LS50THA + LS50C Double Stack

[niallk]

So, I finally got a chance for 1st light DS this morning.  I set up SS first, then screwed on the DS unit, and started tuning the thumb wheel.

As I adjusted, I saw the additional reflections move out of the fov, and the detail on the disc tune in nicely... Then I ran out of range! I would feel more comfortable if I passed through an optimum point, and saw the image degrade - but the limit of the thumb wheel was the best point I saw.

Does this sound like I have a centering issue with the LS50C?  I have to say that the improvement in the views was very noticeable - filaments became quite darkened, and granularity very evident across the full disc.  Proms remained visible too.  I tried clocking for one revolution, but I did not perceive any noteworthy performance gain vs angle.

So the views were very good, very encouraged; looking forward to catching more activity on the disc.  However, I've a nagging feeling about the centering of the DS unit, despite what the DS certified sticker says...

Anyone able to comment on their experience with the tilt tuned front mounted etalons, and whether the optimally tuned location lay comfortably within the overall tuning range of the unit?

I will try again at the next opportunity to explore more: if I could just get a sunny weekend... not asking for too much surely?! 

[Merlin66]

Sounds pretty normal. The tilt tuning works by moving the central wavelength from the red side of Ha towards the blue....

Just check the initial etalon in the LS50 is tuned to give the brightest clear image you can get, and only tilt the front etalon to a minimum to move annoying reflections from the disk.

 

[Pete Presland]

That's  pretty much what I do as well, turn the thumb screw until the "ghost image" is out of the way. I have tried to focus on the "ghost image" by accident as well when imaging. Sometimes I do rotate the D/S unit to give an even field of view when imaging.

[Peter Drew]

1 hour ago, Pete Presland said:

That's  pretty much what I do as well, turn the thumb screw until the "ghost image" is out of the way. I have tried to focus on the "ghost image" by accident as well when imaging. Sometimes I do rotate the D/S unit to give an even field of view when imaging.

Yes, focusing on the "ghost" image for the first time comes as quite a shock. Your first reaction is panic over what might have gone wrong with your expensive instrument.   

[Highburymark]

That's my experience too Niall - I just tune the DS unit until the shadows are no longer in vision and that gives me most surface detail. 

[niallk]

My possibly/probably wrong understanding is that tilting the front etalon does at least two things:

* moves the secondary & higher order images dues to reflections out of the fov

* adjusts the centre of the bandpass response of the etalon

As I begin tilt tuning, I see the reflections move out of the fov.  No problem so far!

Tuning beyond this point is then (to my understanding) optimising the centering of the bandpass of the front etalon to be  approx the same centre as the bandpass of the internal etalon.

Is this correct?

It's this second part that I have my niggling doubts as to the tuning range.

[alanjgreen]

On 24/10/2017 at 15:23, niallk said:

My possibly/probably wrong understanding is that tilting the front etalon does at least two things:

* moves the secondary & higher order images dues to reflections out of the fov

* adjusts the centre of the bandpass response of the etalon

As I begin tilt tuning, I see the reflections move out of the fov.  No problem so far!

Tuning beyond this point is then (to my understanding) optimising the centering of the bandpass of the front etalon to be  approx the same centre as the bandpass of the internal etalon.

Is this correct?

It's this second part that I have my niggling doubts as to the tuning range.

Hi Niall,

Your description does not match my experience with the LS60 double stack.

The objective of tuning the DS is not to get rid of the reflections but to reveal maximum surface detail.

I would forget about the reflections and concentrate on the disk surface. Tilt the DS its full cycle and place it where the surface shows the most stuff. This may or may not be a postion where the reflections are visible.

- if the reflections are annoying you then adjust slighly to move them further away from the disk

At low power, I often have the reflections within the FOV, I just ignore them. What matters is maximising the surface detail.

Alan

[Highburymark]

Niall - I'd agree that as long as you're getting great views, don't worry too much about the tuning mechanism. Just tune it for maximum detail and leave it. The tilt wheel should free up as you turn it to the right (if my memory's right - I'm not at home to check right now) and that increases the tilt of the DS etalon. Turns to the left should meet with a bit more resistance - that direction levels the tilt. So it sounds like yours is probably normal. I find the tuner on my 60mm DS filter has less resistance than my previous 50mm filter, but it does the same job.

[niallk]

Thanks guys.

At one limit of the tuning wheel, the etalon is level with the front of the scope.

Then, as I tune, the etalon unit tilts relative to the scope.

As I monitor the views, the contrast keeps improving as I tilt more.

I then hit the maximum tilt limit, and this also corresponds to the best views.

The reflections are not the problem at all!

The only concern I have is that I am unable to tune through an optimal tilt to where the contrast falls off again.  If I was to see this, then I'd know that I can definitely tune back to some intermediate point which is optimal within tuning range.

The analogy would be in SS mode: starting off with an orangy red 'white light view'; then as I tune the PT, detail comes in.  I go through a range where various details are at their best, then the image will loose contrast as I continue to tune by increasing the pressure.  So I back off to an optimal setting for the feature being viewed.  This passing through an optimal region with tuning range to spare is not what I experience with the DS tilt tuning.  At least with my initial use!

So I see very good views; but should I be able to get even better if I had more tuning range, or if the filter bandpass was centered better?! Hope this makes sense

[Merlin66]

The tilt tuning sounds normal.

When the tilt tuning is "flat" the central bandwidth is just 0.2A above the Ha - into the red wing...

As you tilt the central band width moves towards the blue - through the Ha and then onto the blue wing and sometimes beyond into the continuum.

It's not unusual to find the best tuning close the the end of travel - it does depend on where you have the internal etalon tuned - they are trying to match each other for maximum transmission.

 

[GavStar]

Oddly the Lunt double stack manual (link attached) seems to suggest that the double stack should be tuned to move the reflections out of the fov!

https://luntsolarsystems.com/wp-content/uploads/2015/10/Double-stack_manual1.pdf

[Highburymark]

2 hours ago, GavStar said:

Oddly the Lunt double stack manual (link attached) seems to suggest that the double stack should be tuned to move the reflections out of the fov!

https://luntsolarsystems.com/wp-content/uploads/2015/10/Double-stack_manual1.pdf

Yes - and that's the primary function for most people. At one end of the tuner you see lots of shadow suns, which have to be 'tuned' out. You can keep tuning until the background sky is completely black, or - as described above - you might find that detail on the sun's disc is greatest when you've only moved the shadows a small distance away. The background sky will be redder, but that doesn't diminish surface views. What the Lunt manual doesn't really say is that careful adjustment of the DS tilt mechanism (and clocking of the DS filter to manoeuvre the sweet spot) are very important to achieving the best possible views. 

[niallk]

Thanks again everyone for all the patient, helpful responses

I've lots more to learn about my scope + DS.  I find it straightforward to get to very good views, and with 3 adjustment knobs (pressure tuner, tilt tuner and clocking angle) there's lots of tweaking/refinement to explore There was a recent filaprom that exhibited high sensitivity to the pressure tuner - intriguing!  Just looking fwd to a clear day with decent solar activity and some free time to really delve deeper.

Anyways: just in case anyone comes across this thread, let me just be clear that the DS filter is dramatically enhancing the views, no complaints from me.  It is a significant investment, but I have to say that I'm excited by what I've seen so far, and this on top of the SS views which have plain wowed me.  I'm very glad indeed to have taken the plunge into Ha!