First light of DS Lunt130MT - Need for advice on tuning

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First light of DS Lunt130MT - Need for advice on tuning

Post by H-Alpha »

Hi all,

I hope this finds you all well.

After many cloudy days, today I had some 15 minute of sun in between clouds and could test for the first time my newly acquired DS Lunt etalon for the Lunt130MT. I was partially satisfied in the sense that I could see some ...kind of better 3D aspect in filaments of my captures and I could somewhat just see proms together with a correctly illuminated (not over-exposed) disk. However, the 3D aspect is still far from what I have seen from other fellows here (with Lunt or other DS).

There is so much activity on the sun (I missed that!), and I am now eager for a sunny day to enjoy the DS with so much activity.

Below is one of the captures and further below I have a few questions and kind request on advice, from those of you who have experience with DS and especially with Lunt (Air-pressure knob to tune the etalon).
2022-12-07-1307_3 inverted, PS, colour.jpg
2022-12-07-1307_3 inverted, PS, colour.jpg (1.9 MiB) Viewed 1037 times
2022-12-07-1307_3 inverted, PS.jpg
2022-12-07-1307_3 inverted, PS.jpg (1.07 MiB) Viewed 1037 times

My questions are:

1) Should I be able to clearly see the proms (without over-exposing the disk) while capturing, after achieving a correct tuning? Could you please share a screen capture (not a processed image) of a well tuned DS with proms and surface details, so that I can have an idea?

2) What is your DS tuning method and when/how can we be sure that we are correctly tuned? Theoretically, I should tune the SS and then add the DS and tune it... This is a real pain and apart the time and effort lost, I am afraid I will risk to deteriorate the state of my etalons if I (every couple of days) remove and reposition the DS. Is there an alternative, e.g. having both etalons on the scope and start tuning one and then the second?

3) The best practical advice I found so far by searching was written by Bob: "if filaments are present you generally will be on-band when the filaments are their darkest". Is this the DS tuning rule you all use? (I also found: "Tune in single stack mode for _minimum brightness_ (= max contrast), then in double stack for _maximum brightness_.")

4) Is the angle between the two knobs/etalons indifferent (e.g. when parallel, perpandicular, opposite=180 degrees, other angles) to tuning when rotating one of them. When changing this angle all tuning has to start from scratch? Does rotating the etalons relate only to increase/decrease of the distance of the ghost reflection image? (I have read that 180 degrease, i.e. opposite directions, has the best results).

5) Is the correct tuning a unique place for both knobs, or are there several combinations on the position of both knobs that give a perfect tuning?

6) Is the second image below correctly tuned according to you?



The tuning method I used was: with both etalons on, I tried to turn the original etalon inwards (with the DS knob completely unscrewed) until I had the surface details I was used to have with SS (I reached the same position roughly). Then I started turning the DS knob inwards until the image seemed "staisfying" in my screen (which is not easy because it becomes dimmer at every step inwards and have to re-adjust the Gain).

I can clearly see that in the first of the photos below, I am not tuned well in comparison to the second photo that seems to be much more contrasted, but where should I stop and feel that I am correctly tuned?
2022-12-07-1236_2, not well tuned.jpg
2022-12-07-1236_2, not well tuned.jpg (673.41 KiB) Viewed 1037 times
2022-12-07-1305_5, better tuned.jpg
2022-12-07-1305_5, better tuned.jpg (932.18 KiB) Viewed 1037 times
Thanks for any advice you may provide and all comments are very welcome!

Best wishes,
Alexandros


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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by DeepSolar64 »

I am probably not the best one to ask on DS tuning for I often have issues with it myself, especially while imaging.

These look really nice to me.

James


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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by george9 »

On my Lunt LS80 DSII, by trial and error I found that I liked them 180 degrees apart, but there is not too much difference. I also like them apart because I find it easier to tune that way.

I generally tune them together, both etalons at the same time. I put them both about where I expect them to work well. Go back and forth with both turning inward and then both turning outward for the best view and the darkest view. Then go one turning inward with one turning outward back and forth for the best view and the brightest view. Repeat with both inward, etc.

With both turning inward or both outward, you are picking the center wavelength, and H-alpha is darker than photosphere; thus the darkest view. With the two etalons in opposite directions, you and aligning the two etalons for best overlap; thus the brightest view. "Best view" means dark filaments if they are there, else check the plage and fibrils.

Once you get used to it, it takes seconds to get to a good tuning. And you get good at going off band quickly (both in or both out).

Keep in mind if you have them 180 degrees apart, then "both inward" means moving your hands in opposite directions.

There is a pretty wide range of good performance, but I would not say that there are different combinations of both knobs for the same result. There is an optimal middle.

On your images, I cannot tell if that is a double limb or simply how it is processed. You should not see a double limb.

George


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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by marktownley »

You're definitely not exactly on centreband as on picture 3 the double limb is clearly visible. If you post unprocessed images it will help determine better, number 4 looks like it has had the contrast wrung out of it in post processing (overcooked IMHO!). If you look at #3 you can see the tuning varies from left to right across the image, so you need to look at getting it more even, centre of the disk not the limb is the place to be doing this. George has posted excellent advice and you should follow it. These things take practice to master so keep trying and at some point you will nail the tuning.


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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by Montana »

A great first light :bow :hamster: lots of practice needed though, George is spot on :)

Alexandra


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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by ffellah »

Looking good already, Alexandros !

Franco


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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by MAURITS »

A beautiful first light and great setup.


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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by H-Alpha »

Thank you all for your comments and help! :-)

Special thanks to George for the detailed advice on how to tune Lunt DS.
After posting my message I found a similar post of George9 in another forum, who kindly also offered his experience.
I have just a question:
george9 wrote: Wed Dec 07, 2022 11:26 pm I generally tune them together, both etalons at the same time. I put them both about where I expect them to work well.

George
I know where my original etalon works well and, surprisingly, it is very close to the end while turning inward! I suppose each etalon is not the same, so the DS etalon may work well (be tuned) may tune well before the original, isn't it? Consequently, should I fist remove the original etalon and find where it tunes, or I can start applying the method you kindly described in detail by starting with the DS etalon at approximately the same position with the original etalon?

Both George and Mark reported a double limb that is visible. I can see only a lighter limb edge that may be the result of process in ImPPG, while I was trying to make the prom better visible. I attached below the stacked image with no further process at all. Do you still see a double limb that I should make disappear with better tuning? Can you indicate exactly what could be the result of bad tuning on the limb?

Also, should the prom be much more visible in the unprocessed image?
2022-12-07-1307_3-h-alpha-sun h-alpha_lapl8_ap158.jpg
2022-12-07-1307_3-h-alpha-sun h-alpha_lapl8_ap158.jpg (410.98 KiB) Viewed 917 times
Thank you all once more!

I am waiting now for a beautiful sunny day to restart the tests following your advice.

Best wishes,
Alexandros


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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by george9 »

Hi, and happy to help. I would put the new DS etalon about in the middle of its range and then proceed. Once you get it tuned once, you will remember if this DS etalon is best more outward, in the middle, or more inward.

Also, I assume you have momentarily unscrewed and re-attached the primary etalon to let some air in. When it was new, mine required that only every two months or less. As debris gets caught in the grease over time, it leaks a little more, requiring "burping" every two weeks or so.

I do still see a double limb in the photo. The spicules that form a dimmer rim around the Sun should be homogeneous with the rest of the solar disk. That brighter disc inside the spicules is leaking photospheric light. It can be due to light that normally passes through the side bands of a single-stack etalon. With a double stack, it should disappear. So it probably means one or both are off band. But your filament looks pretty good, so I am somewhat surprised by the strength of your double limb. With a double stack that is on-band enough to show that filament so well, I would not expect to see such a strong double limb. It looks a bit more like a single stack.

Here is what I would do. For this experiment, tune one at a time. Set it up single stack with just the primary etalon and tune that optimally and then don't touch it. Add the DS and see what happens. Is the view darker (it should be)? Does the view change at all when you tune the DS (it should)? You should be able to find a spot where the double limb disappears.

If you can get that to work, then practice the two-at-a-time. The two-at-a-time can be even more perfectly tuned, but the one-at-a-time may be easier to debug.

George


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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by Carbon60 »

Tuning one on its own and then adding the second and tuning that is the way I tackled this when I started double stacking. It doesn’t necessarily mean you don’t need to re-tune the first one again slightly when the second is added as things change with the added weight. It’s all a bit fiddly, but you’ll get the feel of things with experience and learn to tune both together. By the way, I use the limb as my guide and tune to eliminate the double limb when homing in on optimal tuning.

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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by DeepSolar64 »

I usually tune the primary etalon first and then the stacking etalon. It's best done in single stack and then tune the DS etalon after adding it to the already tuned etalon. Once they are in tune often they just have to be tweaked a little and should not vary very much.

I wish I had access to a pressure tuned Lunt to see how they do. I always have problems getting my tilt-tuned Coronados in tune uniformly across the field of view. It will be perfect on one part of the disk and off on another. Visually I can get by this by moving the areas of interest to the tuned sweet spot but it shows up obviously on images. My SMII90 seems to always tune better to the right of center, often not far from the field's edge. It can be annoying. Single Stack does tune a bit more evenly than double stack does.

It can be frustrating. Ha should give as uniform of an image as continuum does!! A friend of mine hesitates doing Ha solar because he wants to just put in an eyepiece and/or camera and see it as continuum does, considering tuning a pain-in-the old arse. I guess for me and the majority of us the reward is worth the efforts of tuning.

James

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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by Bob Yoesle »

Hello Alexandros,
Both George and Mark reported a double limb that is visible. I can see only a lighter limb edge that may be the result of process in ImPPG, while I was trying to make the prom better visible. I attached below the stacked image with no further process at all. Do you still see a double limb that I should make disappear with better tuning? Can you indicate exactly what could be the result of bad tuning on the limb?
The double limb "lighter edge" is not a processing artifact, rather it is the result of the underlying edge of the brighter photosphere which is visible with most single stacked filter systems. Double stacking suppresses this out-of-band "parasitic continuum" light from the photosphere leaking through the "tails" of the transmission curve, so there generally should be little to no double limb with a properly tuned DS filter system.

double stacking non-norm reve graph.jpg
double stacking non-norm reve graph.jpg (369.69 KiB) Viewed 824 times

Unfortunately, none of your images are on-band. You are about 0.5 A above or below the emission line as seen on the left and right below.

Etalon tuning crop.jpg
Etalon tuning crop.jpg (254.17 KiB) Viewed 824 times

My advice is to hold off on double stacking until you've got single stacked tuning nailed down. Only then will you be able to add the second etalon and use it optimally. I realize these are imaging-centric forums. But this has led to many "putting the cart before the horse." Imaging, colorizing, negative images, and all the other things you've attempted should only take place after you learn how to optimize filter use through direct observing experience.

Here's what an on-band single and double stack image should look like. For double stacking note there's no double limb, and a lack of small sunspot detail, etc.

Single v double stacking.jpg
Single v double stacking.jpg (287.2 KiB) Viewed 824 times

So even with double stacking, if your tuning is defective you will see a double limb as if you were only single stacked.


Good luck,

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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by marktownley »

Lots of good advice here!


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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by robert »

Hi Alexandros

I am particularly keen on images which show the surface and proms in the same exposure and processing. This is the advantage of double stacking for me.

I had a short chance with 8 degree elevation sun today to try to show you what I do in an attempt to answer your list of questions!


I set up and get a rough image with the pressure tuner wound out a bit.

Image1210 1-first by Robert Arnold, on Flickr


Then I wind it in beyond the best tuning with the exposure rather high to exaggerate the lightening. I watch the histogram as well to notice the minimum brightness.

Image1210 2-second wound in beyond tuning by Robert Arnold, on Flickr

Tune back to the best flat and even disc.

Image1210 3-midpoint best even disc by Robert Arnold, on Flickr

Add the second etalon which I have clocked and always keep at the same rotation. It is a tilt tuned 60mm which is on band with nearly no tilt. I never adjust this much. I check focus, increase gamma to near 1000, and exposure to maximum of 80% on the histogram. Then take 500 frames. This screenshot shows a single frame with proms and surface exposed together.

Image1210 4-Double stack added gamma exposure and focus by Robert Arnold, on Flickr

Image stacked, sharpened and colourised (without separating proms and surface).

Image1210 2022-12-10-1237_5-U-G-Sun_lapl4_ap453 by Robert Arnold, on Flickr

This is just what I like to do. It is very quick but does involve screwing and unscrewing the second etalon which I think is probably unavoidable.

Hope it makes sense and helps

Robert


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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by DeepSolar64 »

That last colored Ha disc looks great, Robert!!


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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by marktownley »

Thanks Robert, looks great!


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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by H-Alpha »

Thanks a lot George9, Stu, James and Bob for your precious input and advice.

Dear Bob, thank you very much once more for your detailed advice and explanations. Now things are even clearer for me and hopefully for others who will try to enter the DS world. The images you uploaded are really the best way to help others understand, especially regarding the double limb (but not only).
Bob Yoesle wrote: Sat Dec 10, 2022 5:08 am My advice is to hold off on double stacking until you've got single stacked tuning nailed down. Only then will you be able to add the second etalon and use it optimally."
Given that likely I will have no sun for several days :-( to experiment and practice, I have a last question regarding the practical way of achieving the right tuning of DS. After I achieved a perfect "single stacked tuning nailed down" as you advised, when I will add the second etalon, I will start tuning it in the way George9 and others proposed. Once "satisfied" by the result (make the difference between limb and disk minimum or zero), do you confirm that I should go back to the first etalon and slightly re-tune it anyway or only if I keep seeing a double limb? In other words, is the disappearance of the double limb my absolute criterion with which I can feel safe that I am correctly tuned in DS? (I hope it is indeed and I got it right, since you all mentioned the double limb, but just wanted to confirm this)

Bob, all the images you kindly posted are unprocessed single frame images, isn't it? (no stacking including the Full disks?)

As Stu wrote that the weight added by the second etalon (and perhaps other parameters) have an effect that should be addressed by returning the first etalon, so I conclude that I would not be able to achieve right DS tuning without returning to the first etalon to fine re-tune it.

Thank you all once more,
Alexandros
Last edited by H-Alpha on Sat Dec 10, 2022 5:35 pm, edited 2 times in total.


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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by H-Alpha »

Dear Robert,

My previous message left while you were also sending yours.
robert wrote: Sat Dec 10, 2022 3:31 pm
I had a short chance with 8 degree elevation sun today to try to show you what I do in an attempt to answer your list of questions!

Robert
Thanks sooooo much for spending time to answer my questions with images while tuning your DS. It is so helpful to answer with results and images! Yes, it absolutely make sense. :-)

Best wishes to all,
Alexandros


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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by robert »

I can see that you probably have two pressure tuned etalons so it is not as easy as screwing on a front mouted etalon, which is what I do with the LS60. I hope you can apply some of what I described anyway.
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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by marktownley »

Look for when the filaments are at their darkest and plage at it;s brightest to guide you to the tuning of the double stack unit. But the single etalon needs to be on band in the first place.


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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by Bob Yoesle »

Once "satisfied" by the result (make the difference between limb and disk minimum or zero), do you confirm that I should go back to the first etalon and slightly re-tune it anyway or only if I keep seeing a double limb? In other words, is the disappearance of the double limb my absolute criterion with which I can feel safe that I am correctly tuned in DS? (I hope it is indeed and I got it right, since you all mentioned the double limb, but just wanted to confirm this)
As Mark noted, you are on-band when filaments are darkest and plage the brightest. Usually any hint of the double limb means one or both of the etalons is off-band. But as the filter spacers warm up and the etalon gap increases ever so slightly, the filters may red-shift a little bit, and you may find you need to back off on the pressure a little bit. And there are other subtle changes that can occur. There will be no easy answer other than to become a keen observer after getting enough experience to judge the filter settings and make appropriate adjustments. Generally re-tuning the primary etalon is first and foremost for any of these more subtle adjustments.


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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by H-Alpha »

Thanks once more Bob,

I think that now I have all the necessary advice and all I need is the sun to start practicing. :-)
Hope the precious info/advice you have all kindly provided will be useful for other people as well that enter to the beautiful DS adventure for the first time.

Thank you all a lot!

Best wishes,
Alexandros


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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by DeepSolar64 »

Good luck Alexandros. I am sure your results will be excellent.


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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by pedro »

Try using false color in Firecapture to tune your etalon


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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by H-Alpha »

pedro wrote: Mon Dec 12, 2022 8:49 pm
Try using false color in Firecapture to tune your etalon
This an excellent idea/alternative Pedro! Thanks a lot!

I suppose the goal will be the same regarding filaments and plages, but with the false colours we may see the differences in a more clear way. It seems to me that the limb remains 'darker'=violet even when you are tuned. Therefore, I suppose you concentrate your view on the disk, isn't it?

Best wishes,
Alexandros


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Re: First light of DS Lunt130MT - Need for advice on tuning

Post by pedro »

Yes Alexandros

Try different tunnings and the false colour helps to get everything even (FD and HR). At least this is my experience


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