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Tester scope?

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6 replies to this topic

#1 Stargazer

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Posted 25 March 2020 - 08:48 PM

Hi All, 

 

   I have a couple lenses here and want to make a mag scope to take better images well testing with 

Ronchi or Foucault but I am perplexed to say the least...

 

 Can someone please help me understand how this is suppose to work.I have tried holding to two lenses

behind the screen but that only magnifies the screen, now if I hold one in front of and the other behind the

screen then bingo it works and works well from what I could see.

 

I take it I need to make a rig with the Ronchi grating in between the two lenses but how does one know where

to place the grating or is it a trial and error kind of approach to working this out or am I totally off base with this.

 

How do you set up for it?

 

Thanks

 

 


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#2 BGRE

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Posted 25 March 2020 - 10:37 PM

No don't do that, as you will only end up analysing the aberrations of the combination of the test surface and the first lens.
The lenses should be arranged to form a Keplerian telescope (like a finder scope and eyepiece) placed between the eye (or camera) and the grating.
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#3 MKV

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Posted 26 March 2020 - 12:28 AM

The lenses should be arranged to form a Keplerian telescope (like a finder scope and eyepiece) placed between the eye (or camera) and the grating.

waytogo.gif

 

keplerian_3.JPG

 

Here's an example of a 3X Keplerian using Edmung Optics 25 mm stock cemented achromats. 

 

keplerian.png

Trace wavelngth 632.8 nm

 

A singe (monocular) opera glass will do just as well.


Edited by MKV, 26 March 2020 - 05:24 AM.

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#4 Pinbout

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Posted 26 March 2020 - 07:17 AM

I got a cemented doublet 32x78 and press fit it into pvc plumbing with a 32mm plossl eyepiece - the eyepiece needs a little tape on the barrel but it’s pretty close 

 

0D5B76EC-2BAF-458B-9E64-EBD573468C65.jpeg
 

push up behind ronchi/ke

 

B6CAD362-3846-4BBD-A71A-0447BB2B5530.jpeg


Edited by Pinbout, 26 March 2020 - 08:27 AM.

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#5 Stargazer

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Posted 26 March 2020 - 10:01 AM

Nice Danny,

    

  This is what I have from surplus shed...

 1 Cemented doublet achromat, 25.4mm diameter by 87mm focal length. Coated,

got it last year so all I need to do is set say a 32mm eyepiece at the right distance and it will work?

will head off to the hardware store and find a piece of pipe if so.

 

Thanks



#6 Pinbout

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Posted 26 March 2020 - 10:14 AM

Nice Danny,

    

  This is what I have from surplus shed...

 1 Cemented doublet achromat, 25.4mm diameter by 87mm focal length. Coated,

got it last year so all I need to do is set say a 32mm eyepiece at the right distance and it will work?

will head off to the hardware store and find a piece of pipe if so.

 

Thanks

I'm right handed so...

 

hold the doublet in your left hand and 25-32mm plossl in your right and then look thru the plossl and adj distances till you can focus on something.

 

pretty much it.


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#7 Stargazer

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Posted 29 March 2020 - 10:20 AM

Hi all,

Finally got it done, not the prettiest but will do the job.

 

tester scope.jpg

 

 It consist of a 32 mm eyepiece a 25.4 achromat lens,dollar store flashlight, a rigged piece of plastic, elastic

bands and tape,the nice part is the 32 mm eyepiece threads onto the top of the flashlight, the plastic was

needed because it was a 1/4" short in overall length but the plastic slides on the barrel of light casing to focus,

works great, and yes I can now see the pattern of the Ronchi on the mirror smile.gif.

 

 Now to make a rig to hold it behind the tester.


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