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Lunt Calcium Wedge

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#1 dragracingdan

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Posted 03 December 2020 - 08:53 AM

I saw that Lunt has a wedge-style CaK module for their new LS130THA modular telescope. Looks similar to the one for the Lunt 152. Lunt says their standard CaK module is for scopes that are 100mm or less in aperture. My question is would there be any issue with using the wedge-style CaK module  with scopes over 100mm? I don't see it listed on Lunt's website as being sold separately from the focuser portion. This manual for the CaK wedge states it's not to be used with telescopes other than the LS130THA. I honestly don't see why... There is no blocking filter involved since this design lets the heat radiate out the back of the wedge. That's why the manual states the CaK wedge is for the LS130MT scopes that were sold with blocking filters (12mm and 18mm) that are not built into the focuser like the 3400 blocker.

 

Any feedback on this is appreciated as I'm looking to get a CaK filter for my 130mm scope. I also have the option of using a front mounted ERF that lets 393nm through and using the standard Lunt CaK module but I wanted to see what's going on with the Cak wedge.

 

 

Best,
Dan


Edited by dragracingdan, 04 December 2020 - 07:43 AM.


#2 rigel123

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Posted 03 December 2020 - 09:21 AM

I would call Lunt and talk to Faye about this one.


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#3 dragracingdan

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Posted 03 December 2020 - 10:11 AM

I would call Lunt and talk to Faye about this one.

I've emailed and called a few times and can't get through. I imagine they are busy since the sun's been waking up recently. I'll keep trying

 

Thanks,
Dan



#4 MalVeauX

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Posted 03 December 2020 - 10:33 AM

Heya,

 

Looks like they opted to put a thermal load configuration (wedge) on that CaK module to use with their modular scope since it's over 100mm aperture, rather than give you a D-ERF of some kind. There's absolutely nothing unique to the telescope that this CaK wedge is matched to, at all. The CaK module itself would work on any telescope that is well figured for near UV. Instead of using reflective dielectrically coated filters to reflect energy out, they're just using a wedge to handle the heat instead, and then putting a narrow 2.4A (likely) CaK filter after that. I obviously cannot answer for them, but I'm willing to bet that the wedge would work on a 150mm aperture instrument no problem, safely, for imaging, just like any normal 2" wedge with a narrow filter following it.

 

CaK is not a visual wavelength anyways. Imaging only frankly unless you're super young with non-yellowed cornea. If you really wanted to make sure that modular would work a 150mm aperture, since it has a 2" nose, you simply thread on a D-ERF of your choice to handle that. I use a Baader Blue CCD-IR Block imaging filter (2"), just like my Red one, as an internal 50mm D-ERF for CaK imaging with Lunt's B1200 CaK filter module with 150mm aperture refractor and nothing else.

 

Personally I wouldn't get that huge $2.2k+ EU module ($2600 USD?). Instead, just get a smaller Lunt CaK module and call it a day. You're rarely going to be pushing high res with CaK due to seeing (393nm requires excellent seeing to do more than course image scale) conditions being unsupportive, These are just narrow filters, not etalon, they do not use blocking filters, etc. Just energy rejection followed by a mirror followed by a narrow 2.4A 393.4nm filter. Nothing fancy. The 6mm version of course gives a full disc image with a 600mm focal length, the 12mm version can deliver a full disc image at 1200mm focal length. If your goal is full discs, the 6mm version ($750) will do that easy. No need to get more. If your goal is larger sensors and higher resolution attempts, then go with 12mm ($1k) or larger. I've not needed larger than 12mm personally with my larger systems and smaller sensors (1" and below).

 

Here's my 150mm F8 refractor with a Baader Blue CCD-IR Block Filter (2") threaded onto the nose of a 2" tube that inserts into the focuser (internal sub-aperture D-ERF) followed by a Lunt CaK B1200 module. It's thermally stable and I image with this at 120mm and 150mm (with and without barlow, etc). You've seen my Calcium results. I can't imagine spending more to do the same thing. The most critical factor in all of this imaging, especially in CaK, is seeing conditions anyways, not the gear.

 

Solarsetup_04042020.jpg

 

Very best,


Edited by MalVeauX, 03 December 2020 - 10:43 AM.

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#5 dragracingdan

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Posted 03 December 2020 - 10:57 AM

Thank you for replying and I'm on board with what you're saying. I was just concerned with thermal load with the larger refractors. Just adding a simple internal ERF like your CCD-B filter takes away any thermal issues? Have to ask because.... refractors are expensive! I haven't seen Lunt stating anything like that with their standard CaK wedge either but maybe I missed it.

 

 

Thanks,
Dan



#6 ch-viladrich

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Posted 03 December 2020 - 11:14 AM

A friend tested the "classic" Lunt Ca K wedge on its 200 mm refractor.  Well, well, the filter was damaged frown.gif

 

I used the Ca K on my TOA 150 with no problem. Still with this aperture, the solution suggested by Marty with an additional blocking blue filter is certainly preferable.


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#7 ch-viladrich

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Posted 03 December 2020 - 11:15 AM

BTW, the risk is for the filter, not for the refractor.


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#8 dragracingdan

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Posted 03 December 2020 - 11:20 AM

BTW, the risk is for the filter, not for the refractor.

This was my biggest concern. Thanks guys!



#9 MalVeauX

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Posted 03 December 2020 - 11:26 AM

Hey Dan,

 

Refractors are the perfect optic arrangement for solar with respect to thermal handling because the lenses do not absorb or keep any thermal load, they transmit all of it. Obstructions gather heat and transfer heat and mirrors absorb some heat and do not reflect everything. And when we're talking 1~2%, that's a lot of heat at the end of the day from a large aperture when you start to examine the load the focal plane. The unfocused beam is where you do all of the heat regulation because its not at focus and the intensity is spread out over a larger surface area basically. Within a refractor, you can do this at the opening (full aperture) or internally (sub-aperture) because the light cone changes size. You can put a sub-aperture energy rejection filter near the focuser and it will still handle all this energy by reflecting it out (dielectrically coated only) before it gets close to the focus plane and point of focus where all the intensity would be a problem. There is common worry that this allows air in the tube to heat up and be turbulent and have "tube currents." This may be true for some, but so far, I have not had this issue with a sealed tube in 100F+ weather (Florida) directly pointed at the sun with only a 50mm sub-aperture D-ERF and am able to do it with the full 150mm clear aperture of my refractor and if seeing is good (sub-arc-second) I can image high res short wavelength this way (and long wavelength of course, much easier).

 

You are not going to damage the refractor's lenses at all doing any of this. The thermal energy is transmitted, not absorbed. It's the filters down line or camera that will be damaged if thermal energy is not handled.

 

To keep your filters and/or camera from cracking under intensity of heat, you simply reject most of the heat before it ever comes to focus. So this is done with, again, dielectrically coated filters before the point of focus. It can be the full aperture size before your scope, or internally as sub-aperture within the scope somewhere. Many of us opt to use it near the focuser because you can get away with a mere 50mm filter to do this, saving a lot of cost to have a working system that is thermally stable.

 

I use the Baader Red & Blue CCD-IR Block imaging filters for this. They're affordable. They're good for imaging. They're good as sub-aperture internal dielectrically coated energy rejection filters because they reflect all the UV and shorter IR and most visible spectrum energy right back out of the OTA when seated in an unfocused beam that fits through 50mm (ie, near the focuser) of the light cone. This removes enough intensity for me to not crack common filters right after, at focus. These do such a good job at handling heat that I commonly will do just the Baader Red CCD-IR block filter as the internal ERF at the full 150mm aperture of the refractor, then just a Baader ND3 (10 stop) ND filter to reduce transmission (because transmission is so high that my sensor saturates even at 0.032ms and zero gain without it; obviously this is imaging-only, not for visual) and then my camera sensor. The filters never crack. The camera never cracks or melts or overheats. I do the same way for Calcium K and Gband with a Blue version of this Baader imaging filter as an internal D-ERF.

 

Also, refractors are the cheapest way to image solar! Big aperture refractors are rather inexpensive. 102mm to 150mm is a lot of aperture in solar. And achromatic doublets are all you need! In fact, an achromatic doublet is preferred to an ED/APO; it has to do with longitudinal focus. A fairly long achromatic doublet is inexpensive and very much ideal for narrowband solar imaging. You can get 120mm aperture achromatic doublets for peanuts. Just add a good focuser. Even 150mm achromatic doublets are affordable. I'm using an old yard cannon 150mm F8 celestron achromatic doublet that I picked up used for like $250. You can buy them new for more, and others, but they're all fairly inexpensive if you consider what you're getting for solar. I mask the aperture to 120mm F10 often when seeing isn't ideal or when doing short wavelength in less than ideal seeing. I can freely change aperture without having to have a new D-ERF because its internal. So simple! That's the beauty of single wavelength imaging. It's far more expensive to attempt to use any aperture mirror based optic because it requires a full aperture or sub-aperture but front mounted energy rejection system. Solar film is cheap and does this great but that only works for photosphere imaging and does not work for ultra narrowband imaging like HA and CaK. So the cost to get a full aperture D-ERF for a cheap mirror is hugely more expensive than a basic refractor which can be thermally handled for cheap with internal sub-aperture D-ERFs.

 

Very best,


Edited by MalVeauX, 03 December 2020 - 11:35 AM.

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#10 vincentv

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Posted 03 December 2020 - 04:39 PM

I have a question regarding sub aperture ERFs. Is there any concern regarding the inner flocking/matte paint? Could UV fade it?

Probably not a big issue with the cheaper models but a premium scope would give me pause.



#11 MalVeauX

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Posted 03 December 2020 - 05:05 PM

I have a question regarding sub aperture ERFs. Is there any concern regarding the inner flocking/matte paint? Could UV fade it?

Probably not a big issue with the cheaper models but a premium scope would give me pause.

If it were exposed for 8 hours a day, every day, for 10 years.... probably? But by then, I bet the outside of the scope would have even more issues from exposure in the same time frame and treatment?

 

Realistically someone doing this is doing it rather infrequently and for short periods of time. And someone who has a premium refractor like a Tak likely is going to put a full aperture D-ERF on there because it's chump change to someone who can afford premium scope(s). Ultimately, we don't have data to support any inner materials fading or anything that I know of. I've been doing it for years and I'm prolific with time with these things, but nothing looks different inside the scopes, so there's one data point. None of my refractors are premium APOs though. My most "premium" scope I use for solar is my C8 Edge, and that's not premium in reality, just slightly better than a standard C8, nothing special at the end of the day in terms of actual optical figures, but I use a full aperture D-ERF on it because I have to (being a mirror and obstruction based optic).

 

At the end of the day, if you're concerned at all for your scope, just put a full aperture D-ERF on the end of it and pay up.

 

Very best,


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#12 dragracingdan

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Posted 03 December 2020 - 08:37 PM

Thanks for the reply. You mentioned both things I was concerned about, the scope itself and the heat build up in the tube. I thought that heat would indeed build up inside the tube even with an internal ERF especially with larger diameters. I haven't been doing this long enough to tell so information and data points like this are invaluable

Thanks again,
Dan
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#13 BYoesle

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Posted 04 December 2020 - 02:43 AM

I saw that Lunt has a wedge-style CaK module for their new LS130THA modular telescope. Looks similar to the one for the Lunt 152. Lunt says their standard CaK module is for scopes that are 100mm or less in aperture. My question is would there be any issue with using the wedge-style CaK module  with scopes over 100mm? I don't see it listed on Lunt's website as being sold separately from the focuser portion. This manual for the CaK wedge states it's not to be used with telescopes other than the LS100THA. I honestly don't see why... There is no blocking filter involved since this design lets the heat radiate out the back of the wedge. That's why the manual states the CaK wedge is for the LS130MT scopes that were sold with blocking filters (12mm and 18mm) that are not built into the focuser like the 3400 blocker.

 

Hi Dan,

 

I believe you have mis-read something. While the standard CaK modules are stated to be limited to 100 mm of aperture, the Lunt CaK wedge in question states explicitly it is for use with the 130 mm LS130THa - and therefore IS NOT limited to 100 mm. The LS130THa with the built-in B3400 focuser blocker requires a different focuser for alternate nighttime use or CaK, and the CaK wedge can then be used with that scope as well. So it indeed would be safe for a similar aperture telescope which is over 100 mm.

 

A friend tested the "classic" Lunt Ca K wedge on its 200 mm refractor.  Well, well, the filter was damaged. 
I used the Ca K on my TOA 150 with no problem.

Still with this aperture, the solution suggested by Marty with an additional blocking blue filter is certainly preferable.

 

It is only if using a "regular" CaK module with your LS130THa or similar aperture scope that you would possibly need additional filtering. With 200 mm and a CaK wedge similarly additional filtering appears necessary. Generally an "ERF" will let a significant portion of the wavelength in question through. The critical thing is what else the "ERF" lets through. The Baader B-CCD filter lets 1/3 of the visible spectrum (~ 400 - 500 nm) through, and thereafter a bunch of longer IR past about 1200 nm, which by themselves can present a significant heat load to downstream filers, especially if employed with shorter focal ratio telescopes.

 

With really large apertures of 150 mm or above, a KG3 filter (transmission about 85% at 394 nm) should be employed after the Baader B-CCD when it is used as a solar "ERF" for CaK use - as Christian notes to protect the filters, not the telescope. The 400 - 500 nm range could similarly be blocked by a suitable short pass filter.

 

Lastly, don't forget that for CaK line, 100 mm of aperture is equivalent to a 166 mm telescope at the Ha line due to the shorter wavelength (656 nm / 394 nm = 1.66). Your 130 mm aperture scope would be equivalent to and 8.5 inch telescope used for Ha. This is why CaK imaging generally is more seeing dependent than Ha. The internal heating issue could exacerbate this, and where perhaps additional attention should be directed towards mitigating these effects.


Edited by BYoesle, 04 December 2020 - 03:05 AM.

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#14 MalVeauX

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Posted 04 December 2020 - 07:47 AM

On the subject of the Baader Blue CCD-IR block imaging filter, it's known to have rather low transmission in CaK as its so close to the cut-off. It still works of course, but a little gain is required at long focal-ratios (none for full discs so far for me). I need to find a suitable replacement soon. Would love to get a dual bandpass ERF from Beloptik for the 150mm refractor, but he's not making them that big yet. I'm looking for a good filter to block most everything other than the 393~430nm block and let those pass at high transmission as a primary sub aperture D-ERF, followed by something to be the secondary D-ERF to complete the blocking, like KG3.

 

Very best,



#15 dragracingdan

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Posted 04 December 2020 - 07:51 AM

Hi Dan,

 

I believe you have mis-read something. While the standard CaK modules are stated to be limited to 100 mm of aperture, the Lunt CaK wedge in question states explicitly it is for use with the 130 mm LS130THa - and therefore IS NOT limited to 100 mm. The LS130THa with the built-in B3400 focuser blocker requires a different focuser for alternate nighttime use or CaK, and the CaK wedge can then be used with that scope as well. So it indeed would be safe for a similar aperture telescope which is over 100 mm.

 

Hi Bob,

 

Thanks for the reply. You are correct about my OP. The CaKwedge I linked to was for the LS130THA and that was my intent. I will edit the post. Also, I appreciate the input about aperture and CaK imaging - great stuff

 

Thank you!

Dan



#16 BYoesle

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Posted 04 December 2020 - 10:29 AM

On the subject of the Baader Blue CCD-IR block imaging filter, it's known to have rather low transmission in CaK as its so close to the cut-off... I'm looking for a good filter to block most everything other than the 393~430nm block and let those pass at high transmission as a primary sub aperture D-ERF, followed by something to be the secondary D-ERF to complete the blocking, like KG3.

 

Hi Marty,

 

That's what I'm doing with my home-brewed CaK module. Here's the best filter I could find - robust hard-coated on fused silica and 0.25 lamda, to be used along with a 50 mm KG3 for IR for dual-component ERF.

 

EO 390 40 OD6.jpg

 

I'll use Baader's CaK or Apollo's CaK as a secondary blocker in a double or triple stack - and where the EO Florescent will have the requisite higher transmission necessary for the shortest possible exposures due to the stacking.

 

CaK single v triple.jpg

Single versus triple stack CaK contrast. ED100/900.

 

BTW, you can also improve the CaK of most doublet objectives in CaK by increasing the spacing of the elements. For the 6 inch f8, respacing to ~ 3 mm should be about ideal.


Edited by BYoesle, 04 December 2020 - 10:39 AM.

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#17 MalVeauX

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Posted 04 December 2020 - 10:57 AM

Hi Marty,

 

That's what I'm doing with my home-brewed CaK module. Here's the best filter I could find - robust hard-coated on fused silica and 0.25 lamda, to be used along with a 50 mm KG3 for IR for dual-component ERF.

 

BTW, you can also improve the CaK of most doublet objectives in CaK by increasing the spacing of the elements. For the 6 inch f8, respacing to ~ 3 mm should be about ideal.

Thanks Bob,

 

I'm awaiting receipt of a new filter to test from Altair at the moment should be around 395nm if I recall, in the 70% transmission range. Will see what it can handle.

 

Ultimately I want to have a single ERF to handle 393nm and 430nm, but I'm not sure I'll be able to improve something that wide compared to the simple Baader Blue filter at the moment.
 

I thought about just using a 2" Baader K-line filter as a primary internal D-ERF followed by a second filter to handle IR like KG3. Hoping Oliver at Beloptik can get a 150mm dual band D-ERF made soon. That would be ideal at this point.

 

Very best,


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#18 BYoesle

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Posted 04 December 2020 - 11:35 AM

Hi Marty,

 

I think the COVID 19 pandemic has affected Oliver's production, and why the UV/IR block on KG3 is out of stock. So I imagine the dual or tri-band ERF might be a ways off.

 

BTW, where did you see a 2 inch Baader K line filter? That would be awesome and I'll be getting one if they are available.

 

BTW 2 - it appears respacing a 6 inch f8 objective for CaK and stopping it down to 120 mm for f10 would be an ideal CaK scope.


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#19 MalVeauX

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Posted 04 December 2020 - 03:10 PM

Hi Marty,

 

I think the COVID 19 pandemic has affected Oliver's production, and why the UV/IR block on KG3 is out of stock. So I imagine the dual or tri-band ERF might be a ways off.

 

BTW, where did you see a 2 inch Baader K line filter? That would be awesome and I'll be getting one if they are available.

 

BTW 2 - it appears respacing a 6 inch f8 objective for CaK and stopping it down to 120 mm for f10 would be an ideal CaK scope.

Boo! Oh well.

 

Doh, no 2" Baadker K-line. Assumption on my part and incorrect. Dang. Was hoping it existed. Would make some things very easy.

 

Currently I use a 120mm F10 and it seems to handle CaK quite well; I use it the most for CaK these days.

 

Very best,




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