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Eliminating Reflections in a 60mm Lunt

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#1 Gregory Gross

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Posted 03 January 2020 - 01:33 PM

I have really been struggling to solve a problem that I've been having with reflections of the Sun floating around in my field of view when I use my double-stacked 60mm Lunt with 12mm blocking filter. Most of the time (like 99% of the time), I use my Lunt zoom eyepiece at its lowest power setting (21.5mm). When I get my eye positioned just right where it's most comfortable for me to observe, I get a really annoying reflection of the Sun floating around in the field of view. If I move my eye in or out, that reflection either spreads out (making the field of view glow with the glare of the reflection) or shrinks. It's really frustrating.

I don't know if my problem is the zoom eyepiece (poor anti-reflective coatings? poorly chosen optical elements?) or some element in the blocking filter assembly that's causing a reflection. I've toyed with the idea of getting a very high quality Tele Vue Plossl (25mm or 20mm) with better coatings, but I hate to be throwing $100+ at a trial-and-error approach to solving this problem. I have yet to try using an inexpensive neutral density filter (GSO ND96-0.3 50% transmission filter) that I have on hand. I also wonder if adding a single polarizing filter would help reduce glare/reflections.

I've tried all of my eyepieces at the 20-25mm range, and I've settled on the Lunt zoom eyepiece as being the overall best one in terms of overall comfort and having the ability to change magnification as need be. But I really want to solve this problem that I'm having with reflections. I don't recall this being an issue when I used my Lunt zoom eyepiece with my 50mm double-stacked Lunt with 6mm blocking filter before I traded it in for my 60mm.

 

This topic is somewhat related to the "Best eyepiece for Lunt 60" thread that started yesterday, but I think it's different enough for it to warrant its own thread.



#2 slepage

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Posted 03 January 2020 - 02:07 PM

I would suggest that you call Lunt.  They are very easy to get in touch with and i'm sure they can help you.  Just ask for technical support.  In the past, I had the same set up as you, with the same eyepiece and I never had this issue.



#3 hopskipson

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Posted 03 January 2020 - 05:24 PM

I'm not sure if this is relevant but is your scope tilt tuned or pressure tuned?  I remember someone discussing a similar topic where when tuning the double stack etalon that you will see a ghost image of the sun that needs to be "tilted" out of your field of view.  I hope someone with this set up will chime in.



#4 rigel123

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Posted 03 January 2020 - 05:58 PM

That "ghost" image is normal.  Tune your scope to the best contrast in Single Stack Mode, add the DS unit, and then simply use the Tilt Tuner on the DS module and move the reflection out of the FOV.



#5 Gregory Gross

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Posted 03 January 2020 - 07:13 PM

My setup is a pressure turned Lunt. It's not the reflection caused by the double stack module that's a concern for me. I observe with that shadow tilted just away from the Sun itself in order to maximize the amount of rays falling in the sweet spot (that is, when the front-mounted etalon is excessively tilted, the degree to which it is effective is reduced).

 

No, the thing that is of concern for me is the obvious reflection off my eyeball, a reflection that floats around my field of view depending on where my eye is placed. It's obvious that the reflection is coming off my eye: as my head naturally moves slightly when I'm at the eyepiece, I can see that reflection dance around. Moving my eye in and out, I can even manage to bring that reflection in perfect focus.

 

So as I sit there trying to manage that reflection, I'm being distracted from what I'm really trying to see and observe: the Sun.



#6 rigel123

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Posted 03 January 2020 - 08:23 PM

My setup is a pressure turned Lunt. It's not the reflection caused by the double stack module that's a concern for me. I observe with that shadow tilted just away from the Sun itself in order to maximize the amount of rays falling in the sweet spot (that is, when the front-mounted etalon is excessively tilted, the degree to which it is effective is reduced).

 

No, the thing that is of concern for me is the obvious reflection off my eyeball, a reflection that floats around my field of view depending on where my eye is placed. It's obvious that the reflection is coming off my eye: as my head naturally moves slightly when I'm at the eyepiece, I can see that reflection dance around. Moving my eye in and out, I can even manage to bring that reflection in perfect focus.

 

So as I sit there trying to manage that reflection, I'm being distracted from what I'm really trying to see and observe: the Sun.

OK, that’s something I haven’t experienced.  Have you tried a cloak/towel over your head when you view?  I have the same Lunt zoom as well.



#7 Gregory Gross

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Posted 03 January 2020 - 08:39 PM

What I typically do is use a brimmed hat to eliminate any direct glare from the Sun when my eye is at the eyepiece. I'll most often simply cup my hands around my eye to eliminate any glare coming from the side.

 

But I'm pretty sure the reflection is not coming from surrounding glare. I can get pretty dark conditions when I cup my hands around my eye at the eyepiece, and that is when this reflection problem is more apparent.

 

For what it's worth, I just came back in from observing a moon a day or so past first quarter using my Lunt zoom EP, an Orion dielectric mirror diagonal, and my 90mm f/11 achromat. I observed no reflections that resembled what I see when I observe the Sun in my 60mm Lunt... and I really looked for them. To the extent that that was a valid test, I think I've come to the conclusion that my Lunt zoom eyepiece is not the problem.

 

As I said, I had a 50mm Lunt double stacked with 6mm blocking filter, and I used the exact same zoom eyepiece with that scope. I can't remember this being a problem. My 60mm Lunt has a 12mm blocking filter. I'm just throwing out possibilities here: the problem may perhaps be due to the fact that I have a doubly-wide blocking filter now with more surface area to return a reflected image of the Sun off my eyeball back to my eye. Or maybe there's something else going on in the blocking filter itself. I can't imagine the problem is further up the optical train in front of the blocking filter assembly.

 

As slepage suggests, I may take this up with Lunt. But if anyone has suggestions, I'd be happy to hear them.


Edited by Gregory Gross, 03 January 2020 - 08:49 PM.


#8 rigel123

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Posted 04 January 2020 - 06:59 AM

Hopefully Lunt can help you out!



#9 Gregory Gross

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Posted 04 January 2020 - 06:00 PM

I think I solved my problem.
 
Years ago, I got a GSO 1.25" Neutral Density Filter (ND96-0.3 50% transmission) as a gift. Its usefulness wasn't completely obvious to me at the time (I was still very new in the hobby), so I put it in my box of spare parts and largely forgot about it.
 
This past October, when he delivered a talk on solar astronomy to the Rose City Astronomers in Portland, Oregon, I had the pleasure to meet Bob Yoesle in person. In response to my comment that the Sun showed up in my 60mm Lunt with a fair amount of glare around the Sun's disk, he suggested I try out a neutral density filter. With clouds largely frustrating my attempts to do a bit of solar observing this fall and winter (and due to my forgetfulness, too), it took me this long to actually try out that ND filter I had in my spare parts bin.

 

After finally getting around to giving it a go earlier today, I was immediately surprised how much of a difference the addition of a simple ND 0.3 filter costing less than $11 had on the visual experience with my 60mm Lunt with 60mm DS module. That annoying reflection of the Sun off my eye, while still present, was very much reduced to the point where it wasn't bothersome anymore. The filter also helped blacken the background behind the Sun and enhanced contrast of both surface details and subtle prominences. With a nice active area coming around and a large but fainter prominence both visible today, I was fortunate to have something to look at on what has been a very quiet Sun in recent months.

 

To be sure, that filter did not solve all my problems in life and did not make me look ten years younger. But I'm still in a mild state of shock how much of a difference that filter made. It will certainly be living on my Lunt zoom eyepiece indefinitely.

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#10 rigel123

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Posted 04 January 2020 - 11:25 PM

Glad to hear it!



#11 MAURITS

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Posted 05 January 2020 - 10:32 AM

Glad to hear too, I buy one.



#12 vincentv

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Posted 05 January 2020 - 06:29 PM

I had the same problem to a lesser degree. A single polarizing filter got rid of the reflection while barely influencing brightness. If you have one give it a go and compare!


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#13 Gregory Gross

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Posted 06 January 2020 - 11:36 AM

I do have a single polarizing filter and will also give that a shot -- thanks for the suggestion!



#14 Gregory Gross

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Posted 06 January 2020 - 07:41 PM

Update: this afternoon I was fortunate to have sunny skies again. I acted on vincentv's suggestion to try a single polarizing filter and compare to my 0.3 ND filter.

 

Long story short, I didn't see any appreciable difference between the two. In fact, the gut feeling I was left with was that the neutral density filter performed a hair better.

 

Since I have no other use for that ND filter and would simply like to dedicate its use to H-alpha solar observing, I'll stick with the ND filter moving forward.


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#15 Johninuk

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Posted 07 January 2020 - 06:11 AM

My setup is exactly the same as yours Gregory, and l get the same issue with reflection off the eyeball.I can only think reducing the amount of light out of the eyepiece with a filter as has been suggested will reduce this,or have your eyeballs anti reflection coated!!
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#16 stryker66

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Posted 18 January 2020 - 07:17 PM

I just got this scope and I think there was a video I watched that says "if you see like a double image while viewing" turn the tilt tuner until they become one?

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#17 MAURITS

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Posted 25 January 2020 - 03:37 AM

Nice scope.



#18 rigel123

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Posted 25 January 2020 - 07:28 AM

I just got this scope and I think there was a video I watched that says "if you see like a double image while viewing" turn the tilt tuner until they become one?

Actually, you want to tune it first without the DS on until you get your best contrast.  Then attach the DS unit and you will likely see 1 or two “ghost” images as well as the real image.  Adjust your tilt tune on the DS unit to just move those “ghosts” out of the FOV, you don’t want them overlapping the real image.  Here is a link to the Lunt Manual that describes this method:  https://luntsolarsys...ck_manual1.pdf 


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#19 BYoesle

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Posted 25 January 2020 - 04:08 PM

If you can tolerate the ghost image being in the field of view, but not overlapping the main image, it's usually best to apply less tilt than more tilt...


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#20 rigel123

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Posted 25 January 2020 - 05:37 PM

If you can tolerate the ghost image being in the field of view, but not overlapping the main image, it's usually best to apply less tilt than more tilt...

Meant to add that!




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