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Can a usable lens be made from thick glass fused from several layers of thinner glass?

ATM lens making optics refractor
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#1 gbambo

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Posted 10 January 2017 - 08:42 PM

I need to make a full aperture lens that is thicker than the glass available to me.

 

So I suppose one solution is to fuse two thick sheets of plate glass together in a kiln. This works well for a front surface mirror, but I wonder about a refractive element where the fused boundary has light moving through it. Does anyone know if the fused boundary zone will be a source of significant aberrations?

 

I ask, because I am trying to assemble a telescope that calls for a lens thicker than any affordable glass, but less than twice as thick as what I have.

 



#2 syscore

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Posted 10 January 2017 - 09:50 PM

This is probably a dumb question, but how hard is it to melt the glass and make your own blank?



#3 gregj888

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Posted 10 January 2017 - 10:07 PM

That's what a cemented achromat is but for different glass types.  There are several types of cement including Canadian Balsam (Surplus Shed did have some).  Can also use oil for the interface.  Optical supply houses sell better "stuff".

 

If you haven't, check for blanks at Surplus Shed as well as lenses to regrind into what you want.

 

Greg



#4 MKV

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Posted 10 January 2017 - 10:09 PM

I need to make a full aperture lens that is thicker than the glass available to me.

 

So I suppose one solution is to fuse two thick sheets of plate glass together in a kiln. This works well for a front surface mirror, but I wonder about a refractive element where the fused boundary has light moving through it. Does anyone know if the fused boundary zone will be a source of significant aberrations?

 

I ask, because I am trying to assemble a telescope that calls for a lens thicker than any affordable glass, but less than twice as thick as what I have.

Do you have melt data for the glasses? The problem is also how homogeneous the mixture would be. Glass melts have to be accurate to a minimum of five decimal places of refractive index. I doubt you can achieve that in your kiln. 

 

Mladen



#5 DrPete4155

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Posted 10 January 2017 - 10:57 PM

You don't want to just fuse the 2 pieces together, you need them melted.

Then you will have to do a decent job of annealing the glass again.

If your talking about plate glass how thick do you need? I have 1" thick.

Also getting the glass into a crucible that will handle the temperature isn't going to be easy.

Most fire brick only handle up to 3000 degrees F and you will find it may fail. I am talking about

your kiln lining now not the glass.

Lot's of info on the net, most of my data I have is from melting metals and making molds.

Good luck



#6 GJJim

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Posted 11 January 2017 - 12:06 AM

It might work as a condenser lens for a projector. A telescope objective requires extreme homogeneity and layering sheet glass would not achieve that.




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