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102 XLT with Quark Chromosphere?

solar imaging
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#1 gfstallin

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Posted 17 January 2021 - 04:21 AM

So I think I have decided on a Quark Chromosphere. However, I am a little uncertain about whether to go with the combo version or the original version and exactly which refractor to use with it. 

 

My plan is mostly for imaging, though I would definitely do some visual. Full disk imaging is not a primary goal. 

 

Currently, I have an Explore Scientific ED80 triplet which I'm wary of using with the Quark, though I've read people have used their ES ED triplets without issue. To remove doubt, I was planning on getting an achromat. It is a relatively small price to pay for peace of mind. My thinking was to buy a 102 XLT OTA for this purpose. At f/9.8, it is a little longer than Daystar's recommendation of f/4 to f/9. Alternatively, I could get Celestron 120 XLT which is f/8.33. I am not entertaining delusions of having daytime seeing that would allow me to make any consistent use of the potential increase in resolution with the 120, but it is within the F/D range suggested by Daystar. I would like for a pleasing visual image with an eyepiece, even if imaging is my main pursuit. For imaging and with either OTA, I think I should be good on weight with an AVX. I also have a CGX if the 120 proves unwieldy. Would the 102 XLT be fine for imaging in terms of focal length? Would the image be too dim at f/9.8-f/10 visually?

 

Also, I was wondering whether to get the Chromosphere original version or to get the combo version and buy my own telecentric barlow (perhaps a Siebert telecentric 4x). My thinking with getting the combo version would be for future flexibility, even though I don't plan on using SCTs or a Mak for solar imaging. Perhaps it is not worth the additional hassle dealing with barlows for a flexibility I might never need? 

 

I'm also aware that the focuser might be the first thing I'd want to replace eventually. I figure that is a bridge I can cross when I come to it. 

 

I'm sure there are things I'm not considering, so I am all ears. My goal is to avoid that waxing sense of regret I feel as I slowly come to the realization that I've bought one thing when I really should have bought something else that was a similar price and better suited to my needs. That's like every 3rd astronomy purchase for me. 

 

George



#2 MalVeauX

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Posted 17 January 2021 - 09:29 AM

Hi George,

 

Your ED80 refractor will work fine and nothing will be damaged. Refractors transmit all the light, there's no thermal load on your lenses and your lenses are air gaped. Only an oil-spaced lens would be something to be concerned about. But, if you insist...

 

The XLT 102 and 120 are the same focal length and size basically, other than a tiny bit of extra weight on the lens side. It's not much easier to mount the 102mm version than the 120mm version, due to the length. That said, I would suggest the 102mm F10 version for certain. Daystar makes a recommendation based on what will get the etalon close to F30 after the 4.3x telecentric amplifier in it. F4 is not a good idea, it's silly they even recommend it. Even F5 is not a good idea. It works, but it'll be closer to 0.9A and let a lot of photosphere through. F7 should be the starting point in reality, to get to F30. And ideally, longer is better. F10 is great. Don't stop at F8~F9, F10 is where to go if you can get to F10~F11, go for it. This puts the Quark closer to F43+ and gets that etalon where it should be, operating closer to 0.7A~0.65A range to have higher contrast on the 656nm line. It will not be significantly dimmer visually, it will still have a bright enough image to enjoy binoviewers. You will want a new focuser on either scope though likely, so that's something to consider.

 

For you to benefit the combo version with a future SCT/Mak for imaging, you're suggesting you have seeing conditions that will support a 6" or larger SCT/Mak I assume? You will have to buy a several thousand dollar full aperture front mounted dielectrically coated energy rejection filter for that, plus the mounting, to be able to even begin to use those mirror based instruments with a Quark; you can't use solar film with the Quark. And again, you have to have sub-arc-second daytime seeing conditions, sustained, to even think of trying this. Plus, you're close to the Jetstream, so I think half the year towards your fall your seeing is likely greatly effected by that. Going into larger apertures and high-res imaging is not about the equipment, it's about the seeing conditions. You can buy all the right stuff but if your seeing is anything more than 1 arc-second, you're not going to be imaging high res anything over what you'd get with a 4", resolution wise. Know your seeing before you even consider this. I would suggest you get a normal chromosphere Quark version and keep it simple with smaller refractors. Don't worry about big scopes, big apertures, big D-ERFs unless you have the seeing conditions to support that.

 

If you are certain you want a 4" refractor, close to F10, for the purpose of using a Quark... then instead of the XLT F10 with a focuser upgrade, I would look at the following instead:

 

https://www.teleskop...e-Assembly.html

 

As for considering many things, my suggestion is to consider a smaller aperture 60mm or 80mm Lunt instead. Something you can grow into and eventually double stack (greatly increase contrast), something that doesn't die when an electronic piece fails, something that doesn't need a battery, something that has excellent customer support and service and something that will likely get you a much better etalon. Don't get wrapped up in thinking you need huge aperture. Seeing is the limit of everything with this.

 

To get an idea of things, I suggest you take any of your current scopes, like your ED80 or maybe even for your C5, and put some visual grade solar film on the front. See if you can get a sharp limb. See if you can see a sunspot (there's one rounding the limb right now) and see it in sharp focus. See if the limb is in sharp focus at moderate-high power magnification, or if it's a rolling boil. Do this a few times over a few days and different times of day to get an idea of your day time seeing. This will greatly help you not over-purchase in aperture and see the limit of all this, which is seeing conditions.

 

Very best,


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#3 gfstallin

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Posted 17 January 2021 - 03:48 PM

If you are certain you want a 4" refractor, close to F10, for the purpose of using a Quark... then instead of the XLT F10 with a focuser upgrade, I would look at the following instead:

 

https://www.teleskop...e-Assembly.html

 

As for considering many things, my suggestion is to consider a smaller aperture 60mm or 80mm Lunt instead. Something you can grow into and eventually double stack (greatly increase contrast), something that doesn't die when an electronic piece fails, something that doesn't need a battery, something that has excellent customer support and service and something that will likely get you a much better etalon. Don't get wrapped up in thinking you need huge aperture. Seeing is the limit of everything with this.

 

 

Very best,

Marty, 

 

Why are you doing this to me? When I asked for your thoughts, I was looking for confirmation bias. lol.gif

 

I'm (mostly) joking. My first idea had actually been a Lunt 50mm, but then I came down with a minor case of aperture fever and upped my budget. The Chromosphere looked to be the best option. Aperture fever struck even though I am certain that my daytime seeing would rarely ever permit me to use 100mm to full advantage. While I cannot really confirm this seeing assumption with daytime seeing experience (I already had a Baader filter on order for the ED80), there is nothing about my average nighttime seeing to suggest a miraculous suspension of the laws of physics and typical fluid dynamics properties will take place the moment I order solar equipment. You are correct about the jet stream. We do get periods of decent seeing, particularly during stretches in the summer and during winter periods of abnormally warm or cold temperatures (jet stream moving far to our south or north); however, there might be good reason no local club members have indicated that the Washington D.C. area is the nation's best-kept secret for amateur solar physics research. 

 

Also funny that you mentioned that TS refractor. When I was doing the math on focuser upgrades, that refractor (which had always intrigued me) immediately came to mind. I was concerned about the focal length being a little too long, but I see that is not of particular concern.  

 

For me, the Lunt 80 is out of the picture. I could probably buy it within 8 months, but I'm relatively certain it would lead to an intervention by the people who claim to love me most, with my wife leading the posse. "You talked about that time you slipped and fell on the dew-soaked ladder collimating your telescope as if it were funny. You could have died...like our finances did when you bought that little telescope, your seventh." 

 

I digress. The Quark Chromosphere and the Lunt 60 are in the same class for me in terms of initial financial commitment. While I'm working on the assumption that the product I get will function and be supported as advertised, I would err on the side of build quality and what works best for imaging in my seeing conditions. 

 

Thank you for your input, Marty. Lack of reassuring confirmation bias aside, there is also a peace of mind knowing that I listened to the opinions and experiences of knowledgeable folks before making a decision. 

 

George


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#4 MalVeauX

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Posted 17 January 2021 - 04:07 PM

Hey George,

 

All good, I wouldn't rush into anything. A lot of this is very personal, what you will find attractive and interesting versus someone else may be different. It's common to want more aperture and etalon quality and contrast is often just not even in the picture, yet becomes the most important thing after you get your feet wet. You'd be surprised what even 50mm can resolve on the sun. It's huge and near by, you can resolve every major HA feature with a tiny little 40mm aperture no problem. The limit is the seeing, not the aperture so much. And if your seeing is average, poor, or worse, then the smaller apertures are a better bet in general anyways, in which case, it's better to focus more on getting a really good etalon with room to double stack it with another good etalon to get the most contrasty high quality view that your seeing can support in the first place, rather than a really low contrast, but bright, mushy image, from a single stack that is low quality with too much aperture for the image scale or magnification due to poor seeing conditions. It's easy to tell someone something, but they really need to see to know what they like best.

 

If your absolute goal was visual and imaging of prominences and your seeing was average to average-poor, then I would say the Quark + 80mm~102mm refractor is a great option to get more aperture, as a single stack is totally fine for limb prominences and the bigger aperture will help the faint bright ones be visible still and is affordable for the aperture to get into it.

 

However, if your goal was more the disc itself and surface features, with average to poor seeing conditions then I would point you towards a system that can be double stacked eventually. And for cost being a consideration and the quality of the etalon and overall support, I would argue for a 60mm Lunt, especially the newest modular ones that come on a 70mm ED refractor and can be modular for night use, day use and multi-wavelength use, while still having the option to double stack it when you can. No electronics to fail over time. No crazy long focal-ratios to maintain just to have the right performance on the etalon to even take advantage of it. It's just more simple. Yes, you give up some aperture, but your seeing is poor most likely, so that's not going to be a loss in reality. The gain in being able to double stack it eventually makes the biggest impact, again, if your goal is the disc itself and surface features in general. A modular Lunt 60mm will cost the same as a 4" new achromatic doublet plus a Quark. But you can double stack it later on and no electronics to fail.

 

Again its personal. Someone may prefer the larger aperture single stack. And some may prefer the smaller aperture double-stack approach. This also changes significantly if you're into visual more, or if imaging is a big part of this, or its entirety. For imaging you can get away with a single stack more often. Visually though, its so significant with a double stack that you may wonder how anyone survives visually on a single stack. It's that big of a deal visually at least. For my own anecdotal approach, I have a 200mm single stack and sub-arc-second seeing and yet I would much rather do visual with my 60mm double stack overall because I simply like to look at the whole disc and see the surface, proms, etc, all in one view with really high contrast with a binoviewer. Unfortunately you have to just see things and try things to know what will be your preference. Just makes it worse I realize to hear there. There's no right answer here.

 

Without any experience with these filters and the nuances of etalons, sweet spots, visually how it is to experience it, etc, it's hard to suggest someone spend significant money on what is really an entry level product and so its not going to be a premium experience, despite the otherwise rather premium cost to get into just an entry device, let alone what the cost is for the mid-tier stuff. It gets very expensive, very quickly. And it's quite frankly easy to be disappointed in the quality of something after you have some experience knowing what you're paying for the level of quality. Lastly, these etalons from any manufacturer have zero guarantee of anything, there's no standard, no particular metric, every number you read from any of them is totally meaningless and none of them provide a transmission profile to make a statement about their filter quality, finesse, etc. It's a gamble each time! So it's really hard to suggest an entry product with any expectation.

 

Very best,


Edited by MalVeauX, 17 January 2021 - 04:14 PM.

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#5 briansalomon1

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Posted 18 January 2021 - 11:26 AM

I routinely use quark chormosphere in an f5.4 scope and always stop down to ~f7 because there's so much more detail that way but I think it's worth noting that at ~f5 the quark chromosphere does perform like a prominence model, showing more prominence at the expense of detail.


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