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Solar mod using a double stack etalon?

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Solar mod using a double stack etalon?

Post by hopskipson » Sun Sep 29, 2019 4:13 am

I've been running this idea around in my head and have wondered if anyone has tried this and if it turned out successful. I was thinking of using a Lunt pressure tuned etalon for their 80mm scope (https://luntsolarsystems.com/shop/solar ... ck-module/ ) and adapting it to be modular to fit refractors or SCT's. Besides adapters to attach to the different scopes is there anything that should go before the etalon? I have a full aperature DERF for the SCT would I need an IR blocking filter for the refractor? I'm thinking of using the Andover blocking filter after the etalon (656.3nm Bandpass Filter, FWHM 1nm, 25mm dia. 656FS02-25). Is this adequate? I know with the PST mods that the etalon needs to be 200 mm before the focal plane, will there be a similar offset using the Lunt? I was considering the PST but my luck with finding a good one is about 0% :lol: If this works out maybe I'll try to double stack it with a PST or my Quark. Thanks for reading and if you can offer any insight I would greatly appreciate it!

James

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Re: Solar mod using a double stack etalon?

Post by marktownley » Sun Sep 29, 2019 9:01 am

Yup, a few people on here have done it, here are some images from Brian from a few days ago viewtopic.php?f=4&t=26627 I've used my Lunt 50 scope etalon housing on my 8" SCT. Lunt systems are f7, so whatever the free diameter of the etalon x 7 is what the back focus needs to be. Similarly this is the same distance to the focal plane the other side of the etalon. The Andover blocker won't work, this only works with the Daystars, you will need a coronado or lunt blocking filter.
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Re: Solar mod using a double stack etalon?

Post by MapleRidge » Sun Sep 29, 2019 2:23 pm

Hi James...

As Mark mentioned, I have used the DSII module for the LS80T as a mod on a pair of Celestron refractors...first test was on a 4", f10 OTA and the current setup is fitted to the 6", 8 CR-150 OTA. This has been running since some time in 2012 and it has worked very well for me.

I have a 110mm Baader ERF fitted inside the tube, and a Moonlite motor focus behind the etalon. A local machine shop made up an adapter flange to mount the DSII to the scope (stock focuser and reducer flange are removed). I based the position of the etalon by finding focus as setup on the LS80T, then positioned the etalon to reach focus on the mod. I could probably fine tune the position a bit more but have never bothered.

Since the Lunt scopes are f7, the 'sweet spot' is limited to the centre of the field in my mod, so the f10/f8 scopes I use only are on band near the centre of the field. With a 3x barlow the field of view with the ZWO174MM camera pretty much crops out the best part of the field. It isn't a full disk imaging system ;)

I have used a Quark Combo to DS this system with some success, but limited time and solar activity during the summer has not allowed a lot of testing. I also tried to mount the DSII module to my C9.25 Edge (Daystar full aperture ERF), but I could not reach focus. I suspect I need to have a lower profile adapter made but that is on the back burner for now.

That's just a quick overview of the mod, let em know if you have any questions,
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Re: Solar mod using a double stack etalon?

Post by hopskipson » Sun Sep 29, 2019 3:32 pm

Are the single stack and double stack etalons basically the same? I ask as I might want to go with a 60 mm Lunt scope to get the blocking filter and etalon for around the same price and have the scope to boot. Also would putting a reducer before the etalon to bring it closer to f/7 be advised or would it introduce CA?

I’m no optical expert by any means but would moving the etalon up the tube increase the sweet spot? With the sct moving the mirror and with the f/8 refractor shortening the tube bringing the etalon higher in the light cone or am I over thinking this?

Thanks much for any advice !

James

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Re: Solar mod using a double stack etalon?

Post by MalVeauX » Mon Sep 30, 2019 11:03 am

Attached is Harald Paleske's unigraph with lunt etalons placed in the imaging train. See images for more info on his setup. This isn't an SCT, it's a huge folded refractor, but it still gives an idea of how these things are used in larger systems quite successfully.
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Re: Solar mod using a double stack etalon?

Post by hopskipson » Mon Sep 30, 2019 4:37 pm

That Unigraph is one very impressive piece of engineering! Don't think I have the space for such a scope. Thanks for the picture though. I was thinking of starting off single stack first.

As in my previous post, is the double stack 80 mm etalon the same general etalon as in the Lunt LS60THa PT 60 mm or does it need some special lens to bring it on band? I realize it would have a smaller sweet spot than the 80 and the position in the scope will be different but are they basically the same type of etalon?

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Re: Solar mod using a double stack etalon?

Post by MalVeauX » Mon Sep 30, 2019 6:54 pm

I'm not entirely certain; I'm curious if a double stack intended etalon has higher transmission (the ones labeled "must be used with another... blah blah"). With the internal Lunt DS options, they don't have ERFs, just the etalon, so you can control as much as possible that way. The front mounted options have glass in front of the etalon, colored, tilted, etc, meant to already face the sun so less control. From what I've seen from others, even a Lunt 50mm DS etalon has great transmission, but a tiny sweet spot of course. The real challenge is of course getting the focal-ratio right for the etalon in the focused position with a scope like a SCT that is F10.

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Re: Solar mod using a double stack etalon?

Post by george9 » Wed Oct 02, 2019 1:42 am

James, I use a Lunt DSII etalon (made for LS80) with my Quark on a 155mm f/7 refractor. I picked it because I already owned it and because the f/7 matched. It works well with only a slight reduction in sweet spot size; pretty much unnoticeable visually. It goes:

Baader 160mm DERF -> 155mm f/7 scope -> PreciseParts adapter -> DSII -> Lunt adapter -> focuser and spacer -> Quark -> diagonal -> binoviewer

More recently I swapped a SolarSpectrum 32mm filter + TZ4 for the Quark, and it worked even better. My lowest power is inside the sweet spot.

The DSII has a collimating lens pair for f/7 before and after. The LS80 internal etalon must also I assume, and I think the first lens of the internal one reflects IR guessing from the Lunt LS60 schematic. I am not sure if there is another ERF in front of the internal etalon on the LS80 and if so whether it is detachable.

I assume if you use an f/7 DSII in an f/10 scope, you just have to pull it back so that you are only using the inner 25mm (i.e., the f/10 cone within the wider f/7 cone). So you would be wasting etalon, but I would think it would work.

I am not sure about the small sweet spot.

Other mods use the raw etalons (35mm, 50mm, etc.) and come up with their own collimation solutions.

Oh, on spacing, my DSII is probably out a quarter inch too far from the objective, but it doesn't seem too sensitive to that. I can rack it out an inch further without detecting a difference in the view once I refocus with the second focuser. I calculated the proper distance by just measuring where the beam focused in an LS80 and aimed for the same location in the 155mm.

George
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Re: Solar mod using a double stack etalon?

Post by george9 » Wed Oct 02, 2019 1:45 am

Also, the Lunt LS60 might be f/8.3, which would be even closer to f/10. But it was nice using the LS80's DSII so that I did not have to modify it in the process; I just tighten it in. George

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Re: Solar mod using a double stack etalon?

Post by hopskipson » Wed Oct 02, 2019 8:22 pm

Thanks everyone for the useful information. I’m not sure exactly which way to go. I’m leaning towards the 60 mm scope since the price is similar, will come with a blocking filter and if it doesn’t work out I will still be able to use it by itself and possibly double stack it with the Quark. I’m trying not to over analyze this just would like something more reliable or better quality than a PST mod. Does this sound reasonable or would I be better off with the 80 DS? If anyone has more information or opinions to add I’m open to it. Thanks again!

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Re: Solar mod using a double stack etalon?

Post by MapleRidge » Wed Oct 02, 2019 11:55 pm

Hi James...

I see that Georges' mod is very similar to my own and has the advantage of a f7 light cone. Looks good George!!!

As for which is better, that is a bit harder to say since we each have different intents. I already owned the DSII module, so like George it was an easy choice. It is not much use on its own, so a scope that you can use as a stand alone solar scope and pull the etalon out of it to use on a larger scope makes a lot of sense. The mods all have some shortcoming in trying to mate equipment that wasn't meant to be used together, the sweet spot seems to be the most variable, but there are lots of examples of successful modding posted here.

Just my 2 cents worth ;)

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Re: Solar mod using a double stack etalon?

Post by george9 » Thu Oct 03, 2019 7:31 pm

Thanks, Brian and thanks for the info. Awesome. I was considering trying mine at f/10, too.

It seemed to me that a system designed for f/7 should work fine for f/10, as long as you place it so that the final focus (i.e., back focus without any equipment) is the same place as it would have been at f/7. You'll just be wasting the outer ring of etalon.

Do you think your narrower sweet spot is specifically the f-ratio mismatch, or just the usual side effect of double stacking?

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Re: Solar mod using a double stack etalon?

Post by hopskipson » Sat Oct 05, 2019 9:20 pm

Looks like I'm going to go with a LS60 Pressure tuned scope with a 1200 blocking filter. I'm sure I'll have more questions once I find one. Can someone share any experience or direct me to instructions with this type of mod? Thanks.
James

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Re: Solar mod using a double stack etalon?

Post by Valery » Sat Oct 05, 2019 11:30 pm

hopskipson wrote:
Sat Oct 05, 2019 9:20 pm
Looks like I'm going to go with a LS60 Pressure tuned scope with a 1200 blocking filter. I'm sure I'll have more questions once I find one. Can someone share any experience or direct me to instructions with this type of mod? Thanks.
James
This scope may be good for using it "as is" or as double stacked with LS60FHa etalon. But it is the worst for modding using it's PT etalon in abigger telescope.


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Re: Solar mod using a double stack etalon?

Post by hopskipson » Sun Oct 06, 2019 1:32 am

Valery wrote:
Sat Oct 05, 2019 11:30 pm
hopskipson wrote:
Sat Oct 05, 2019 9:20 pm
Looks like I'm going to go with a LS60 Pressure tuned scope with a 1200 blocking filter. I'm sure I'll have more questions once I find one. Can someone share any experience or direct me to instructions with this type of mod? Thanks.
James
This scope may be good for using it "as is" or as double stacked with LS60FHa etalon. But it is the worst for modding using it's PT etalon in abigger telescope.


Valery
Hi Valery

I truly respect your opinion can you please elaborate on this. What is your feeling on the DS 80 etalon for a mod? Is there a difference between the etalon used in the single stack scope and the DS 80 besides its size?

James

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Re: Solar mod using a double stack etalon?

Post by Valery » Sun Oct 06, 2019 12:24 pm

hopskipson wrote:
Sun Oct 06, 2019 1:32 am
Valery wrote:
Sat Oct 05, 2019 11:30 pm
hopskipson wrote:
Sat Oct 05, 2019 9:20 pm
Looks like I'm going to go with a LS60 Pressure tuned scope with a 1200 blocking filter. I'm sure I'll have more questions once I find one. Can someone share any experience or direct me to instructions with this type of mod? Thanks.
James
This scope may be good for using it "as is" or as double stacked with LS60FHa etalon. But it is the worst for modding using it's PT etalon in abigger telescope.


Valery
Hi Valery

I truly respect your opinion can you please elaborate on this. What is your feeling on the DS 80 etalon for a mod? Is there a difference between the etalon used in the single stack scope and the DS 80 besides its size?

James
This is only my speculation: best 50mm etalons should be in LS80THa - as main SS etalon. The DSII etalon for this telescope does not have to be very very good one. It must be bright and about 0.7-0.8A.
So, my guess is that LS80THa etalon (50mm) is better and will bring larger sweet spot (useful FOV).
One also can test the telescope and see if the etalon in the telescope is good enough for further steps in modding. It also has excellent resale value.


Valery
"Solar H alpha activity is the most dynamic and compelling thing you can see in a telescope, so spend accordingly." (c) Bob Yoesle.

Largest full size 185 - 356mm Dielectric Energy Rejection Filters (D-ERF) by ARIES Instruments.

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Re: Solar mod using a double stack etalon?

Post by hopskipson » Sun Oct 06, 2019 6:15 pm

Valery wrote:
Sun Oct 06, 2019 12:24 pm
hopskipson wrote:
Sun Oct 06, 2019 1:32 am
Valery wrote:
Sat Oct 05, 2019 11:30 pm


This scope may be good for using it "as is" or as double stacked with LS60FHa etalon. But it is the worst for modding using it's PT etalon in abigger telescope.


Valery
Hi Valery

I truly respect your opinion can you please elaborate on this. What is your feeling on the DS 80 etalon for a mod? Is there a difference between the etalon used in the single stack scope and the DS 80 besides its size?

James
This is only my speculation: best 50mm etalons should be in LS80THa - as main SS etalon. The DSII etalon for this telescope does not have to be very very good one. It must be bright and about 0.7-0.8A.
So, my guess is that LS80THa etalon (50mm) is better and will bring larger sweet spot (useful FOV).
One also can test the telescope and see if the etalon in the telescope is good enough for further steps in modding. It also has excellent resale value.


Valery
I understand the 80 mm SS etalon will be better than the 60 mm, but you don't think it's even worth using the 60 as a mod? How would the 60 "stack up" :roll: with say a PST or Lunt 50 mm mod? My thinking would be that I could get a better etalon from the 60 Lunt than from a PST or am I mistaken. My issue between the 60 and 80 is the price difference. Maybe in a year or 2 I might be able to swing the 80 hopefully trading in or selling the 60.

Anyone else have any opinions or experience to add?

Thanks
James

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Re: Solar mod using a double stack etalon?

Post by Valery » Sun Oct 06, 2019 7:00 pm

James,

better wait and take an 80mm scope and if it really good (as they mostly are) then try to modify it.

The etalon in 60mm telescope and it's surrounding lenses are designed for work with a singlet objective. It will not work well in modding as you can't find a telescope with aberrations close to what are in a singlet objective.


Valery
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Re: Solar mod using a double stack etalon?

Post by hopskipson » Sun Oct 06, 2019 8:19 pm

Thanks Valery for that explanation.

I guess I will be looking for a decent PST to mod as using the Quark in my C8 at over 8000mm focal length is very difficult at my location or are there any other mods that might be more consistent than a PST without breaking the bank?

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