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New lens making method


Froeng

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10 minutes ago, vlaiv said:

I wonder when we will see first "plastic" lens telescope?

We already have eyepieces that don't contain glass but rather some sort of plastic material / polymers, right?

 


I remember seeing perspex lenses made by the legendary John Wall (inventor of the Crayford Focuser) at BAA meetings in the 1970s: https://adsabs.harvard.edu/full/1977JBAA...88...28W

Inability to obtain a fine polish was the main problem I think

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27 minutes ago, Ags said:

Not the problem here - with this technique, the polymer lenses are not polished at all! The smooth surfaces are formed by surface tension.

I wonder how consistent the figuring and polishing accuracy achieved by surface tension is across the whole diameter of the lens at the levels that we astronomers want ?

I'm not trying to be skeptical, it's just that astronomy is so demanding !

 

 

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One of the big potential problems with plastic or polymer lenses is that as they age they tend to yellow and darken. 

BTW plastic is a specific type of polymer made up of long chain polymers  whereas polymer is made up of smaller more uniform molecules. All plastics are polymers bit not not all polymers are plastic.

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15 hours ago, johninderby said:

One of the big potential problems with plastic or polymer lenses is that as they age they tend to yellow and darken. 

BTW plastic is a specific type of polymer made up of long chain polymers  whereas polymer is made up of smaller more uniform molecules. All plastics are polymers bit not not all polymers are plastic.

"Plastic" refers to the type of deformation it can undergo. Plastic deformation is where the material stays in the same shape after being deformed (eg when putting marzipan over a cake, something I've just done) as distinct from Elastic deformation where the material springs back into shape after being deformed.

There are thermoplastics (Mst of the common types used in packaging or in FDM printing) and thermosetting, where the material cannot be melted again without decomposition, eg epoxy resins. There are also photopolymers, eg in SLA printing.

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2 minutes ago, vlaiv said:

Why? I really like the idea - 100% 3d printed telescope :D - even lens.

It won't be very useful telescope, but I find it interesting project.

Sanding it? If he's modeling it from am existing lens, then molding a pitch lap would be best.

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Yes, I know. He said it was rather rough (More so than he intended), my beef was with his methods, just grabbing the lens and running emery cloth over it, then buffing on a wheel. Not gonna have 1/20th wave and 099 strehl!

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2 minutes ago, DaveS said:

Not gonna have 1/20th wave and 099 strehl!

That is for sure, but I do wonder if we could make a scope to throw up any sort of image - like moon at x15 magnification that shows at least largest craters?

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