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Stacking two external Lunt DS filters

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Marcus444
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Stacking two external Lunt DS filters

Post by Marcus444 » Wed Oct 30, 2019 11:41 am

I’m wondering whether two stacked 60mm Lunt DS units (with a Televue 85 refractor and B1200 blocking filter) would deliver improved surface detail over the standard LS60/60 DS scope? Does anyone use a similar set up, and how challenging might it be to deal with shadows/reflections with two external etalons? I know there are forum members who use two Coronado filters, but I haven’t seen anyone with equivalent Lunt units.
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Re: Stacking two external Lunt DS filters

Post by MAURITS » Wed Oct 30, 2019 9:27 pm

I have the LS60F Ha as double stack (two pieces) used in the past but I prefer the LS60F Ha frontfilter as single stack, much nicer and clearer views.
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Re: Stacking two external Lunt DS filters

Post by Marcus444 » Wed Oct 30, 2019 10:42 pm

Thanks Maurits. Difficult to get a clear consensus on the performance of two external Lunt filters with a standard refractor.
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Re: Stacking two external Lunt DS filters

Post by MapleRidge » Wed Oct 30, 2019 11:31 pm

Hi MArcus...

Back when the Lunt line was launched, I bought their 50mm and 75mm etalons as well as a B1200 blocking filter. I double stacked the pair on a Celestron C102 OTA (1,000mm focal length) and once I got the hang of tuning the pair they gave great views and images. Visually, the view was on the dim side with the 50mm being the limit for light gathering.

How it would compare to the DS 60's on the Teleview scope is hard to say...personally I much prefer the double stack using the 75mm on my LS80T compared to anything I did with the double stacked external pair on the C102. Just my take on it.

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Re: Stacking two external Lunt DS filters

Post by Valery » Thu Oct 31, 2019 4:43 pm

It is a mistake to use two etalons which are rated as Double stacked model (which require more tilt to come to H-a core).
The pair must be:

1. Standard LS60FHa etalon for single stack view. Require very very little to no tilt to come to H-a core. This etalon must be main etalon and installed on the objective of the telescope used.

2. Etalong rated as "Double stack" etalon. This etalon require more tilt to come to H-a core. This made specially to get rid of interreflections between the etalons.

But now another ways is even better - to get two standard etalons and install a circular polarizing filter between them.


Hope this helps.

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Re: Stacking two external Lunt DS filters

Post by Marcus444 » Fri Nov 01, 2019 1:06 am

Thanks both. Very interesting.

Valery, I have what I thought was the standard LS60Fha filter (which has the ‘double stack verified’ sticker) - I presumed all Lunt external 60mm filters were the same?
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Re: Stacking two external Lunt DS filters

Post by Merlin66 » Fri Nov 01, 2019 4:54 am

I'm a double SM60 external stack user....being able to rotate one etalon relative to the other is almost mandatory. I'd assume the same for two Lunt filters.

Valery, I like the theory, but where do you get optical circular filters of the size needed? Then there's the cost $$$ of a special adaptor plate.
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Re: Stacking two external Lunt DS filters

Post by MAURITS » Fri Nov 01, 2019 8:41 am

Marcus444 wrote:
Fri Nov 01, 2019 1:06 am
Thanks both. Very interesting.

Valery, I have what I thought was the standard LS60Fha filter (which has the ‘double stack verified’ sticker) - I presumed all Lunt external 60mm filters were the same?
No, they are not, there are differences between them, even in combination with the Lunt blokking filters who have differences too.
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Re: Stacking two external Lunt DS filters

Post by Valery » Fri Nov 01, 2019 3:35 pm

Merlin66 wrote:
Fri Nov 01, 2019 4:54 am
I'm a double SM60 external stack user....being able to rotate one etalon relative to the other is almost mandatory. I'd assume the same for two Lunt filters.

Valery, I like the theory, but where do you get optical circular filters of the size needed? Then there's the cost $$$ of a special adaptor plate.
A 55mm or a 60mm circular polarizing filters are not rare at all. They are also of different quality and density. If to buy a B&W filter then it will have the best transmission and the best optical quality. It is easy to make an interface bwteen two etalons where you can make a thread to place the polarizer here.


Valery
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Re: Stacking two external Lunt DS filters

Post by Marcus444 » Fri Nov 01, 2019 5:41 pm

I thought I knew the Lunt range pretty well but have finally tracked down evidence - as Valery says - of an alternative white 60mm external filter. Only place I could find it was OPT in the States - not even on Lunt website (or Bresser in Europe). So suspect they’re not produced any more and not much chance of tracking one down in the UK. Longer term I’ll aim for an LS80 or Solar Spectrum I think - but thanks for the contributions.
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