Vixen 102M primary lens marks?

[inspectapart]

Posted 22nd April 2009 at 09:28 PM by inspectapart

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Can someone tell me if they have ever seen a primary lens with several perfect concentric circles in the centre of the front lens? The circles cover about a 10mm in diameter

My Vixen 102m has these markings. They are very faint and look as though they are part of the coating or an integral part of the lens.

They are not easy to see and I don`t think they are on the surface. More like in the coating. The scope gives excellent views and as far as I can see, good refraction patterns in and out of focus. so could this be a coating fault?

Many thanks, Bob

[John]

I've owned a Vixen 102M and now a Vixen ED102SS and neither of those had marks like that on their lenses. Are they actually marks or just patterns of refracted light ?.

Can you see them if you look from the rear element through and out the front element ? (you will need to remove the lens cell from the tube to do this).

John

[inspectapart]

Thanks John. The marks do look a bit like refracted light I suppose, but they are definitely there. I haven`t checked if they can be seen from the eyepiece end of the tube. They can`t be seen when using the scope. I don`t want to remove the primary lens cell because the scope seems very well collimated, and I don`t want to disturb this.

[Grotemobile]

Hi ,

Iv got a Vixen 102mm & the lens is clear .

No marks at all .Perhaps yours has got a later

type of lense .

Steve

[inspectapart]

i HAD ANOTHER LOOK TODAY. iT LOOKS LIKE THE VERY CENTRE OF THE LENS HAS A DARK SPOT AROUND 5MM THEN THERE ARE SEVERAL CONCENTRIC RINGS GETTING FAINTER AND THINNER TO ABOUT 15MM DIAMETER. STRANGE AS IT DOESN`T AFFECT THE VIEW. MIND YOU, IVE NOT LOOKED THROUGH ANOTHER 102M.

[John]

i HAD ANOTHER LOOK TODAY. iT LOOKS LIKE THE VERY CENTRE OF THE LENS HAS A DARK SPOT AROUND 5MM THEN THERE ARE SEVERAL CONCENTRIC RINGS GETTING FAINTER AND THINNER TO ABOUT 15MM DIAMETER. STRANGE AS IT DOESN`T AFFECT THE VIEW. MIND YOU, IVE NOT LOOKED THROUGH ANOTHER 102M.

I wonder if the 2 lens elements are touching in the centre ?. They are separated by 3 small pieces of foil which you can see spaced equally out around the edge of the lens. I guess it's possible that one or more of those could be out of position so that the lens elements are in contact in the centre.

John

[canuck]

Posted 22nd April 2009 at 09:28 PM by inspectapart

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Can someone tell me if they have ever seen a primary lens with several perfect concentric circles in the centre of the front lens?

Do you mean Newton's rings? Newton's rings - Wikipedia, the free encyclopedia

I would expect to see them in a Vixen refractor like yours. If that's what you're seeing, don't try and remove them...they're a good thing.

[inspectapart]

Thank you so much Canuck !!!! I checked the Wikipedia link you gave me, and lo and behold.....These are indeed the very same marks. (NEWTONS RINGS). If these are a good thing, I can`t understand why they don`t appear on other Vixen 102m scopes??

Thanks again for your help. I thought for a moment that I`d bought a lemon. I knew the view through my scope was good even with the marks. I just didn`t know if it should be better without marks. Many thanks, Bob.

No, I haven`t tried to remove them.

[buddyarrows]

Hi, IMHO the interference is caused when two surfaces touch according to Wikipedia quote, "alternating light and dark rings centred at the point of contact", this may mean that one or possibly more of the lens separators have dropped or the lens cell retaining ring is two tight. I had a 2" refractor some years ago that had the separators missing and gave this distortion. Cured with thin a plastic ring fitted between the lenses.

Hope this is of value.

Clear skies

David

[roundycat]

If they are Newton's rings I believe they will be coloured, like oil on water. It is most likely some kind of drying mark left over from manufacture. If you can only see them by reflected light ignore them.

Dennis

[inspectapart]

Thanks for that. There is no colour to the rings and I can only see them as you say; as reflected patterns. I really don`t fancy re-collimating the scope as the views through it are very good.

Bob

[acey]

I would agree they're Newton's rings and the reason you don't see colour is because of the coatings. The lens elements must be touching (or very close) at the centre. If you've done a star test and are happy with things then leave well alone, otherwise get a professional to look at it.

[inspectapart]

I spoke to a technician at Orion Optics today. He said that these rings are fine and are to be expected in a refractor of this type, and do not affect the viewing in any way.

So, I`m happy with that.

Many thanks for all your replies and info.

"If you can learn something every day you should be pretty smart by the time you get dementia!!"

bob.