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Celestron #94115-A Blackened & Flocked

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#1 Sky Muse

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Posted 21 August 2018 - 04:33 AM

I've had this Celestron star-prism diagonal for a while...

 

Celestron 94115-A3.jpg

 

I finally got around to it...

 

http://lh3.ggpht.com....jpg?imgmax=800

 

blackening.jpg

 

I cleaned the streaks off the non-painted areas before reassembling.

 

I didn't want the set-screws digging into the prism, so I added aluminum-foil tape over the paint for them...

 

blackening2.jpg

 

The insides of the diagonal's body, the nosepiece, and a small portion of the eyepiece-holder, were blackened.  I also applied flocking to one side of the prism's greyish-black paper backing, and faced the flocked side towards the prism...

 

blackening3.jpg

 

I used a laser-collimator and a flat mirror to check the collimation.  It's spot-on...

 

blackening4.jpg

 

Keep in mind that this particular diagonal was used in conjunction with my Celestron "AstroMaster" 70mm f/13 achromat, and when I saw a practically tack-sharp Airy-disc and a blade-like first-diffraction ring of Polaris A, and at...

 

...225x.  Believe it or not.


Edited by Sky Muse, 21 August 2018 - 04:40 AM.

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#2 TOMDEY

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Posted 21 August 2018 - 06:59 AM

Nice! Have you noticed any use-improvement after the baffling, blackening and support mod? I have several of these and like them a lot.  Tom


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#3 Sky Muse

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Posted 21 August 2018 - 02:32 PM

I haven't tested it yet, as it's been cloudy and a little wet here, but clear skies are forecast for tonight and the next seven days. smile.gif



#4 Sky Muse

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Posted 26 August 2018 - 06:12 PM

Success; no more glaring, and the views are... meditation.gif .


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#5 Joe1950

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Posted 26 August 2018 - 06:29 PM

Very good, Alan. I'll have to do that also!

 

One Q. On the inside of the housing, did you use paint or flock to darken it?

 

Thanks.


Edited by Joe1950, 26 August 2018 - 09:00 PM.

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#6 Adun

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Posted 26 August 2018 - 08:54 PM

Nice!


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#7 Sky Muse

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Posted 26 August 2018 - 09:15 PM

Very good, Alan. I'll have to do that also!

 

One Q. On the inside of the housing, did you use paint of flock to darken it?

 

Thanks.

I only used flocking for the backing of the prism.  I simply attached it to one side of the original grey-black paper backing.  The inside of the housing was painted, and with this sprayed into a peanut-jar cap...

 

ultra-flat.jpg

 

Remove the set-screws before painting.  You can mask the housing and spray the paint, or you can simply brush it on from the pool of paint within the cap.  When reinstalling the prism, close it all up, battening down the chromed-screws, and then insert the set screws.  However, with the prism under pressure after closing it up, I don't really see the need for the set-screws.  Now, that is per my sample.  I went ahead and installed the set-screws, however, and torqued them down just a bit.

 

You may also want to reblacken the inside of the nosepiece, possibly.  Mask off the outside, then spray the paint at an angle into one end, as you twist it around on a stick, then flip it and paint that end, too.  The goal is to blacken all of the chromed threads within it.  For the eyepiece-holder, I blackened only the inner surface of the lower rim, just below where an eyepiece would seat, which can be painted by hand with a small brush.  Roughen all smooth and shiny surfaces to be painted with sandpaper for improved adhesion, wash the components with soap and water, then wipe with alcohol, and before applying the paint.  I also used a tack-cloth right after the alcohol, then painted.  I used 100% acetone and cotton swabs to clean the excess paint off of the prism; one swab, one wipe per tip, one after another.  The prism can also be masked off, when painting only the sides as I did.  I started painting it by hand, but then I finished it up by masking it off and spraying the remainder required.  Blue painter's tape works a charm.


Edited by Sky Muse, 26 August 2018 - 09:26 PM.

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#8 Joe1950

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Posted 26 August 2018 - 10:00 PM

Excellent, Alan! I happen to have a full can of that paint, and the blue masking tape, so I am all set!

 

Thank you very much!

joe


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#9 MeridianStarGazer

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Posted 26 August 2018 - 11:00 PM

I blackened the sides of my Amici prism. I got smudges on surfaces somehow. I need to open it back up and clean them. I did not think of flocking. Sharpy is too thin. Nail polish is thicker. I'll go back and at least get the corners of the transmissive surface too.

Thank you for posting. There are so many places we can fight scatter.
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#10 Sky Muse

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Posted 27 August 2018 - 12:43 AM

It's also a good idea to give the unpainted portions of the prism a good wiping-down with a lens cleaner, prior to reinstalling it.  When handling a prism after the final cleaning, and when reinstalling it, always wear a thin-plastic, un-powdered glove.


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#11 Sky Muse

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Posted 27 August 2018 - 01:08 AM

I blackened the sides of my Amici prism. I got smudges on surfaces somehow. I need to open it back up and clean them. I did not think of flocking. Sharpy is too thin. Nail polish is thicker. I'll go back and at least get the corners of the transmissive surface too.

Thank you for posting. There are so many places we can fight scatter.

I'll probably end up doing the same to my GSO 90° Amici, depending on the difficulty.  I also have a new old-stock Parks hybrid-prism diagonal, in addition to a couple of vintage/classic, Japanese, .965" prism diagonals, and all that could probably benefit as well.



#12 Starman1

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Posted 27 August 2018 - 02:57 PM

What Baader says about prism surfaces:

"Many people would question the usefulness of any kind of reflective coating on any prism (the reflective, not refractive, surface) and they are right - in the first year. The problem is with aging. Over time, a total reflection prism surface will get stained from mould and moisture. Many of the zero-cost Chinese and Japanese prism diagonals have their hypotenuse face separated from the housing with nothing more but a black cardboard - directly touching the prism face. Over time the cardboard gradually makes ever more contact with the glass. If you want to know, take your prism body apart and see what´s inside. A ten year old prism theoretically should be as bright as on day one owing to total reflection properties. In fact, the prism reflective face will age and gradually loose brilliance - with the observer being in total acclimatization with the slowly degrading prism. Much to the contrary, the Baader-BBHS® coating as applied onto prism surfaces is sealed for life. Even after 20 years have passed, our customers of T-2 and 2" prism diagonals cannot distinguish any lack of brilliance - not to say lack of brightness - on their prism faces. "No news is good news". "

I.e. a reflective coating on the hypoteneuse keeps the glass from staining or from black paper touching the surface, which reduces reflectivity.

The application of silver or aluminum to this surface (especially silver), followed by a paint overcoat to protect the coating, can keep the reflective surface nearly perfect for the life of the prism.


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#13 Joe1950

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Posted 27 August 2018 - 03:55 PM

Hi Don! They are saying that nothing should be in contact with the prism reflecting face such as black cardboard, or flock in this case, or foam cushion as I have seen?



#14 Starman1

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Posted 27 August 2018 - 04:58 PM

That's what they're implying.  In a 90° prism, reflection is close to 100% at exactly the correct angle of incidence.

In many binoculars, those surfaces are slivered or aluminized or even multi-layer dielectric coated to guarantee nearly the same reflectivity as the angle changes.

Baader's comment about a dark surface contacting the glass resulting in lower reflectivity was something I had never read before.  Makes sense, I guess.


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#15 Joe1950

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Posted 27 August 2018 - 05:00 PM

Understood. Thanks Don!



#16 Sky Muse

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Posted 29 August 2018 - 03:29 AM

Hmm, what of backing the prism with acid-free white paper?

 

I did read before that the backside of the prism should not be painted...

 

blackening8.jpg

 

I wouldn't mind a silver coating on the backside, but never aluminum.  And I can understand getting used to a slow, steady degradation, and being oblivious to it; bad prospect, that.

 

I think I'll compare white paper with flocked paper, during observations, and note the difference, if any.

 

Oh, here's the portion of the holder that I blackened, actually flattened, and again, just below where an eyepiece would seat...

 

blackening12.jpg

 

Here are the fillers...

 

blackening7.jpg

 

...a gallery of rouges, it has turned out.


Edited by Sky Muse, 29 August 2018 - 03:47 AM.

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