Lunt 50 with >100mm Lense

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amendola
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Lunt 50 with >100mm Lense

Post by amendola » Thu May 04, 2017 5:16 pm

Hello all,

So after studying this for a bit I've hatched a new scheme to get more resolution. Please chime in!

I'd like to add resolution to my Lunt 50mm by:
1) removing the objective lens.
2) Extend the tube -- I've got lots of thoughts for this but nothing concrete yet.
i) One idea is to get a threaded aluminium tube the same diameter as the double stack. Use it to connect the objective end, to a lunt filter telescope adapter. Then attach the adapter to an aluminium tube
3) add a new larger diameter F/7 lens to the end of the tube.
4) add an ERF

I'm not having much luck fnding a large F7 lens though. I've found F7.8,6.5 etc. Does anyone know where I can buy one? Or does anyone know what F value would be close enough?

Looking through http://alag3.mfa.kfki.hu/astro/giantlenses/127mm.htm I find several, but have no idea how to buy one. The links all seem dead, or not meant for purchasing by mortals.

This one is 7.3, and pretty cheap...
http://www.telescope.com/Telescopes/Ref ... 103111.uts

This one is 6.3 and also cheap...
http://www.telescope.com/Telescopes/Ref ... 116659.uts

Jamie







Jamie

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Re: Lunt 50 with >100mm Lense

Post by GreatAttractor » Thu May 04, 2017 8:43 pm

Hi Jamie, you may find this thread to be of interest: viewtopic.php?f=9&t=19238
BTW, this Starblast looks like the Celestron SkyScout I used in my mod.
My software:
Stackistry — an open-source cross-platform image stacker
ImPPG — stack post-processing and animation alignment
My images

SW Mak-Cass 127, ATM Hα scope (D=90 mm, LS50 etalon), Lunt LS50THa, ATM SSM, ATM Newt 300/1500 mm, PGR Chameleon 3 mono (ICX445)

amendola
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Re: Lunt 50 with >100mm Lense

Post by amendola » Thu May 04, 2017 11:42 pm

Looks like you had some great results!

So I'm poking around a bit more, what do you think about using an es 152mm F6.5?

It's more money, and the F ratio isn't a perfect fit, but it's got more aperture!

Jamie

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Re: Lunt 50 with >100mm Lense

Post by GreatAttractor » Fri May 05, 2017 6:21 pm

I don't see why not, go ahead.

Are you going to use a full-aperture ERF? As I remember, someone reported image deterioration due to thermals with a small sub-aperture ERF, cured by using a front-mounted one.
My software:
Stackistry — an open-source cross-platform image stacker
ImPPG — stack post-processing and animation alignment
My images

SW Mak-Cass 127, ATM Hα scope (D=90 mm, LS50 etalon), Lunt LS50THa, ATM SSM, ATM Newt 300/1500 mm, PGR Chameleon 3 mono (ICX445)

amendola
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Re: Lunt 50 with >100mm Lense

Post by amendola » Fri May 05, 2017 11:32 pm

I will use a full aperture ERF.

So I'm actually thinking of going back to my earlier idea. Remove the objective lens. Get a thread that fits into the objective end of the scope, screw that into the scope then into a lunt filter adapter then attach a tube that will hold my new objective lens. This way I just try and find a good quality objective lens and some adapters + ERF. I also have a double stack which will sit between the new tube and the lunt tube.

As for the F7 aspect. I've seen several posts that say you need to use a F7 objective lens with Lunt 50 mods. I'm honestly not sure exactly why, but it seems that the Diagonal filter that comes with the lunt 50 has some optics that require it.

I've found quite a few lens options on aliexpress, and elsewhere but I never seem to be able to find F7. Do you know why they recommend f7? Is there some lens in the diagonal that I can remove or replace to be able to switch to a different ratio?

Jamie

amendola
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Re: Lunt 50 with >100mm Lense

Post by amendola » Sat May 06, 2017 12:06 am

OK, I think that I'm getting it...

So the B600 that I have is good for a focal length of 600mm, so that's why there is the issue. As long as I keep it under 600 I should be fine. So a scope with Less than 7 should help keep the focal length down...

Jamie

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Re: Lunt 50 with >100mm Lense

Post by GreatAttractor » Sat May 06, 2017 8:22 am

It's not about the diagonal, but the collimating lens in the etalon assembly (the negative lens facing the objective). Its diameter, focal length and etalon's diameter are prepared to accept an f/7 light cone. If you use a smaller F-number objective, some of its light cone will be clipped in the etalon assembly, giving a smaller effective aperture. Larger F-numbers will give smaller resolution than what's possible. Neither of those problems is critical, so an f/6.5 objective will do.
My software:
Stackistry — an open-source cross-platform image stacker
ImPPG — stack post-processing and animation alignment
My images

SW Mak-Cass 127, ATM Hα scope (D=90 mm, LS50 etalon), Lunt LS50THa, ATM SSM, ATM Newt 300/1500 mm, PGR Chameleon 3 mono (ICX445)

amendola
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Re: Lunt 50 with >100mm Lense

Post by amendola » Mon May 08, 2017 4:17 pm

Thanks for explaining that to me! So I am going with an ES 127 acro. It didn't look like I'd save any money just getting a lens, and this way I've got another scope.

Jamie


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