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Lunt etalon

Posted: Fri Sep 06, 2019 6:49 pm
Is there a big difference between the Lunt LS50F Ha and the Lunt LS50c Ha front filter.

I know, white color vs red color ...
Difference thread M90 vs M80 ...
I mean a REAL difference about tuning, technic, visual use, imaging use ...?

I see that the LS50F Ha in some places are discontinued to 25% less, make this a difference to buy the white one instead of the red one?

Re: Lunt etalon

Posted: Sat Sep 07, 2019 7:54 am
Thanks for the feedback.
Other opinions....?

Re: Lunt etalon

Posted: Sun Sep 08, 2019 7:26 pm
by marktownley
Heya Chaps!

Sorry Maurits, i've had this flagged to reply for a while.

I have both etalons, the red one and the white one. You've noticed all the physical differences M80 v M90 thread size. The red one has a hinge tuner, same as the coronado SMxx etalons, the white one the etalon is tilted within the housing and the housing remains static. Essentially the red one is cheaper to manufacture.

BP, I measured mine, the free aperture of the ERF is 50mm and the free aperture of the etalon is definitely 50mm.

I have to be honest, with both red and white ones it's bit of a roll of the dice in terms of what performance you get from the (any!) etalons. Both my red and white ones have the 'Lunt Double Stack Certified' sticker on them, however they (mine) couldn't be more different. My red double stack etalon is the most on band etalon I have ever owned, and as a result I use it as a single stack etalon. It's a keeper, I will never sell it. The white one is definitely double stack only, if use it on it's own it doesn't even come close to being on band.

I've used both as double stackers too; the red one with a PT scope is sublime, great views! The white one on a PT scope is good, but there is a small gradient across the disk because it is off centre line. This wouldn't be a problem for most people but i'm a perfectionist with these things. Here's where it gets weird; the red one double stacking my SM90 doesn't work, weird ghosts that won't shift, it's bang on band with zero tilt - hence the ghosts! The white one works OK, again, with a slight gradient as before.

I've also tried double stacking each other, here, when DS two external etalons, the one that's closest on band needs to go closest to the objective, with the one with most tilt the outer etalon. In my case it meant the white one was on the end of the red one. The setup works really well, but there is a caveat; the weight of the white etalon on the end of the red one adds a turning moment, this imparts tilt, and as we know tilt takes an etalon off band. Problem is this turning moment is not as predictable as I would like, and as a result it isn't a quick system to setup, which with unpredictable weather isn't a help. I had all the proper adaptors made up for this too.

So, I come back to what i've always said about external etalons; there are 3 choices - either pay for something like a solarscope etalon, where it is made individually to be on band where you live, pay extra for a retailer to cherry pick a etalon for you from a wide range of stock (there are probably only 3 or 4 people globally who I would choose to do this), or, the way i've done, is to keep buying etalons until you find one that is fit for the purpose you desire. Unfortunately I find as a solar imager becomes more experienced then their expectations become higher! Also, the demands for imaging are much higher than visual; ever tuned an etalon visually then put a camera on to image only to find you have to retune to get an even field?

I just think the quality of all budget etalons is an unknown!


Re: Lunt etalon

Posted: Mon Sep 09, 2019 7:28 am
Hallo Mark,
A big thanks for the great explanation, sort of review about the Lunt LS50T Ha filter.
I read it very well, but I did not know there is a difference between the single stack and the double stack module.

When the Lunt "Double Stack Certified" sticker on them, is it than only for double stack useful as real first frontfilter with a second filter(front or inside the scope)?

When I want to use only the filter as "single stack" it would be better to not use the "Double Stack Certified "filter, if I understand it correctly.

The problem is mainly that the individual modules only are "Double Stack Certified" and NOT "single stack" ...
The only separate filters are included the B600 ... blocking filter as one set, so I have already this blokking filter B600.
How can I solve this, so I get a good combination?

Re: Lunt etalon

Posted: Mon Sep 09, 2019 6:34 pm
When I read about the Lunt LS60F Ha filter I think this is a better choice for my 60mm scope.
So, more aperture and maybe some more details to see visually, I hope so ...

Re: Lunt etalon

Posted: Tue Sep 10, 2019 3:57 pm
My mind is made up, I'm going for the Lunt LS50T Ha double stack etalons, most of the time for visual use.

Re: Lunt etalon

Posted: Tue Sep 10, 2019 5:08 pm
by marktownley
Having a look online it seems all Lunt etalons are stickered as double stack certified.

If, you can, try before you buy Maurits!

Re: Lunt etalon

Posted: Wed Sep 11, 2019 10:09 am
Thanks Mark for the info.