5 replies to this topic

[betacygni]

I’ve read quite a few posts talking about getting slower scopes to optimize surface detail with the quark, but haven’t seen much about how to optimize for prominences.

So far I’ve primarily used my quark with a 60mm F6, and have been happy with the results. Today I briefly tried the quark with my tsa120 at f7.5, but wasn’t that impressed with the difference. Image scale was larger, and I could see maybe a bit more in the sunspot area, but the prominences were at best about the same, maybe even a bit worse, certainly less “pop.” Maybe no wow factor was due to seeing? Edge of the sun seemed fairly stable, but I haven’t really observed solar enough yet to recognize really good seeing vs bad. It certainly didn’t feel worth the extra setup time.

So far I’ve not been that interested in surface detail, as it doesn’t seem to change much, maybe I just need to wait for a more active sun. But it got me wondering if I’d be better off with a fast large aperture, like maybe an Orion 120mm f5? Something bigger maybe? It goes against my night observing instincts for something that cheap, but I know we don’t need apo for h-alpha. Would an f5 to f6 actually outperform slower scopes in this case? Any suggestions on the ideal scope to maximize prominence detail and image scale for getting up close to them? Ideally with a focuser that could handle quark + binoviewers?

Edited by betacygni, 27 February 2021 - 08:41 PM.

[MalVeauX]

Heya,

 

Running F5~F6 into a Quark is going to show prominences brighter in general, because the resulting focal-ratio is going to be around F21~F25, which will correspond with about a 0.9 to 0.8 angstrom bandpass on that mica spaced etalon. It lets in more light is the bottom line, so things are brighter. It works well on prominences because there's no photosphere behind the prominence, so you get brighter prominences. But your surface is washed out because of all that photosphere light coming through, killing contrast, so filaments will be low contrast and active regions will be low contrast, the surface in general will be low contrast and very bright. Again, without that photosphere, as bright as it is, behind a prominence, you can use loose bandpass to view prominences and allow that tolerance of extra brightness and benefit from it on prominences. But only prominences.

 

 

Mean while, for the surface, getting to F45+ so that you're operating closer to 0.65~0.63 angstrom will have better contrast on the surface, same performance on prominences, but overall a little less bright due to a more narrow peak centered on 656nm if you're on band.

 

The surface is not popping right now because its a solar minimum. Even the prominences are rather small (not this past week though!). When the solar maximum returns, you'll want a high contrast view of the surface when there's several active regions popping off every day. And it changes hourly.

 

Yes, the 120mm F5 is actually good for a prominence setup with a Quark, if you know you're purposefully trying to operate it with a looser bandpass for the purpose of brighter everything, specifically targeting prominences. The stock focuser of the Orion copy of this scope is junk and I wouldn't trust your Quark + binos to it; you'd have to replace it (GSO linear bearing, Moonlite, etc). The SkyWatcher version has a better stock focuser, but I can't speak to how much better it is.

 

Here's how that setup looks:

 

 

Very best,

Edited by MalVeauX, 27 February 2021 - 08:55 PM.

[betacygni]

Awesome, thanks for the very detailed response, that was quite helpful. For the price of entry the Orion 120mm f5 certainly sounds like it’s worth a go (and I’ll be far less worried about the birds flying over that objective than I was with the takahashi today...)

Quick follow up question, so assuming one were comparing scopes with the same focal ratio, my understanding is increase in aperture is going to gain you increased magnification while maintaining brightness, but does the gain in resolving power also play a significant role in solar? Guess I’m wondering if solar details are small enough in general to warrant increases in aperature, say my 60mm vs 120mm. I imagine seeing will create diminishing returns at some point. Guess I’m wondering if there is a “sweet spot” aperture wise, given average seeing?

[MalVeauX]

Awesome, thanks for the very detailed response, that was quite helpful. For the price of entry the Orion 120mm f5 certainly sounds like it’s worth a go (and I’ll be far less worried about the birds flying over that objective than I was with the takahashi today...)

Quick follow up question, so assuming one were comparing scopes with the same focal ratio, my understanding is increase in aperture is going to gain you increased magnification while maintaining brightness, but does the gain in resolving power also play a significant role in solar? Guess I’m wondering if solar details are small enough in general to warrant increases in aperature, say my 60mm vs 120mm. I imagine seeing will create diminishing returns at some point. Guess I’m wondering if there is a “sweet spot” aperture wise, given average seeing?

Heya,

 

Increasing aperture will increase the potential angular resolution that you can resolve; limited by seeing conditions. So the useful magnification you can achieve with a larger aperture, is higher, potentially, again limited by seeing conditions. The difference from 60mm to 120mm on the limb, even at 100x is very noticeable visually, even if the seeing is not great.

 

Visually, you can get away with larger apertures, to the limit of the seeing, but the tolerance visually is higher.

 

There's no sweet spot for aperture, there's just seeing conditions. That said, I would argue that not knowing the seeing conditions, 60mm is the defacto "it will always work" aperture for solar, and if you think you have a little better seeing conditions then a 102mm aperture will probably be ok visually sometimes too. But again, this doesn't matter, its just anecdotal because most people do not have great seeing conditions during the day and seeing conditions are the best way to determine what your limits on aperture can and will be.

 

Check out Meteoblue and plug in your location, under sports and stuff there's astronomical seeing. This is just a prediction, not what it actually is for you, but you can at least get an idea of what seeing is potentially like in your area in day time and go from there to know what's likely possible.

 

Very best,

Edited by MalVeauX, 28 February 2021 - 08:45 AM.

[dswtan]

This thread is interesting to me as I have been considering moving my Quark from an old ST80 to something larger as a "prominence machine".

 

One of the things I was wary of was the ERF, as full aperture is so expensive. In re-checking the manual, I see 120mm is the recommended limit before a full aperture one is required, so while I don't expect crazy things to happen at 120.1mm, I did want to add this consideration to the thread as see if anyone can confirm that 120mm is just hunky dory with a regular UV/IR in the front of the diagonal. Thanks!

 

Ref:
http://www.daystarfi...QuarkManual.pdf

 

"For  telescopes  under  approximately  120mm  of  aperture,  a  screw  in  UV/IR  cut  filter  can  be  employed in front of the telescope diagonal.  The UV/IR cut filter reflects UV and IR light back out the front of the telescope, reducing temperatures inside.    Do  not  use  a  UV/IR  cut  filter  with  oil  spaced  objective  telescopes,  or  any  telescope  with an integrated rear field flattener or Petzval lens.  The UV/IR cut filter must be the first optical element to receive concentrated light."

[MalVeauX]

Heya,

 

You can use your Quark with apertures as large as 150mm (refractor only) with just a UV/IR block filter. Daystar's old info stated 120~127mm. Daystar's update is 150mm (its on their website under support and tech knowledge base).

 

That said, I don't recommend just a UV/IR block filter. Instead, I recommend a red + UV/IR block filter to take out even more thermal energy. Specifically, I suggest the Baader Red CCD-IR Block Filter (2" size).

 

But yes, you can use the 120mm aperture with just a UV/IR block filter. It will be fine.

 

Very best,