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Quark's Newts?

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#1 SloMoe

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Posted 13 August 2020 - 07:57 AM

As some of you know I'm getting interested in solar observation, visual only.

 

Didn't think of this yesterday, can you use a quark in a Newtonian, like a 114?



#2 MalVeauX

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Posted 13 August 2020 - 08:22 AM



As some of you know I'm getting interested in solar observation, visual only.

 

Didn't think of this yesterday, can you use a quark in a Newtonian, like a 114?

Not without a full aperture or sub-aperture (but front mounted) energy rejection filter.

 

So yes, but with that caveat, which means very expensive. Not worth it. Use a refractor. smile.gif

 

Here's how a big D-ERF looks on a newtonian with a Quark:

 

32881881387_d889580dce_c.jpg

 

Very best,


Edited by MalVeauX, 13 August 2020 - 08:24 AM.

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#3 SloMoe

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Posted 13 August 2020 - 08:36 AM

Morning Marty, I'm a little confused, if I'm using a quark then I want a focal ratio of f/7 or slower?

 

In the ads it reads for an f/15 to f/30, ? 



#4 MalVeauX

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Posted 13 August 2020 - 08:44 AM

Morning Marty, I'm a little confused, if I'm using a quark then I want a focal ratio of f/7 or slower?

 

In the ads it reads for an f/15 to f/30, ? 

Heya,

 

The effective focal ratio at the etalon of the Quark is ideally at F30 or longer (F40+). The Quark has an internal 4.3x telecentric amplifier, so basically F7 or longer base focal-ratio will be the most appropriate. It works however even with F4~F5 stuff. I would always suggest going longer than shorter with these kinds of Daystar filters.

 

Very best,



#5 SloMoe

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Posted 13 August 2020 - 09:10 AM

How large of an aperture before and ERF would be needed?

 

I also noted in the ad's that it works well in SCT's,

I have an old 8i, what else would be needed to use it with a quark?



#6 bandazar

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Posted 13 August 2020 - 09:11 AM

Wonder if someone could invent a semi transparent coating on a newt mirror so that only a weak percentage of the sun's light gets transferred.  Then you would not need an ERF.   Or is something wrong with that theory?  I know the coating probably would not be cheap.



#7 MalVeauX

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Posted 13 August 2020 - 09:21 AM

How large of an aperture before and ERF would be needed?

 

I also noted in the ad's that it works well in SCT's,

I have an old 8i, what else would be needed to use it with a quark?

All apertures, when it comes to a folded optics mirror like Newtonian/SCT/Mak, need a front mounted ERF (as long as the aluminium reflective coating is intact). These designs require energy rejection filters on the front aperture (full aperture or partial sub-aperture). But they're required for these designs.

 

Refractors do not absorb/reflect anything, they literally transmit the energy so the glass doesn't get hot at all, so a sub-aperture D-ERF can then reflect the unwanted energy back out again without it being absorbed or reflected off the lenses; this is why the Quark works in a refractor with nothing more than a UV/IR block filter (which is just reflecting UV and IR wavelengths back out). The nose of the Quark has a D-ERF on it that rejects 95% already, so that just helps it when apertures are over 80mm and up to 150mm. But only with refractors, for the reason stated.

 

Mirror based optics cannot do that; they all reflect, so some energy is parted onto all the things in the light pathway, including the secondary mirror holding system, etc.

 

Wonder if someone could invent a semi transparent coating on a newt mirror so that only a weak percentage of the sun's light gets transferred.  Then you would not need an ERF.   Or is something wrong with that theory?  I know the coating probably would not be cheap.

There are custom mirror coatings that can be gotten that basically turn a newtonian's primary mirror into a big dielectrically coated ERF for HA; basically you would want the mirror to reflect HA (to increase transmission), but not reflect the other wavelengths and let them pass through the mirror. So this means the aluminum coating and dielectric coatings are not going to be like a standard mirror at all. And no, its not cheap, you're making a narrowband filter that is huge, so it's very expensive. This is not something to do when just dabbling or starting out and it's not even reasonable for smaller apertures due to cost and limitations, compared to just getting a full aperture D-ERF. Big D-ERF's are getting common now, several companies make them, unlike before, where you had basically one option. Now there's 4+ options easily for D-ERFs thankfully (BelOptik, AiryLab, Baader, Altair, etc).

 

Very best,


Edited by MalVeauX, 13 August 2020 - 09:28 AM.


#8 UniversalMaster

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Posted 13 August 2020 - 09:42 AM

I thinking the same thing a while back, and got the same great reply :-)
The good news is that a 6" or less achromat can be had quite cheaply, especially used. Since I realized this, I have not been thinking about Newtons and quarks :-)

#9 MalVeauX

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Posted 13 August 2020 - 10:02 AM



The good news is that a 6" or less achromat can be had quite cheaply

Precisely this, a 6 inch achromatic doublet is less expensive than dealing with all the fuss of mirrors, secondary mirrors, and having an unobstructed aperture, 6 inch is a big aperture for solar in reality because it's rare that seeing will even support its resolution potential, very rare frankly. This can be done much less expensively yet still provide the potential resolution. This can be used with a Quark with just an internal sub-aperture D-ERF in the form of a common Baader Red CCD-IR Block filter serving as the internal UV/IR/non-red-visible spectrum rejection filter. Granted, it's no joke mounting a 6" refractor, but not much different than trying to mount a large newtonian with special mirror coatings, or a D-ERF either. This is why so many favor the SCT build for larger aperture (over 6 inches) because of the compact size, but the cost of the D-ERF is where the money goes in that build. A refractor setup at 6" can be done much less costly and yet still provide fantastic resolution. Without knowing your seeing conditions and whether they support this or larger anyways, I wouldn't go beyond a refractor for this in the first place at least for HA purposes.

 

Another thing that is commonly not considered is that the larger your aperture and focal-ratio ends up, with a Quark for example, the more limited the FOV to the point where you won't be able to see entire large HA structures in one FOV (be it eyepieces or camera sensor; especially with camera sensors). Many AR's in HA are massive!

 

+++++++++++++++++++++++

 

(without pushing processing to the point of clearly over-sharpening):

 

For reference, here's a 150mm aperture resolution near limits:

 

50179977118_89867baffb_b.jpg

 

50159351027_d03fe23190_b.jpg

 

Here's 200mm aperture resolution, not quite at its limits, but a bit higher resolution than the 150mm was able to get to, under good seeing:

 

50192586706_3d721c6815_b.jpg

 

50206466916_beb44faa5c_b.jpg

 

50206465381_cea125c6b9_b.jpg

 

The jump from a 6" refractor to a 8" or larger mirror based optic with D-ERF is frankly not worth it unless your passion is high resolution and you have excellent sub-arc-second seeing conditions often that you can benefit with it.

 

6" aperture fracs are plenty frankly!

 

Very best,


Edited by MalVeauX, 13 August 2020 - 10:08 AM.


#10 bandazar

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Posted 13 August 2020 - 05:33 PM

I wasn't thinking of a dialetric coating..  I know about those, I was thinking of a semi-transparent coating.  A coating that would only reflect a certain percentage of the light (for example maybe 10% reflectivity), so that by the time the light gets to the eyepiece area, it would be very bright, but not so bright as to require a front ERF. 

Sort of like a moon filter for example that lets in a certain percentage of light.   Suspect it would still be expensive, and it might require re-coating every couple of years.  Or maybe instead of coating, maybe using a different kind of glass that has impurities in it.



#11 George9

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Posted 14 August 2020 - 09:24 AM

The challenge is that you need 100% of the H-alpha light and 5% or less of the other frequencies. That is why Marty suggested the dielectric. If you use an uncoated mirror, you can do white-light observing (with further ND filtering), but H-alpha will look black after an H-alpha filter. In other words, the output of an H-alpha filter will look about 20 times dimmer than those currently in use, and they are already only borderline bright enough. H-alpha filters don't have a big ND component that you can remove to make up for the loss at the mirror.

 

George




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