Doublestack for mod

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Doublestack for mod

Post by Ivan »

Hello everyone,

I recently built a mod using William Optics Megrez 90 and etalon Lunt50. It doesn't work badly, but I want to double the stack.

What are the options for this?

I heard that you can use Quark after etalon Lunt, but quarks are scary in their spread in quality, and besides, 4x Barlow is built in there. I am not familiar with Quark and I fear that I will not find normal visibility for the 4x621mm focal length of my telescope. Of course, if I didn't mess anything up :)

A more expensive option and more convenient and predictable (in my opinion) is to use aperture etalon. The aperture of my telescope is 90mm. So I thought to order a double stack of Coronado. Like this one:
https://optcorp.com/collections/solar-t ... er-package
But the description says that it cannot be used without secondary interference filter. Is it really so?
If yes, then it turns out that I need this one:
https://optcorp.com/collections/solar-t ... ter-w-bf15
In this case I I'm out of my budget :( And besides, I didn't want to buy a filter unit yet.

Most likely, 90mm of my telescope is not being used, 100%, something cuts off etalon Lunt50, the problem is that I do not know which aperture is used. And I thought that maybe knowing it, I could choose a smaller and cheaper front filter, for example, 60mm Lunt with or without a block filter, for example:
https://optcorp.com/collections/solar-t ... h-focusers

Please advise on how to proceed optimally.

Ivan


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Re: Doublestack for mod

Post by Bob Yoesle »

Hi Ivan,

First, what do you mean by "it doesn't work badly"? It doesn't work very well? For example, if you have an objectional "sweet spot," or the image is not bright enough, double stacking will make these things worse.

Did you make the modification? There seems there's too little information (nor any images) about your current "mod" to be able to provide an informed answer. If the 50 mm etalon is on the front of the telescope ahead of the objective, that is not a "mod." Are you using a Lunt blocking filter with that? Where is the "etalon 50 mm" placed, are you using a collimator system, etc.? If you're already using the 50 mm etalon and a collimator system internally with a Lunt blocking filter, and want to add a 90 mm front etalon to double stack, that would obviously work. The issue that you may not realize this would be concerning. However, double stacking with a second 60 mm etalon and reducing your aperture from 90 mm does not seem a good trade-off for double stacking.

Additionally, it seems you might lack needed knowledge about H alpha solar filter systems and what the basic components are: If you "built a mod" solar telescope using a Megrez 90 and a Lunt 50 etalon - and yet apparently don't know why an etalon might need a "secondary interference" blocking filter, or whether or not need one (which you should already have for use with the LS50FHa), it seems you probably shouldn't be attempting anything else to begin with.


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Re: Doublestack for mod

Post by Ivan »

Bob Yoesle wrote: Fri Oct 01, 2021 9:57 pm Hi Ivan,

First, what do you mean by "it doesn't work badly"? It doesn't work very well? For example, if you have an objectional "sweet spot," or the image is not bright enough, double stacking will make these things worse.
Thanks for the detailed answer Bob,

Several photos with a × 2 Barlow lens, I have posted them for you to rate them:
3.jpg
3.jpg (365.21 KiB) Viewed 8037 times
2.jpg
2.jpg (360.54 KiB) Viewed 8037 times
1.jpg
1.jpg (314.01 KiB) Viewed 8037 times
Photo of the mod itself:
6.jpg
6.jpg (687.49 KiB) Viewed 8037 times
There are no filters on the side of the lens. In front of the red sub-aperture erf Lunt50 is mounted with a slight slope of 2 "cls. Based on your answer, my questions can be reformulated:

1. Is it possible to use Quark as DS in my telescope?

2. This particular model DS coronado (it says that it cannot be used without the main filter) can be used as an aperture filter (etalon Lunt50 with BF will be in the back of the mod):
https://optcorp.com/collections/solar-t ... er-package

From your answer, I realized that aperture filters less than 90mm will degrade the result.

Thanks,
Ivan


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Re: Doublestack for mod

Post by Bob Yoesle »

Hi Ivan,

Thanks for the pics - they provide all the missing information, and your system is doing very well!

You're using a pressure-tuned LS50 internal etlaon/collimator system with a Lunt blocking filter, so all you need is the SM90 front etalon, and no additional Coronado blocking filter. I think the Quark would be inferior, but if you went that route you wouldn't need the B600 Lunt blocking filter, as the Quark incorporates that in its filter stack.

Even though the SM90II and SM90III RichView etalons are generally not as good compared to the original tilt-tuned only SM90s, they generally will be OK for use as a double stacking etalon, and the Quark quality generally seems to be no better - and might prove worse.

So despite my misgivings about RichView tuned Coronado's, that would be my choice for double stacking your telescope - and avoids the excessive increase in the focal length from the built-in 4.2 x Quark telecentric lens.


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Re: Doublestack for mod

Post by Rusted »

Bob,

Would adding another pressure tuned etalon in series be a better option?


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Re: Doublestack for mod

Post by Bob Yoesle »

From what I have observed - no. With an internal primary etalon, I would always go with a front mounted external etalon as the first choice for double stacking.

The Secondary internal double stacking modules seem to produce more prominent and difficult to mitigate internal reflections, which due to the collimating lenses become out of focus larger discs and increase background image brightness/noise. This then requires additional filtering such as can be done with a circular polarizer. This however will cut image brightness by about 50%. Front mounted etalons which are tilt-tuned make retro-reflections in a double-stacked system a much easier to resolve issue.


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Re: Doublestack for mod

Post by Ivan »

Bob, thank you so much for your professional advice and invaluable experience. :bow

I have heard that DS Coronado does not tolerate transportation well. I have heard of several cases of etalon decontact.
Do you know how common this situation is? And are there any packaging methods that can minimize this chance?

Thanks,
Ivan


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Re: Doublestack for mod

Post by Bob Yoesle »

Hi Ivan,

I don't have any hard data on how common this might be, but given the etalon is no longer secured on the sides and poorly supported on the bottom, this seems like it would be a common occurrence:

SM90 v SM90II.jpg
SM90 v SM90II.jpg (238.1 KiB) Viewed 7976 times
Left: An original SM90 with side silicone buttons for support. Right: SM90II with NO side buttons, a "smear" of silicone appears to be the only support. I would be sure to have some degree of RichView pressure applied before shipping - but not too much - in order to help minimize etalon movement in the etalon chamber.

At a minimum you'd need to double box with generous cushioning. I like to enclose the etalon in a sealed plastic bag, generously wrap with bubble wrap, fit in a tight fitting box. Place this in a larger box with thick rigid foam insulation on all sides. Place this box in another cushioned and thick rigid cardboard box, and there's not a lot more you can do. Be sure to have the shipment insured if possible and inspect immediately on receipt for de-contacting:

Decontacted etalon.jpg
Decontacted etalon.jpg (120 KiB) Viewed 7976 times

Good luck ;-)


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Re: Doublestack for mod

Post by Ivan »

Thanks again, Bob!

Ivan


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Re: Doublestack for mod

Post by Ivan »

Bob Yoesle wrote: Sat Oct 02, 2021 2:30 pm Hi Ivan,

Thanks for the pics - they provide all the missing information, and your system is doing very well!

You're using a pressure-tuned LS50 internal etlaon/collimator system with a Lunt blocking filter, so all you need is the SM90 front etalon, and no additional Coronado blocking filter. I think the Quark would be inferior, but if you went that route you wouldn't need the B600 Lunt blocking filter, as the Quark incorporates that in its filter stack.

Even though the SM90II and SM90III RichView etalons are generally not as good compared to the original tilt-tuned only SM90s, they generally will be OK for use as a double stacking etalon, and the Quark quality generally seems to be no better - and might prove worse.

So despite my misgivings about RichView tuned Coronado's, that would be my choice for double stacking your telescope - and avoids the excessive increase in the focal length from the built-in 4.2 x Quark telecentric lens.

Bob, tell me, what if use Quark Combo as DS? Will this work in my refractor at f / 6.9? The instructions for the Combo indicate that it is designed for f / 15 or more. I ask because I'm afraid that the four-fold telecentric of the classic Quark will excessively increase the focal length (621mm), with a small aperture of 90mm.

Ivan


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Re: Doublestack for mod

Post by marktownley »

Hi Ivan

The Quark is only ever going to work when presented with ~f30 beam, so, with your current setup use a 4x telecentric ahead of it and will work well. But, that 4x scale increase is only going to reduce your field of view.

No such thing as a free lunch in solar, if you can get a good 90mm etalon, Like Bob says, would work great with your setup...

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Re: Doublestack for mod

Post by Ivan »

Thanks Mark,

I understand that there is no free lunch. I am very grateful for the help gave me.

I want and can buy a DS90, but it scares me very much that there may be trouble with it during transportation. Above, Bob showed the differences between the front etalons. And I know of at least two cases of de-contacting during transportation. That is why the question of Quark has arisen again.

Ivan


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Re: Doublestack for mod

Post by DavidP »

I have a tilt-tuned Lunt front mounted double stack. When mounting it one time, I accidentally dropped it to the ground from 4 feet above. Although the earth was fairly soft, I was horrified, and was sure I had broken the unit or at least had de-contact. To my surprise everything was fine. This is not to say that they are indestructible, only that some of them are pretty well-built. I wouldn’t worry too much about buying a new unit from the manufacturer simply because you’re afraid of shipping. If you were looking for secondhand, I would simply stipulate your shipping requirement.


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Re: Doublestack for mod

Post by EGRAY_OBSERVATORY »

Interesting comment about dropping one of those DS's David. Glad yours appears to be fine. :hamster:

It happened to me a few years back in the observatory. Although the observatory is carpeted throughout and separated from the concrete foundation by a wooden floor (the carpet obviously on top), the DS did suffer a broken-element inside. :oops:

On contacting my UK supplier, they agreed that it can be sent back to the then new Lunt Europe in Germany. :arrow:

Knowing the price of a new one, I contacted my insurance company, who confirmed all the SolarScope gear was covered. :P
It was duly taken to the supplier and a few days later, a replacement was received and picked-up from the supplier. :band2

The charge was just £500/670.65US-DLRS/585.50-EUROS (at the time), so I didn't make the insurance-claim. :roll:

I personally know - as with most things - "aviation and flying", when accidents do occur, they are investigated and hopefully a resolving-answer/recommendation(s) to prevent such accidents occurring again. So the cause was that the DS is heavy compared to its' size as well as the outside can be slippery to grasp, but the paramount-problem is that the threading used to attach the DS is quite a fine one and requires many turns to release it, as well as it really has to be put-on very squarely/accurately to start screwing it back-on, which is not really as easy as perhaps one might like. :shock:

The remedy for holding the DS more securely in the hand after unscrewing, or for applying it to the scope, is to cover the outside with thick rubber-bands, which were readily available at home and easy to purchase. :lol: :bow

No slippage and definitely a useful modification, with virtually no cost of effort at all. :D :beanie:

I know of one other case of a similar problem with another Solar astronomer, who has applied the same method as myself and agreed it very well deals with the problem... So perhaps others who have these Lunt DS's and have the need to attach or remove them, "RUBBER BANDS" can save you much dosh... :P :movie

Terry


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Re: Doublestack for mod

Post by DeepSolar64 »

Ivan,
I hope this is at least a little encouraging. I accidentally dropped my SMII60 DS etalon while removing it from the scope back during the summer. It hit the ground with a thud. I expected the worst. But I put it back on and it worked as if nothing happened! Surely nothing in travel would happen this badly if it's well packed for transport.

James

And Terry, Am I the other solar astronomer? I remember us conversing about rubber bands at the time I dropped the etalon. I had one already as a grip for the helical focuser when the original broke and came off.


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Re: Doublestack for mod

Post by Ivan »

Friends, thanks for your comments. James, I remember the day your etalon fell on the grass, you wrote about it.
I'm glad that you and David are doing well. I will take into account your experience and Terry's experience in the future.
I hope I'm lucky and if I decide to buy and everything will be all right.

Ivan


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Re: Doublestack for mod

Post by DeepSolar64 »

Good luck with your purchase Ivan. With whatever you decide to do. I bet you do wish they were a producer of good quality etalons in Russia!

James


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Re: Doublestack for mod

Post by EGRAY_OBSERVATORY »

To be honest, James you are almost certainly correct in being that other person, that we spoke about and to use rubber-bands in future. :hamster:

My DS is attached to the LS in the Main observatory and with the low-down Sun, may not see day-light (or should I say Sun-light) for a while, but the rubber-bands will act as a reminder of what happened some years ago, so a double whammy for reminding to grip well... :bow

And Ivan, if all suppliers would do what I have recently experienced with a SkyWatcher 80ED Triplet scope, where not only was this supplied in its' aluminium flight-case, but the outer-packaging was ultra-reinforced cardboard with H.D. lining and (would you believe it), the rubber-ball element of several tennis balls !! :lol: :lol: :lol:
The packaging itself must have cost much, but far-cheaper than having returns due to damage, so very well done SKY-WATCHER and thanks too... :bow

Cheers
Terry


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Re: Doublestack for mod

Post by EGRAY_OBSERVATORY »

Just found the images taken in July-2021 of the SkyWatcher 80ED when delivered. :shock:
The rubber-balls can clearly be seen within the very-well designed and built flight-case. :lol: :lol: :lol:

Innovation, design and perfection for transporting the excellent 80Ed Triplet has been well thought-out by SkyWatcher...!! :bow

Terry
Attachments
IMG_1820 Delivered 7-2021.jpg
IMG_1820 Delivered 7-2021.jpg (487.29 KiB) Viewed 7721 times
IMG_1823 SW 80ED on mini-obsy base 7-2021.jpg
IMG_1823 SW 80ED on mini-obsy base 7-2021.jpg (1.85 MiB) Viewed 7721 times
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Re: Doublestack for mod

Post by Ivan »

DeepSolar64 wrote: Sun Nov 14, 2021 2:30 pm Good luck with your purchase Ivan. With whatever you decide to do. I bet you do wish they were a producer of good quality etalons in Russia!

James
Thanks a lot James, luck is what need! The production of etalons in Russia - alas, this is absolutely impossible: (the maximum I would like is for the ruble to stop depreciating, but even that is not possible :)

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Re: Doublestack for mod

Post by Ivan »

EGRAY_OBSERVATORY wrote: Sun Nov 14, 2021 3:37 pm Just found the images taken in July-2021 of the SkyWatcher 80ED when delivered. :shock:
The rubber-balls can clearly be seen within the very-well designed and built flight-case. :lol: :lol: :lol:

Innovation, design and perfection for transporting the excellent 80Ed Triplet has been well thought-out by SkyWatcher...!! :bow

Terry
Terry, thanks for the detailed description! SkyWatcher's packaging is beyond competition!

Ivan


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Re: Doublestack for mod

Post by DeepSolar64 »

Terry and Ivan,
I like Sky-Watcher. Their customer service is really good and they care about what they do. I have had positive experiences with them twice. Hopefully Orion can fix Meade and they can be the same. And the U.S. Dollar isn't worth much anymore either. You have to get a lot of them to buy anything anymore.

James


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Re: Doublestack for mod

Post by DeepSolar64 »

And I wish Synta/Celestron/Sky-Watcher made Ha-CaK solar telescopes and filters. If they did they would really tip the balance of competition between the solar manufacturers. Meade only got into it because they bought a struggling Coronado. A previously existing company.

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Re: Doublestack for mod

Post by EGRAY_OBSERVATORY »

Thanks Ivan and James.
It is again "what you pay" often equals the quality and service, but not always.

The problems I have experienced with Orion, do not reflect the above remark though and unless Orion can pull something out of the bag to improve their own quality and customer-service, then they are certainly not the people to make a substantial-difference in improving the Meade etc., scenario - as of late.

One must always remember that Solar-viewing is a relatively small market compared to night-sky observing/imaging and therefore any investment into producing Solar-filters of any sort and specialised Solar-scopes too, needs a reliable and consistent market to pay-off their investment(s).

I dare say that COVID-19 (being still a threat), has shuddered the market somewhat over the last 2-years, but for longer-term purposes, that Solar market is still quite small.

So hopes for other firms to come into the Solar market, would seem unrealistic at present, but of course competition can be a good-thing, but not always, as that competition often reduces the quality of items available - to fight for a larger market at lower-prices...

Terry


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Re: Doublestack for mod

Post by DeepSolar64 »

Terry,
I think you are right about the market being small. Narrowband solar is a small slice of the astro-pie and it's an expensive slice at that. I think that thwarts many manufacturers from getting into it. But I feel if the Chinese manufacturers like Synta ever get into it that it's gonna be a game changer.

James


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Re: Doublestack for mod

Post by EGRAY_OBSERVATORY »

Yes I agree James, where clearly China have been well involved over the last decades in producing much of what goes into astro-gear for various manufacturers around the globe. Presumably allowing prices to be kept lower due to the lower production costs in China.

I wonder how many of us really know that the Synta Technology Corporation of Taiwan actually own much/or all of the Orion/Meade, SkyWatcher, and Celestron, companies and no doubt manufacture part for many other companies too, with their main operation in China.

https://telescopenights.com/celestron-v ... kywatcher/ confirms this.

Whether it is a good thing that Synta have taken over this major part of the telescope manufacturing world, albeit maybe keeping some prices to the end-user lower for some, is one matter. And whether that affects the other manufacturers such as Vixen, Takahashi and so on, as far as their abilities to produce and sell their excellent products at the usually higher-prices is another matter, where competition may-not be a good thing.

Terry


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Re: Doublestack for mod

Post by DeepSolar64 »

Synta and Sunny dominate the amateur telescope market with companies like Celestron, Sky-Watcher, Orion and Meade but they are not the only Chinese manufacturers. Astro-Tech, Astronomics brand of ED-APO refractors are Chinese manufactured but not by Synta or Sunny. I read this somewhere but I cannot remember who the manufacturer is. SharpStar is another ED-APO brand that is Chinese but not Synta or Sunny.

I hated the Chinese optics at first. Quality was very hit or miss when compared to Japanese, American or European optics but in recent years they have gotten much better. But I must admit, they have made amateur astronomy much more affordable. I would be really curious what they could do with narrow band solar.

But now Meade has their Coronado scopes made in Mexico!


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Re: Doublestack for mod

Post by Ivan »

Hi, everybody,

I want to share with you a small mod that (as I would like to believe) works.

I dreamed of doubling the stack for about a year, but for financial reasons I postponed the purchase of an aperture DS from Coronado, as Bob advised, and then, for all known reasons, such a purchase and delivery to my country became impossible. I had to look for options in the domestic market and settled on another Lunt50.

I knew that Vladimir (CSVE), very successfully implemented DS PST+Lunt50, working under F10, but my already modest short-focus tube WO Megrez90 works under F7, besides, when I decided to buy used solar telescopes on sale, there was nothing.

Then there was an unsuccessful attempt to buy a great copy in Cyprus, I tried everything I could and realized that I had hit a wall. As a result, I persuaded my friend to sell me his Lunt50. Ohhh

Connect two etalon Lunt50 it was risky, but Brian's experience gave hope

After receiving the second etalon, I ordered an adapter so that there was a minimum distance between them. In case of a ghost, the adapter provided a thread for the filter (fortunately, the ghost did not come and the filter was not needed).

When assembling the first mod to find the etalon position, I used the camera technique described by Filip. But it was not possible to focus two standards on the Lunt50 lens at once, because its pipe interfered. Perhaps I should have unscrewed the lens and built something like an optical bench, but I did not dare to take this step.

I did this: focused each etalon separately, connected them together, and screwed them to the Megrez90. An adapter was installed on the telescope (the length of which was determined by the method described by Filip). I assumed that there would be no focus, as it was not on Lunt50, but it was worth checking. As a result, the old adapter was unscrewed, and I, holding the camera with etalons in my hands, manually found the focus. Then a new adapter was ordered, the production of which was delayed, and only a couple of weeks ago I received it.

The setup process is quite original, (I haven't dealt with DS). I thought it would be easy to set up, and I completely unscrewed the second tuner, believing that I would tune the first one first, and then the second one would simply improve the picture. But I was very surprised when I turned the first one almost completely, I found only faint traces of the chromosphere, I was out of the band. Only after starting to twist the second tuner, the picture improved. It turned out that both filters work only in pairs. I wonder if this is a feature of all systems with internal DS?

My impressions are very contradictory, I can't say I'm happy, but I'm not disappointed either. I see that the double limb has almost disappeared, but I also see the unevenness of the band. Some part of this problem lies in the sagging of the focuser under the weight of the camera, this can be solved if everything works optimally, and I'm not sure about that. In addition, the picture does not look crisp and contrasting, although it may be a matter of processing.

I am attaching some photos so that you can evaluate whether this device works as a DS and maybe you can advise me something.

In all photos, except for the mosaic, I used only deconvolution for processing.

It is better to open the first 2 photos in a new window:

ImageComparison_1 by Ivan Sirotin, on Flickr

Image24.10.22_DS_3 by Ivan Sirotin, on Flickr

Image24.10.22_DS_2 by Ivan Sirotin, on Flickr

Image24.10.22_DS_1 by Ivan Sirotin, on Flickr

Image27.10.22_DS by Ivan Sirotin, on Flickr

The first experience of a mosaic shot on DS already published here earlier:
ImageFD_24.10.22 by Ivan Sirotin, on Flickr

Telescope Photo:
Image20221024_134836 by Ivan Sirotin, on Flickr

Image20221024_135310 by Ivan Sirotin, on Flickr

Thanks,
Ivan

ps
Since I was shooting at the end of October, seeing was very bad, besides there were so few gaps in the clouds that I could not shoot the same areas in the Sun on SS for a more correct comparison.


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Re: Doublestack for mod

Post by marktownley »

Great mod Ivan!


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Re: Doublestack for mod

Post by DSobserver »

I've tried too to DS lunt50.

Despite many newton rings...I came to the conclusion that the picture is darker and gives an impression of higher contrast

No real new info on the "DS" picture Vs "SS" picture

Would be interesting to compare your mod with a camera, the same day with DS vs SS...


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Re: Doublestack for mod

Post by Ivan »

marktownley wrote: Mon Oct 31, 2022 8:21 pm Great mod Ivan!
Thank you Mark!
I would like to hear criticism and advice :) although this season I will hardly be able to see the Sun through it again.

Ivan


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Re: Doublestack for mod

Post by Ivan »

DSobserver wrote: Tue Nov 01, 2022 9:03 pm I've tried too to DS lunt50.

Despite many newton rings...I came to the conclusion that the picture is darker and gives an impression of higher contrast

No real new info on the "DS" picture Vs "SS" picture

Would be interesting to compare your mod with a camera, the same day with DS vs SS...
Hello,
Unfortunately, I won't be able to make photo comparisons this season. We have already had the first snow, and although it has melted, the weather promises nothing but heavy, low clouds.

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Re: Doublestack for mod

Post by Bob Yoesle »

Hi Ivan,

I'm not sure how it looks visually, but via the images, your DIY double stacking system looks like it's performing much better than I would have estimated it would - and you're especially fortunate that you're not having to deal with internal reflections and use of a circular polarizer to suppress them. The full disc mosaic image is wonderfully detailed, and I see little to no trace of a double limb on it. I think it would take considerable resources and effort to improve on what you've accomplished, and the improvements would be incremental...

Congratulations!

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Re: Doublestack for mod

Post by Ivan »

Bob, thank you so much for your feedback, I really appreciate it. You made my day!
:bow :bow :bow

Ivan


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Re: Doublestack for mod

Post by DeepSolar64 »

Ivan,
Congratulations on your doublestack mod! You mention tuning. I usually have to tune BOTH my etalons to get on band. One is internal and one external. The same on both Coronados. Also I find the primary etalon without stacking gives a more evenly tuned and illuminated disk on my scopes. I tend to use doublestack more for visual use and single stack more for imaging. But it could be in part from my imaging inexperience.

I await your results once the sun rises higher again and warm weather returns. Keep us posted!

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Re: Doublestack for mod

Post by OlegLviv »

Nice Ivan congratulations!
Sorry friends all serial numbers models Lunt 50Tha have F7 and they doublet telescopes?
Thank you!


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Re: Doublestack for mod

Post by OlegLviv »

Sorry friends all serial numbers models Lunt 50Tha have F7 and they doublet telescopes?
Anybody say me?
Ivan whitc is the camera diagonal and pixel you have QHY?
Thank you!


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Re: Doublestack for mod

Post by marktownley »

My LS50 is a doublet Oleg


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Re: Doublestack for mod

Post by Ivan »

OlegLviv wrote: Tue Jan 03, 2023 11:58 am Sorry friends all serial numbers models Lunt 50Tha have F7 and they doublet telescopes?
Anybody say me?
Ivan whitc is the camera diagonal and pixel you have QHY?
Thank you!
Oleg, sorry for the long answer. I haven't been in this topic for a long time.

As far as I know, all Lunt50 duplets and f7.

I have a very old qhy img0s CCD, the diagonal is 7.6 mm, the chip size is 5.8×4.95 mm, the pixel size is 4.65 microns.

Ivan


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Re: Doublestack for mod

Post by OlegLviv »

Ivan thank you for your answer!
I have focal lenth 900 mm and camera 432mm the diagonal 14mm the chip size is 14x9 and am scary sweet spot will be small that you.....


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Re: Doublestack for mod

Post by Ivan »

Hello everyone This animation shot on July 26 shows the difference between SS and DS.

ImageDS vs SS by Ivan Sirotin, on Flickr

Several months of operation revealed both the pros and cons of this installation, I will write about them a little later.

Ivan


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Re: Doublestack for mod

Post by Ivan »

ImageDS vs SS by Ivan Sirotin, on Flickr


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Re: Doublestack for mod

Post by OlegLviv »

Today was a good weather and test my double stack with two lunt 50mm etalon! Thank you Ivan for idea!
But I see that sweet spot less with two etalons that one and me need do it big focus lenth :cry:
A few photos test double stack without lens barlow with 432mm and 429mm cameras.
A photo viber_2024-02-26_11-44-39-412.jpg with one stack!


But have a few questions!

1.Why sweet spot less with two etalon?
2.Why when two etalon near sweet spot its too dark? But when 1 etalon bright near sweet spot.
3.On photos this is really DOUBLE STACK??? If yes what is the bandwidth there now I have 0.6A?
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Re: Doublestack for mod

Post by marktownley »

The rear etalon is not square (orthogonal) with the first etalon, you can see that in the photo of the scope. This is the reason the sweet spot is not central. As bandpass decreases then also does sweet spot size. You need to zoom in further!

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Re: Doublestack for mod

Post by OlegLviv »

Thank you Mark seeing on winter not good but on photos this is really DOUBLE STACK???
If yes what is the bandwidth there now I have 0.6A?
Between the two lunts I put filter ND 0.6 to avoid unwanted glare and double suns but bought Baader 2" polarisation filter too.
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Re: Doublestack for mod

Post by MalVeauX »

Hi Oleg,

What is the base scope you're using (aperture, length, etc)? Are you using collimating lenses internally or a telecentric?

The jacquinot spot will shrink as bandpass becomes more isolated in a collimated system. If they were front mounted, it wouldn't be noticed. If they were behind a true telecentric it would not be noticed. In those two situations, the field & acceptance angles are more similar, so there is less of a noticed jacquinot spot or outright not jacquinot spot at all.

Your system is coming on band, and it is indeed double stacking well, you can see features in high contrast, somewhere around 0.5~0.6A FWHM probably in your best areas. The next steps are to perfectly tune both etalons together so there's uniformity. And if you want to increase the jacquinot spot size or eliminate it, you need to revisit the above ideas of using a telecentric if these two etalons are internal or rear mounted.

If you're using the stock collimating lens, it's probably not the correct position for two etalons like this, as it was designed with a length meant for one. If you're using a stock collimating lens, the rear lens is before your 2nd etalon and so that etalon is not in a collimated light cone, so it will develop a very small jacuiqnot spot as you see in your images.

It's likely the collimating lens relative to your donor scope parameters. A telecentric would solve both.

Very best,


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Re: Doublestack for mod

Post by OlegLviv »

MalVeauX thank you for answer!

1.About my telescope.
I use a Ts Optics 150/900 f5.9 telescope, but before the first lunt 50 etalon I screwed in the Baader Glasspathcorrector 1:1.25 to get to f 7.5 so that the aperture is not cut.
Am using collimating lenses internally because I'm afraid to disassemble the lunt 50 for the telecentric circuit and my balcony is short for telecentric system.

2.About not the correct position for two etalons.
Yes, I use a standard collimating lens and I know about the incorrect position of one etalon relative to the other,
but I made an experiment and put another Baader Glasspathcorrector 1:1.25 between the two etalons at the measured distance, accordingly, the distance should be correct.

3.Yesterday the weather was good and tried do it double stack and have question about this photo tell me this good because as for me this seet spot its too dark when rotated two etalons or not plese tell me because I'm afraid that I left the lane HA that's why it's so dark.
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Telescope: TS 152/900/Bresser 102/1350
Baader D-ERF 160MM
2xBaader 1.25 GPC
2xLunt 50mm
Lunt Cak B1200
Coronado BF15
Camera: Apollo Max 432M/ Apollo Mini 429M/Player One Mars II 462M/QHY 290MM
Mounh: 2xSky Watcher AZEQ6
Telecentric Lense: Televue Powermate 2/2.5x/4X/5X
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Re: Doublestack for mod

Post by MalVeauX »

Hi,

Well, the fact that you have an obvious jacquinot spot makes it apparent that whatever measurement you used for collimating lens placement for both etalons is simply not positioned correctly. I'm not sure which etalons you're using, but many of the internal ones have a collimating lens set before and after the etalon chamber that you cannot remove without destroying the pressure system of the chamber. So when you add that 2nd etalon behind that, unless it has its own collimating lenses, I'm not sure how its seeing a collimated light cone since the 2nd lens after the first etalon returns the light cone to normal (a cone, rather than cylinder).

The presence of that jacquinot spot and how small it is means your field angle and acceptance angles are not similar, they're rather divergent. Since the etalons are not front mounted, this then becomes a relationship of the objective aperture relative to the aperture of your etalons, and so you're seeing the result here. Even a collimating lens will not fix this. When you do this with a large aperture and a tiny etalon with collimating lenses, the jacquinot spot will be there and be small, so the instrument becomes a high res system and basically only good with a small camera sensor to only use that FOV within the jacquinot spot. If you want to increase the jacquinot spot or remove it, you need to move to true telecentrism. If you cannot do this due to collimating lenses, then see previous comment about just using a smaller camera sensor and working within your jacquinot spot size.

If your first etalon is correctly positioned with its collimating lens you should have a pretty good FOV; similar to what you would see in the results in my thread on the Lunt 60 mod. You can then add a telecentric after this and a 2nd etalon behind the telecentric to further the setup, as you've seen in my current system. The jacquinot spot will be small (not full disc) but it will be big enough to use a smaller sensor FOV and do moderate to high res imaging, which is what you're interested in with a 150mm lens anyways.

But, it depends on what kind of etalon you're using as the double stack and if it has collimating lenses or not.

Overall this is why front mounted tilting etalons are the easiest ones to do this with, no lenses.

Very best,


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Re: Doublestack for mod

Post by OlegLviv »

Hello friends a few days ago will be good seeing and want see a few photos my and Ivan modification 2xlunt50 pressure tune!

Ts150>first lunt>first part adapter (inside adapter 2.0 Baader ND.06)>second part adapter have tilt and shifter and Baader Glasspathcorrector 1:1.25 >second lunt>focuser 1.25>bf15>Powermate 2.5x>429mm camera. 2850mm focus/f19

Have a fun!
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https://www.facebook.com/oleg.lavigne/
https://www.astrobin.com/users/RamonLviv/
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Telescope: TS 152/900/Bresser 102/1350
Baader D-ERF 160MM
2xBaader 1.25 GPC
2xLunt 50mm
Lunt Cak B1200
Coronado BF15
Camera: Apollo Max 432M/ Apollo Mini 429M/Player One Mars II 462M/QHY 290MM
Mounh: 2xSky Watcher AZEQ6
Telecentric Lense: Televue Powermate 2/2.5x/4X/5X
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Re: Doublestack for mod

Post by Martin_S »

Wow that's amazing , well done.


H alpha : ,Skywatcher 120mm F8 open frame refractor, a tilted 2" 7nm H-alpha filter as a sub energy rejection filter, Baader TZ4 telecentric focal extender, Player One energy rejection filter, Combo Quark Chromosphere, Naked PST etalon for double stacking, ASI74mm camera
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