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Double-Pass Ronchi Testing (a.k.a. DPAC) of APM APO SD 152mm F/6

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#1 Howard_C

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Posted 03 April 2024 - 09:33 AM

Here is my test bench (messy to add authenticity):

 

DSC_0448 Cropped  Resized 3.jpg

 

For testing this scope I used  my new coated 12.5” flat.  The flat holder and stand were custom made by Mark at Astrogoods.  Adjustment bolts on the back of the flat holder make it a snap to fine tune alignment of the flat with the scope!  The screen/LED holder in the focuser (made by CN member Moshen) holds the 3mm RGB 4-lead LED, which is connected to the home brew switch box (on the white board) which has a separate dimmer control for each color.  There’s a separate screen/LED holder for the white LED.  The power supply is my bench supply, but a cheap wall wart works just as well.  My old World Books temporarily taken out of retirement hold the scope, and a Nikon D40 with a 18-55mm lens (set at 55mm) was used to take the pics.  Paint.net was used to package the images.

 

Here are my results (each row shows inside of focus, at focus, outside of focus images):

 

Collage 2.jpg

 

My interpretation of the pics is that the scope is moderately overcorrected in blue, with lesser overcorrection in green, and slightly undercorrection in red.  Based on that, my guess is that best correction is in between in green and red, in the yellow range.  Overall correction seems to be pretty good for a 6” f/6. The in-focus pics show a zone in the center of the objective, and at the edge at 1 o’clock and 6 o’clock.  I don't see any turned edge. Any ideas what caused the zones at 1 o’clock and 6 o’clock?

 

During use, I don’t notice CA at low to moderate magnification, but it is there at high magnification, for example when using my XW 3.5 EP.  Overall I’m satisfied with the scope, considering the aperture and short focal length.

 

 I'm still a beginner in DPAC testing and have a great deal still to learn, so your comments and recommendations are especially welcome!

 

Thanks,
Howard

 

 


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#2 Jeff B

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Posted 03 April 2024 - 09:55 AM

Here is my test bench (messy to add authenticity):

 

attachicon.gif DSC_0448 Cropped Resized 3.jpg

 

For testing this scope I used  my new coated 12.5” flat.  The flat holder and stand were custom made by Mark at Astrogoods.  Adjustment bolts on the back of the flat holder make it a snap to fine tune alignment of the flat with the scope!  The screen/LED holder in the focuser (made by CN member Moshen) holds the 3mm RGB 4-lead LED, which is connected to the home brew switch box (on the white board) which has a separate dimmer control for each color.  There’s a separate screen/LED holder for the white LED.  The power supply is my bench supply, but a cheap wall wart works just as well.  My old World Books temporarily taken out of retirement hold the scope, and a Nikon D40 with a 18-55mm lens (set at 55mm) was used to take the pics.  Paint.net was used to package the images.

 

Here are my results (each row shows inside of focus, at focus, outside of focus images):

 

attachicon.gif Collage 2.jpg

 

My interpretation of the pics is that the scope is moderately overcorrected in blue, with lesser overcorrection in green, and slightly undercorrection in red.  Based on that, my guess is that best correction is in between in green and red, in the yellow range.  Overall correction seems to be pretty good for a 6” f/6. The in-focus pics show a zone in the center of the objective, and at the edge at 1 o’clock and 6 o’clock.  I don't see any turned edge. Any ideas what caused the zones at 1 o’clock and 6 o’clock?

 

During use, I don’t notice CA at low to moderate magnification, but it is there at high magnification, for example when using my XW 3.5 EP.  Overall I’m satisfied with the scope, considering the aperture and short focal length.

 

 I'm still a beginner in DPAC testing and have a great deal still to learn, so your comments and recommendations are especially welcome!

 

Thanks,
Howard

Well done Howard.

 

I'm impressed both with the scope and your test set up & images.

 

This is a very fast, large ED doublet with decent performance and seems to follow a recent pattern I've noticed with Asian sourced objectives being a bit over corrected in green with best correction towards orange/red with the blue a bit off in both focus and SA.  But I find that a nice visual balance.

 

Visually, do you notice any coma and/or astigmatism?

 

Also, if I may suggest, try stopping it down the 5" and retest  The center zone will be more pronounced but the result might be interesting.

 

Well done!

 

Jeff

 

I f


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#3 peleuba

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Posted 03 April 2024 - 10:04 AM

Very nice.   I have a question about your LED...  Is it a single LED "module" comprised of four colors where you can turn on/off one color at a time?  You mention a "4 lead LED" and I am having trouble visualizing this.   I use a similar setup as yours, but have individual LED's for each wavelength (color). 

 

The scope looks decently good.   And, the Nikon D40 is an oldie but a goodie.  Which lens did you use and did you hand hold it, or place it on a tripod? 

 

Thanks.  Nice job.


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#4 fate187

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Posted 03 April 2024 - 10:25 AM

Is this the doublet? Aren't there like two prototypes 150 f/6 out there as well? Thank you for testing and posting Howard bow.gif


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#5 Howard_C

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Posted 03 April 2024 - 10:40 AM


Visually, do you notice any coma and/or astigmatism?

 

Also, if I may suggest, try stopping it down the 5" and retest  The center zone will be more pronounced but the result might be interesting.

 

Thanks Jeff, I will do that!  Should be interesting.  I have not noticed astigmatism, but on the other hand I have some uncorrected astigmatism in one eye, so may not be able to notice astigmatism from the scope!  (-:

 

Thanks,

Howard



#6 Howard_C

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Posted 03 April 2024 - 10:48 AM

Very nice.   I have a question about your LED...  Is it a single LED "module" comprised of four colors where you can turn on/off one color at a time?  You mention a "4 lead LED" and I am having trouble visualizing this.   I use a similar setup as yours, but have individual LED's for each wavelength (color). 

 

The scope looks decently good.   And, the Nikon D40 is an oldie but a goodie.  Which lens did you use and did you hand hold it, or place it on a tripod? 

 

Thanks.  Nice job.

Hi Paul -

 

The RGB LED has individual leads for R, G, and B, plus a ground lead.  They are connected to the switch in the center of the box, and allow me to turn individual colors on/off without disconnecting individual R, G, and B LED holders on the focuser (I still have a separate White LED holder though).  Each LED (W, R, G, and B) has a separate pot (see the 4 knobs on the outside of the control box) connected to it, so I don’t have to adjust brightness every time I switch between LEDs.  This box has saved me lots of time and makes my pics more consistent. 

 

I use the 18-55mm Nikon lens that came with the camera, and for taking these pics it was set at 55mm.  The scope sits on top of a stack of my ancient World Books, and the ancient camera sits on top of my ancient Webster’s Unabridged.  They complement each other very nicely!  (-

 

Thanks for your comments! 

 

Howard


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#7 Jeff B

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Posted 03 April 2024 - 10:52 AM

I believe Denis of bno-viewer fame has one of these too and really likes it.  It's "bino-friendly" I believe, which is one of Paul's favorite visual accessories (wink.gif ).

 

Jeff



#8 Howard_C

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Posted 03 April 2024 - 10:55 AM

Is this the doublet? Aren't there like two prototypes 150 f/6 out there as well? Thank you for testing and posting Howard bow.gif

Hi Michael -

 

Yes, it's the doublet.  I'm not near the scope at the moment, but I believe it is SN#2 or 3, so I'm sure it was one of the first sold.

 

Thanks,

Howard


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#9 denis0007dl

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Posted 03 April 2024 - 10:57 AM

Here is my test bench (messy to add authenticity):

 

attachicon.gif DSC_0448 Cropped Resized 3.jpg

 

For testing this scope I used  my new coated 12.5” flat.  The flat holder and stand were custom made by Mark at Astrogoods.  Adjustment bolts on the back of the flat holder make it a snap to fine tune alignment of the flat with the scope!  The screen/LED holder in the focuser (made by CN member Moshen) holds the 3mm RGB 4-lead LED, which is connected to the home brew switch box (on the white board) which has a separate dimmer control for each color.  There’s a separate screen/LED holder for the white LED.  The power supply is my bench supply, but a cheap wall wart works just as well.  My old World Books temporarily taken out of retirement hold the scope, and a Nikon D40 with a 18-55mm lens (set at 55mm) was used to take the pics.  Paint.net was used to package the images.

 

Here are my results (each row shows inside of focus, at focus, outside of focus images):

 

attachicon.gif Collage 2.jpg

 

My interpretation of the pics is that the scope is moderately overcorrected in blue, with lesser overcorrection in green, and slightly undercorrection in red.  Based on that, my guess is that best correction is in between in green and red, in the yellow range.  Overall correction seems to be pretty good for a 6” f/6. The in-focus pics show a zone in the center of the objective, and at the edge at 1 o’clock and 6 o’clock.  I don't see any turned edge. Any ideas what caused the zones at 1 o’clock and 6 o’clock?

 

During use, I don’t notice CA at low to moderate magnification, but it is there at high magnification, for example when using my XW 3.5 EP.  Overall I’m satisfied with the scope, considering the aperture and short focal length.

 

 I'm still a beginner in DPAC testing and have a great deal still to learn, so your comments and recommendations are especially welcome!

 

Thanks,
Howard

Thanxs for datas provided!

Enjoy in your beauty!

 

Denis


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#10 peleuba

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Posted 03 April 2024 - 11:27 AM

The RGB LED has individual leads for R, G, and B, plus a ground lead.  

 

 

Thank you, Howard.  My confusion comes from wondering how you fit all of the LED's inside a single "Moshen inspired" eyepiece.   I use a similar setup but have multiple eyepieces each with a single LED.  Your setup seems more elegant as it allows you to switch wavelengths without switching eyepieces.  I have to swap eyepieces to change colors/wavelengths during testing.  Admittedly, this is a first world problem as my eyepieces/LED all have been fitted with RCA plugs, so its truly plug-n-play for me.  But, I'm always interested in a better mouse trap so-to-speak.  

 

Agree on the use of a potentiometer when using LED's to test.  Its super nice to dial in the brightness to so as to capture fine surface detail in the null images.    

 

At some point, send me a photo in a PM of this LED module, or you can point me to a web source so I can see if it will work for me.

 

Thanks.  Nice to see another telescope being tested.



#11 Howard_C

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Posted 03 April 2024 - 12:18 PM

Paul -

 

I sent you a PM with links to the LED and also the micro drills I used to modify Moshen's LED holder for the 4 pin LED.

 

Howard


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#12 Howard_C

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Posted 04 April 2024 - 06:51 AM

Posted per request from a CN member, below is an interferometric report for another sample of the APM APO SD 152mm F/6  (SN#001).  The testing was performed by Wellenform.  Again, this is NOT the scope I tested, but you may find it interesting.  The text is in German, but the pictures/tables and optical terms are familiar.

 

 

Howard

 

 

Zertifikat_APMDoubletSDAPO152F6_SN001 1 Resized 50 percent.jpg

Zertifikat_APMDoubletSDAPO152F6_SN001 2 Resized 50 percent.jpg

Zertifikat_APMDoubletSDAPO152F6_SN001 3 Resized 50 percent.jpg

Zertifikat_APMDoubletSDAPO152F6_SN001 4 Resized 50 percent.jpg

Zertifikat_APMDoubletSDAPO152F6_SN001 5 Resized 50 percent.jpg

Zertifikat_APMDoubletSDAPO152F6_SN001 6 Resized 50 percent.jpg

Zertifikat_APMDoubletSDAPO152F6_SN001 7 Resized 50 percent.jpg

Zertifikat_APMDoubletSDAPO152F6_SN001 8 Resized 50 percent.jpg


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#13 davidc135

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Posted 04 April 2024 - 07:48 AM

Both are good but yours is better.  David


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#14 RichA

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Posted 04 April 2024 - 09:13 AM

Here is my test bench (messy to add authenticity):

 

attachicon.gif DSC_0448 Cropped Resized 3.jpg

 

For testing this scope I used  my new coated 12.5” flat.  The flat holder and stand were custom made by Mark at Astrogoods.  Adjustment bolts on the back of the flat holder make it a snap to fine tune alignment of the flat with the scope!  The screen/LED holder in the focuser (made by CN member Moshen) holds the 3mm RGB 4-lead LED, which is connected to the home brew switch box (on the white board) which has a separate dimmer control for each color.  There’s a separate screen/LED holder for the white LED.  The power supply is my bench supply, but a cheap wall wart works just as well.  My old World Books temporarily taken out of retirement hold the scope, and a Nikon D40 with a 18-55mm lens (set at 55mm) was used to take the pics.  Paint.net was used to package the images.

 

Here are my results (each row shows inside of focus, at focus, outside of focus images):

 

attachicon.gif Collage 2.jpg

 

My interpretation of the pics is that the scope is moderately overcorrected in blue, with lesser overcorrection in green, and slightly undercorrection in red.  Based on that, my guess is that best correction is in between in green and red, in the yellow range.  Overall correction seems to be pretty good for a 6” f/6. The in-focus pics show a zone in the center of the objective, and at the edge at 1 o’clock and 6 o’clock.  I don't see any turned edge. Any ideas what caused the zones at 1 o’clock and 6 o’clock?

 

During use, I don’t notice CA at low to moderate magnification, but it is there at high magnification, for example when using my XW 3.5 EP.  Overall I’m satisfied with the scope, considering the aperture and short focal length.

 

 I'm still a beginner in DPAC testing and have a great deal still to learn, so your comments and recommendations are especially welcome!

 

Thanks,
Howard

The lens doesn't look that bad from a correction standpoint, I seem to recall in the dim past that larger scopes were often produced slightly undercorrected to cope with continually falling nighttime temperatures.  However, APM is kind of playing fast and loose with the term, "apo" based on the white image.  Would be interesting to see a ES 152mm f/6.5 achro put up against it. 


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#15 peleuba

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Posted 04 April 2024 - 10:19 AM

Both are good but yours is better.  David

 

Agree.  And its interesting both samples had an identical (or nearly so) wide central zone.  Consistent, for sure.   


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#16 denis0007dl

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Posted 04 April 2024 - 01:52 PM

The lens doesn't look that bad from a correction standpoint, I seem to recall in the dim past that larger scopes were often produced slightly undercorrected to cope with continually falling nighttime temperatures.  However, APM is kind of playing fast and loose with the term, "apo" based on the white image.  Would be interesting to see a ES 152mm f/6.5 achro put up against it. 

My uncle have Celestron 150 f/8 achro, and it have TONS of false colours comparing to my APM 152, its night and day difference.

 

Optically, Celestron does not only suffer from noticable more false colours, but also is less sharper at same magnification, with less contrast.

 

Mechanically, huge difference.

 

Denis


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#17 scooke

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Posted 04 April 2024 - 04:15 PM

Paul -

 

I sent you a PM with links to the LED and also the micro drills I used to modify Moshen's LED holder for the 4 pin LED.

 

Howard

Would you mind sharing with me as well?  Very nice design.


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#18 Howard_C

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Posted 05 April 2024 - 04:38 AM

Thanks scooke.  This is what I used, purchased from eBay::

 

3MM RGB LED 4-pin Diffused Tri-Color Red Green Blue Common Anode Nipple Pkg Resized.png

 

Note that these LEDs are "common anode": 1 (+) pin and 3 (-) pins.

 

I adapted Moshen's 2-pin LED holder by drilling 2 more holes for the 2 additional leads.  This allows the 4-pin LED to remain in the same ideal center spot as a 2-pin LED. 

 

I used one of the smallest drills shown here:  https://www.amazon.c...e?ie=UTF8&psc=1

 

You can even get additional colors (e.g., yellow) by powering multiple pins and adjusting color mix using the pots.  I guess the elegant way to do this would be with an Arduino controller, which I seriously considered but decided to stick with the manual switch and pots.

 

Thanks,

Howard


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#19 scooke

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Posted 06 April 2024 - 08:51 AM

Thanks Howard.




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