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