I would argue that if you want a dedicated solar scope, don't bother with a triplet APO as you're spending funds on color correction (and some very slight increases in general quality) that won't matter, and you're simply adding a lot of weight to the overall grab & go system without gaining much of anything, especially for visual. A doublet achromatic refractor will do essentially the same job for a lot less cost and a lot less weight. Use the saved funds to then get the most aperture hydrogen alpha filtration system you can afford instead as that's far more important. Now, that's not to say you will not benefit from a better telescope in general such as better machining, better quality focuser, better optical figures, etc. Just stressing that color correction optics don't do anything for narrowband at this tight of a bandpass (you're filter out all those wavelengths!) and you're just adding cost & weight by looking at triplets. So, if this is just for solar, I'd so go with a doublet APO at the most. Otherwise, a doublet achromatic is going to do virtually the same thing. If you plan to use it for more than solar, such as night time use, then by all means, get the better scope(s) if they're in your budget.
If you plan to continue using your Quark for this, a 400mm focal length will provide a full disc FOV with a 25mm eyepiece.
Visual with a Quark in general is often very much more about higher magnification views and you benefit from being able to use larger apertures. If you're really into full disc FOV viewing, it will be very important to keep the focal length short (400mm).
That said, it's very, very important to look at the focal-ratio with the Quark. The Quark really likes to work with a F30 light cone. If you get a really fast focal-ratio instrument, you may find the view is very bright, but also not very contrasty on the surface (proms will be fine either way). If you want to look at surface features you will need to try and keep that focal-ratio slower, to achieve F30 (or even longer!) with the Quark. I've tested it with an F5 instrument and then stopped it down to F10, making for F21 vs F43 and the difference was significant in terms of seeing surface features. This assumes you've dark adapted your eyes under a shroud (I know this is odd, but a realty of visual even for solar) and that you're tuned on band for the surface (which will also show proms perfectly fine by the way; thus I tune my Quark for the surface only, proms come through regardless). This mean that whatever scope you choose, you may want to consider stopping down the aperture to something along the lines of F6.5~F7.5 This is going to give you something much closer to F30 on those instruments. And something F8 to F10 is going to be even better for surface contrast.
Some scopes to look at:
(Just upgrade the focuser on this one, it's the same as an ST80, rebranded, put a 2" GSO focuser on it or equivalent and you're set for cheap)
I also highly recommend a sun blocker. You can get them pre-fabricated, or make your own. But they help you to keep your vision adapted and to keep you from glancing at the sun and from getting too hot!
I used to use a PST for true "grab & go" solar. It worked. But, it was also a very tiny scale, so it was mostly a blank disc with some proms on the limb. But, it at least worked, was light weight and inexpensive. But the view was not something I would call blowing anyone away. It was also too difficult to do things with like binoviewers and stuff. I wanted more modular approaches. So I sold my PST eventually. Great starter scope, but I needed more and stayed with the Quark. The Quark on a short scope is a vastly better visual experience, and crazy better for imaging, even though its still considered an entry tier filter.
For my grab & go solar, I actually use a humble old Orion ST80 (400mm F5 doublet). I mask it to 60mm (F6.667) or to 40mm (F10) when using the Quark. I can't tell the difference in ultranarrow band between it and my 80mm APO, even when imaging. So I just use the inexpensive achromat for this. I upgraded the focuser to a 2" GSO to handle the weight of the Quark, plus I image with it. It's small and light and works on a small and light weight alt-az mount for true grab & go. I start with a 25mm eyepiece for full disc views. I love being able to see the surface features instantly when I'm operating it at F40+. This is currently on a Twilight Nano mount which handles it great.
I installed a Televue sol-finder on it. Or you can use a Heliopod (Dynapod) to quickly put it on the sun. Here my ST80 is masked to 40mm F10 with the Quark and a 25mm eyepiece:
My 4 year old can use it even.
Here's the same scope with a 60mm aperture mask (F6.667) that I use for imaging. You can take a look at my images to see the results. Edge to edge, the glass of the ST80 is solid. No APO needed.
Now, this assumes you want to continue using your Quark for grab & go visual. Maybe you want to get a dedicated, unpowered scope? If so, I would definitely look into a Lunt 60mm or Coronado 60mm. 60mm is plenty of aperture to really see some things with good detail. Quick to use with no fuss. Nothing heavy. Easy on light weight mounts. You can also purchase the front mounted versions where the etalon & ERF are a single unit installed on the front of a donor scope and a blocking filter in the back and you're set, which gives you more modular options.
I think this is a superior way to go personally. No power required. One single unit. The only reason I didn't is budget. I already have a Quark and I do 99% imaging with it. For a visual instrument, I'd want a dedicated scope instead. But, they are also costly. And I also use all my scopes for several purposes. So, for now, I'm using the Quark on several instruments.
Edited by MalVeauX, 10 August 2018 - 11:04 AM.