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"Newton's Rings" on SP-C102 Achromat

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#1 arachman

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Posted 30 March 2018 - 09:20 PM

Hello all,

 

I was happy to find this thread because I just picked up a SP-C102 locally. I know it seems that this thread is dedicated to ED and Fluorite but my new scope is neither of these. Still pretty good, I think but, still just the "Plain Jane" version. My reason for intruding is to ask about the "Newton's Rings" apparent on the objective. Attached are photos of the label and the lens. I have delved into this once in the past and, rightly or wrongly, came to the conclusion that Newton's Rings occur on some individual scopes and are not detrimental to the image and are not worth doing what is necessary to eliminate them.

 

Your opinions would be gratefully considered as I am a relative newcomer to astronomy.

 

Now that I'm into it two more questions come to mind:

1) I didn't include a photo but, my Super Polaris mount has white painted tips on the legs.

    I don't remember seeing this before. Another area where I need education.

 

2) I have never seen a photo of the label on a ED or Fluorite C102.

    Are they just like the label on my scope except saying C102ED and C102F?

 

I would hope to own a fluorite version in the not too distant future.

 

Thanks in advance for your help.


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#2 arachman

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Posted 30 March 2018 - 09:29 PM

Forgot to post photos.

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#3 arachman

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Posted 30 March 2018 - 09:32 PM

OOPs ring photo too big? Says less than 500 KB. Well I'll make it smaller.

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#4 grif 678

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Posted 31 March 2018 - 08:58 AM

Hello all,

 

I was happy to find this thread because I just picked up a SP-C102 locally. I know it seems that this thread is dedicated to ED and Fluorite but my new scope is neither of these. Still pretty good, I think but, still just the "Plain Jane" version. My reason for intruding is to ask about the "Newton's Rings" apparent on the objective. Attached are photos of the label and the lens. I have delved into this once in the past and, rightly or wrongly, came to the conclusion that Newton's Rings occur on some individual scopes and are not detrimental to the image and are not worth doing what is necessary to eliminate them.

 

Your opinions would be gratefully considered as I am a relative newcomer to astronomy.

 

Now that I'm into it two more questions come to mind:

1) I didn't include a photo but, my Super Polaris mount has white painted tips on the legs.

    I don't remember seeing this before. Another area where I need education.

 

2) I have never seen a photo of the label on a ED or Fluorite C102.

    Are they just like the label on my scope except saying C102ED and C102F?

 

I would hope to own a fluorite version in the not too distant future.

 

Thanks in advance for your help.

I have had three of the SPC-102 achro's, and they all were wonderful scopes. If you check these out on Excelsis, you will find out on the reviews from owners of the 102, some think that they are fluorites when they look through them. I sold my last 102 achro last year, when I purchased my new to me 102 Fluorite. Due to weather and other hic-cups during the year, have not had a chance to use it yet, but when Jupiter and Mars hit the evening skies, it will come out for sure. I can not wait to see if the Fluorite is as good as every one says, or if it is not that much better than the achro.



#5 Erik Bakker

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Posted 31 March 2018 - 02:21 PM

Distance between the 2 elements is the cause of this and a natural byproduct than can be caused by the close spacing between those 2 elements. Seen it in many doublets, including some FL 102 S fluorites. They should be concentric and aligned with the lens cell though, when viewed on the optical axis. 

 

These SP-C102 achromatic scopes are generally fine performers waytogo.gif


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#6 grif 678

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Posted 31 March 2018 - 06:45 PM

I would not mess with the newton's rings, the best optically one that I had of the three I owned had these rings. I thought it needed to be fixed, An optician told me that it was because that one of the three silver spacers between the lenses was too thin. He sent me some of the replacement  spacers, I replaced them. The rings went away, but so did the greatest optical quality of the three, wished I had never listened to him. That scope had superior images when it had the Newton's rings. 

Later I was reading somewhere that knowledgable observers prefer the scopes with these rings.


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#7 SkyGibbon

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Posted 31 March 2018 - 08:51 PM

There you go, sounds like you may have a good specimen.



#8 AndresEsteban

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Posted 31 March 2018 - 09:30 PM

I would not mess with the newton's rings, the best optically one that I had of the three I owned had these rings. I thought it needed to be fixed, An optician told me that it was because that one of the three silver spacers between the lenses was too thin. He sent me some of the replacement  spacers, I replaced them. The rings went away, but so did the greatest optical quality of the three, wished I had never listened to him. That scope had superior images when it had the Newton's rings. 

Later I was reading somewhere that knowledgable observers prefer the scopes with these rings.

My vintage 76,2mm f/16.4 achromat has Newton rings too! It happens because the lenses of the doublet are very close to each other. Do not change this distance, given by the spacers, unless you know what you're doing! Best advice is: leave the objective alone! 
Remember that not all doublets have lenses so close as to produce Newton rings, therefore the fact that some achros don't have them doesn't mean there's something wrong, ok?

Newton's rings in 3in doublet

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#9 arachman

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Posted 01 April 2018 - 01:04 AM

Thanks for your input. I guess I had it right the first time.  It need some cosmetic work, I'll just do that and be happy with the Newton's Rings and leave the lens cell alone.  Any comments about the SP mount with white tips on the legs?


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#10 Erik Bakker

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Posted 01 April 2018 - 02:43 AM

I would leave any optic alone the performs well. Only a gentle cleaning every now now and then. If an optic performs fine, newton rings are not something that need to be fixed. Just a by-product of narrow spacing. And that spacing is tuned in many a factory to create optimum performance on an individual basis. Hence some performers show them, others don't. But if you start messing with spacing to get rid of newton rings in a fine performer, that performance generally goes down the drain. Only people in the know should tune spacing if need be, of which their are only few.


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#11 HARRISON SCOPES

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Posted 01 April 2018 - 02:53 AM

The only thing to note is they should be central, they can look offside if you look at an angle that is normal. Just get at the correct position and check the pattern is centred. Many objectives have this and it just an interference pattern caused by close proximity.
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#12 sg6

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Posted 01 April 2018 - 05:24 AM

It might just be that the spacers seperating the lens are compacted and so the rear element is in contact with the front element. I would say they shouldn't be in contact. The size of the interior circle would half suggest the contact.

 

Whether or not you want t odo anything about this possibility is up to you. Any chance that the previous owner took the lens apart, cleaned and reassembled. Just they may have made the retaining ring a bit tight or the lens centers are a bit off so the peak of one contacts the dish of the other now.

 

I would guess this is the cause as the rings appear off center. Although the rings themselves are concentric.

 

Your choice I am afraid, I would pull apart and reset/reseat, but I have assorted bits of glass rolling around, so 2 lens is more a fun project to me.



#13 Jeff B

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Posted 01 April 2018 - 09:34 AM

The only thing to note is they should be central, they can look offside if you look at an angle that is normal. Just get at the correct position and check the pattern is centred. Many objectives have this and it just an interference pattern caused by close proximity.

I too noticed that the rings looked off center.

 

I have a 6" F5 Jaegers lens that displays them prominently.  At first, they were off center.  As this is a low power only scope, I really didn't see any impact to the fidelity of the image. 

 

But it bugged me.  So, I loosened the lens retaining ring slightly (not for the faint of heart with this lens) and gently tapped on the side of the cell until the Newton rings were centered in the objective.  I then gently snugged the retaining ring down a bit.  They are now, and have remained, centered. 

 

And I feel better, my astro-nervosa is calm and I'm grateful I avoided the usual "better is the enemy of good" disaster.

 

Stopping my instrument down to 90mm shows a nice airy disk and sharp lunar images though I did not use a stop before I fiddled with the lens so I can't really tell if centering the Newton rings really made any sort of visual difference.

 

If you get nice sharp views now then, take it from someone who often caves to his astro-nervosa, don't fix it.  smile.gif

 

Jeff

Attached Thumbnails

  • Newton Rings.jpg
  • With 90mm Aperture Stop.jpg

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#14 Uwe Pilz

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Posted 02 April 2018 - 12:57 AM

Fraunhofer used Newton rings for collimating his scopes. I don't think you should worry about that.


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#15 aa6ww

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Posted 02 April 2018 - 02:12 AM

 I don't think this thread or rather, forum is dedicated to ED and Fluorite refractors at all. I think the majority of people out here are happy with the simplicity of achromat refractors. I have both, the ED scopes only get used about 5 percent of the time, which is why i find myself always selling them.

 Id love to see your SPC-102 mounted on your mount. Its a potent 4" refractor that many out here appreciate for what it is. 

 

...Ralph 

 

Hello all,

 

I was happy to find this thread because I just picked up a SP-C102 locally. I know it seems that this thread is dedicated to ED and Fluorite but my new scope is neither of these. Still pretty good, I think but, still just the "Plain Jane" version. My reason for intruding is to ask about the "Newton's Rings" apparent on the objective. Attached are photos of the label and the lens. I have delved into this once in the past and, rightly or wrongly, came to the conclusion that Newton's Rings occur on some individual scopes and are not detrimental to the image and are not worth doing what is necessary to eliminate them.

 

Your opinions would be gratefully considered as I am a relative newcomer to astronomy.

 

Now that I'm into it two more questions come to mind:

1) I didn't include a photo but, my Super Polaris mount has white painted tips on the legs.

    I don't remember seeing this before. Another area where I need education.

 

2) I have never seen a photo of the label on a ED or Fluorite C102.

    Are they just like the label on my scope except saying C102ED and C102F?

 

I would hope to own a fluorite version in the not too distant future.

 

Thanks in advance for your help.


Edited by aa6ww, 02 April 2018 - 02:13 AM.


#16 PETER DREW

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Posted 02 April 2018 - 08:00 AM

I have the Vixen 102mm achromat and the 102mm flourite in front of me right now. Both show Newton Rings under monochromatic light. I like to see NR's in an objective if possible, it tells me two things, whether the components are centred and whether there is any pinching which would deform their circularity.  smile.gif


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#17 daquad

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Posted 02 April 2018 - 08:56 AM

I too had a Jaegers 6" f/5 achromat and the Newton's rings were very prominent and perfectly centered.  The Airy stellar discs were textbook perfect.



#18 davidc135

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Posted 02 April 2018 - 09:21 AM

arachman- Looks as if the rings aren't centered. Maybe that's due to an air wedge because the spacers vary in thickness or the ring is too tight, as has been said. If the star test shows any problem it might be relevant. But maybe it doesn't matter.

The two surfaces could be either mutually concave or convex and show fringes. I've just been taking apart and cleaning a 3inch objective. Surfaces 2 and 3 are 10 waves concave with Newton's rings. I should think the bullseye marks where the surfaces are most nearly parallel rather than necessarily closest.

 

David



#19 Peter Besenbruch

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Posted 02 April 2018 - 12:54 PM

My Japanese C102 had Newton's rings as well. The objective was defective. I sent the lens away for refiguring; the lens returned in good shape, and the Newton's rings were still there. Enjoy the scope.



#20 arachman

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Posted 03 April 2018 - 04:00 PM

The fact that the rings are not centered bothers me a bit. I am the type that finds it hard to leave well enough alone. I would love to remove the lens cell and carefully take it apart. I have done this many times before with my 60 mm scopes and have never had any of them come out worse afterwards.  Still thinking about it, I have other scopes to work on. We'll see.

 

Thanks for all your input.


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#21 sg6

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Posted 04 April 2018 - 05:52 AM

My main concern would be that the 2 lens appear to be in contact with each other and eventually that will scratch both lens.

 

There the option that the previous owner has taken the cell apart, cleaned and replaced the front element the wrong way round and so the higher dome is now at the rear and projects more and so contacts the second element. Even with the spacers in place and correct.

 

I have presumed a Fraunhoffer doublet construction.

 

Could also explain the off center rings, they will have stopped screwing it all down at the first conctact and the 2 elements could just not be lever so contact is a bit off to one side.



#22 Tom Masterson

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Posted 04 April 2018 - 09:03 AM

Since the main question has been covered I'll venture a answer to your question about white tripod tips. I suspect it was done to help prevent tripping over the tripod in the dark. I've often commented on the fact that it seems like black is a poor choice of colors to paint tripod feet, but a lot of manufacturers seem to do it. I understand it might look a little odd in the daytime, but at night is when it counts. I put white reflective tips on my tripod feet. Both my 12" and 6" have stout tripods so it hurts when I hit them with my toes in the dark.

 

 Congratulations on the scope. Those are very nice refractors.



#23 hottr6

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Posted 04 April 2018 - 11:51 AM

Any comments about the SP mount with white tips on the legs?

My SP tripod has white tips.  What’s the big deal?  shrug.gif



#24 Peter Besenbruch

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Posted 04 April 2018 - 03:01 PM

My SP tripod has white tips.  What’s the big deal?  shrug.gif

From an aesthetic perspective, white tips are only appropriate when set off with blue and green, flashing LEDs. You know, something tasteful. ;)



#25 Marco1968

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Posted 04 April 2018 - 04:28 PM

Greetings,

 

maybe a bit late but still willing to add my (hopefully interesting) two cents...

 

I own a very early Vixen 102M f=1000mm refractor, one of the first ones imported in Italy at the time of its introduction.

 

My telescope objective shows prominent and centered Newton rings, clearly visible in daylight (see picture below), the cell has three couples of collimating screws.

 

Overall objective and cell looks to me identical to these of the Celestron refractor owned by TO and I am pretty sure that this OTA is in fact a Vixen product like mine, marketed in US by Celestron (hence re-labeled).

 

I had been told by the gentlemen who sold me the telescope that these early Vixen achro doublets were in fact made by Carton. Vixen later changed the 102M introducing an objective lens that no further showed the rings and was mounted in a non collimable cell.

 

About the optical quality, my Vixen achromat is truly excellent with text-book perfect star test and barely noticeable chromatic aberration.

 

As last note, I read that Newton rings were used by past master opticians to very finely tune the spacing and collimation of the objective, their appearance and position being very sensitive to minimum adjustments of the spacers and the collimation screws.

 

If the OT telescope shows a good star test and nice images  I would definitely not try to adjust anything... but it's just me!

 

Enjoy the views!

Marco

 

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  • 20180402_212655-1270x1412.jpg

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