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Doing away with 130pds mirror clips?


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I would think it needs to totally obscure the clips, when I researched this everyone who installed one on their Newtonian totally covered the clips, not sure how much it affects the f ratio of the scope but I Carnt be much my clips only just protruded onto the mirror slightly, I ended up siliconing my mirror to its cell and cut the prongs off the clips and used the rest of the clip assembly to put the mask on, I noticed collimation would change slightly depending on where the scope was pointing, siliconing the mirror to its cell should help it keep its collimation no matter where it’s pointed now 

Edited by Craig a
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50 minutes ago, Xoc1 said:

If the clips are not the problem does the baffle need to have an inside diameter small enough to completely obscure the clips, or does it only need to obscure the mirror edge effectively leaving more of the mirror to capture those precious photons?

If the clips are still on show behind the baffle you would still have some amount of diffraction from them as any hint of them would block some light getting to the mirror. 

 

8 hours ago, ONIKKINEN said:

I doing some work on my tube which is not the 130PDS, but if i understood correctly the mirror clips are not to blame with stellar halos? So in this case the blue bit, the edge of the mirror is the cause and not the mirror clips (in red)?

I bought some black 2.0 paint for some other work but i was wondering if i could just paint the edge black while i have the mirror out and that would do the job of an aperture mask? Just thought id sanity check this as a reasonable thing to do before i unnecessarily start painting mirrors.

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I don't think that rim on your mirror has anything to do with it as that rim doesn't exist on a Skywatcher mirror. It's just glass up to the edge.

Using the baffle won't remove all of the halo but will reduce them significantly. As I said about, any hint of the clips still on show would continue to cause diffraction in the smaller halo.

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3 minutes ago, Xoc1 said:

Ok Thanks . I have 3D cad and a Printer so should be an easy project and looks to be well worth the effort.

It definitely can't do any harm and it's completely reversible if you're not happy with the results. To be honest, it's the best mod I've made to the 130PDS. 

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Thanks for your input Ricochet. I will measure up & make a best guess at what is necessary. looking at some of my images even Polaris would allow me to assess the effect, so would be an easy target to do some testing on.

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On 05/10/2021 at 09:08, Craig a said:

. Has anybody done this to their 130pds and how secure is the mirror when the silicone is cured?

Hi

Yes. It's easy to do and makes the diffaction even and smaller; there are no dark areas in the diffaction pattern. 

The silicone blobs should be applied so they flow up the side of the mirror where the clips were when the mirror is replaced. Practise the amount you need to achieve this by using a curved block of wood. Apply the correct amount of neutral silicone, push the mirror gently into the cell and leave to cure in a horizontal surface for 24 hours. Unless you plan on hitting the tube hard whilst upside down, the mirror will not shift.

The main advantage of this method however is not the tighter stars, rather the ability to hold collimation at all angles, before and after meridian flips, and between sessions, even if you transport the tube between locations.

Cheers and HTH

 

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I am surprised that siliconing the mirror in three places does not give you issues due to stresses being placed on the mirror as temperatures change. On my Bresser the mirror clip "posts" are adjustable and there is a fine line between having them set to prevent mirror movement and pinching the optics. If I was designing a mirror cell to hold the mirror via silicone I would have a central siliconed support and allow the mirror to float over the other supports. 

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On 29/10/2021 at 20:45, Ricochet said:

On my Bresser

Silicone responds well to any constraints placed upon it without introducing any of its own. A rigid adjuster allows the mirror to slide or introduce stress. On our Bresser f3.9, silicone is the only way we've found which allows us to retain collimation throughout a session. That has a 9 point support. 

Placement of the silicone is pretty straightforward; wherever you have cork/felt/nylon to glass contact. On the small 130 mirror, it's self explanatory.

Cheers

Edited by alacant
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Ricochet's second image shows there is still an issue if the clips are removed. It looks to be a problem with the very edge of the mirror causing detraction blur/spikes and the clips causing a shadow within that blurry/spiky zone. Cover the edge of the mirror => no diffraction => clips won't show as shadows in diffraction because its not there anymore. 

 

Still leaves the question of how much to cover, I'd assume the just the very edge. 

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7 hours ago, PlankWithANailIn said:

there is still an issue if the clips are removed

We're sure that the theory is good, but it's not what we find in real life.

The main advantage of silicone isn't the reduction of star size, rather the retaining of collimation at any angle.

Cheers

Edited by alacant
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I had one DIY scope with silicone as solution for primary mounting. This was terrible solution! Constantly had problem with image at EP, until I remove silicon and made normal clips, not tightened to much.

After that I always had  good image at EP. If you want to eliminate pattern on pictures than mask is best solution.

Regarding changing F number just measure diameter with mask installed an after f/d calculation you will know...

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