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Cleaner Stars - How to install an aperture mask on your Newtonian

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36 replies to this topic

#26 calypsob

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Posted 19 December 2022 - 08:46 AM

Nice to see this old thread resurrected...I have done the exact same thing with my Newt,as well as cutting 5/8" of the focuser drawtube that was intruding into the light path as well.

And removing the mirror in it's cell is just a matter of taking out a few small screws. I know some manufacturers are now sending out scopes with preinstalled masks.


You could also raise the primary by 5/8 if you dont have the ability to cut the focuser tube

#27 Tom62e

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Posted 19 December 2022 - 08:50 AM

Interesting. Why would raising the primary by 5/8ths help?

That might be easier than cutting the tube. Some simple spacers and slightly longer screws is all it would take I think

#28 Astroyesmer

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Posted 19 December 2022 - 09:13 AM

So in the end would it be ok to place such a mask at the front top of the OTA rather than the bottom?
I suppose looking through the focuser with a collimation tool would give the answer but maybe someone has the answer!

#29 unimatrix0

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Posted 19 December 2022 - 10:07 AM

I printed mine from black ABS plastic for GSO 200mm f/4 imaging newtonian OTA. The inner/outer dimention of the mask ring is 192/224 mm, just enough to hide the three clips and the outer edge of the mirror. The mask ring is 3mm thick with three 2 x holes to allow installing on top of the original rubber spacers on mirror edge. The mask and mirror are then retained by the original three metal mounting plates and original screws. One drawback of using aperture mask is the aperture is reduced to 192mm, making slower aperture of f/4.2. 

I just downloaded the same thing not long ago, but I haven't printed it yet. I got some issues with my 3D printer printing PTEG material. This Elegoo Saturn S2 printer (Ender 3 clone) is not as good as I hoped it to be. 



#30 cmooney91

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Posted 19 December 2022 - 11:00 AM

I've been hunting down non-spider diffraction for a while too. 

 

First I printed some low profile circular mirror clips. No luck. Next I altered the design to combine an edge mask ring with the clips. 

gallery_280529_10874_27924.jpg

gallery_280529_10874_92909.jpg

 

After testing on a star, I saw no decrease in the non-spider diffraction. Curiously the exact pattern of diffuse diffraction spikes and voids was unaffected. I would have thought providing a new edge would have at least resulted in a new pattern, like a finger print, or a CSI bullet rifling comparison.  

This lead me to make a secondary mask in case the majority of the diffuse diffraction spikes were coming from the secondary edge.

gallery_280529_10874_5829.jpg

This  did have a small effect on the diffuse diffraction spikes, a couple  disappeared, but 80% of the bulk was still there. 

 

Temporary link to star comparison

 

 

This made me wonder if the the non-spider diffraction was coming from a rough mirror surface, or leftover machine grinding marks from mass production. I took a way-defocused stacked and averaged star image, to see if I could see any striations. 

gallery_280529_10874_21799.jpg

I think I can see some slight radial marks, but a knife edge test would be better.  My coatings are also nearing end of life so maybe its just pin holes and oxidation roughness.


Edited by cmooney91, 19 December 2022 - 11:02 AM.

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#31 Tom62e

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Posted 19 December 2022 - 11:02 AM

Ha. I just bought the Ender 3 S1 Plus and I haven’t had a successful print yet.

I’ve tried the free filament supplies with the printer (absolute garbage) and my own PTEG. All fails! Played with every setting as well.

I’ll try one more filament and if that doesn’t work - then I pack it up and send it back.

#32 TelescopeGreg

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Posted 19 December 2022 - 01:16 PM

Ha. I just bought the Ender 3 S1 Plus and I haven’t had a successful print yet.

I’ve tried the free filament supplies with the printer (absolute garbage) and my own PTEG. All fails! Played with every setting as well.

I’ll try one more filament and if that doesn’t work - then I pack it up and send it back.

What isn't successful?

 

I have the older Ender 3 V2, and it works pretty well.  The S1 looks like they integrated several of the upgrades that one often does to the V2, just as the V2 integrated fixes and upgrades to the original Ender 3.



#33 Tom62e

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Posted 19 December 2022 - 02:18 PM

The filament gets all balled up under the extruded as its printing. I tried raising and lowering the Z-vertical adjustment but with no success. It starts printing the skirt fine, but once it starts the main print, it started accumulating melted filament under the extruded and the printer doesn’t layer correctly.

Build plate adhesion is phenomenal. In fact, it’s stupid. Its extremely difficult to release the print from the build plate, despite it being a removable, flexible plate. I have to use a heat gun in the back of the build plate. I guess that’s a better problem to have than the opposite.

#34 Tom62e

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Posted 19 December 2022 - 02:19 PM

Sorry for all the typos.

#35 TelescopeGreg

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Posted 20 December 2022 - 01:08 AM

The filament gets all balled up under the extruded as its printing. I tried raising and lowering the Z-vertical adjustment but with no success. It starts printing the skirt fine, but once it starts the main print, it started accumulating melted filament under the extruded and the printer doesn’t layer correctly.

Build plate adhesion is phenomenal. In fact, it’s stupid. Its extremely difficult to release the print from the build plate, despite it being a removable, flexible plate. I have to use a heat gun in the back of the build plate. I guess that’s a better problem to have than the opposite.

Interesting.  Mine started doing something similar last week, after a year of good prints.  Discovered that the plastic base of the filament feeder had cracked, so the feed wasn't consistent.  The pinch pulley wasn't pinching properly.  If I pushed on the filament to force-feed it, it started working a lot better.  You might try that as a diagnostic, if nothing else.  The other thing I've done since nearly the beginning is to put a thin coating of the washable Glue Stick on the heated bed (I have the carborundum glass one) to encourage the filament to stick, but with reasonable force to remove it.  Washes off easily for the next print.

An all-metal feeder is on order, should be here on Wednesday (or so).  BUT, I believe your printer already has the all-metal one, so that doesn't make sense.  {shrug}  Perhaps try the glue stick.

 

To the thread topic, if anyone has an STL for a clip mask for an 8" Newtonian, I'd be interested in trying it.  Once I get the printer fixed, that is.



#36 Tom62e

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Posted 20 December 2022 - 09:39 AM

Thanks Greg.  I’ll give it a shot asap.  I’d hate to return this thing.

 

And yes, it does have the all metal extruded.  



#37 ccaissie

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Posted 08 April 2023 - 12:39 PM

They shouldnt be touching the mirror, technically they are just a fail safe to prevent the primary from falling out in transit. Some people will put a shim between the primary clip/mirror and fill the void with silicone and then remove the shims, this prevents astigmatism and lets you ditch the clips, kinda sketchy though imo. One of my primaries has silicone tipped screws that grab the mirror but it still uses clips as a fail safe. They are hard to avoid unless you go with a conical mirror which has no clips or you can get a turned edge beveled mirror where the clips do not cover any reflective surface.

In Flexed mirror cell design, the mirror is held against the support cushion by the flexing tension, so there is no issue with the mirror shifting or falling out.  No clips or other strain points.

 

I finish my mirrors with a light face grind with 5 micron power, so there is no tiny TDE...rather a stunning perfect diffraction ring. Since spherical mirrors are null tested, the idea of an undetected TDE is moot.   The smooth sphere with a good edge is the basis of a smooth accurate paraboloid when flexed.  

 

https://skyandtelesc...-MirrorFlex.pdf




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