Replacement mirror or prism query / question…

[RT65CB-SWL]

Hi everyone.

Not sure whether this is the right section to ask, but here goes. Somehow the mirror on one of my star diagonals has got damaged. Images of the star diagonal are when below.

This afternoon I have managed to remove the damaged mirror. 

I don’t know whether I should replace the mirror with the one that I salvaged from my ETX-105 flip-mirror housing from many years ago when it got damaged.

Should I get a replacement mirror or replace with a prism?

If anyone can recommend anywhere that sells either or what I should look for before I purchase the replacement. I have had a look at https://www.edmundoptics.co.uk/ but I am confused by the different types of glass, coatings, etc.
I have also had a look at some prisms on some of the online warehouse sites as well .

Another question... If the salvaged ETX mirror is OK size wise [I have temporarily mislaid it, so unsure at the time of posting] what should I use to stick it the star diagonal body? I was thinking of something like a silicon sealant rather than an adhesive/glue or 3M self-adhesive tape/pads.

Tnx in adv.

Edited June 19 by RT65CB-SWL

[Carbon Brush]

Not sure if I'm missing something here.
I assume the existing mirror is bonded/glued to a backing plate?
If so I would put the ETX mirror on there using a thin layer of silicon adhesive.

You can use the more expensive non corrosive cure (doesn't smell like vinegar, acetic acid) type.
Or use ordinary 'smelly' cure and make sure you don't leave the diagonal in an enclosed space with bright and shiny metal things.
In other words don't leave the diagonal in a bag or small box with the shiny screws etc. found in most scopes. Or you will come back to corroded screws.
Keep it open to the air until the adhesive has fully cured - it can continue to release a bit of acetic acid for days.

On the option of buying a mirror from Edmund or others.
I would just buy a standard diagonal, new or used, in the price/quality range I can justify.
I mean reflectivity, and features like non-marking clamp, quick release, etc.

HTH, David.

[RT65CB-SWL]

The mirror was supposed to be ‘stuck down’ with a strip of thin double-sided adhesive tape to the body.

The mirror has always been loose since new and I never gave any further thought about making it secure. There was about a gap of 1mm either side of the mirror to the body sides and retained in place by some moulded clips, so the lateral movement was sideways, if that makes any sense.

Yesterday was the first time that I had opened it up.

At least I have a couple of TeleVue/Vixen and a Circle-T star diagonals to use… and I decide whether to keep it or bin it!

[RT65CB-SWL]

Ok… an update.

Found the ‘salvaged’ mirror from my ETX flip-mirror rear end  - it is about 5mm shorter than the damaged mirror and width is about 2mm narrower. [image below]. 

So my question is: What adhesive do I use? - I have some Gorilla glue… will this be ok? or should I use something that is slightly flexible to allow for variation of temperature extremes, etc? @Carbon Brush mentions silicon adhesive. Can anyone recommend a brand? Tnx in adv.

 

 

Edited Tuesday at 21:54 by RT65CB-SWL
added an image…

[Alan64]

This is a diagonal, but from a Newtonian...

I had used 100% silicone on that, that for aquariums and other.  The toothpicks were used to space the flat from its stalk until the silicone cured.

But that's not a 90° star-mirror diagonal.

In the case of your own, you will need a pre-collimated laser-collimator to install a star-mirror within its housing.  That is, if you want the sharpness of views afforded by a collimated flat.

[Alan64]

As for the spent shard, it reminds me of my days, and nights, in the adult venues.

Further, to illustrate, this is a star-mirror that ended up being free from Amazon, an SVBONY SV188P.  All I did was attempt to return it, and wonder of wonders, they didn't want it back.  Later, someone knowledgeable about the make and model  stated that the dielectric, reflective coating was not up to snuff...

Yes, that's probably how many of us ended up getting one; so very attractive, the red covers.  Isn't marketing a beautiful thing...

There's a slot, and everything, for the flat; how luxurious.  But simply sliding the flat in and battening down the covers isn't going to get it.  This is how the mirror was secured...

...gunk.  It looks like a dead chicken. 

If I remember right, that flat would need to be elevated slightly, and by the use of proper shimming techniques.  The shims can be of hardwood veneers, micro-lumber; or, of metal, and plastic even.  Shims must be fitted, tested, first.

The flat must be collimated, and the shims play a part in that. 

At this scale, a pin-point laser-spot would be heaven-sent. 

The laser is inserted into the visual-back, and centred.  Quite a few visual-backs are wonky in that regard, so check for that. 

On a small piece of gift-tissue, a tightest tracing of the nose's outer-rim opening is made.  Then, a pin-point of ink is placed precisely in the centre of that.  The paper is then fitted, centred, over the nose's opening.  You want the laser collimated itself, centred in its seat, and its spot lining up with the pin-point on the tissue.  The laser-spot is guided to its target by the shimming actions for the flat.  In the end, the flat is removed, the shims secured, but don't use too much adhesive, hardly any at really, else the collimation will be thrown off.  It's a bit of work, going back and forth, then again, and again.

Now you don't have to wonder as to why that wasn't done at the factory.

In the end, I did get a fine housing for a star-mirror.  One day, I might try to find a standard flat for it, a non-dielectric.  

Edited Wednesday at 16:12 by Alan64

[RT65CB-SWL]

15 hours ago, Alan64 said:

… 

This is how the mirror was secured...

...gunk.  It looks like a dead chicken. 

…

It looks more like something that comes out of the chickens other rear orifice… and I don’t mean eggs! 

Edited Thursday at 07:19 by RT65CB-SWL