22 replies to this topic

[Psion]

I had a Ronchi tester designed and manufactured for testing DPAC. I use high-quality gratings from Edmund Optics. The device is controlled by Arduino Uno and RGBW LEDs. This allows you to switch colors + white with a single button and easily control their brightness, which is stored in memory. The tester allows for quick checking of optics without replacing LEDs.

Because I also wanted to be able to define the measured spectrum precisely, the device includes a drawer for small Altechna filters with FWHM of 10 nm and 480 nm, 546 nm, 589 nm, and 656 nm.

https://www.edmundop...s-slides/12117/

 

https://youtube.com/...I?feature=share

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[GalaxyPiper]

What you have there is very interesting, however...Astrophotography is not in a laboratory setting.

The sky conditions aways change requiring the user to very timing on each filter to suit their needs to get the results they want.

 

So using filters as some sort of dialed in by-the-numbers session will never be accomplished.

They only thing with this device I can see to be used for is for evaluation the "quality" of each filter and perhaps relaying that here or create a "Blue Book" of filters for the end user.

 

Wratten numbers created early in the twentieth century, last millennium, and the amount of light measured, or filtered, recorded.

 

So this would be for Quality testing of said filters. Still a valid effort.

[mikef0924]

Thanks for sharing your design. I am setting up a DPAC on my test bench and might do something similar.

Your approach with the multi color LED and line filters is interesting. Do you any closeups of the LED/ronchi housing to share?

Mike

Edited by mikef0924, 23 June 2025 - 08:55 AM.

[peleuba]

What you have there is very interesting, however...Astrophotography is not in a laboratory setting.

The sky conditions aways change requiring the user to very timing on each filter to suit their needs to get the results they want.

 

So using filters as some sort of dialed in by-the-numbers session will never be accomplished.

They only thing with this device I can see to be used for is for evaluation the "quality" of each filter and perhaps relaying that here or create a "Blue Book" of filters for the end user.

 

Wratten numbers created early in the twentieth century, last millennium, and the amount of light measured, or filtered, recorded.

 

So this would be for Quality testing of said filters. Still a valid effort.

 

 

I don't understand this post, at all.   I think you're missing the point.  Or, I missed the point of your post (which is certainly possible!). In either case I will clarify my POV and maybe we can hash this out...

 

This tester that @Psion has developed, the LED he uses as well as the filters have nothing to do with astrophotography, sky conditions, or visual observing.  Its a Ronchi tester to be used with an optical flat set up in autocollimation (aka "DPAC").  Its purpose is to bench test refractors.  The different LED's shine at specific wavelengths so the test results can be noted and compared.  Due to the wave nature of light - ie. the different "sizes/lengths" of the waves (long vs. short) - these differing wavelengths behave differently when traversing through a lens.  Further, aberrations in the lens appear will appear more or less severe depending upon wavelength.  This tool will easily demonstrate this and will allow for an accurate, qualitative assessment of the "goodness" of the lens under test.

 

CN has an entire library of tests using a similar methodology HERE.   

Edited by peleuba, 23 June 2025 - 11:26 AM.

[Psion]

I don't understand it either, it almost looks like a response from AI

[Jeff B]

I had a Ronchi tester designed and manufactured for testing DPAC. I use high-quality gratings from Edmund Optics. The device is controlled by Arduino Uno and RGBW LEDs. This allows you to switch colors + white with a single button and easily control their brightness, which is stored in memory. The tester allows for quick checking of optics without replacing LEDs.

Because I also wanted to be able to define the measured spectrum precisely, the device includes a drawer for small Altechna filters with FWHM of 10 nm and 480 nm, 546 nm, 589 nm, and 656 nm.

https://www.edmundop...s-slides/12117/

 

https://youtube.com/...I?feature=share

Love it and I like knowing the light frequencies involved as opposed to my having to guess what the processing software uses to isolate the color channels of my white light "master images.

 

Pretty cool sir.

 

Jeff

[Psion]

Thanks for sharing your design. I am setting up a DPAC on my test bench and might do something similar.

Your approach with the multi color LED and line filters is interesting. Do you any closeups of the LED/ronchi housing to share?

Mike

We used an SK6812 LED from a strip, which also includes a driver for controlling it.

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[GalaxyPiper]

I don't understand this post, at all.   I think you're missing the point.  Or, I missed the point of your post (which is certainly possible!). In either case I will clarify my POV and maybe we can hash this out...

 

This tester that @Psion has developed, the LED he uses as well as the filters have nothing to do with astrophotography, sky conditions, or visual observing.  Its a Ronchi tester to be used with an optical flat set up in autocollimation (aka "DPAC").  Its purpose is to bench test refractors.  The different LED's shine at specific wavelengths so the test results can be noted and compared.  Due to the wave nature of light ie. the different "sizes/lengths" of the waves (long vs. short) different wavelengths behave differently when traversing through a lens.  Further, aberrations appear differently (more/less severe) depending upon wavelength.  This tool will easily demonstrate this and will allow for an accurate,  qualitative assessment of the "goodness" of the lens under test.

 

CN has an entire library of tests using a similar methodology HERE.   

Thanks for giving me better background on this. I was not trying to mislead at all.

My post was because I was thinking of application to a astrophotography setting only.

Collimation was not what I was thinking about, auto or otherwise. Just end user.

Not everyone knows what DPAC is. It's these acronyms that are only for the initiated that are not explained or expanded on.

[Psion]

Love it and I like knowing the light frequencies involved as opposed to my having to guess what the processing software uses to isolate the color channels of my white light "master images.

 

Pretty cool sir.

 

Jeff

Thank you Jeff!

 

For the first version, I measured the peak colors of the RGB LEDs with a spectrometer as follows:
R: 630 nm
G: 510 nm
B: 450 nm
I will work on this version RGBW in the evening.

Edited by Psion, 23 June 2025 - 10:17 AM.

[Psion]

Thanks for giving me better background on this. I was not trying to mislead at all.

My post was because I was thinking of application to a astrophotography setting only.

Collimation was not what I was thinking about, auto or otherwise. Just end user.

Not everyone knows what DPAC is. It's these acronyms that are only for the initiated that are not explained or expanded on.

The very first topic in the Refractor thread is called:

 

Double-Pass Ronchi Testing (a.k.a. DPAC) - .....

[peleuba]

Not everyone knows what DPAC is. It's these acronyms that are only for the initiated that are not explained or expanded on.

 

No worries.  I am glad you brought it up as we all learn like this. 

 

 

<<<standing on soap box>>>

 

 

I hate the Acronym "DPAC" because it does not describe the optical test. 

 

DPAC = Double Pass Auto Collimation.  And it literally means double pass - double pass.   Its a redundant term that does NOT describe anything about the test; it only speaks to the manner in which its performed.  But, its been called DPAC by ATM's and opticians for many years, longer then I have been alive.  

 

When a test is performed in Autocollimation, by definition, its being performed in double pass.  Meaning that the light passes through the test article twice.  The benefit of this is that's its twice as sensitive as a normal single pass test.  Aberrations are easier to see and quantify.

 

In my mind, the correct way to describe this optical test is:  the Ronchi Autocollimation test or the Ronchi Double-Pass test.  Ronchi being the test and Autocollimation (or double-pass) being the method the test employs. 

Edited by peleuba, 23 June 2025 - 01:53 PM.

[GalaxyPiper]

Every time I hear or read "DPAC" I think of that rapper.

 

DPAC Shakur...

 

Oh wait, that's Tupac Shakur...unless I am seeing Double...

[Jeff B]

Every time I hear or read "DPAC" I think of that rapper.

 

DPAC Shakur...

 

Oh wait, that's Tupac Shakur...unless I am seeing Double...

Only in Passing..... 

[Cbaxter]

Only in Passing.....

🤣 I like a good pun.

Edited by Cbaxter, 23 June 2025 - 12:51 PM.

[Cbaxter]

Very cool, OP. I think this sort of direction for autocollimation ronchi testing will help improve consistency across tests on the same bench.

[AZStarGuy]

This is one of the more unique and innovative things I've seen here on CN!!  Thanks for posting -  

[peleuba]

Collimation was not what I was thinking about, auto or otherwise. Just end user.

Not everyone knows what DPAC is. It's these acronyms that are only for the initiated that are not explained or expanded on.

 

 

Optics can be very confusing, for sure... 

 

One thing I wanted to mention and I forgot to do so earlier - the term Collimation, in this instance, has nothing to do with optical alignment like when "collimating" a Newtonian.  Here, collimation is describing one aspect of the nature of light whether a point source, generated from an LED, or whatever.   Basically, when one speaks of collimated light, they are saying that the rays are parallel. 

Edited by peleuba, 23 June 2025 - 04:40 PM.

[drprovi57]

I had a Ronchi tester designed and manufactured for testing DPAC. I use high-quality gratings from Edmund Optics. The device is controlled by Arduino Uno and RGBW LEDs. This allows you to switch colors + white with a single button and easily control their brightness, which is stored in memory. The tester allows for quick checking of optics without replacing LEDs.

Because I also wanted to be able to define the measured spectrum precisely, the device includes a drawer for small Altechna filters with FWHM of 10 nm and 480 nm, 546 nm, 589 nm, and 656 nm.

https://www.edmundop...s-slides/12117/

 

https://youtube.com/...I?feature=share

Can you share the design details?

 

Thanks

[Psion]

Do you mean complete production documentation, parts list, and software?

[Psion]

I'm slowly getting closer to the final product. I'll do some more tests and then it'll be done.

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[rainycityastro]

Thanks Psion for your design. Would it be possible for you to share your 3d model when you are ready, either in Fusion or OpenSCAD or whatever format you are using?

[Psion]

Yes, I will have STL or FCStd.

[Psion]

The uncoated 200 mm mirror has arrived from USA, PV 0.071 (lambda/14), Strehl 0.98. I am curious to see the test results now.