34 replies to this topic

[Psion]

After a long time I pulled the TEC 140ED (year 2011) out of storage to compare it with the Askar 203mm, and on that occasion I did a little DPAC test. It is obvious that Yuri can do it! The optics are amazing even if not completely free of chromatic aberration, but the focus was on eliminating other optical defects.

 

 

 

 

Edited by Psion, 23 March 2025 - 04:54 AM.

[Darren Drake]

It looks virtually perfect.  There's maybe a trace of sa in blue.  Is there a pic of a null test?

Edited by Darren Drake, 23 March 2025 - 06:28 AM.

[CHASLX200]

Maybe mine will be as good.

[Erik Bakker]

After a long time I pulled the TEC 140ED (year 2011) out of storage to compare it with the Askar 203mm, and on that occasion I did a little DPAC test. It is obvious that Yuri can do it! The optics are amazing even if not completely free of chromatic aberration, but the focus was on eliminating other optical defects.

 

TEC140ED_Ronchi_RGB-1.jpg

 

TEC_140ED_R.jpeg

 

TEC_140ED_G.jpeg

 

TEC_140ED_B.jpeg

Wow! 

[rachnoman]

It looks virtually perfect.  There's maybe a trace of sa in blue.  Is there a pic of a null test?

Would also like to see a null test. That will reveal what you've got.

[Psion]

I've tried to make it, but I can't the area is almost completely uniform, without any zonal defects.

[rachnoman]

My null test uses a 1/10 wave silvered flat and a simple knife edge Foucault tester. No lens can escape detection of any defects with this basic direct test. 

[Psion]

Unfortunately, I don't have a Foucault tester; perhaps I should make one.

[saemark30]

Superb! Best DPAC I ever seen!

[Scott in NC]

Very nice!  

[scoale]

Interesting.  This tests far better in blue than the other two TEC 140 ED tests we have seen.

[rachnoman]

Unfortunately, I don't have a Foucault tester; perhaps I should make one.

A good guide for making one can be found in Sam Brown's book called "All about telescopes". The out-of-print book can be found on the used market.

[PatientObserver]

That is a nice looking DPAC.

[PKDfan]

I'd take that scope in half a heartbeat Psion !!

Just a Beautiful correction profile.


CSS
Lance

[Scott in NC]

I noticed that all of your images are presented here as monochromatic, so I’m curious as to how you derived the individual R, G, B colors (separate colored LEDs, like I did when I first started out, or separation of colors by software processing, like Jeff B. and I do now).

[Psion]

I separated the colors using PixInsight.

[Maciek_Cz]

I have a question about your photos and analysis by AOS. What ronchi screen did you use? In the AOS parameters you entered 10 lines/mm, but the photo does not show diffraction effects, which with such a grid in the double pass system should be significant. Wasn't it something like 4-5 lines/mm?

[Scott in NC]

A few questions: 

 

1. First, should “Ronchi Autocollimation” be checked rather than “Ronchi at Focus” on the AOS program?

 

2. Second, could you let us know whether these images were taken inside of focus or outside of focus? I’m assuming the former, given the parameters entered into AOS.

 

3. Third, would you mind also posting the “at focus” and “outside focus” images, if you took any?

 

4. And last of all, were the Ronchigrams cropped in any way? It doesn’t look like it to me, but just wanted to confirm.

 

Thanks!

[Maciek_Cz]

1. First, should “Ronchi Autocollimation” be checked rather than “Ronchi at Focus” on the AOS program?

Scott, yes option "Ronchi Autocollimation should be checked when we consider DPAC configuration.

[Jeff B]

A quick question Maciek, something I have been meaning to ask you.

 

There is also the "Moving source" check box.  I have been checking it because my screen and LED are in the same holder and move together while focusing and I assumed that is the purpose of that check box.  Is my assumption/reasoning correct.

 

BTW, I ran my TEC 140ED DPAC images in AOS, each side of focus, spherical only (which is reasonable for this objective) and the average spherical only Strehls are essentially .99 in green, ~.98 for red and ~.81 in blue.  I got good simulations with the same "Dist from ROC/Foc" parameter for all colors.  

 

Jeff

Edited by Jeff B, 24 March 2025 - 11:31 AM.

[Psion]

I have a question about your photos and analysis by AOS. What ronchi screen did you use? In the AOS parameters you entered 10 lines/mm, but the photo does not show diffraction effects, which with such a grid in the double pass system should be significant. Wasn't it something like 4-5 lines/mm?

You're right, I'm sorry, I entered the wrong value. I normally use Ronchi 10 lines/mm, but in this case I used a different instrument with 5 lines/mm.

[Psion]

A few questions: 

 

1. First, should “Ronchi Autocollimation” be checked rather than “Ronchi at Focus” on the AOS program?

 

2. Second, could you let us know whether these images were taken inside of focus or outside of focus? I’m assuming the former, given the parameters entered into AOS.

 

3. Third, would you mind also posting the “at focus” and “outside focus” images, if you took any?

 

4. And last of all, were the Ronchigrams cropped in any way? It doesn’t look like it to me, but just wanted to confirm.

 

Thanks!

Let me see, somewhere I have photos taken outside of focus. I only evaluated the ones inside of the focus.

 

The Ronchi image is not cropped in any way and is as captured by the Olympus camera, only the black edges are cropped.

[Maciek_Cz]

You're right, I'm sorry, I entered the wrong value. I normally use Ronchi 10 lines/mm, but in this case I used a different instrument with 5 lines/mm.

Thank you.
Now you should redo AOS analysis:-)

[Maciek_Cz]

A quick question Maciek, something I have been meaning to ask you.

There is also the "Moving source" check box. I have been checking it because my screen and LED are in the same holder and move together while focusing and I assumed that is the purpose of that check box. Is my assumption/reasoning correct.

Hi Jeff,
Your reasoning is correct. In this setup where led moves with ronchi screen we should check "Moving source" checkbox:-)

[Psion]

Thank you.
Now you should redo AOS analysis:-)

I tried to do the analysis again, and it comes out similarly