LS35/ST80 Frankenscope build making progress

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michael.h.f.wilkinson
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LS35/ST80 Frankenscope build making progress

Post by michael.h.f.wilkinson »

After some advice on ths forum I decided to go for a collimator-based LS35 mod first. I should get an F=-174mm negative mensicus lens later this week, which will be fitted into a 2" helical focuser attached to an ST80 with internal 63mm ERF. The ST80 is attached to a vixen dovetail bar, which also holds the LS35. I can remove the ERF of the latter I suppose, but will initially keep it on. A shroud will be fitted over the etalon assembly and helical focuser. I realise the short focal length of the ST80 will increase spherical aberration, but I had one anyway, and it keeps the scope compact. The magnification of the initial Galilean scope is 2.3x in this configuration, yielding a total focal length of 920mm. My LS35 has a B1200 blocking filter (could get one for 5 euro more than a new B600, so that was a no-brainer), so that should be big enough. I am expecting sweetspotting issues, but certanly no worse than the 6" LS35 Frankenscope I have seen here.

The configuration shown uses the original gude-scope rings of the LS35 to allow tuning the alignment of the set-up, but I might replace these by a special purpose set I am making. My hunch is these will be more rigid, and might be less fiddly, hopefully requiring less re-tuning

I will keep you posted on the progress.
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Solar kit: GP-C8 with Thousand Oaks Solar filter, APM 80mm F/6, Lunt Herschel Wedge, Solar Spectrum 0.3Å H-alpha filter, Beloptic Tri-Band ERF (80mm free aperture), Thousand Oaks 90mm ERF, Coronado SolarMax II 60mm with Double Stack Unit. Lunt straight B1800 Ca-K module.
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swisswalter
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Re: LS35/ST80 Frankenscope build making progress

Post by swisswalter »

Hi Michael

that looks very good. Looking forward to your first light


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michael.h.f.wilkinson
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Re: LS35/ST80 Frankenscope build making progress

Post by michael.h.f.wilkinson »

Thanks, Walter. I should get the final bit (the meniscus lens) later this week, but the weather is not looking good, so first light might well be some way off. Aligning the beast is going to be a challenge, I assume.


Solar kit: GP-C8 with Thousand Oaks Solar filter, APM 80mm F/6, Lunt Herschel Wedge, Solar Spectrum 0.3Å H-alpha filter, Beloptic Tri-Band ERF (80mm free aperture), Thousand Oaks 90mm ERF, Coronado SolarMax II 60mm with Double Stack Unit. Lunt straight B1800 Ca-K module.
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Re: LS35/ST80 Frankenscope build making progress

Post by mdwmark »

Question?
You say your are going to use a -174mm meniscus lens. What made you decide to use that design and not a Plano concave lens.
Mark W.


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michael.h.f.wilkinson
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Re: LS35/ST80 Frankenscope build making progress

Post by michael.h.f.wilkinson »

Negative (!!) mensicus lenses tend to keep spherical aberration down, just like best-form lenses have lower SA than plano-convex. Besides, I could get a coated one cheaply :D. I could of course have a colleague of mine run the design through Zemax, to test thoroughly what is optimal, but as this is largely an experimental set-up I did not bother. It can be replaced easily should I want to.


Solar kit: GP-C8 with Thousand Oaks Solar filter, APM 80mm F/6, Lunt Herschel Wedge, Solar Spectrum 0.3Å H-alpha filter, Beloptic Tri-Band ERF (80mm free aperture), Thousand Oaks 90mm ERF, Coronado SolarMax II 60mm with Double Stack Unit. Lunt straight B1800 Ca-K module.
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