CONTACT!

Frankenscope? Let's see it!***be advised that NOTHING in this forum has been safety tested and you are reading and using these posts at your own peril. blah, blah, blah... dont mess around with your eyesight when it comes to solar astronomy. Use appropriate filtration at all times...
RobBower

Re: CONTACT!

Post by RobBower »

Yeah I do spin my plates dry first! When they get sticky, that is where the most glass is in contact. As far as even goes... Not sure. The etalon I am trying to fix has 3 spacers. The one I got from brian has 4. So not sure if 1 is missing, or if its just a new way of doing it?

I have done the contact dry. But not dried by hairdrier. Just wiped and allowed to evaporate. The remaining residue.


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Re: CONTACT!

Post by Merlin66 »

Rob,
I don't know about "spinning" the plates! I'd be concerned that the spacers may impact with each other (if they are on different sides) and damage/ dislodge...
It's just a matter of visual inspection to see where the spacers are and mark the edge accordingly.
I had the plates in position "floating" on the acetone and just evaporated it away - thumb pressure at the end to see if it made any difference, and the spacers appeared to "bond" - no fringes visible.....


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Re: CONTACT!

Post by RobBower »

Yes Ken. You have to be watching the plates or know where they are as to NOT jam against another spacer! You can however feel the point where there is more drag on the plates than any other spot! And I am pretty sure there is now way I can visually tell when the space between is perfect! No eyeball is that good......

One of my plates is smaller than the others... So to see the contact of all in a uniform manner would be very tough! However.... The evaporation technique has my interest! If I must go for round 3..... That will be the method I attempt! After that... It may be replacing spacers....


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Re: CONTACT!

Post by Merlin66 »

Looking at the tuning spreadsheet, it seems the "optimun" spacers are 0.18mm thick...not sure that's a standard size at Home Depot or B&Q (UK);-)


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Re: CONTACT!

Post by RobBower »

Lol likely not.... I mentioned to Walter earlier about the microscope slides little square glass covers. I think they are in that range? Would be cheap and readily accessible ..... Something that might be considered?


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Re: CONTACT!

Post by RobBower »

Its not origional equipment. But a box of 100 of these in the perfect thickness is about 7 bucks! Each is about 22x22mm so you get loads of spacers per slide! :woohoo:


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Re: CONTACT!

Post by Merlin66 »

Hmmmm
Check out the spreadsheet - I think they may be too thin...
Also, I assume one plate may be 0.13 and another 0.17 etc - how do you tell the difference???
(Edit: I see these are "Pearl" finish - not optically polished flat finish..they may not make "contact")


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Re: CONTACT!

Post by RobBower »

They do have boxes of a single size. And you can pay for better quality versions as well! They also have a .18mm version made of plastic. Not sure if that would work or not. But they are made to seal micro things to microscope slides..... So.... For spacers they may work?


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Re: CONTACT!

Post by Merlin66 »

Rob,
Keep that in mind for "Plan B".....in the meantime see if you already have fixed the problem.....


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Re: CONTACT!

Post by RobBower »

If this contact didnt work... Im going to try your Evaporation method next. After that....I will grab some slides and start cutting. Lol


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Re: CONTACT!

Post by swisswalter »

Hi all

there must be a reason why older etalons have less spacers then newer ones. I noticed that on the PST etalons as well as on the LUNT LS50 Etalons. More restistance to decontacting ?


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Re: CONTACT!

Post by swisswalter »

Hi all

in order to transmit only 656.28 nm, I always thought that the distance of the two plates are the most important Parameter. If that is true, we have to know the exact thickness of the spacers, don't we ?


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Re: CONTACT!

Post by Merlin66 »

Walter,
Yes indeed.
The spreadsheet that Gert prepared for the pressure/ tilt tuning of etalons can provide an answer. According to the transmission graph for a tilted etalon, it appears that a 0.19mm spacing would give good performance.

Attached files etalon_tilt_pressure_v4.zip (78.7 KB)


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Re: CONTACT!

Post by Merlin66 »

I enclose a couple of images of the SM40...
The first couple shows the temporary card spacers used to centre the etalon in the housing in preparation of the "injection" of the twelve dabs of RTV - I cleaned the holes with a 2.5mm drill bit and used a medical syringe to pump the small amount needed.
I pre-loaded the etalon onto the backing foam with a 200gm load.
The other image shows (if you look carefully) the spacers around the edge.







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Re: CONTACT!

Post by swisswalter »

Hi Ken

thank's for the fine pics


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