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Author Topic: EC90 DS 0.5A solar scope - no ERF!  (Read 4711 times)

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Offline Merlin66

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EC90 DS 0.5A solar scope - no ERF!
« on: 05:40:45, 25 May, 2008 »
OK, call me nuts, or maybe even masochistic, but I could n't sleep....
I'm going to modify the EC90 concept to give a double stacked 0.5A capablity WITHOUT an expensive ERF!
Before you all jump up and down about safety and risk assessment, here's what it's all about.

Use a 90mm objective, a 50/50 mirror bend the light to another 50/50 mirror which sends the beam back towards the objective but 100 above the original optical axis... with me so far.... This will reduce the amount of heat/ light energy by 75% ( ie a 90mm objective becomes the equivalent (heat wise) of a 45mm lens) A -200mm barlow is then placed in the light path to give a collimated beam...
This return beam is then directed to a PST double stacked with a SM40, this should give a resolution of 0.5A with an effective clear aperture of 90mm!!
Because the SM40 is already designed as its own ERF, the reducion of the heat load with the mirrors will not subject it to any more energy than it was originally designed for.
Thinking about the central obstruction on the SM40... this should make no difference what so ever... you don't notice it at the moment, why would it be any different in this set-up.
So, I've already got one 50/50 mirror about 50mm square and can use a 2" diagonal for the other ( initially with an ERF up front!), got a 2" TV Big barlow; got the double stacked PST, I'll remove the PST Black Box and use the Revelation focusser+ BF5 (until I can find a BF10) .... only need a few hours to hang it together.

C11, C9.25 SCT, 4" Genesis, NEQ6pro, modded 1000D,  ATik314L+, DMK41AF04, SM60DS/BF15, and Spectroscopes (many!).
http://tech.groups.yahoo.com/group/astronomical_spectroscopy/
"Astronomical Spectroscopy for Amateurs", "Grating Spectroscopes-How to Use them" -Springer

Offline colinsk

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Re: EC90 DS 0.5A solar scope - no ERF!
« Reply #1 on: 06:07:17, 25 May, 2008 »
Well, the SM40 is an ERF so you are not in a big risk. Perhpas you can get a mirror that only rejects the IR and UV? I have seen them on projectors.

Offline michaeloconnell78

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Re: EC90 DS 0.5A solar scope - no ERF!
« Reply #2 on: 09:11:56, 25 May, 2008 »
You might want to have a look at this:

http://translate.google.com/translate?u=www.sonnen-filter.de%2F&hl=en&ie=UTF8&sl=de&tl=en



It offers excelllent protection in UV but very little in IR.
Personally, I would prefer an IR blocking filter at the front as well. I really don't understand why they don't include this at the objective. At present, as I understand, it is the little blocking filter which takes all the brunt of the IR energy and as a result can fail over time.

In terms of what you are doing, it makes sense. Slightly complicated setup though.

Michael.
Regards,
Michael
www.astroshot.com
Gemini G41 Observatory+ Mount; 16" LX200 SCT, TEC140; Pentax75SDHF; PST CaK, PST Ha.

Offline Solar B

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Re: EC90 DS 0.5A solar scope - no ERF!
« Reply #3 on: 10:22:47, 25 May, 2008 »
0.5 is the modding "Holy Grail" .
                             Brian

Offline NickH

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Re: EC90 DS 0.5A solar scope - no ERF!
« Reply #4 on: 14:12:57, 25 May, 2008 »
0.3A is even better..

Seen the Daystar stuff at that bandpass!

Keen to see if this works.

Celestron C11: DSI-C/Toucam Pro 2 ICX mod and SC1.5 mod/ Meade LPI/EOS300D/ED80/WO80ZS/Shoestring guider. PST/PST CaK/ART285

No time....always bloomin cloudy...need to build the Obsy..

Offline colinsk

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Re: EC90 DS 0.5A solar scope - no ERF!
« Reply #5 on: 16:20:48, 25 May, 2008 »
Etalons are bad at reducing the side band light. A double stack is much better. A double stack to .7 is better than a single .7 for contrast. I have heard the holy grail is a .5A Lyot filter with two 1A Lyot elements. I have an article from the 60s on making one from quartz but the whole thing is a couple of feet long! It would end up with something like 5% transmission on band! But zip for off band. You could use it on any aperture and it would cost about $1000.


Offline Merlin66

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Re: EC90 DS 0.5A solar scope - no ERF!
« Reply #6 on: 07:48:39, 26 May, 2008 »
Michael, have some K for finding Hobel's site!!!!!
Some VERY interesting stuff there.
Looking closely at the SM60 results: the resolution of his spectroscope doesn't show the resonance "bands" of the elaton but just the overall shape of the spectrum transmission curve, which looks very similar to the Wratten #25. The front BF element is, as thought, a broadband ha filter, 600 to 700nm, peaking at 45% transmission at Ha.
The results for the rear Bf filter I found confusing. The general curve shows no transmission below 750nm, but the detailed graph shows the narrowband 655.9 to 656.8 bandwidth, passing about 65% at Ha.
This would infer that we need a 1nm Ha filter to act as a BF to the etalon...
I'd really like to get a high resolution spectrum with the SM40 etalon, just to see the resonance bands and their width.
Good stuff!!
C11, C9.25 SCT, 4" Genesis, NEQ6pro, modded 1000D,  ATik314L+, DMK41AF04, SM60DS/BF15, and Spectroscopes (many!).
http://tech.groups.yahoo.com/group/astronomical_spectroscopy/
"Astronomical Spectroscopy for Amateurs", "Grating Spectroscopes-How to Use them" -Springer

Offline colinsk

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Re: EC90 DS 0.5A solar scope - no ERF!
« Reply #7 on: 15:16:31, 26 May, 2008 »
I was surprised to seen how much off band light got through the blocking filter too. The 1nm bandpass sounds about right. That would match an etalon with a FSR of 1nm. I hope you get a chance to measure one.

Offline Solar B

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Re: EC90 DS 0.5A solar scope - no ERF!
« Reply #8 on: 20:36:41, 26 May, 2008 »
Talking about the 0.5 being the Modders "Holy Grail" which i believe to be true....certainly at this apeture.

How come the SolaRedi can manage 0.3 without an oven.....sure you can goto 0.2 with a S Spectrum but that needs
an oven.....it must have a triple etalon system.http://www.daystarfilters.com/SolaREDi/SolaREDiAlpha.shtml
 
                                                                                   Brian     

Offline michaeloconnell78

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Re: EC90 DS 0.5A solar scope - no ERF!
« Reply #9 on: 21:03:24, 26 May, 2008 »
You don't necessarily need an oven - look at Daystar's T-Scanner series.
I looked through a Solarspectum 0.2A filter at the Winter Star Party in Florida earlier this year.
Proms and surface detail were visible.
Truly a class filter.
Views were absolutely stunning!
Regards,
Michael
www.astroshot.com
Gemini G41 Observatory+ Mount; 16" LX200 SCT, TEC140; Pentax75SDHF; PST CaK, PST Ha.

Offline Solar B

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Re: EC90 DS 0.5A solar scope - no ERF!
« Reply #10 on: 22:59:04, 26 May, 2008 »
Right i did,nt realise the T-scanners were power free units  :roll:
                                                   
                                                                     Brian                                                                           
 

Offline colinsk

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Re: EC90 DS 0.5A solar scope - no ERF!
« Reply #11 on: 04:46:49, 27 May, 2008 »
Quote
Specifications:

Clear Aperture: 35mm
Focal Length: 320mm
Limiting Resolution: 4.7 Arcseconds
Operating Temperature: approx. 50-90° F
Wavelength Shift range: 2.5Å
100% safe and fully blocked directly through the OTA


Did you see the temperature range?

However with 35mm of clear aperture I think this is the modders choice! We will see if enough of them are created to get people modding them. Mica is more tolerant of angle deviations than air spaced etalons making the optical side of a larger aperture easier.

Offline Merlin66

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Re: EC90 DS 0.5A solar scope - no ERF!
« Reply #12 on: 11:54:50, 27 May, 2008 »
Well, just finalising the optical train and laser aligning. A bit dissappointed to find that the Meade diagonals are NOT set exactly at 90 deg; just a bit more fiddling!!
Proof of concept prototype should be finished tomorrow ( just in time for the rain to stop!)
The attached photo shows the ED90 square tube with the two 2" diagonals feeding up to a 2" Barlow then into the PST fitted with the SM40, Revelation focusser and BF5 at the end.
By bending the optics back on themself, you get quite a compact design only 590mm long.
Hoping it all works as planned....

[attachment deleted by admin]
C11, C9.25 SCT, 4" Genesis, NEQ6pro, modded 1000D,  ATik314L+, DMK41AF04, SM60DS/BF15, and Spectroscopes (many!).
http://tech.groups.yahoo.com/group/astronomical_spectroscopy/
"Astronomical Spectroscopy for Amateurs", "Grating Spectroscopes-How to Use them" -Springer

Offline NickH

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Re: EC90 DS 0.5A solar scope - no ERF!
« Reply #13 on: 12:14:43, 27 May, 2008 »
Extreme modding...

Look forward to the results on this

Celestron C11: DSI-C/Toucam Pro 2 ICX mod and SC1.5 mod/ Meade LPI/EOS300D/ED80/WO80ZS/Shoestring guider. PST/PST CaK/ART285

No time....always bloomin cloudy...need to build the Obsy..

Offline Merlin66

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Re: EC90 DS 0.5A solar scope - no ERF!
« Reply #14 on: 09:32:57, 28 May, 2008 »
Ok, ready to rock and roll!!!
Everything looks tight and laser aligned, just need some sunshine and we can test it out.
Moved the mounting wedge to get better balance on the HEQ5Pro, but everything is still there to allow a quick change over back to a base EC90 model.
I'll do the initial trials with the C-ERF and the Meade diagonals; still waiting on a second 50/50 mirror from Surplus Shed to complete the "final design"
C11, C9.25 SCT, 4" Genesis, NEQ6pro, modded 1000D,  ATik314L+, DMK41AF04, SM60DS/BF15, and Spectroscopes (many!).
http://tech.groups.yahoo.com/group/astronomical_spectroscopy/
"Astronomical Spectroscopy for Amateurs", "Grating Spectroscopes-How to Use them" -Springer

 

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