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Has anyone tried a Combo Quark visually at f/15?

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#1 bobito

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Posted 25 March 2019 - 12:59 PM

Hello,

I purchased my first Ha scope (Lunt LS60THa) a few months ago and have been loving the Ha experience.  So I'm now looking into future plans for... wait for it... MORE APERTURE!!!  wink.gif

 

I'm considering going the Quark route on this so I can utilize my existing APM 140 refractor.  However, after reviewing the details, I ended up thinking the 140, with its 980 focal length, was just going to be too much scope since the Quarks need f/30 so my 140 would be operating at about a 4116mm focal length.

 

Most days with my LS60 I'm lucky to get over 50x here in turbulent CT.  If I use the original Quark, with it's built in 4.2x focal extender, on my 140 I'd be at 75x with a 55mm Plossl.  So I'll be hunting around for a bunch of long focal length 2" EPs trying to find ones that will perform at f/30 that I won't get any use from otherwise.

 

I then noticed that the Combo Quark states it's good from f/15 - f/30.  If I use a 130mm ERF and a 2x Focal Extender I'll be at f/15 with only a focal length of 1960mm on the 140. With this config I'd get 50x with a 40mm EP so I can just use 1.25" EPs.  This certainly seems like the way to go.  But will the view be good at f/15 since everything else ever written about Quarks, or other Ha devices of this type, says they need f/30 or slower?

 

So, for visual use, does anyone use the Combo Quark at f/15?  If so, does it show good detail and/or have you compared it at slower focal lengths? I.E. It works at f/15, but it's better at f/30?

 

Thanks in advance for any replies!


Edited by bobito, 25 March 2019 - 01:04 PM.


#2 MalVeauX

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Posted 25 March 2019 - 05:33 PM

Hey Bob,

 

Your 140mm with the Quark operating at 4116mm is fine, if your seeing supports the resolution, because you can use a long focal length eyepiece. My 150mm F8 refractor is 5040mm with the Quark, and I use a pair of binoviewers with 20mm. This is 252x magnification, 0.28 degree FOV. My seeing is agreeable in the morning with this. In terms of what that means when I look at the solar limb, it's not as much magnification as you see even in the images I make usually, which is generally around 0.26 degree FOV when I image that you've seen with that refractor. So your 140mm and Quark will be significantly wider FOV, and that's great. Plus, you can use significantly longer FOV eyepieces, like a 32mm. No need to use wide AFOV type eyepieces, I would just use high contrast plossls or similar. With your 140mm and a 32mm plossl, you're at 0.4 degree FOV, nearly half a degree. That's plenty! And the magnification is only 128x. So it's a rather wide FOV if you think about it. If you have binoviewers and two eyepieces, it would be quite stunning. I say go for it!

 

But, if your seeing doesn't agree with the aperture, stick with the 60mm. You could double stack it and just push magnification when seeing allows. 60mm resolves a lot!

 

Personally I would not bother with a Quark at F15 visually, nor imaging-wise. The contrast will be low. Basically good for looking at prominences with the wider bandpass it will result in, they will be bright, but the surface will be bright and lack contrast, so you likely won't see good definition of structures on the surface. If your goal is just to camp out on the limb, then it will be fine. But when you compare F15 to something like F40, it's significantly different. I view at long focal lengths with the Quark for this reason. It matters, because contrast is everything if you want to see the detail.

 

As an alternative, you could look into a Celestron 102mm F9.8 Omni XLT. Fantastic scope for this. They're dirt cheap too. Similar FOV to what you would have with your 140mm. But, the 102mm aperture is a lot more agreeable with poor seeing. And the F9.8 puts you into some really contrasty views with a Quark.

 

Very best,


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#3 gnowellsct

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Posted 25 March 2019 - 05:37 PM

Actually the range I was given for the Quark was f/14 to f/15 or f/28 to f/30.  And I was told in no uncertain terms that I needed to acquire one and preferably two power mates (telecentrics), the 2x, and the 4x.  

 

In all cases, for me, the 4x power mate has yielded better results than the 2x power mate.  The 2x power mate you use for noobs who need to see the whole disk of the sun to get oriented at the eyepiece--not everyone "gets it" when they see just a fraction of the solar disk.  AND, it is hard to acquire the exit pupil of the eyepiece in daytime, so we might as well help them when we can.

 

In most cases the views seem best with a 30mm ocular.

 

81 mm f/7.7 Vixen= 4 x power mate f/30.8 results good, the best for that scope; 2x power mate shows full disk, everything is there, but not with same sharp detail

102 mm f/6.5 Vixen = f/26, results good, the best for that scope--and respectable overall, better than the 81 f/7.7; 2x power mate shows full disk, everything is there, but not with same sharp detail

93 mm f/6.9 CFF triplet = f/27.6 with 4x power mate and among the best views of the sun I've had including at NEAF.  I'm a little doubtful of my own opinion here I need to set the 102 up and look through it again.  And hopefully to check things out again at NEAF.  At 2x the views are entertaining, again sort of a noob level, and very useful for acquiring the image since of course everything that is not the sun is black.

 

My guess is that you'll be personally happy with the 4x power mate and f/28, just as I'm having a great time at f/27.6.  In fact you are "in the zone."  

 

But a 30mm will be, I imagine, around 137x which, you know, isn't that bad really.  It's less than 1x per mm of aperture.  You will probably want the 2x power mate if you expect to share the views.

 

Now Valery Deryuzhin has suggested higher focal ratios and not being so constrained by the specifications I got from Daystar.  He suggested f/42 and to do that I would need to mix a 4x power mate with a 1.5x barlow sold by Starizona for $75.  I'm not quite sure I want to do this and I think it might be an imaging thing.  Anyhow at f/55 (2x and power mates together) I was not able to get a definite focus on the edge of the sun.  And just using my eyepieces in the scope at its native f/6.9, I did not have enough in-travel to reach focus.  

 

I am tempted to get the ERF for my 5" refractor and see how that is.  Aperture definitely renders more detail, as I saw between the 81 mm and 102 mm, even though the focal ratio "favored" the 81.  

 

In the CFF I was seeing the fringe of spicules that are captured in some but not all of the images here.  These are small and dynamic and I'm not sure I've ever seen them in my other scopes.  So I am obliged to run that experiment when I have time, but that won't happen for weeks.  In other words I don't know whether I'm getting dramatically improved detail and seeing things I've never seen before, or alternatively, just paid attention more to the image.  Visual observers don't often talk about the spicules on the limb.

 

regards

Greg N


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#4 bobito

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Posted 25 March 2019 - 08:34 PM

Thank you for the replies, very informative! 

 

My biggest concern is too high a magnification, I don't recall going over 75x with the 60mm or 100x in the 140 using a wedge. I have not been at it long, so one steady day and my perceptions on magnification may change. It sounds like I do want to be near f30, and that's 75x with a 55mm which is just too much for most days in my experience.  Shelling out all the dough for an ERF that will see little use is a hard sell, could get a nice 80mm triplet with that money and forego the ERF.

 

I'm now thinking of splitting the difference and going for a 100mm ERF.  This way I can take advantage of the 140's focal length to increase the focal ratio without increasing focal length.  At f9.8 I could use a 2.5x extender to get f24.5 but keep my effective focal lenght at 2450.  Now I'm 61x with a 40mm.  I could also get the 130mm ERF and stop down on days I can't push the magnification.  Hmmmm....

 

The answer may just be that my seeing isnt good enough here in CT to justify a large apeture Ha scope since I would rarely get the chance to magnify enough to take advantage of the aperture.

 

Whelp, I have lots to think about.  Good thing whatever I end up with isn't in my budget yet!  :)

 

Thanks again!



#5 MalVeauX

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Posted 25 March 2019 - 09:09 PM

Thank you for the replies, very informative! 

 

My biggest concern is too high a magnification, I don't recall going over 75x with the 60mm or 100x in the 140 using a wedge. I have not been at it long, so one steady day and my perceptions on magnification may change. It sounds like I do want to be near f30, and that's 75x with a 55mm which is just too much for most days in my experience.  Shelling out all the dough for an ERF that will see little use is a hard sell, could get a nice 80mm triplet with that money and forego the ERF.

 

I'm now thinking of splitting the difference and going for a 100mm ERF.  This way I can take advantage of the 140's focal length to increase the focal ratio without increasing focal length.  At f9.8 I could use a 2.5x extender to get f24.5 but keep my effective focal lenght at 2450.  Now I'm 61x with a 40mm.  I could also get the 130mm ERF and stop down on days I can't push the magnification.  Hmmmm....

 

The answer may just be that my seeing isnt good enough here in CT to justify a large apeture Ha scope since I would rarely get the chance to magnify enough to take advantage of the aperture.

 

Whelp, I have lots to think about.  Good thing whatever I end up with isn't in my budget yet!  smile.gif

 

Thanks again!

You don't need an ERF with a Quark with the 140. It helps, but it's not needed.

 

If you simply mask the aperture of your 140 to 127 or 102,  you get a nice long focal ratio, better seeing handling, and you require zero extra ERF for this. A Quark with a 2" UV/IR block filter is all that is needed at these apertures. No big expensive ERF needed at all.

 

Very best,


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#6 bobito

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Posted 25 March 2019 - 10:57 PM

I've read that not using an ERF at these apertures causes heat in the tube that degrades the view. I also am a bit wary of sending all the UV/IR energy through my scope twice. I use a Wedge with the 140, but all the energy goes out the back with that.

But if I'm going to stop down the aperture to 100mm, I may be good with just using the cut filter.



#7 MalVeauX

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Posted 26 March 2019 - 06:58 AM

I've read that not using an ERF at these apertures causes heat in the tube that degrades the view. I also am a bit wary of sending all the UV/IR energy through my scope twice. I use a Wedge with the 140, but all the energy goes out the back with that.

But if I'm going to stop down the aperture to 100mm, I may be good with just using the cut filter.

It's fine. And you don't have anything to do worry about with your glass or scope. Everything is reflected out of the scope.

 

At 102~127mm apertures, you don't need anything more than the Quark & UV/IR block filter.

 

I do recommend a D-ERF for larger apertures for keeping tube currents down, but you start out with massive tubes, full of lots of air, and that's a lot more volume. I experienced it myself going from 120mm to 150mm. With my 120mm, I never had issues with "tube-seeing" and my Quark was always on band, so the heat was handled. But with my 150mm, there was obvious immediate seeing issues, and my Quark would sometimes go off band from the heat. When I added an ERF to my 150mm, those problems went away. Just my own anecdotal evidence. But that said, again, at 120mm aperture, in the Florida summer sun, there were no issues. Some of my best images were made with that thing.

 

Very best,


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#8 George9

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Posted 31 March 2019 - 02:34 AM

I observe from CT mostly and I prefer my 155mm to my 130mm for H-alpha high-power views, especially proms. And Iā€™m inland in the hills where you would think seeing would be worse. I would say over half the time, the seeing is good enough that the 155mm shows more than an 80mm in H-alpha at high power. Less often a 250mm (in white light) shows more than the 155 (also in white light).

George
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