42 replies to this topic

[Astrojensen]

Thomas, I think it's diffraction effects (Talbot effect) rather than turned edge.

Note that the colleague uses a Ronchi screen of 10 lines per mm which enhances this effect. Of course, I can be wrong.

Quite possibly. I just noticed it, and I saw the same thing in my first APM 152ED, which had a very strong turned down edge. How it had passed quality control is a mystery to me. 

 

 

Clear skies!

Thomas, Denmark

[Scott in NC]

Thomas, I think it's diffraction effects (Talbot effect) rather than turned edge.

That’s what I was thinking as well.

[davidc135]

It's mostly diffraction, I think. The objective could be masked down a little and the Ronchi test repeated to see if it appears much the same.

 

David

[*ocean*]

Eyespy is probably right.

 

Is that last picture from the same telescope? Because it's different from everyone else.

(At least for me they are different.)

In earlier photos there was a clear zone in the central part of the lens, now it is practically invisible. Maybe you took the last photo at a different distance to the artificial star?
The last photo is taken much closer to the focus, and here the Ronchi method is the most sensitive, so the zone should be even more visible.

 

Edit: Though now I'm trying to do a simulation in AOS and indeed it might look like this.

If you could post a photo taken on the opposite side of the focus but also so close that would be great. And about two or three photos in the vicinity of the focus itself, a bit before, at and behind.

 

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Edited by *ocean*, 05 June 2023 - 07:45 AM.

[*ocean*]

Hi guys, last night I managed to do the test with real stars.
this is the result with Altair and later with Vega

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Edited by *ocean*, 09 June 2023 - 12:45 AM.

[eyespy]

Hi Ocean,

 

What did an actual ‘at focus’ image look like at say 60x per inch ? Plus visual in and out of focus views ? ie during actual use and not with the Ronchi.

 

Thanks,

 

Doug…..

[*ocean*]

Hi Ocean,

 

What did an actual ‘at focus’ image look like at say 60x per inch ? Plus visual in and out of focus views ? ie during actual use and not with the Ronchi.

 

Thanks,

 

Doug…..

this is my star test. 
The star is spica

With Asi 224.  the sensor is 6mm

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[orion69]

Anyone?

[RichA]

this is my star test. 
The star is spica

With Asi 224.  the sensor is 6mm

It's hard to quantify, but it looks like 1/4 wave SA.  The "Foucalt" part of the Ronchi test looked like it has a central zone.  Interesting.

[eyespy]

Hi Ocean, I meant what do the images look like using your eye through a regular higher power eyepiece and not the Ronchi screen.

 

Doug….

Edited by eyespy, 09 June 2023 - 06:11 PM.

[*ocean*]

Hi Ocean, I meant what do the images look like using your eye through a regular higher power eyepiece and not the Ronchi screen.

Doug….

I did not understand. all these tests arise because I don't seem to have a good contrast when compared to other instruments, i also see a halo around the star. but it can be caused by the prism that I use in visual and I haven't tried the new dielectric mirror diagonal yet

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Edit: I wrote an email to markus ludes and also sent him a message from the forum.

I asked him if he can view the telescope and if necessary fix it under warranty given the various aberrations present.
the aberrations are a very large central zone, turned edge and some spherical abberation. they have a great reputation and that's why I got my telescope from them. I hope they live up to their hype.

 

edit: He was very kind and quick to respond.

he telling me that the telescope is as good as all his 140 SD and and respects the 0.92 in green

 

 

 

 

 

 

Edited by *ocean*, 10 June 2023 - 03:13 AM.

[Maciek_Cz]

I can only confirm with AOS analysis that your lens has a Strehl factor of ~0.92 in green. You have provided few photos in the focus area and therefore the analysis is difficult. But the range of results I got gives an average of around 0.92.
Good job!

[*ocean*]

I can only confirm with AOS analysis that your lens has a Strehl factor of ~0.92 in green. You have provided few photos in the focus area and therefore the analysis is difficult. But the range of results I got gives an average of around 0.92.
Good job!

thank you all and you in particular for the time you spent for me.
at this point I'm sure that the telescope will give me beautiful images and what I saw in the only night under a dark sky (due to work and bad weather) was caused by something else.

[Maciek_Cz]

If you took more at focus photos, each in a slightly different position of the focuser, so as to examine the focus area as with Foucault's knife, it would be possible to select the parameters more precisely. And yes, the results jumped between 0.96 and 0.90. Remember that AOS does not do a full analysis of the wavefront, but only evaluates how many of the ~120,000 test rays hit the Airy disk, then the best result is found around the focus, i.e. the so-called best focus. But since the results oscillate in such a range as I wrote, Ludes's result is very likely. Do you have any certificate?

 

 

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[*ocean*]

No certificate.
Nice work thanks

[orion69]

I did not understand. all these tests arise because I don't seem to have a good contrast when compared to other instruments, i also see a halo around the star. but it can be caused by the prism that I use in visual and I haven't tried the new dielectric mirror diagonal yet

 

Please let us know how stars look like with dielectric mirror.

 

[*ocean*]

 

Please let us know how stars look like with dielectric mirror.

 

 

Ok, I'll try with a 2" TS dielectric and 2" and 1.25 eyepieces

Edited by *ocean*, 13 June 2023 - 11:23 AM.

[*ocean*]

 

Please let us know how stars look like with dielectric mirror.

 

 

last night I went under a black sky, same place as last time, same telescopes as last time plus another C8.
the problems encountered the first time did not occur, with the dielectric diagonal aiming at M5, M13, M57, etc.
the telescope gave me beautiful images, with a dark sky background and well-detached objects, even with increasing magnification, all objects remained appreciably contrasted and defined. The clusters were easily resolved by returning beautiful and immersive images.

Making a comparison with the other telescopes present, last night it was my APM that returned the best images

Edited by *ocean*, 17 June 2023 - 03:46 AM.