223 replies to this topic

[CharlieB]

If you haven't gone through this thread:

 

https://www.cloudyni...m-dpac/?hl=dpac

 

I had just started DPAC testing and making simple equipment.  I still use the same setup and it still works fine.

 

Unitron 105 (50/700) and a flipped Tasco 50/600.  Makes it easy to see what is good and what has a problem.

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[peleuba]

What is the beam splitter for in this post.  In your test set-up in other posts it doesn't look like you use it.  If you do, what is it's configuration?

Beam splitter is to allow for viewing of the return beam of the generated artificial star.  

 

LED light goes through the device/beamsplitter, then through the telescope.  It then reflects off of the flat, round trips back through the telescope ( ("double pass") through the device and the beam splitter directs the light upward to allow for viewing with an eyepiece.

 

You are star testing the telescope in double pass.  

Edited by peleuba, 26 September 2018 - 03:49 PM.

[peleuba]

If you haven't gone through this thread:

 

https://www.cloudyni...m-dpac/?hl=dpac

 

I had just started DPAC testing and making simple equipment.  I still use the same setup and it still works fine.

 

Unitron 105 (50/700) and a flipped Tasco 50/600.  Makes it easy to see what is good and what has a problem.

 

The Unitron looks nice - how is it under the stars?

 

When you say the Tasco was "flipped" do you mean one of the lens elements was in backwards?

 

Post a picture of your test setup.

Edited by peleuba, 26 September 2018 - 11:11 AM.

[CharlieB]

The

 

The Unitron looks nice - how is it under the stars?

 

When you say the Tasco was "flipped" do you mean one of the lens elements was in backwards?

 

Post a picture of your test setup.

The Unitron is fantastic under the stars, spitting doubles to the resolution limits of a 50mm scope, giving superb solar and lunar views and excellent planetary results.  One of the two best 50mm scopes I've ever used - the other is my RAO R-51 (labeled Mirador Super) 50/750mm.

 

The Tasco had a flipped crown element.  It was much better after I re-flipped the element, but nowhere near the quality of the Unitron.  

 

I think there are photos of my setup in that thread.  If not, I'll post it here later.

Edited by CharlieB, 26 September 2018 - 01:27 PM.

[peleuba]

 

I think there are photos of my setup in that thread.  If not, I'll post it here later.

 

Yes - I just looked at the thread and you did several pictures of your setup including how you made the Ronchi eyepiece.  Thanks for pointing me to it.  Back in 2017 I was reading the same thread as you were posting the results of the various telescopes.

 

Hopefully Dave G, Chuck Hards et. al. will chime in on this thread...  

Edited by peleuba, 26 September 2018 - 01:25 PM.

[SandyHouTex]

If you haven't gone through this thread:

 

https://www.cloudyni...m-dpac/?hl=dpac

 

I had just started DPAC testing and making simple equipment.  I still use the same setup and it still works fine.

 

Unitron 105 (50/700) and a flipped Tasco 50/600.  Makes it easy to see what is good and what has a problem.

Thanks.  That helped a great deal.

[Jeff B]

So over the space of a few days I've managed to cycle through 15 OTAs in DPAC.  In order of the testing, they were:

 

1.  AP 6" F9, Blue Tube Star Fire

2.  6" F10 "Phoenix", reworked 6" F9 pre-ED AP Star Fire, reworked by Roland and Ceragioli

3.  AP 7" F9, Blue Tube Star Fire

4.  6" F10, Istar Achromat

5.  6" F5 Jaegers Achromat

6.  TMB 152 F8 LZOS triplet

7.  TEC 140ED

8.  CFF 160mm, F6.5 triplet

9.  TMB 130SS

10. AP 127, F8 pre-ED Star Fire, reworked by Roland

11. SW 120ED

12. Orion 80ED

13. Celestron 100ED

14. TEC 7 Mak

15. Intes MN76 Mak-Newt

 

With the exception of the two maks, I tested them in Green, Red, and Blue light.  I just tested in green for the Maks.  For the refractors, I looked at and subjectively "graded" each scope in each light for SA.  I also, for all scopes, looked for and "graded" any astigmatism, edge performance, zones and overall "smoothness"  at focus, all in green light.  

 

This was extremely educational and, for me anyway, fun.  With the exceptions of the CFF and AP 127, I have owned these scope over multiple years but have extensively observed with all of the, including the CCF and AP 127 of late.  I know these samples very well optically.

 

So before I get into more detail about the results (and it may take a couple of long-ish posting to do so), let's have some fun.

 

There was one refractor which "won" based upon my "grading" during DPAC.  Yes, it's subjective but I was, I believe, very consistent in how I DPAC "graded".  And the "top 5" were all very close in DPAC "performance".

 

So, everyone, please take a guess as to which refractor "won".   Also, which one did the worst.

 

Jeff

[starman876]

I bet either the AP 127 or the Phoenix won The Intes most likely came in last. 

Edited by starman876, 27 September 2018 - 10:48 AM.

[Darren Drake]

Another way to easily test new scopes indoors involves using a larger high quality scope and a focuser insertable artificial star.  This summer my astronomy program received 10 new Skywatcher dobsonian 8 inch telescopes.  I tested them all during the daytime and came up with a general optical report for each one using my 18 inch dob with a 1/16 wave Pegasus mirror.  Fun fun.  I've been testing scopes in my living room for many years with this method.   

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Edited by Darren Drake, 27 September 2018 - 12:09 PM.

[Darren Drake]

Here's an article I wrote here on CN describing this process further.

https://www.cloudyni...null-test-r1586

[peleuba]

Another way to easily test new scopes indoors involves using a larger high quality scope and a focuser insertable artificial star. 

 

Yes - what are you are doing is using the larger telescope as a collimator.  Meaning the light shining backwards (from focuser to secondary to primary then out of front aperture) is paralell and not resolvable as an extended object by the telescope under test.  For all intents and purposes the telescope "sees" this as a star.

 

You article is informative   and for many years this is what I have done (using a large Zambuto equipped dob) to generate an artificial star.  Something to note is that any wavefront error in the larger Newtonian will be cumulative and directly added to the error you see in the telescope under test.  I know you mentioned it was 1/16th wave - I am guessing this is Foucault measurements as that is how Pegasus quotes numbers.  The true error on the surface will be much larger then that.  Probably around 1/5-1/8 wave.

 

I had my Zambuto tested by a very skilled operator on a Zygo.  It measured 0.9601 - an average of 8 interferograms and about 1/6 wave PtV with a very smooth surface.

 

Barlows stacked in the focuser work very well to make the diameter of the artificial star smaller.  And as you know, eyepieces work, too.  But, If using an eyepiece it should be symmetrical in design such as a 4 element plossl.  The 5 element "super plossl" and the more complex designs don't work as well as a simple short focal length symmetrical eyepiece.

 

Your astronomy program looks awesome, BTW.   

Edited by peleuba, 27 September 2018 - 01:10 PM.

[peleuba]

So, everyone, please take a guess as to which refractor "won".   Also, which one did the worst.

 

 

 

 

Best was the TMB/LZOS 152 F/8

 

"Worst" was the CFF 160mm  In this design, there is some offsetting HSA that will be visible in the tests.

 

I am not sure on the others...  I bet the ED80 was excellent and certainly the price/performance leader.  I have seen a couple of these and they are quite good.  The older AP's you have were figured by Roland prior to having an interferometer.  He used DPAC to test them, so they are probably very nice, too.

Edited by peleuba, 27 September 2018 - 12:57 PM.

[Darren Drake]

Yes - what are you are doing is using the larger telescope as a collimator.  Meaning the light shining backwards (from focuser to secondary to primary then out of front aperture) is paralell and not resolvable as an extended object by the telescope under test.  For all intents and purposes the telescope "sees" this as a star.

 

You article is informative   and for many years this is what I have done (using a large Zambuto equipped dob) to generate an artificial star.  Something to note is that any wavefront error in the larger Newtonian will be cumulative and directly added to the error you see in the telescope under test.  I know you mentioned it was 1/16th wave - I am guessing this is Foucault measurements as that is how Pegasus quotes numbers.  The true error on the surface will be much larger then that.  Probably around 1/5-1/8 wave.

 

I had my Zambuto tested by a very skilled operator on a Zygo.  It measured 0.9601 - an average of 8 interferograms and about 1/6 wave PtV with a very smooth surface.

 

Barlows stacked in the focuser work very well to make the diameter of the artificial star smaller.  And as you know, eyepieces work, too.  But, If using an eyepiece it should be symmetrical in design such as a 4 element plossl.  The 5 element "super plossl" and the more complex designs don't work as well as a simple short focal length symmetrical eyepiece.

 

Your astronomy program looks awesome, BTW.   

Thanks on the astro program.   I'm not sure why you suspect the mirror may be more like 1/6 wave.  Perhaps its because it's rare to have such good big mirrors.  In this case in very confident this is accurate.   This is based on the virtually perfect star test it consistantly puts up.  This is a very sensitive test and John Hall was a competant optician.  In any event this precise a mirror isnt necessary to conduct tests on smaller scopes in general.   Good smoothness and lack of zones is most important however.  Btw I plan to have this scope at Okie Tex.  

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Edited by Darren Drake, 27 September 2018 - 01:51 PM.

[peleuba]

Thanks on the astro program.   I'm not sure why you suspect the mirror may be more like 1/6 wave.  Perhaps its because it's rare to have such good big mirrors.  In this case in very confident this is accurate.   This is based on the virtually perfect star test it consistantly puts up.  This is a very sensitive test and John Hall was a competant optician.  In any event this precise a mirror isnt necessary to conduct tests on smaller scopes in general.   Good smoothness and lack of zones is most important however.  Btw I plan to have this scope at Okie Tex.  

 

John Hall was a good optician and I was not criticizing you, your mirror (or telescope) whatsoever.

 

What I meant by my comments is this:  Foucault derived PtV are in most cases overly generous.  I am sure its a good mirror.  My own 14.5" Zambuto mirror had similar stats as yours but when placed on an interferometer was "only" about 1/6 PtV.  But it was smooth and had a good RMS and Strehl.   

 

I am sure if you get yours tested by Interferometry it will be worse then the John Hall quoted numbers, probably by an order of ~3.  At least in my years of comparing stats gleaned through Foucault with those from an interferometer this is typically what I have found.   Foucalt tests don't measure the entire surface and its PtV, RMS and Strehl calculations are based on assumptions of figures of revolution "goodness" and others. 

 

I don't want to get into a debate/discussion on test methods.  And I as not calling out the quality of your mirror.  I was, however, pointing out that when using a larger telescope as a collimator all errors in the "collimator" are 1:1 additive to the final test results you see in the telescope under test.  And secondly, that Foucault calculated PtV, RMS and Strehl often represent an overly optimistic picture of quality.       

Edited by peleuba, 27 September 2018 - 02:08 PM.

[Jeff B]

So over the space of a few days I've managed to cycle through 15 OTAs in DPAC.  In order of the testing, they were:

 

1.  AP 6" F9, Blue Tube Star Fire

2.  6" F10 "Phoenix", reworked 6" F9 pre-ED AP Star Fire, reworked by Roland and Ceragioli

3.  AP 7" F9, Blue Tube Star Fire

4.  6" F10, Istar Achromat

5.  6" F5 Jaegers Achromat

6.  TMB 152 F8 LZOS triplet

7.  TEC 140ED

8.  CFF 160mm, F6.5 triplet

9.  TMB 130SS

10. AP 127, F8 pre-ED Star Fire, reworked by Roland

11. SW 120ED

12. Orion 80ED

13. Celestron 100ED

14. TEC 7 Mak

15. Intes MN76 Mak-Newt

 

With the exception of the two maks, I tested them in Green, Red, and Blue light.  I just tested in green for the Maks.  For the refractors, I looked at and subjectively "graded" each scope in each light for SA.  I also, for all scopes, looked for and "graded" any astigmatism, edge performance, zones and overall "smoothness"  at focus, all in green light.  

 

This was extremely educational and, for me anyway, fun.  With the exceptions of the CFF and AP 127, I have owned these scope over multiple years but have extensively observed with all of the, including the CCF and AP 127 of late.  I know these samples very well optically.

 

So before I get into more detail about the results (and it may take a couple of long-ish posting to do so), let's have some fun.

 

There was one refractor which "won" based upon my "grading" during DPAC.  Yes, it's subjective but I was, I believe, very consistent in how I DPAC "graded".  And the "top 5" were all very close in DPAC "performance".

 

So, everyone, please take a guess as to which refractor "won".   Also, which one did the worst.

 

Jeff

Awe come on now, no other guesses?

 

Hey, this is the internet, where opinions fly!

[Darren Drake]

I'd sy the Tec 140 won and the 7 inch tec mak did very well but might have had some slight higher order spherical aberration.   The Orion 80ED may have don very well also...

[hottr6]

This is an APM 150 ED scope.   Lines are clearly not straight, but how bad is the error on this scope? If I paid $3000 for it, should I be concerned?

 

It could one of the early models with the defective cell.  I ran my new APM 152 ED through DPAC this morning -->  https://www.cloudyni...19#entry8849902   and got straight bars that resemble my high-performing Royal 76mm F15.  One of my better refractors -- but not my very best.    Once again, DPAC correlated with my star & sky tests, as well as the detail in my planetary imaging.

That may explain the two dogs I received... and returned. 

Edited by hottr6, 28 September 2018 - 07:14 PM.

[TG]

Yes. All the details. I helped put it together and currently have possession of it. Yes, the beam splitter must be uber-high quality. The Baader FFC helps mitigate some of the the aberrations in the beamsplitter, but its (beam splitter) surface flatness is better then 1/8 wave.

BTW, I came across an artificial star device you created using an LED, an eyepiece and some plumbing. I am about to make it for myself for quick use indoors. Thanks for publishing it.

It would be great to provide a schematic, if that's possible for you.

Re. the artificial star, I have two pieces of advice after building and using it: baffles are better than black paint, and use a microscope eyepiece at the right distance from the LED (usually something like 160mm or so for old microsocopes). It works better having no spherical aberration. Avoid infinity corrected objectives which will have spherical aberration. Those are expensive anyway.

Tanveer

[TG]

Yes. All the details. I helped put it together and currently have possession of it. Yes, the beam splitter must be uber-high quality. The Baader FFC helps mitigate some of the the aberrations in the beamsplitter, but its (beam splitter) surface flatness is better then 1/8 wave.

BTW, I came across an artificial star device you created using an LED, an eyepiece and some plumbing. I am about to make it for myself for quick use indoors. Thanks for publishing it.

It would be great to provide a schematic, if that's possible for you.

Re. the artificial star, I have two pieces of advice after building and using it: baffles are better than black paint, and use a microscope eyepiece at the right distance from the LED (usually something like 160mm or so for old microscopes). It works better having no spherical aberration. Avoid infinity corrected objectives which will have spherical aberration. Those are expensive anyway.

Tanveer

[starman876]

could you please repeat that again

[Bomber Bob]

"That may explain the two dogs I received... and returned."

 

I think we're seeing something similar to the early APM 152s with the first deliveries of the Sky-Watcher Evostar 150 ED -- the cell doesn't keep the elements from rotating.  My 1958 Goto taught me how critical element alignment is.  Its objective is a rare contact doublet, and MUST be at the marks, +/- a couple of millimeters or performance slides downhill fast.  Once I figured that out, I taped the edges, and the views have been near-APO ever since.

[Jeff B]

Ok, so only a few informed people bothered to take the guess (and you were very close to correct).  So the "winning" refractor was......

 

The Orion 80ED.

 

I knew it was a really good sample just based upon observing and star testing but the DPAC results were outstanding.

 

So using my highly subjective "grades" of Exceptional, Excellent (E), Very Good (VG), Good (G), Fair (F) and Poor (P), based upon the degree of straightness or bowing of the lines observed (3 of them with the 133 LPI grating) I got the following for the 80ED:

 

Green: Exceptional, dead perfect straight, no wiggles

 

Red:    Vg-E, very slight in-ward bow inside focus

 

Blue:   E, no bowing 

 

I also looked for astigmatism ("clocking" of lines thru focus or any wavy patterns or some such ) Edge, "smoothness", and zones.

 

Astigmatism: None (I knew that going into the DPAC test based upon previous star testing)

 

Edge: Perfect, no hooking of any kind, even locally

 

Smoothness:  Excellent, no visible roughness at focus

 

Zones, None visible, and I looked for them, a great null at focus in green, maybe a bit of an aspheric in red.

 

So the aperture runt was an exceptional sample in DPAC and I knew it was a great sample going in so DPAC confirmed what I saw at the eyepiece.  Whatever Orion's OEM is doing, they're doing it very well indeed for the 80ED!

 

Jeff

[starman876]

Ok, so only a few informed people bothered to take the guess (and you were very close to correct).  So the "winning" refractor was......

 

The Orion 80ED.

 

I knew it was a really good sample just based upon observing and star testing but the DPAC results were outstanding.

 

So using my highly subjective "grades" of Exceptional, Excellent (E), Very Good (VG), Good (G), Fair (F) and Poor (P), based upon the degree of straightness or bowing of the lines observed (3 of them with the 133 LPI grating) I got the following for the 80ED:

 

Green: Exceptional, dead perfect straight, no wiggles

 

Red:    Vg-E, very slight in-ward bow inside focus

 

Blue:   E, no bowing 

 

I also looked for astigmatism ("clocking" of lines thru focus or any wavy patterns or some such ) Edge, "smoothness", and zones.

 

Astigmatism: None (I knew that going into the DPAC test based upon previous star testing)

 

Edge: Perfect, no hooking of any kind, even locally

 

Smoothness:  Excellent, no visible roughness at focus

 

Zones, None visible, and I looked for them, a great null at focus in green, maybe a bit of an aspheric in red.

 

So the aperture runt was an exceptional sample in DPAC and I knew it was a great sample going in so DPAC confirmed what I saw at the eyepiece.  Whatever Orion's OEM is doing, they're doing it very well indeed for the 80ED!

 

Jeff

I had a feeling it was the 80ED.  They are really good scopes as can be seen with the images taken with the 80ED.  Which was the worst?

Edited by starman876, 29 September 2018 - 12:23 PM.

[Jeff B]

Which do you think was the worst...of the refractors?

[sqrlman]

Which do you think was the worst...of the refractors?

That would have to be #5. The Jaegers 6" F5.  

 

Steve