PST etalon (or similar) in a telecentric beam

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Re: PST etalon (or similar) in a telecentric beam

Post by marktownley » Sun Dec 27, 2015 8:50 am

I rediscovered this topic having a read around on grey winters day.

I have a TZ4 now (after saying a year ago I was going to get one!), I've got a couple of experiments I want to try with it on my ED80 refractor, first off the PST etalon on it, secondly the Quark on it (minus it's native telecentric and blocker and with new, larger blocker fitted), and thirdly the PST etalon and Quark on it in stacked configuration. Don't expect anything quick in terms of results - mid february at the earliest, and that is with good weather - mid winter now with the sun at it's lowest. Plus I need to expand my collection of T-thread adapters for maximum connectivity options.

Over a year on, and maybe a little wiser(?), we talk about 2 types of etalons - air spaced, the Coronado and Lunts, and solid etalons, the Daystar and Solar Spectrums. However I wonder realistically if the first type can be divided down into 2 sub categories - Those designed to sit on the front of a scope infront of an objective and those designed to be used in a collimated optical setup - basically external and internal. I also wonder how these are designed differently? We talked earlier about a 0.5a air spaced (eg PST etalon) running in an f30 telecentric beam and said that it would be effectively working at 1.2a, but when you look at the shots Frederic is getting with the 8" HaT and PST etalon in an f27.8 telecentric they certainly look a lot more contrasty than what a 1.2a bandpass would give.

I wonder how sensitive etalon performance is in situations like this to 'perfect' telecentricity? In other words like with the 8" HaT where you have a telecentric designed bespoke for the optical system (8" Edge HD) then you would expect to get 100% perfect results as this is what you are designed for. However, say with the TZ4 on the back of a (random) refractor, say my ED80 for example, you get less than perfect telecentricity but still a reasonable result, maybe analogous to the quark - where people use the same telecentric system on a wide variety of scopes and focal ratios, it works to a point but only sub optimally (we don't know what optical configuration the telecentric on the quark was designed for). Then maybe a step further and take the example of a Televue Powermate, allegedly telecentric and used widely with daystar filters on a wide variety of optical configurations of scopes, maybe we're only getting a fraction of the performance we could with this setup?
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Re: PST etalon (or similar) in a telecentric beam

Post by marktownley » Sun Dec 27, 2015 9:36 pm

I guess it's appropriate to include a link to this - very relevant http://www.cloudynights.com/topic/48759 ... t-filters/
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Re: PST etalon (or similar) in a telecentric beam

Post by Valery » Mon Dec 28, 2015 1:55 am

Thanks, Mark, for your info.



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Re: PST etalon (or similar) in a telecentric beam

Post by marktownley » Mon Dec 28, 2015 7:48 am

Thanks Valery, yes, the more experiences we have of these etalons and combinations the better :)
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Re: PST etalon (or similar) in a telecentric beam

Post by GreatAttractor » Mon Dec 28, 2015 7:56 am

Valery wrote: I found that my BF10 Coronado is absolutely the best blocker I ever used. It is 3x brighter and a bit more contrasty that two my Lunt B1200 and 5x brighter than Lunt B1800.
Valery,
Interesting, perhaps I will take a BF10 instead of a Lunt B1200 when I'll be replacing my B600. Can you unscrew the eyepiece holder and 1.25" nosepiece from the diagonal? Does it have T2 threads underneath like Lunt diagonals?
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Re: PST etalon (or similar) in a telecentric beam

Post by marktownley » Mon Dec 28, 2015 8:02 am

GreatAttractor wrote:Can you unscrew the eyepiece holder and 1.25" nosepiece from the diagonal? Does it have T2 threads underneath like Lunt diagonals?
On mine with a bit of force initially to break the threadlock which Coronado seems to like using it will come apart, but i'm fairly certain it's not T2, not sure what it is without measuring. Should be easy enough to make an adapter though.
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Re: PST etalon (or similar) in a telecentric beam

Post by solarmax2016 » Tue Feb 09, 2016 12:22 am

I have a PST MOD on my Meade 102ED that produces good images in the range of a .4 to .5 Angstrom quality Etalon.
Looking at the recent comments on discarding the front and rear collimators, I erroneously tried inserting a Losmandy
Telecentric lens in front of the front collimator lens which of course did not work. The idea of removing the front and
back collimators and substituting the Losmany Telecentric only sounds sensible. In making the PST MOD to suit my
demands I machined its entire optical unit in Anodizing grade aluminum which I anodized bright black. Integral
focus was achieved with a Lunt variable focuser. It takes either a Lunt 12 mm Blocker in diagonal or straight-through
Lunt 12 mm blocker focusing perfectly. The minus 200 focal length required by the PST etalon places a 2" nosepiece
at 1-1/2 inch length right up against the Meade 102 focuser racked in as far as it goes. The Meade 102 was made for
this application with a very long focal outreach. The unique thing about the Losmandy Telecentric is that its 2" barrel
fits right into a regular focuser and its rear threads are in a T-thread, so only a T-thread adapter to the 50 mm Metric
are required to fit into the front PST Etalon. That thread is what machinists call a difficult thread to cut - substituting
either a 42 or 46 British Thread to substitute for it. It cost me well over $150.00 to make this rig . Comments?

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Re: PST etalon (or similar) in a telecentric beam

Post by Valery » Mon Feb 22, 2016 11:58 am

Very interesing.
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Re: PST etalon (or similar) in a telecentric beam

Post by Galosimo » Wed Feb 24, 2016 6:06 pm

I read your discussion and I wanted to share with you but experience. I apologize but I use the translator. I use a successful hack as previous therad, 152/900 that before I replaced the pst front lens with a -120 for my reach, then still not happy because there was still the sweet spo very visible I did do a telecentric 5 x own for my focal of 900. Now I have the image completely in h-alpha without sweet spot I mounted a BF15 and wait to find a second .pst to double the bandwidth. I also modified by the addition of an h-alpha omega optical filter placed before or after the telecentric which greatly improves the contrast. plus I added a tube to the telescope to avoid the big rush and I assure you that the image is excellent.

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Re: PST etalon (or similar) in a telecentric beam

Post by Galosimo » Wed Feb 24, 2016 6:27 pm

Versione 1.jpg
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It is very well known extension

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Re: PST etalon (or similar) in a telecentric beam

Post by Galosimo » Thu Feb 25, 2016 9:27 am

I used this a h-alpha filter:
http://www.ebay.com/itm/Optical-Interfe ... 1670196736
the light fades slightly but the filter must use with t2 tilting.
The telecentric system is hidden inside the tube, and this week I build a tilting to erf that menterò the wire of the telescope where it starts that particular flange then I will have a tilting to erf very convenient. I look only to find the second pst to add the x doblestuck.

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Re: PST etalon (or similar) in a telecentric beam

Post by marktownley » Thu Feb 25, 2016 11:31 am

Some nice mods there!
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