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Refractor Doublet Lens Spacer Material

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45 replies to this topic

#26 Kasmos

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Posted 08 February 2020 - 03:06 AM

How do you folks who use a non-adhesive foil, make them stay in place? Fold over and tape to edge?

 

Also, What cement or technique do you use for re-adhering loose original spacers? 

 

I don't have a way to measure them, but the spacers in my APL Shrine Manon seemed thicker than all the other lenses I've taken apart and are the only ones I remember seeing (so far), that are folded over the edge of the lens.


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#27 rcwolpert

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Posted 08 February 2020 - 04:55 PM

See my posting in the third message above for links for the Cricut® Adhesive Foil.

 

As Stelphen said, I've also found that this is really the best. I gave away all of mine except for one small piece in case I ever need to redo spacing on a refractor.

 

Here's where you can get it (besides Michaels):  https://www.amazon.c...,aps,231&sr=8-5


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#28 Kasmos

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Posted 08 February 2020 - 11:55 PM

As Stelphen said, I've also found that this is really the best. I gave away all of mine except for one small piece in case I ever need to redo spacing on a refractor.

 

Here's where you can get it (besides Michaels):  https://www.amazon.c...,aps,231&sr=8-5

Robert,

Thanks to you I was able to repair a few objectives whos spacers were either missing, crumpled, or have lost their adhesive.

And very likely 3 more lenses in the near future.

Thank you again!


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#29 rcwolpert

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Posted 09 February 2020 - 05:04 PM

Robert,

Thanks to you I was able to repair a few objectives whos spacers were either missing, crumpled, or have lost their adhesive.

And very likely 3 more lenses in the near future.

Thank you again!

My pleasure! So glad the material was put to good use!


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#30 Longislandsky

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Posted 09 February 2020 - 06:55 PM

Thin edge element toward the stars. The faces that mate have the same curve, just opposite. Generally the shallower curve faces the sky, the steeper curve is the mating curve.



#31 clamchip

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Posted 09 February 2020 - 06:55 PM

Something to watch when making spacers is the cutting, whether done with a knife or

scissors will leave a bur making the spacer thicker.

I flatten mine in the vise to remove this bur.

I use a micrometer to measure the original spacers and my new ones. The measuring

surface of a micrometer is perfect for our spacers.

Robert

 

Scan0002.jpg


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#32 Longislandsky

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Posted 09 February 2020 - 06:57 PM

I double Checked today thin lense was facing stars large lense the focuser. I noticed a staight line drawn on the side does the twisting of the lenses horizontally have any effect on what you view or could the foil tape be to thick you think?

#33 Jeff B

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Posted 11 February 2020 - 10:43 AM

A more generic question.  In general, how does changing the spacing between elements in an achromat, change the SA corrections and longitudinal "CA" for RGB?

 

Jeff



#34 Terra Nova

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Posted 11 February 2020 - 11:05 AM

A more generic question.  In general, how does changing the spacing between elements in an achromat, change the SA corrections and longitudinal "CA" for RGB?

 

Jeff

 

http://hyperphysics....oopt/aber2.html

 

The last section allows solving for proper spacing.


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#35 deepwoods1

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Posted 11 February 2020 - 12:40 PM

If anyone wants some Cricut foil, I’d be happy to send some out. No need for all of us to pay $20 for a lifetimes supply. Just PM me!


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#36 DAVIDG

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Posted 11 February 2020 - 01:15 PM

A more generic question.  In general, how does changing the spacing between elements in an achromat, change the SA corrections and longitudinal "CA" for RGB?

 

Jeff

 Just understand that both spherical aberration and  color correct change at the same time but by different amounts with spacer thickness. So you need to test the lens in red, green and blue light to determine if a chance in spacer thickness  has made a positive difference. If you only test in one wavelengths, things may  look like they approved but can be worse in the other wavelengths. So I would take with a bit skepticism those that claim they have improved the correction of lens by changing the spacer thick unless they provide test data in all three wavelengths.

 

                        - Dave  



#37 G-Tower

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Posted 11 February 2020 - 05:06 PM

So, how is the spacing calculated and controlled on cemented doublet or triplet? 



#38 Russell Smith

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Posted 12 February 2020 - 08:31 PM

How do you folks who use a non-adhesive foil, make them stay in place? Fold over and tape to edge?

 

Also, What cement or technique do you use for re-adhering loose original spacers? 

 

I don't have a way to measure them, but the spacers in my APL Shrine Manon seemed thicker than all the other lenses I've taken apart and are the only ones I remember seeing (so far), that are folded over the edge of the lens.

The spacers on my H.O.C. Mayflower also are folded over the edge. One was crumpled and I flattened it out.

I'll need to buy a micrometer to check thickness. Also, will use a green laser and paper to see what I get there. Hopefully I will have time this weekend. 

Interesting and useful thread.

P.S. Thanks Deepwoods


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#39 Russell Smith

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Posted 12 February 2020 - 08:46 PM

http://hyperphysics....oopt/aber2.html

 

The last section allows solving for proper spacing.

So if my doublet is at it's best I'll see a hint of green?

Assuming no coatings interference?



#40 clamchip

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Posted 12 February 2020 - 08:59 PM

For micrometers my favorite is what is called a 'Speed Mike' or 'direct read' these are

nice because you don't need to think, you just look at the numbers in the little windows.

My favorite is a vintage Slocomb, nurse Mendy is showing it off here:

 

post-50896-0-18583200-1427324067_thumb.jpg


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#41 clamchip

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Posted 12 February 2020 - 09:04 PM

So if my doublet is at it's best I'll see a hint of green?

Assuming no coatings interference?

I'd say if everything is correct and focusing on a object at infinity (a couple miles away) at focus

should be clean with no color.

Just slightly to one side of focus will show yellow green, and the same distance other side of focus

will show a red purple fringe.

 

Robert



#42 Russell Smith

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Posted 12 February 2020 - 09:04 PM

For micrometers my favorite is what is called a 'Speed Mike' or 'direct read' these are

nice because you don't need to think, you just look at the numbers in the little windows.

My favorite is a vintage Slocomb, nurse Mendy is showing it off here:

 

attachicon.gifpost-50896-0-18583200-1427324067_thumb.jpg

Yes. Old school. 

Thanks Nurse Mendy. wink.png


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#43 Longislandsky

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Posted 13 February 2020 - 11:37 PM

So I did The tape put them back in the same spots. they old tape left marks. Everything is put back exactly in reverse and I have A halo effect when viewing in day light or night time that looks like cracked lense. ( best way I can Describe) you can see the image but it’s got light interference. Anyone know what I’m talking about and how can I do A process of elimination to start diagnosis and get back to using my scope

#44 strdst

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Posted 14 February 2020 - 12:23 AM

Halos make me think of angels... and also objective elements not in their proper orientation. It is easier (more possibilites) to mis-match the lenses. If you are sure you put them back as found perhaps someone before you wasn't so sure :)

#45 Longislandsky

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Posted 14 February 2020 - 03:13 AM

So after I did The foil and replaces missing and old pieces I’m still getting light distortion. The image comes thru but the light looks like it’s going outward... i have a reflector that has a corrector lense in the focuser and to colimanate u must remove this lense. When I put It back the first time I did It backwards and the images where quite similar. Could it be I put The thicker of the two doublet lenses in backwards upon install????

#46 Kasmos

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Posted 14 February 2020 - 04:23 AM

My Swift 839 was missing it's spacers so I installed some and somehow I put the crown (front), lens in backwards. When I looked at Jupiter or a bright star they had a really bright halo around them. I took it out and thought I had corrected it, but somehow put it in backwards again! Checking it one more time made it right.

 

The steeper curve of the crown lens faces the concave of flint lens.The shallower curve faces the sky. On longer focal length lenses it sometimes can be really hard to tell what side has more curve. Therefore, do the tilt test. Carefully place the lens on a flat surface (I tape down the four corners of a lens tissues to rest it on), gently press on the edge of the lens and observe how much it tilts. Flip it and check the other side. The side that tilts more has more curve.   


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