14 replies to this topic

[gnowellsct]

Club members and I spent about 4 hours solar observing today in breezy weather with temperatures in the 40s. The idea was to get out there with all kinds of configurations and see what kind of bang you get for the buck. The only time I've seen more scopes and solar filters in use has been at the Northeast astronomy forum.

The budget option was an SV bony one arm alt azimuth mount with a Celestron 102 mm f/6.5 optic. It had an SVbony or similar Herschel wedge.

The theory of using an achromat for solar is that solar observing is done in narrow bandwidths and therefore it doesn't matter if you're not using a scope with fancy glass correction.

It is the case that the hundred millimeter budget refractor with the budget Herschel wedge will deliver good views. But if you swap out the 102mm and put in a vixen 81 mm SD 81s with the exact same Herschel wedge and eyepiece you get a better view in spite of the smaller aperture. And you get a sharper clearer focus with better contrast. In short the budget 102 mm is good but the vixen delivers value for the extra money spent. And it is to be noted that it does more with less aperture.

Here we pause and I will deliver my customary diatribe against poor mounts. It was very difficult to focus on the SV bony, And when it's hard to reach focus the views are compromised.

The lesson was demonstrated in a couple of other ways. One was a very long focal ratio 100 mm refractor from The '50s of indeterminate brand then actually was delivering some good views with a mylar film solar filter. But it was unstable in our windy conditions and very difficult to focus as a consequence. It was on a g11 Mount but in this case Even the ultra reliable g11 was challenged by the long moment arm of this particular refractor and the windy conditions. This old scope has its limitations. Fortunately the owner brought his skywatcher 120 mm Apo. This scope has juice. He had a Mylar filter with a kind of orange tint to the views. I looked very closely at this and compared it to the Herschel wedges. It's hard to define why one has the sensation that the Herschel wedges deliver a sharper view. Because if you really look everything that you can see in the wedge seems to be in the film filter. I speculate that the background green color actually helps bring out more contrast. And yeah we had a couple of mylar filters on the field and they performed and you saw activity on the Sun and you saw some details including some other granulation But it seems to be a case of you get what you pay for. The Herschel wedges do better.

And there was a guy who brought his Paramount ME and FS 128. He was feeling too lazy to drag his power supply out of the car and was attempting to use The rig with the clutches disengaged. Well it was jittering and bouncing all over the place And it was impossible to focus and I shamed him into hooking up his power supply and engaging the clutches and thereafter we got some very good views.

NO SHORTCUTS ON THE MOUNT PEOPLE. PAY ATTENTION TO THIS ONE.

We had a lunt 80 mm H alpha where everything is built into the optical tube. Probably The top selling brand in H alpha although I have no data. It was riding on a Mach 1 mount and the whole thing was stable and dandy and the views were sharp and detailed. With excellent definition on the prominences and great disc detail around the sunspots and filaments. You could make out multiple plages.

In the past I did a shootout with this 80 mm scope and one of my ED scopes, maybe my 81 mm, with the Daystar quark combo and concluded at the time that the quark combo was doing a better job of surface detail and the lunt was doing a better job on the prominences. This time the circumstances of the comparison were radically different The quark combo was on a 130 mm triplet apo. Also I've said multiple times that they whole disk views in the quark combo with a 2x powermate were not that impressive.

I don't know what was different today maybe the quark was fully dialed in and fully warmed up to optimum temperature but the 2x full disc views were excellent And the 4x views gave a great deal of detail that were not accessible in the 80 mm H alpha.

The main lesson of this particular comparison is that for visual use these two H alpha configurations had a great deal to offer. But aperture appears to play as big a role in delivering performance as the H alpha unit.

Put it another way. If you're mixing and matching an 80 mm H alpha to a 130 mm scope with a Herschel wedge that's one thing. And if you have a 130 mm scope with H alpha and an 80 mm with a Herschel wedge that's quite a different thing.

The Herschel wedge made the rounds to a wide variety of scopes. Wherever it replaced film it did a better job. And it did better on the bigger scopes. It was wonderful on my 92 mm but it performed even better on the 120 mm, 128 mm, and 130 mm ED and apo scopes that were there.

The genius of the quark combo is that it turns any white light scope into an H alpha performer. But a word of caution here. It has to be a white light scope with a superior focuser. The vixen SD81s is a very fine scope but its OEM focuser is not suited for the quark combo. And what's true for the vixen 81 mm is triple true for the Celestron achromat f/6.5. And that's the thing to bear in mind if one is thinking about pairing the quark combo with an inexpensive refractor. You're probably going to overwhelm the focuser and would be better off using a Herschel wedge.

The lessons of the day seem to have been:

1. Bigger aperture is mo betta, not always. The Herschel wedge on the 102 mm achromat was outperformed by an 81 mm ED with the same Herschel wedge. But the Herschel wedge moving from scope to scope showed a trend to deliver more performance on bigger apertures.

2. Don't cut corners on the mount it interferes with optical performance.

3. Lunt H alpha is excellent.

4. The particular quark combo we had is also excellent. In fact I was surprised I didn't remember it being this good. Maybe it's very cranky about its operating temperature and was doing very well because it was 40° out. I won't know till next summer when it's warmer.

5. More aperture is mo betta in H alpha well as in white light.

6. Herschel wedge outperforms the film filters. We had several film filters on the field everybody has them because they're inexpensive and they continue to have them until such time as they decide to pop for Herschel wedge to see what the fuss is about.

7. Very likely if one has an f/15 D and G 5-in achromat with a top-notch focuser and a mount adequate to the task of holding a giant, it will do as well in h alpha or with a wedge as a 130 mm triplet apo at half the focal ratio. But you're not going to see 10 ft long D&G on an observing field where there is an impromptu solar party. Taking into account what was there today and what I have seen in the past at NEAF solar parties, The fancy premium refractors tend to deliver more performance even if you are observing in only one wavelength. So if you want to optimize your views you get value back for higher levels of outlay.

8. A 102 mm achromat on a one arm alt azimuth budget Mount, with a budget Herschel wedge, gets you into the game. And it might even be the best way to get into the game because a couple of years working with that gear will train you in observing and help you get more out of your upgrade gear if you go that route.

As far as star parties go this was a great and convivial time. It's not as cold as a night time star party. It's very relaxing you don't have to worry about trying to find this or that object. There's only one thing to look at. If you need to fidget with something there's plenty of light. If you drop something it's easy to find. You don't have to worry about antagonizing your observing fellows with your vehicle lights as you arrive or leave. And the sun is a dynamic object so as you watch it things change. Finally, you don't have to worry about light pollution and the sun is minimally impacted by smoke from fires 3000 miles away and if the transparency isn't perfect so what. Greg N

[bigdob24]

Sounds like a great solar party , where did this all happen

[gnowellsct]

Sounds like a great solar party , where did this all happen

About 30mi W of Albany NY.

[Spectrum222]

Great report, as always! 

 

I am guessing the full aperture filters (mylar) yielding the slightly yellow/orange views may have been a budget no-name, or maybe the Helios ones offered by Seemore these days - they are nice, but Baader AS film units still out-perform them. I also suspect that a good, commercial AS film filter, like the Euro EMC or Baader ASTFs have better overall results possible for that film since they are optimized for the film and have very stress-strain free mountings. Homemade throw together ones usually do not take this as well not account, unless the "craftsperson" uses care when making one. (sorry just the way it is. I have seen some pretty rough-looking AS film cells that absolutely KILL the good views!)

 

Also I agree that wedges > film in general. I assume these wedges had polarizers and not just a ND post filter after the ND3.0. If not, that also makes a big difference. 

 

Also, IMO, and experience, a 2" wedge typically does better than a 1.25" for several reasons:

 

1) larger prism = better heat load handling - this is why many makers of wedges suggest limits on their wedges for certain apertures. 

2) Most better well-known larger 2" wedges have at least a 1/8 to 1/10 wave or better rating, which equals better views in general, especially with a good APO. 

3) Larger Aperture usually will result in better views, but seeing DOES play a part. Sometimes, less is more, depending upon conditions. My experience has the 90-120mm as a sweet spot for observing in general on solar, but even my little 80mm doublet ED can hold its own sometimes (that's an f/7). However, I LOVE my 6" scope on solar when seeing is nearly perfect - just too much fun!!!

4) If one uses a wedge or film on an achromat in FULL spectrum WL, they will have challenges getting the best views for that scope. Use of a Baader SA (Semi-APO) or Fringe Killer filter after the polarizer DOES allow these to do pretty respectably in what I call "RSWL" - reduced spectrum white light. The biggest challenge on a general achromat, especially a shorter one with f/7, is also having good focuser on it. But in general, a good to excellent APO should win out, as you saw in the testing.

5) IM experience, a good wedge delivers superb results and can really do well if one "tunes" the brightness/contrast for the conditions. When done right - WOW.

 

Thanks for sharing!

 

Darren

[gnowellsct]

Great report, as always!


1) larger prism = better heat load handling - this is why many makers of wedges suggest limits on their wedges for certain apertures.

Did not know this. I'm not clear on why the baader Herschel wedge should get hot at all. It has a built-in UVIR.

UVIR keeps the quark combo cool to the touch...

Thanks for sharing your experience And knowledge.

Greg N

[Spikey131]

Did not know this. I'm not clear on why the baader Herschel wedge should get hot at all. It has a built-in UVIR.

UVIR keeps the quark combo cool to the touch...

Thanks for sharing your experience And knowledge.

Greg N

I have used a 1.25” Herschel wedge with a 5” refractor, which is pushing the recommended limit.  The heat sink gets quite warm, but not burn-your-fingers hot.  I avoid leaving the scope uncovered longer than necessary.

 

There is a recent post in which I reported temperature measurements with the same refractor and the Quark.  The bottom line is that it only gets a little warm.  I suspect that this is partly due to the UV filter, but the Quark itself also has a blocking filter which is reflecting a lot of UV back out of the scope.

[gnowellsct]

The bottom line is that it only gets a little warm. I suspect that this is partly due to the UV filter, but the Quark itself also has a blocking filter which is reflecting a lot of UV back out of the scope.

I believe a dielectric diagonal also has a blocking effect. My scope always seems to be ambient. Never had anything that made me want to pull out the IR gun and measure.

Greg N

[BYoesle]

Great comments.

 

I believe a dielectric diagonal also has a blocking effect. My scope always seems to be ambient. Never had anything that made me want to pull out the IR gun and measure.

 

There are some (mostly high-res planetary observers) that argue a dielectric diagonal, while generally having higher reflectivity than a standard aluminum coating, often has greater light scatter...

 

 

I would add that if using a full-spectrum white light filter at low solar altitudes above the horizon - and with good seeing - an atmospheric dispersion corrector may come in handy.

 

 

Otherwise, a Baader Continuum filter will eliminate this need, and is designed for the best corrected wavelength (e line) of most refractive optics.

 

telescope-optics.net

 

ED100/900, Continuum filter, PGR Chameleon, six pane mosaic.

 

Obviously atmospheric dispersion is not generally applicable to narrow wavelength systems, but spherochromatic aberration is, especially at shorter wavelengths (e.g. CaK), and is highly dependent on the particular telescope's optical correction:

 

Summing it up, the magnitude of secondary spectrum is only a part of the equation - and not necessarily the most important one - when it comes to the chromatic correction level of refracting objectives. Its existence itself does not prevent achieving sensibly perfect chromatic correction. Even the standard achromat will do if left long enough, and it only gets easier with glass combinations that have it reduced or even eliminated. But as the secondary spectrum diminishes, another chromatic aberration - spherochromatism, or variation of spherical aberration with wavelength (also called tertiary spectrum) - takes the front seat. In general, it increases exponentially with the relative aperture (D/f), and in proportion with the aperture diameter. Thus, a zero secondary spectrum does not necessarily mean great chromatic correction, and could, in fact, accompany a less than perfect, or sub-standard one.

Edited by BYoesle, 10 November 2024 - 09:45 AM.

[gnowellsct]

Is a continuum filter an alternate name for UV/IR cut?

Edited by gnowellsct, 10 November 2024 - 10:39 AM.

[BYoesle]

No. See filter curves here.

 

The UV/IR filters generally pass a lot of VIS, while the Baader Continuum (new version) not only blocks UV/IR, but has a narrower transmission centered at 540 nm for spherochromatic aberration control.

[Scott99]

>>1) larger prism = better heat load handling - this is why many makers of wedges suggest limits on their wedges for certain apertures.

 

I replaced my 1.25" Lunt Herschel wedge with the 2-inch in case I want to use it on a 5 or 6-inch refractor.  I was worried about the effects of the longer light path degading the image but the 2-inch appears super sharp on my 4-inch.  They recommend using the 1.25 only up to 4" aperture.

 

To me the wedge seems like a huge upgrade over the Baader film I was using before - much cleaner views.  Solar is fun because it expands the amount of time you can observe.  When it's always cloudy like it usually is here it's great to be able to take a scope out when you see blue skies. 

 

The east is under a very unusual high pressure ridge that is causing lots of trouble with drought but many clear nights and days which is highly unusual for us.  I've been able to view the comet about 20 nights so far which is unbelievable for this part of the world!

Edited by Scott99, 11 November 2024 - 01:31 AM.

[Spectrum222]

Totally agree Scott! 

 

A good wedge and refractor really does bring out the best the sun has to offer in full (or reduced) spectrum views.

 

Having the ability to trim brightness for best overall contrast really helps. With a fixed filter, you just cannot quite do this well. Even when one is observing in spring-fall seasons where the sun has higher altitudes, being able to adjust ever-so-slightly the details during the daylight as these change with extinction, light haze, etc. just makes all the difference. 

 

Also, not knocking AS film filters, but not having to worry at all about them coming off, or getting poked is a nice feeling as well. (I chuckle on this last one, as if executed correctly this is not much of an argument really, other than maybe a mixed outreach with a lot of young folks around). 

 

However, I DO have to say that the views in my APM 120SD binos with Euro-EMC filters (AS film) is pretty hard to beat; and it comes pretty close - ALMOST - to the views in my larger refractors with a wedge. Not quite, but if a nearly ideal wedge image is a 10, these are in the 8.5-9/10 regime!

 

Darren

[Sebastian_Sajaroff]

I fully agree with your conclusions.
An ED provides better views than a same aperture achromat. It’s not only about chromatic aberration, other optics defects are better controlled on a decent ED.
Diagonal is a fundamental -and often neglected- part of the equation. Cheap diagonals lead to poor views, because the overall experience is always determined by the weakest link.
I agree that a Herschel wedge gives a noticeable cleaner view than glass and film filters, sunspots and faculae details being the typical test.
Finally, I’m really happy with my Prominence Quark even if I’m using it on an F/6 and it’s not a Chromosphere one.

Edited by Sebastian_Sajaroff, 12 November 2024 - 01:12 PM.

[gnowellsct]

I
Finally, I’m really happy with my Prominence Quark even if I’m using it on an F/6 and it’s not a Chromosphere one.

Not sure I've ever seen one of those in operation. GN

[gnowellsct]

I should have mentioned that all the telescopes in my original post are in a thread, with pictures, in the refractor forum.  Not because one MUST use a refractor to look at the sun.  But because when we put out on the web site that a gang was going out to do solar viewing, everyone who showed, showed with a refractor.

 

Here's the link  https://www.cloudyni...ent/?p=13788160

 

Greg N