Why does detail gradually appear during Hydrogen alpha Solar observation, but remain constant in White Light?

[Giles_B]

I've now been regularly observing the sun in both Ha and white light for about six months, and I've noticed an odd feature of Ha viewing - the view gets gradually more detailed and as I spend time observing.

I fear I'm not describing it very well, so I'll try describing it a different way. When I observe in white light I can immediately see all of the features of the sunspots and any granulation. There is no real change to the view, and certainly if the seeing is good enough for lots of detail it doesn't fade in or out - the seeing stays very constant to outward perception. However, when I then use my Ha scope in the same session, the view often begins with a low level of detail - that is, the detail is quite unfocused and not always obvious, but as I maintain my visual attention on a particular feature, further detail seems to emerge, as if, without touching the focuser, I were bringing a rather soft focus into sharper relief.

Has anyone else notice this? What is causing this effect?

Is it because the solar surface is changing as I look at it (in which case why does the detail always grow but never begin to fade)?

Is it all in my head? Or is it some known artefact of using a Hydrogen Alpha filter (or indeed the type of filter I am using - a Daystar Quark)?

Edited January 13, 2023 by Giles_B

[MalcolmM]

I have a little Lunt 50 and experience something similar. I have put it down to features moving in and out of the 'sweet spot' (possibly a feature of the Lunt 50), the large brightness difference between the surface and surface features and proms; it's almost as if you concentrate on a filament your eye adapts to its brightness and you see it 'well'. Move your eye away and your eye is blinded by the surrounding brightness, and the filament fades. I also find when observing with the sun high in the sky there is a lot of heat disturbance which can affect the view.

There is no science behind these thoughts!

Malcolm

[Elp]

Think it's just the way your brain works. There's more to see in ha and it's constantly moving even if it's very slow and more very bright and dark spots so concentrating your vision and brain eventually resolves more detail.

It's a bit like when you look at a Snellen chart when having an eye test and can't clearly see a letter, a few seconds looking at it and sometimes you can resolve the letter a bit better.

For me white light is as is, concentrating more doesn't reveal any more detail.

[Peter Drew]

I believe it is a combination of one's eye getting accustomed to the view and the Ha etalon warming up to achieve its optimum band width.      🙂

[Highburymark]

Can’t say I’ve seen this effect, but Peter’s suggestion about the etalon warming up sounds the most likely explanation. Don’t know what set up you have, but the mica type filters (Quark/Sundancer/Solar Spectrum etc) are obviously very sensitive to temperature, so if the in-built ‘oven’ is taking a long time to reach the required temperature, it would certainly result in the gradual improvement in detail you are seeing.   
If you have one of the  Lunt/Coronado solar scopes, it could be the temperature of the blocking filter that is affecting detail, particularly at this time of year. Lunt actually sells a heater to keep the blocker warm in cold weather, otherwise it won’t operate effectively.

[Highburymark]

Just noticed you have a Quark - so it definitely sounds like a temperature issue to me. Every Quark is different. There are a couple of reports I’ve read by owners who say they don’t even turn the heater on in warm weather - the filters operate best without. Sounds like yours takes time to reach optimum heat.

[Elp]

I've had this with a Coronado pst too. Breaking visual contact and going back to it required the same one or two minutes until much more detail was resolved.

[markse68]

I get it when looking at Mars- at first I see very little but then the detail gels over time. Could it be that the details are more colour based in Ha rather than brightness in white light? Using different cells/perception in the eye?

Mark

[Peter Drew]

I noticed gradual image improvement in PST's following initial solar exposure.  Airspaced etalons are tuned either by pressure or tilt, in each case temperature can have an optical effect.  The Quark etalons are intentionally temperature controlled so the variation in performance due to the temperature reaching its optimum level is to be expected.        🙂  

[JeremyS]

I’ve noticed this with Lunts and with a Quark.

I thought I was just a matter of my eye getting tuned into  to the scene, contrast level etc.

[Rusted]

Despite my 60-odd years of visual observing I had to learn to see in H-alpha.
I could see the sun's disk but it took real effort and concentration to tease out the detail.
It was like trying to see details in the red coals in the bed of a fire.
At first I really thought I had completely wasted my money. 150mm f/8 PST mod.
I could never use the original PST because of its rusty ITF filter.
So I stripped the PST almost straight away and fitted a Maier replacement ITF for my mod.
 

[Paz]

I have a quark and I get this effect. I'm actually quite happy observing with the quark before it has warmed up. When its cold it's like white light observing with a red filter and as it warms up the Ha features emerge and get more refined.

[Oldfort]

I too have the same experience with a PST.  Some is due to the marked sweet spot on the PST, but there is a significant improvement with time and con encentration.  However I only see it with surface detail and not prominences.

[niallk]

I notice my eye 'tuning in' - from being blasted by sunlight, to putting my head under a towel to observe with my LS50DS.  This happens even when the scope has been out for a few hrs, and has reached equilibrium- and I've come back for another look.

I enjoy how very fine detail becomes more apparent as one observes!

Just had it out today for the first time in quite a while, and a joy to see the activity on show 😎

[Elp]

A towel is essential