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Skywatcher Evostar 100ed

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#1 Unfocusedastrophoto

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Posted 02 March 2021 - 06:37 AM

Ian there any way to fix these diffraction spikes? I’ve heard it may be an issue with pinched optics. I was going to loosen the ring that’s holding in the primary lens but it looks like it’s been glued in at the factory. I really don’t want to destroy the scope and figured there’s someone here that can help me out. I used the Starizona apex .65 reducer and it magnified the issue to the point that it’s all can see, with or without the reducer. Any advice would be very appreciated. Thanks

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Edited by Unfocusedastrophoto, 02 March 2021 - 08:38 AM.

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#2 PirateMike

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Posted 02 March 2021 - 06:56 AM

I don't see any spikes. Can you add a picture showing your problem?

 

 

Miguel   8-)

 

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#3 Unfocusedastrophoto

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Posted 02 March 2021 - 08:35 AM

I thought I did but I guess not. I can’t even add photos to make my own album...

#4 jmillsbss

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Posted 02 March 2021 - 09:44 AM

This is interesting.  I almost looks like an internal obstruction or something (screw tip, clip, retaining screw) in the light path.

 

I say that because I switched out my focuser and there was 3 screws holding it in the tube and one of them had a boogered up tip. All three went just a tad bit deeper into the tube because the holes in the new focuser were countersunk a little too deep.  Anyway, when I rotated the screws to different holes it was clear there was one that was different.  I filed all 3 down just a tad and didn't just twist them as tight when re-installed..... it was fine after that.

 

However after looking at your photo again the flare seems to rotate around the field.  Maybe my report is unrelated...

 

Now, I may be ENTIRELY WRONG, and I'm sure somebody will say so  lol.gif ,   but that's just my experience and that's all I can say.

 

Good luck!!!   Jay



#5 Mike in Rancho

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Posted 02 March 2021 - 03:11 PM

It'll help if you can post the image here, so more can see it and respond.  My tablet wanted me to log into FB.  Now, my phone can do that, but I've been avoiding it for months lol.  Just use Gimp or something to scale the image to say, 800px across, export to jpg, and choose compression percentage to keep it below 500kb.  If it's not the first post in a thread you can find uploading in the "more reply options" button.

 

I am not sure which halo anomaly you are most interested in, but I assume the pizza-shaped shadow wedges?

 

Not uncommon it seems, and as much as it is discussed on the internet I don't believe it is pinched optics.  Of course, every telescope is an individual.

 

If you look through astrobin you will note several common halo errors.  In fact, I'm not sure any were completely clean.  And of course these are presumably the photos that imagers have fully post-processed, cleaned up, and are the most proud of.  Similar halo problems are also not limited to either the Evostar or Sky-Watchers, but here is what I see with the 100ED - 1.  Radiating wagon-wheel like spokes of thin bright spikes with dark borders.  2.  Pizza-shaped shadow wedges, typically opposing.  3.  Unbalanced halos that cast off stronger in a particular direction.  4.  A semi-matching secondary glow just outside the primary halo.

 

I have all four, and would end up among the worst half of those posted on astrobin (though not the very worst).  I believe these are all caused by errors in setting the final aperture circumference.  Chances are you will not see anything wrong with visual observation, and laser collimator, Cheshire eyepiece, and defocused star testing will all be just fine.  If you have something to make an aperture mask (or just remove the center cap from your dewshield dustcap, though that really cuts it down quite far) you should be able to test if particular errors go away - though keep in mind it will not have a perfect edge so some new ones could be created.

 

I am currently in the middle of a project to resolve these issues on my 100ED, and I think I am getting pretty close.  Essentially I will be trying to use an o-ring seated below the retaining ring to set the final aperture, similar to the Esprit line of higher-end Skywatchers that are more directly aimed at photography.  On our Evostars, however, not only is it more difficult to get close to a perfectly smooth and circular circumference with the metal and plastic rings therein, but there are three such concentric rings, which are each so close to 100mm (when the bending of light by the outer lens is considered) that they might end up stepping on each other.

 

You can find posts regarding this in the rather large 100ED thread in the refractors forum, here: https://www.cloudyni...-ed-apo-thread/

 

If you go back far enough, you can find my earlier questions about it, my eventual removal of the retaining ring and trimming of spacer pads on the footer ring (thus fixing the wagon-wheel spokes), and ultimately disassembly of the lens cell itself.  All with descriptions, measurements and photos.  Of course, no warranties for anyone who tries to copy me!  The o-ring modification, though, would not require removal of the lenses, just the retainer and footer rings.

 

Anywho, Amazon should be delivering my next sized o-ring today for further testing, and I will post what I come up with in the 100ED thread.  And if it works perhaps I will ultimately make a separate thread focused just on this.


Edited by Mike in Rancho, 02 March 2021 - 03:14 PM.

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