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Celestron and others Special Coatings

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#1 clamchip

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Posted 09 December 2018 - 12:06 PM

My 1980 orange C8 has a 'Special Coatings' sticker on the tube and the coatings are a brown color.

Usually in most examples I've seen these special coatings are blue.

This particular C8 serial 807853 with motor dates 4-80 came from Goodwill without a case and I have

no history of it's past.

It also just so happens this particular C8 is perfection, exactly the same diffraction pattern just inside

and the same just outside focus. Zero image shift, zero mirror flop. The focuser is smoother than smooth

and you would never know there's a mirror attached to it even with the tube at zenith.

Thats all I know about the scope. 

 

Any ideas on these brown coatings?

 

Interestingly this time at Celestron all the accessories, finders, eyepieces, porro prisms, zenith prisms, focal

reducers, all were coming from Vixen in Japan, and I've seen the brown coatings on some of these.

I thought well maybe the tube was sent back to Celestron for new optics but the Starbright coatings are

also blue. I have not seen the latest generation coatings Starbright XLT, anyone have one? brown or blue?

 

I was thinking it might be interesting to see what everyone's coatings color is, post it here. You don't need

to post a photo just the color and something about the make and model.

The top photo is a 1980 C8 with brown coatings, middle 1976 C5 blue, bottom 1999 C5 Starbright coatings.

Robert

 

post-50896-0-41201000-1515204694_thumb.jpg

post-50896-0-76653900-1515204703_thumb.jpg

IMG_8817.jpg


Edited by clamchip, 09 December 2018 - 12:08 PM.

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#2 clamchip

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Posted 09 December 2018 - 12:21 PM

Whoa! I nearly had a coronary! I thought this was a big Ol' clamchip! it sure looks like one! scared me there for a second

I felt my heart miss fire!

 

post-50896-0-76653900-1515204703_thumb.jpg


Edited by clamchip, 09 December 2018 - 12:23 PM.

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#3 petert913

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Posted 09 December 2018 - 12:52 PM

The corrector plate is sure clean as a whistle !


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#4 clamchip

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Posted 09 December 2018 - 03:01 PM

I did a little digging and I think the brown coating may be Calcium Fluoride CaF2 ? and is pretty much the

same? as the blue coating Magnesium Fluoride MgF2 ?

The CaF2 may have a slightly broader wavelength range.

Here you can see the two coatings:

https://www.canon-op.../materials.html

https://www.canon-op...roductlist.html

Robert


Edited by clamchip, 09 December 2018 - 03:04 PM.

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#5 clamchip

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Posted 09 December 2018 - 03:21 PM

Here's a little more:

https://www.lenstip....ansmission.html

I did also read the amber/brown tint can be just standard Magnesium Fluoride formulated for

a different wavelength possibly because of the blue color shift in a higher density glass. I should

probably see if my corrector is plate glass.

 

Robert


Edited by clamchip, 09 December 2018 - 04:08 PM.

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#6 rolo

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Posted 10 December 2018 - 09:12 AM

The pictures should be taken under the same type of lighting. One in the sun, one under fluorescent, and one under what seems to be tungsten lighting will show a different coating color.



#7 Geo.

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Posted 14 December 2018 - 11:08 AM

Per Bob Piekiel, the "Special Coatings" show grayish under "standard" fluorescent lighting, which probably means warm white color, ~52 color rendering index and 3000K color temperature. Your fluorescents may vary. Special Coatings or Special Coating, refers to the coatings on the corrector only. there were no anti-reflective coatings on the mirrors. Meade's EMC were similarly limited to the corrector.



#8 jjack's

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Posted 15 December 2018 - 10:05 AM

The answer is probably there : https://www.cloudyni...an-old-reducer/



#9 jjack's

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Posted 15 December 2018 - 10:15 AM

The color reflected can vary with the thickness of the coating


Edited by jjack's, 15 December 2018 - 10:17 AM.


#10 sbrewster

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Posted 16 December 2018 - 03:02 PM

The pictures should be taken under the same type of lighting. One in the sun, one under fluorescent, and one under what seems to be tungsten lighting will show a different coating color.

Looks to me that none of the 3 photos was taken 'using' fluorescent lighting... yes the top 2 were taken 'under' fluorescent lighting (on the ceiling)... which were NOT turned on! Both were taken using the same tungsten light.  The 'flare' in the 2nd photo may have been caused by the tungsten light being in a slightly different position.

 

I agree the last picture, taken in daylight, would have been better represented if taken in same light as the 2 photos above it.

 

Steve


Edited by sbrewster, 16 December 2018 - 03:05 PM.


#11 clamchip

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Posted 16 December 2018 - 04:51 PM

These two photos were taken with the same lighting, a 2 bulb fluorescent shop light and a 

tungsten lamp, all were turned on.

I just wanted to show the obvious 'brown' and 'blue' of these 2 Celestron Special Coatings.

Under any lighting including natural outdoor the difference remains the same.

The familiar blue whether on a SCT corrector, or a objective lens, or eyepiece, is definitely

blue in color and  likely Magnesium Fluoride.

The brown I have seen on camera lenses before, and my 1980 C8 corrector, may also be

Magnesium Fluoride but a slightly different recipe, that's all I've been able to dig up.

 

Robert


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#12 jjack's

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Posted 17 December 2018 - 04:05 AM

Amber reflectance shift the transmittance to the blue part. Maybe to compensate the lesser reflexion of the silver coating on the mirrors. Maybe your mirrors were silvered ...?

How many C8 were made with this amber coating ? Just a few ? It could be a rare collector scope :)



#13 clamchip

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Posted 17 December 2018 - 11:03 AM

The mirrors look aluminized, zero tarnish or failing coating around the edge typical of the silver coated

Celestrons.

Celestron did play around with silver coatings, so did Meade, with disastrous results.

I should make note again that this is a perfect specimen. In all my years I've never owned another

that displayed such perfection, if that means anything.

 

Robert




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