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Meade-Vorce "Polaris" 90mm f/10 Achromat OTA

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#51 Sky Muse

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Posted 04 October 2018 - 08:12 AM

focusser housing3.jpg


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#52 tony_spina

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Posted 04 October 2018 - 09:52 AM

With all the stripping, flocking, and masking that Alan has been doing with a bunch of scopes lately it feels like the scope porn channel lol.gif

 

Geez what's next? Pictures of heavenly bodies?! grin.gif


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#53 Sky Muse

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Posted 04 October 2018 - 12:23 PM

With all the stripping, flocking, and masking that Alan has been doing with a bunch of scopes lately it feels like the scope porn channel lol.gif

 

Geez what's next? Pictures of heavenly bodies?! grin.gif

Here's another...

 

drawtube4.jpg

 

Yep, inside before there was that orangey, rusty cast to the factory blackening, but no more.



#54 Sky Muse

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Posted 04 October 2018 - 12:42 PM

What am I going to do with this?  That center opening is a full 65mm in diameter, and for a simulated 65mm f/14...

 

dust cap2.jpg

 

I would like to make use of that, for special occasions, but I can't have either the cap itself or the aperture-cap snapping into place, and then to mar the pristine ultra-flat blackness of the paint or flocking.

 

See that shiny rim around the 65mm opening; that has to be blackened.

 

I'll think of something. idea.gif



#55 Sky Muse

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Posted 04 October 2018 - 08:01 PM

Here, I went over the entire cap with #0000 steel-wool, and to dull down the gloss.  The perimeter of the 65mm aperture and the underside of the cap will be blackened...

 

dust cap3.jpg

 

dust cap4.jpg

 

I also removed the raised ridges from around the cap's perimeter, but it still fit too tightly when inserting it into the flocked dew-shield.  I'm now going to try to reduce the diameter further by sanding it down.  I shouldn't have to take too much off.  If that fails, I'll have to cut the solid-walled perimeter, leaving only three tabs, but I'd rather not, but it's got to fit just how I want it to fit.  I'm not going to let the design of this cap prevent me from doing just that. 



#56 Sky Muse

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Posted 04 October 2018 - 10:00 PM

Success; it fits like a glove now, with little pressure, and I can turn it upside down, shake it, and it will not fall out...perfect...

 

dust cap5.jpg

 

dust cap7.jpg

 

Now to blacken it, and then to tackle the aperture-cap.


Edited by Sky Muse, 04 October 2018 - 10:00 PM.


#57 Sky Muse

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Posted 04 October 2018 - 11:07 PM

The aperture-cap had even thicker ridges all round, and to snap it into place.  I shaved all of them off, but then I had a considerable gap to fill.  Self-adhesive, red felt to the rescue; fits like a glove...

 

dust cap8.jpg

 

I just love altering and improving junk components like this.

 

The last thing to do is to blacken...what I had said I needed to blacken within the last post.


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#58 SchoolMaster

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Posted 05 October 2018 - 05:55 PM

SkyMuse.

 

I have access to both a precision laser cutter and a 3D printer, so a custom aperture cap with, say, sub-aperture solar filter built in is doable in wood, PLA plastic, acrylic, or some combination of the three.


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#59 Sky Muse

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Posted 05 October 2018 - 08:28 PM

SkyMuse.

 

I have access to both a precision laser cutter and a 3D printer, so a custom aperture cap with, say, sub-aperture solar filter built in is doable in wood, PLA plastic, acrylic, or some combination of the three.

You could indeed create solar-filters for the telescopes of larger aperture you've acquired and are about to acquire.  However, I will not be creating a sub-aperture filter for this achromat.  I will be utilising the full aperture.  I've had a sheet of Baader film for quite some time now, and I can't think of a better instance in which to use it than for this refractor, and in the near future.

 

Incidentally, for any and all Newtonians you acquire, you'll want to create off-axis filters for those.


Edited by Sky Muse, 05 October 2018 - 08:53 PM.


#60 Sky Muse

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Posted 05 October 2018 - 10:26 PM

The dust-cap is now complete, front(left) and back(right)...

 

dust cap9.jpg

 

On the front, the blackened rim of the 65mm aperture is not actually that lop-sided, as there's a shadow there on the right.

 

I didn't have to blacken the back of the cap, but I did.  I simply wanted everything near to the doublet dead to all light, and whilst in use.  I don't need to blacken the back of the aperture-cap, for once it's in place the doublet cannot be used. lol.gif



#61 Sky Muse

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Posted 06 October 2018 - 11:06 AM

Once in a great while, I'll treat myself, and to a packaged pastry of some sort, albeit artificially-flavoured...

 

cherry.jpg

 

Mmm, TASTYKAKE®; they most certainly are tasty.  Usually, I'll get the cinnamon rolls, and they're quite tasty too, but this time round I settled upon the cherry; no cinnamon, and to live a little. 

 

I cut out this portion of the pastry's tray-liner, and for an experiment...

 

cherry2.jpg

 

Hmm, that certainly does look familiar.  Here, I've flipped that portion over, and with its corrugated side exposed, there on the left...

 

cherry3.jpg

 

...and on the right, the corrugated side of one of the two drawtube bearing-strips of the 1.25" focusser.


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#62 Sky Muse

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Posted 06 October 2018 - 11:54 AM

The forward-facing tip of the chromed rack has been flocked, the original adhesive removed, the surfaces scored, and epoxied...

 

rack tip.jpg



#63 Sky Muse

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Posted 06 October 2018 - 06:16 PM

Before...

 

focusser housing2b.jpg

 

After...

 

focusser housing4.jpg

 

A strip of self-adhesive, 0.030"-thick PTFE was applied to the adjustable, black-plastic bearing-strip, and now the substrate for the PTFE.  That was easy enough.  

 

Two layers of aluminum-foil tape, one layer of clear double-sided tape, and one layer of 0.020" PTFE were applied to the two remaining bearing-substrates, each.

 

The distance from the outer surface of the drawtube to the inner surface of the housing's flange is 18mm to 18.5mm, all round...

 

focusser3.jpg

 

Where the drawtube exits out the back...

 

focusser2.jpg

 

That, too, is evenly spaced, regardless of the camera's angle.

 

Quite unlike it was upon its arrival, there's absolutely no slop now, even when racked fully outward, yet when cranking on the knobs the motion is butter-smooth and requiring very little effort...

 

focusser4.jpg

 

Working with this metal focusser was an absolute pleasure!  Everything clicked into place as I went about its renovation.  I can't say the same when working with the plastic ones, not by the longest shot.

 

Now, there will never be a 2" focusser attached to this achromat, ever.  The telescope will be for medium-to-high powers only, particularly the higher, and with 2x and 3x barlows.

 

Just a few touch-ups with the ultra-flat black, and the focusser will be ready to install.


Edited by Sky Muse, 06 October 2018 - 06:18 PM.


#64 Sky Muse

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Posted 06 October 2018 - 09:06 PM

The focusser is attached, but I'll need to shim the flange with a single thickness of aluminum-foil tape.

 

To light, dead as a door-nail...

 

focusser5.jpg



#65 Sky Muse

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Posted 06 October 2018 - 09:21 PM

Okay okay okay, here's a shot without the flash; a veritable black hole it is...

 

OTA2.jpg

 

Mind you, the room is fully illuminated, and with eleven light-bulbs.


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#66 Sky Muse

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Posted 07 October 2018 - 02:44 PM

At long last...

 

kit.jpg

 

Incidentally, Meade offers that achromat with the EQ-2 there, and as a kit in its own right.  Despite the extra weight of the tube-rings and the dovetail-bar, the mount still supports it quite well.

 

The objective...

 

objective.jpg

 

Now, to wait until dark...


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#67 Sky Muse

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Posted 07 October 2018 - 02:52 PM

Oh, the objective, before, and after...

 

before & after.jpg


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#68 Sky Muse

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Posted 08 October 2018 - 01:38 PM

First-light with the renovated achromat was early this morning, around 4:30 AM.  By that time, Orion and the Pleiades were riding high in the sky; perfect.  

 

The doublet's retaining-ring was battened downed tightly upon its arrival from the factory, and I could see the effects of that during that initial star-test, along with the ill-applied factory-spacers of the doublet.  The pinching may have been responsible for some astigmatism I had noticed.  In the end, the retaining-ring, when reinstalled, was screwed down until it stopped, then backed off 1/4th of a turn; much improved now, with practically no astigmatism detected, and no spacers visible on the edges during the star-test, the patterns themselves round and identical on both sides of focus.  I now know why I went to all of this trouble, and after the fact.

 

The Trapezoid of Orion: pinpoints of light filled the view through the 10mm "Titan", and at 90x.  The well-defined nebula was like an island, as its ghostly, glowing "shores" dropped off into a jet-black "ocean", to the right and away from the Trapezoid.  I had never seen the nebula contrasted that well with its surroundings before.  Stars were present in the "water" as well.  What a beautiful sight, with no glaring and only subtle traces of light-scattering about the stars themselves.  The view was quite close to being in 3D.  I strained to detect first-diffraction rings about the brighter stars, and I think that I saw one or two.  I then placed the 10mm into a 2x barlow, and said rings became a little more apparent; very thin and wispy.  The view was dimmer, of course, at 180x.

 

Yes, it was well worth the effort.


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#69 tony_spina

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Posted 08 October 2018 - 01:58 PM

Great job Alan!

 

Time to renovate another scope grin.gif


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#70 Steve Allison

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Posted 08 October 2018 - 02:33 PM

...the patterns themselves round and identical on both sides of focus.

 

Sounds like it was well worth the effort! But...

 

I have never seen fresnel rings that were identical (exactly alike) on both sides of focus in any telescope I have ever looked through, or in any photograph of these rings I have ever seen. Very similar in the best lenses, yes, but never identical as I understand the meaning of the word.

 

Has anyone ever seen diffraction patterns that were truly identical? Can anyone post a picture of what they would consider to be identical patterns? I am curious more than anything.

 

Steve


Edited by Steve Allison, 08 October 2018 - 02:35 PM.

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#71 Sky Muse

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Posted 08 October 2018 - 08:52 PM

Sounds like it was well worth the effort! But...

 

I have never seen fresnel rings that were identical (exactly alike) on both sides of focus in any telescope I have ever looked through, or in any photograph of these rings I have ever seen. Very similar in the best lenses, yes, but never identical as I understand the meaning of the word.

 

Has anyone ever seen diffraction patterns that were truly identical? Can anyone post a picture of what they would consider to be identical patterns? I am curious more than anything.

 

Steve

This is an example of a perfect star-test...

 

http://www.oarval.org/perfect.gif

 

I have seen that, once, clear like that, and through my Takahashi FS-102, a 4" apochromat; although not a true apochromat being a doublet, but awfully close.

 

For the achromat in question, I didn't see the patterns quite that clear, but they did appear identical.  Atmospheric seeing plays a large part in the ability.



#72 Sky Muse

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Posted 08 October 2018 - 09:20 PM

Just as night fell, I placed the achromat on my Voyager I alt-azimuth, and aimed it towards the south; glamour shot...

 

100818.jpg

 

I wanted a last look-see at Saturn, before it disappeared into the void; and there was Titan as usual, disappearing when I would look directly at it.  I then swung over to Mars.  I think I saw a dark feature, however the false-colour was apparent, as Mars is still a bright li'l booger.

 

I then spied the "Teapot", and thought, "There's a globular-cluster there, somewhere", so I went inside and brought up Stellarium just to see what was there in the neighbourhood.  I went back out and just started scanning in the general area, and all of the sudden a faint cloud appeared, but it wasn't a cloud.  It was M22, a globular-cluster.  When I looked directly at it, it was just a "cloud", but then I looked off to the side and saw within a peppering of stars.  That was a most refreshing sight, given what I had been viewing beforehand.

 

The telescope works well on the Voyager I.  With the pier-extension attached, I can point straight it up at the zenith, and with plenty of clearance. 

 

Later, I'm going to take it out again, and explore the N-NW portion of the sky a bit.  I'd like to see the galaxy in Andromeda...


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#73 Sky Muse

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Posted 08 October 2018 - 09:24 PM

Great job Alan!

 

Time to renovate another scope grin.gif

Thanks, Tony.  Can you guess which one I'm about to do next?  I'll give you a hint: look for it in the "Classic Telescopes" forum in future.



#74 Jaimo!

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Posted 08 October 2018 - 09:34 PM

Great job Alan, most impressive.  It's amazing what a skilled person can do with modest tools.

 

Jaimo!


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#75 Steve Allison

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Posted 08 October 2018 - 10:10 PM

This is an example of a perfect star-test...

 

http://www.oarval.org/perfect.gif

 

Nice try, but if look closely you will see your example is really just a pairing of the exact same image, not a real inside and outside focus shot.

 

I have looked at every star test image I could find on the internet, but have never found "identical" in and out of focus images. The best test was of a 100mm Zeiss, but even there slight differences in the intensity and sharpness of the images were present.

 

Go to the Aberrator web site and try to find even one telescope with test identical images. You can't. Even the best telescopes show slight differences.

 

Even if your 90mm achro had the best lens ever made, the inner and outer images could not be identical due to chromatic aberration, which causes the outer diffraction rings to be different colors. If you cannot see the color differences,  you may want to be tested for color blindness.

 

Maybe we just have different understandings of what the word "identical" means. To me it is pretty much absolute, where your definition apparently allows for minor color and sharpness differences.

 

Still, you did a nice job on the telescope and I am sure it puts up some great views.

 

Fussy Steve


Edited by Steve Allison, 08 October 2018 - 10:15 PM.

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