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Double Stacking a 60mm Lunt Solar Scope

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#1 Gregory Gross

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Posted 20 July 2019 - 03:17 PM

I thought it'd be helpful and interesting to start a fresh thread for discussing the experience that folks have had with double stacking their 60mm Lunt solar scopes. I was out late this morning and took some time to jot down some of what I saw at the eyepiece with my pressure-tuned 60mm Lunt both in single- and double-stacked mode. I have a 12mm blocking filter and the larger 60mm (as opposed to the 50mm) double-stack module.
 
In single-stacked mode, I observed an impressive prominence, another tiny prom, a row of three or four smaller prominences, a pair of subtle smudge-like filaments, and, perhaps most apparent during this quieter day on the Sun during this period of solar minimum, a mild orange-peel texturing across the disk of the Sun. A good amount of reddish glare surrounded the disk of the Sun and extended out past its limb and into the field of view for a length equivalent to perhaps three-quarters of the Sun's diameter.
 
With my 60mm double-stack module attached, my experience was completely different and vastly improved. The Sun appeared dimmed somewhat, but that dimming was not objectionable. Granulation became far better contrasted and much finer, the difference in fineness being comparable to coarser white table sugar versus powdered sugar. That granulation had somewhat of a scale- or web-like appearance. The double-stack module largely eliminated (but did not completely eliminate) the reddish glare that was plainly visible around the Sun in single-stacked mode. As a result, prominences took on a bolder appearance. That impressive prominence was visible, of course, as was that row of what now seemed more definitely like four smaller prominences. Other more subtle prominences that I didn't recall seeing were now visible. One of those prominences seemed to be paired with a fine filament (a "filaprom" forming?) that I utterly did not see in single-stacked mode. That pair of smudge-like filaments had better definition. To top it off, a tiny bright spot was visible, one corresponding to a small active area that turns up as a mild active area on the SDO HMI Magnetogram and the AIA at 1700 Å and especially at 304 Å (see the SDO data page). Clearly, the improvement in contrast made that tiny bright spot more readily visible. All in all, the addition of a double-stack module transformed my 60mm Lunt into a whole other scope, one that was far more capable in showing fine and subtle detail in the Sun's chromosphere.

To my eye, the images that area available on the GONG H-Alpha Network Monitor closely resemble what I see at the eyepiece in my double-stacked 60mm Lunt. Whatever prominences, filaments, and active areas that are visible on those images are generally visible to me in the eyepiece. I can't seem to find the specific webpage that indicated this, but I seem to remember that GONG uses cameras equipped with 60mm H-alpha filters. (If someone can point me to that webpage, I'd appreciate it.)

In addition to working the tuning wheel on the double-stack module, one key tip I can offer is to rotate the module itself to obtain optimum tuning. After playing around with my particular scope, I found that, if I fully screwed the module on to the scope and then backed it off by just a half-turn, the view was more pleasing in the eyepiece. Patient trial and error was necessary for me to settle on the best combination of double-stack module position on the scope itself and the position of the tuning wheel.

In terms of weight distribution, the scope in single-stacked mode is definitely tail heavy. Adding a double-stack module balances the weight across the center of the scope far better. It's almost as if the scope wants to be double stacked. With that extra length added to the front of the scope and the blocking filter diagonal nose pulled out about an inch and a half from the focuser draw tube (one won't achieve focus by not doing this), the scope grows to 19 1/2" in length and looks formidable:
 

DSed 60mm Lunt Solar Scope
 
All in all, I'd go so far as to say that my 60mm Lunt solar scope seems incomplete without its double-stack module attached. My experience was the same when I had a 50mm Lunt scope, too. It's a financially painful experience to spend nearly as much for a double-stack module as what one spent on the scope itself, but it's worth every penny. If I were faced with the choice between a single-stacked but larger aperture solar scope or a double-stacked but smaller aperture solar scope, I'd definitely opt for the latter.

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#2 TOMDEY

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Posted 20 July 2019 - 03:42 PM

Yes. I had that exact same setup and it worked wonderfully. Took a lot of images, too. Eventually went to the 80mm DS... larger image and better resolution. The nice thing about your configuration is that you can easily screw-off the front module to get a better view of the proms sticking out at the sides. In practice, I rarely did that, though. Just left it on... seems fine.    Tom

 

{Here Tom hits [Post] and finds out whether the CN Naughty Filter redacts the phrase "screw-off"...]


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#3 rigel123

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Posted 20 July 2019 - 04:18 PM

Nice write up, and although my DS is Tilt Tune only that pretty much describes what I observed today too!


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#4 dscarpa

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Posted 20 July 2019 - 04:48 PM

 How hard was it to get the hang of tuning when DSing with the Lunt 60? I have yet to be able  to do it with my Coronado 90 III DS which has 3 tuners only one of which I can reach while looking through the eyepiece.  That the mostly not all that bright proms showed well in your scopes DSs gives me hope that they will in mine as well. David


Edited by dscarpa, 20 July 2019 - 04:50 PM.


#5 bandazar

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Posted 20 July 2019 - 06:08 PM

DSing with my lunt was very easy with the 50mm front stack.  I didn't even really have to tune it.  Actually I did try and tune it and saw the ghost image coming in and out of view.  Double stack did improve surface details a little bit.  Not enough that I would consider buying one if I were starting out.  But I guess this is something that is subjective to each person. 

Double stacking with my coronado 90mm was a pain if I remember correctly.  I could never get the ghost image out of view unless I was okay with mediocre views with the scope being slightly out of the best position for h-alpha details.   The telescope was also long to the point where it was hard to tune things on the front end, and then walk back to the eyepiece to see what had changed.  The image was also a lot darker than single stack.  

This is not to say that the coronado is inferior to lunt.  It could, possibly be, that the coronado simply had a much smaller angstrom value with the double stack as compared to the lunt which is why it was so dark.  I suspect that was the case probably as the level of change in image was more different in the 90mm coronado than the lunt.  I remember the sun resembling a grapefruit when viewed in double stack mode with the coronado. 



#6 descott12

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Posted 20 July 2019 - 07:42 PM

Question: since your DS is 50 mm, have you not basically downgraded your 60 mm scope to a 50 mm?  Is there still some advantage to your setup over mine which is the 50 DS?

 

I never quite understood why Lunt did that. Was it simply to allow a 60 mm scope to be double-stacked without having to create a 60 mm etalon??


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#7 bandazar

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Posted 20 July 2019 - 08:08 PM

Possibly.  It has to do with the double stacking craze I think.  Manufacturers will basically produce something if people want it and there is enough profit in it.  Double stacking is an easy way to increase profits.  And yes, there is some benefit to double stacking.

I prefer larger aperture though, given the choice between it and double stacking. 

No, there is no advantage to your setup over mine.  Except in maybe small apertures, I don't think there is all that much difference if you only go up 10mm.  The only advantage in my setup is that I get to have a single stacked 60mm if I want to. 



#8 dscarpa

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Posted 20 July 2019 - 09:01 PM

 My Coronado 90 III is quite a bit darker with 2 etalons. So far I haven't been able to tune it to show proms well when DSs and have  tried for over 8 hrs. David



#9 TOMDEY

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Posted 21 July 2019 - 01:25 AM

Question: since your DS is 50 mm, have you not basically downgraded your 60 mm scope to a 50 mm?  Is there still some advantage to your setup over mine which is the 50 DS?

I never quite understood why Lunt did that. Was it simply to allow a 60 mm scope to be double-stacked without having to create a 60 mm etalon??

Note that Gregory is using the 60mm front etalon. Lunt has the 60mm, but it costs a lot more than the 50mm. The 60mm is what I used on mine... otherwise the resolution and brightness go WAY down with the 50mm.    Tom



#10 andreww71

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Posted 21 July 2019 - 08:06 AM

I'm new to solar observing, most of my participation in this hobby is deep-sky observing with large Dobs. I've seen the sun a few times in the past through both a Daystar set-up on a 10" SCT and a larger Lunt (80 or 100mm) at Craters of the Moon National Monument last year after the eclipse. I knew what to expect with H-alpha solar observing. I recently took the plunge and picked up a well cared for 60mm pressure tuned scope with a complete list of accessories from a member here on CN. Included was the 50mm DS filter. As noted above, Lunt sold this combination (60mm scope / 50mm DS) as a package. I too wondered why only a 50mm DS until I looked at the price difference!

 

I have not taken the DS filter off the scope - it was on when I purchased it and I'm getting incredible views. Besides, like other people have commented here, as well as this scopes previous owner, once you view the sun with the DS installed there is very little incentive to take it off!

 

As far as what's visible with this combination, RickV's post from yesterday (07/20) shows a number of features on the limb that I could clearly see with this scope. I use a 8mm-24mm LV Zoom Eyepiece (came with the scope). I didn't note what magnification I was using with the zoom but my best estimate is probably between 30 - 40x. The sun was just west of the meridian and the transparency about a 6 -7. I have found that stray light at the eyepiece is big issue when trying to see these faint details on the limb. To eliminate this problem I place one hand over my non-observing eye and the other around the edge of the eyepiece while I'm observing. This proved to be the trick and greatly increased the contrast in the view. Of course, the disc shows tremendous detail once I dial the pressure tuner in.

 

Andrew


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#11 bob71741

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Posted 21 July 2019 - 09:02 AM

"Question: since your DS is 50 mm, have you not basically downgraded your 60 mm scope to a 50 mm?  Is there still some advantage to your setup over mine which is the 50 DS?

 

I never quite understood why Lunt did that. Was it simply to allow a 60 mm scope to be double-stacked without having to create a 60 mm etalon??"

 

Dave-

When Lunt went into business, back in 2007, one of their offerings was a 60mm H-α telescope with 0.5 Å performance; one way to get the 0.5 Å bandwidth was to use a double pass etalon system. They had problems getting the double pass to work consistently for production run units, so to fulfill their obligation to the people that prepaid for a double pass telescope, Lunt's quickest and cheapest solution was to produce a 50mm etalon to screw on the front of the objective making a double stacked telescope to get the 0.5 Å bandwidth. 



#12 dscarpa

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Posted 21 July 2019 - 10:37 AM

 How much power can you use with the Lunt 60s using the 60mm etalon? I'm thinking about getting one for my tilt tune Lunt 60 BF1200. That way I could have my Coronado 90 III with one etalon and the DSs Lunt 60 out at the same time or visa versa. I also think it would be easier to learn to DS tune with the simpler Lunt.  Years ago I ordered one but then canceled  because I was concerned about only being able to use lower powers in it DSs. I use 90X-110X part of almost every day it's out .  However now that I've got the Coronado 90 III that's excellent for high power single etalon viewing that's not an issue.  The Lunt 60 is on a WO EZTouch whose axis don't lock well so being balanced would be a big plus.  David


Edited by dscarpa, 21 July 2019 - 02:02 PM.


#13 Gregory Gross

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Posted 22 July 2019 - 02:20 AM

 How hard was it to get the hang of tuning when DSing with the Lunt 60? I have yet to be able  to do it with my Coronado 90 III DS which has 3 tuners only one of which I can reach while looking through the eyepiece.  That the mostly not all that bright proms showed well in your scopes DSs gives me hope that they will in mine as well. David

I found that it wasn't hard at all to get the hang of tuning a double-stacked Lunt 60. Basically, I simply leave the tuning wheel on the DS module alone and work only the pressure-tuning cylinder on the scope.

 

Question: since your DS is 50 mm, have you not basically downgraded your 60 mm scope to a 50 mm?  Is there still some advantage to your setup over mine which is the 50 DS?

 

I never quite understood why Lunt did that. Was it simply to allow a 60 mm scope to be double-stacked without having to create a 60 mm etalon??

As others have pointed out on this thread, the cost of producing a larger etalon goes up steeply with only a small increase in aperture. The cost savings of internal etalons due to their smaller size is the whole reason why they are often more attractive than externally-mounted etalons. The downside to internal etalons is that they require a collimating lens in front of the etalon and a refocusing lens in the back, additional optics that add to the complexity of the system. In spite of that complexity, however, the sheer fact of having that smaller etalon makes them cheaper to produce than external etalons.

 

For what it's worth, I've looked through 60mm Lunts with both 50mm and 60mm DS modules, and I have to say that the performance between the two is pretty comparable. I opted for the 60mm because I wanted to get as many photons through the scope and get as much resolution as possible with it. But I was very tempted simply to go with the 50mm DS module. I was really impressed with its performance.

 

Also bear in mind that, when comparing the 50mm scope with 50mm module and 60mm scope with 50mm module, it's not a simple matter of aperture. The Lunt 50s and 60s have different optical trains between the objective lens and eyepiece, namely a larger etalon in the case of the 60mm scope. To my eye, the 60 had a larger sweet spot than the 50 had. (I have to confess that I'm not 100% sure that larger etalons directly result in larger sweet spot size. I'd appreciate better information in case I'm wrong.)

 

 How much power can you use with the Lunt 60s using the 60mm etalon? I'm thinking about getting one for my tilt tune Lunt 60 BF1200. That way I could have my Coronado 90 III with one etalon and the DSs Lunt 60 out at the same time or visa versa. I also think it would be easier to learn to DS tune with the simpler Lunt.  Years ago I ordered one but then canceled  because I was concerned about only being able to use lower powers in it DSs. I use 90X-110X part of almost every day it's out .  However now that I've got the Coronado 90 III that's excellent for high power single etalon viewing that's not an issue.  The Lunt 60 is on a WO EZTouch whose axis don't lock well so being balanced would be a big plus.  David

Since I enjoy full-disk viewing, I rarely go above the lowest power that my Lunt zoom eyepiece gives me. At the 21.5mm eyepiece setting on the zoom EP, that gives me approximately 23x magnification.



#14 Eddgie

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Posted 22 July 2019 - 07:58 AM

Possibly.  It has to do with the double stacking craze I think.  Manufacturers will basically produce something if people want it and there is enough profit in it.  Double stacking is an easy way to increase profits.  And yes, there is some benefit to double stacking.

I prefer larger aperture though, given the choice between it and double stacking. 

I don't think it is really a "Craze."   Double stacking does make a difference on surface detail and having used single stack and double stack, I think that difference is worth the expense to many people.

 

That being said, when the sun is active, even a single stack PST with a good blocking filter can give thrilling views.   I personally am fine using a larger single stack to a smaller double stack because I enjoy the ability to get extra magnification, and dollar for dollar, that is the trade-off that is usually involved with the decision between single and double.

 

It is like when I went from the PST single stack to the Lunt 60 DS.   The surface detail on the single stack PST was far better than I had expected (my first solar scope!) but I just could not magnify it enough to see much structure.  The double stacked 60 gave enough aperture increase to use much higher power and because of that, I thought the upgrade was well worth the 3 times higher dollar cost (bought the Double Stack 60 off of ebay at a great price).. Still, I could use more power but not enough power.  So, now I am moving to an 80 because I could just not get the details (especially prominence detail) large enough in a 60mm.  Some of that was due to the dimming of the double stack.  Powers above about 60x were pretty dim.   I used a single stack 80mm scope a while back and I have to say that the ability to reach up far higher in magnification was kind of a good trade-off to the wonderful low power full disk views of the 60mm DS.    

 

It is a difficult decision (smaller DS vs larger SS).  Probably the most debated topic in equipment selection.   While I think most say that a smaller DS is better than a larger SS, I can say that having owned both, I can make a great case for either position and when the sun is busy, either choice can provide hundreds and hundreds of hours of enjoyment.  

 

(I think that while people think of solar H-a as being expensive, I do more solar than night time because it just works out that way in my life. Spending $3000 on an 80mm scope that gets used more than a $2000 Apo seems to be a pretty fair value proposition to me, and frankly, after 30 years, the planets and the moon have gotten boring.  The sun on the other hand, serves up something new almost every day.)


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#15 dscarpa

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Posted 26 July 2019 - 11:07 AM

 I at long last got the DS working on my Coronado 90 III!  Proms show well with it at 100X-135X . After using the 90 DS with the single etalon Lunt 60 I think it's a great combo. I like the contrast of the 2 types of images a lot!  The 90 shows me where to look for surface features in the Lunt  which in turn serves as scout for faint proms.  I'm going to hold off on DSing the Lunt for now. If I couldn't get the 90 working well for proms DSs I probably would have DSs the 60 and mostly used the bigger scope with one etalon. David  


Edited by dscarpa, 26 July 2019 - 11:14 AM.


#16 viewer

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Posted 26 July 2019 - 11:22 AM

Good point David. Many people can or want to have just one dedicated solar telescope. I'm apparently one of them. You are using the combination well I think. For me it's the proms, will 'forever' miss out on the filaments (will wait for white light coming up too!). Anything dimming the view of my 40 mm aperture scope can't be good wink.gif


Edited by viewer, 26 July 2019 - 11:28 AM.



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