking at the Moon.  I have been going up and down the terminator with an HD 60 4.5mm eyepiece, giving a nice 200X.  I have found those six element eyepieces show more detail and have as much light transmission as my Orthos, with a 60 degree field, instead of 45.  In one crater, I could not only make out wall colapses, I could also see rubble almost all the way from the rim to the central peak.  A couple scarfs have stood out very well as well as some of the sinuous lava flows and other interesting formations.  The tones in features have been really nice.

 

The only things I have done to the scope so far, have been to darken the bevel on the primary mirror and put some strips of flocking inside the focuser to take up some extra clearance around the draw tube.  What I thought was a tiny center dot on the primary ended up being a particle of some sort, so I put a dot in the middle with a Sharpie pen.

 

I need to work on tripod wiggle and I need to shorten the 12 inch controls to little stubby knobs.  Using the gear for a motor on RA to move the scope does not cause a lot of wiggle, but using the long cable on the other side does.  Using the long cable on the Dec adjustment also causes a lot of extra wiggle.  I will probably put some dowel rods or rolled steel rod inside the lower legs and build a really heavy eyepiece rack to work as a fulcrum.  I already am using some dampening pads on the bottom of the legs that help some.  The pads are half inch plywood squares, about three inches on a side, with five two inch squares of material from a "mouse mat" glued to the plywood with window caulk applied around the rim of each piece of the material.

 

I checked out how centered the secondary mirror is and found it to be in the right place, except that to post is a bit long....maybe actually designed for an f/5 scope instead of an f/8.  Anyway, as far as I can tell, collimation is now dead on the money.

 

On Jupiter, I can see four bands.  If the Great Red Spot is out, I can see it clearly with the blue filter.  At times, I can see three or four dark spots on the North Equatorial band, plus some irregularities along its inside edge.  Sometimes, I can see diagonal lines going across the space between the two equatorial bands.  The two temperate bands vary a lot in how much I can see them, but I can always see them at least a little bit.  I saw a bit of a show with what I think was Io coming out from behind Jupiter.  With Jupiter, 100X seems to be the magic magnification with the blue filter.  I cannot see very much without the filter.

 

With the Moon out, I really have not tried for any DSOs or anything like that.  I may try to get up early in the morning, assuming I can wake up enough, and have a look before the Sun comes up!

 

Bill


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Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#2 MistrBadgr

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Posted 22 June 2018 - 06:43 PM

Just thought I would post a picture of the two 4.5 inch scopes I now have.  The one in front is an Eclipse View 114, which has a three inch sun filter built into the lens cover.

 

The other, a Polaris 114, was bought to use as part of  a project to view st least some of the objects covered in a book called J'OBSERVE Le Ciel Profond, by Jean-Raphael Gilis.  This scope is proving to be a nice one.  The book is in French, which I do not know, but the objects were observed using a 60mm refractor and 115mm reflector with objects sketched by the two teenagers that did the observing.  I can pick out a few words, but the value for me is primarily the sketches, which I respect.  I will be using an Infinity 60, the Polaris 114, and possibly the EclipseView 114 sometimes. 

 

Both of the 114 mm scopes in the picture have needed work on the focusers to take up some of the extra clearance between the draw tube and the focuser body. The two focusers are quite different in terms of the design of their parts in a cosmetic way.

The two, I think, are actually coming from different sources, due to some of the design consideration differences in some parts.  On the Eclipse View I had to paint the inside of the open end ring flat black.  It was yellow, casting a yellow tinge over the whole image when viewing the Moon.  The Eclipse View has four thin blades for a spider with the secondary mirror being bare and glued to its central post, while the the Polaris secondary is on a stalk with the secondary mirror being contained in a holder cell.  The primary mirror on the EclipseView has a small central dark ring for collimating while the Polaris does not.  I took the primary mirror out of the Polaris, blackened the bevel around the outside edge and carefully placed a small central dot for laser collimation.

 

The Eclipse View seems to have a mirror that is a bit sharper, being parabolized.  It seems to behave like a mirror with almost no spherical aberation.  I cannot see any differrence between inside and outside of focus.  Therefore, I believe it is accurate to within a tenth of a wave in spherical abberation.  The Polaris mirror, being an f/8 spherical, should be a little better than a quarter wave, if perfect.  It does seem to match reasonably well with the quarter wave images in Mr. Suiter's book on astronomical telescopes.

 

At 100x, using HD60 eyepieces, the images were pretty much the same.  The EclipseView seemed to show more detail, while the Polaris had a tiny bit better contrast.  To go to a higher magnification, the Eclipse View needed a Barlow, and the contrast really fell off.  The Polaris could go from the 9 to 6.5 mm HD 60 eyepiece, but the atmosphere was not the best and the image did loose some contrast as well as detail.

 

The EclipseView, on its stool, was not subject to any wiggle, while the Polaris'wiggle is noticeable, which I will be working to decrease.  The long tube and weight of the OTA has a significant angular inertia to it, by its basic nature, and behaves as I would expect.  I also need to turn the RA control from maybe twelve inches long to a little stubby thing to keep it from hitting the OTA sometimes.  Naturally, the equatorial mount of the Polaris is not as intuitive as the the single arm Dobsonian of the Eclipse View, but is easier to control its position at higher magnifications.

 

Which one is actually best, will simply depend on the tastes of the users.  Both are nice scopes that I will enjoy using.

 

Thanks for reading!

 

Bill Steen

 

 


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Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#3 MistrBadgr

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Posted 22 June 2018 - 06:44 PM

The pictures did not go through.....shucks!


Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma




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