Heating AFTER a Solar Wedge

[Macavity]

<Wibble Warning>

It may be deemed "too technical" a question, but I
have confidence that "Two (SGL) heads" etc. etc.

Playing with various filters AFTER a Herschel wedge
I begin to have minor concerns about heating tho!
(I assume everyone has noted eyeball safety)

I read that the SUN produces about 1kW / sq.m
of Energy (of which 50% is light & 50% Heat). 

Most *Amateur* solar scopes are less 100mm
aperture (unless you're very rich! lol) -- So that
(assuming scopes are square!) is about 1/100th
of a square metre? Total energy of 10 Watts? 

I learn that a Herschel Wedge reflects ~5% of
(Light & Heat) into the scope. So say 0.5W ?!?

(Hobby) Electronic Messing taught me that...
"5W resistors get Hot, 0.5W Resistors don't".
I know there are graphs to calculate stuff but!

But has anyone ever *experienced* problems
with "stuff" placed AFTER a Herschel Wedge?
"Destroyed" a Camera, Cracked a Filter etc.  

I wonder if I am right assuming the "ND 3.0" 
filter in a Herschel wedge "just standard"???

[DRT]

Chris,

Some Herschel Wedges (e.g. Lunt) have the ND3.0 filter permanently mounted after the wedge element whereas the Baader has a mounting ring that can be used to mount multiple filters, including the ND3.0, Solar Continuum and the various grades of ND filter supplied with the wedge. The ND3.0 must always be closest to the wedge with the others behind it. I have played around with different configurations of these filters during sessions with my Evo 150 and have never detected any heat when swapping them in and out. I also use a single polarising filter on the nose of my eyepiece to allow me to vary the brightness and again no heat has ever been detected, even when I have the scope on a tracking mount.

Hope that helps

Derek

[Stu]

5 minutes ago, Macavity said:

I wonder if I am right assuming the "ND 3.0" 
filter in a Herschel wedge "just standard"???

The ND3.0 filter is essential to keep the levels down, reducing by a factor of 1000 ie taking the 0.5W to 0.0005W. 

With this fitted I've never experienced any heating issues.

[Macavity]

1 minute ago, Stu said:

The ND3.0 filter is essential to keep the levels down, reducing by a factor of 1000 ie taking the 0.5W to 0.0005W. 

With this fitted I've never experienced any heating issues.

Which is indeed miniscule! But, to me, the question remians...
Is the ND 3.0 a "special" filter... Or can I (eyeball safety aside)
use other / standard / combination ND filters in its place.

[DRT]

I don't the ND3.0 is a "special" filter but it needs to be there.

I do not know whether or not 2x ND1.5 filters (or any combination of NDn.n that adds up to 3) equals an ND3.0 filter. What I do know is that these filters are polarising filters, so combining them gives variable brightness depending on their orientation to one another.

[Macavity]

48 minutes ago, DRT said:

Chris,

Some Herschel Wedges (e.g. Lunt) have the ND3.0 filter permanently mounted after the wedge element whereas the Baader has a mounting ring that can be used to mount multiple filters, including the ND3.0, Solar Continuum and the various grades of ND filter supplied with the wedge. The ND3.0 must always be closest to the wedge with the others behind it. I have played around with different configurations of these filters during sessions with my Evo 150 and have never detected any heat when swapping them in and out. I also use a single polarising filter on the nose of my eyepiece to allow me to vary the brightness and again no heat has ever been detected, even when I have the scope on a tracking mount.

Hope that helps

Derek

Thanks Derek (for both posts)

It does indeed help! Interesting to learn Baader do allow *various* ND Filters. 

Indeed the Lunt has an "integral" ND3.0. It is my cunning plane to (safely) swap
it for an ND 1.8 specifically for CaK filter experiments! The CaK filter does not have
additional threads to stack filters. May have to slightly redesign my concept! More
minor "bits and pieces" to buy! lol. But it seems *sensible* to put the (whatever)
ND filter FIRST in the optical path. Working on an "idiot (me!) proof" system. 

Thinking now of swappable e.p. holders - Paint the CaK one RED as warning.  

[Stu]

Chris, I think as long as you are talking about imaging, with frying a camera the biggest risk, then do experiment. Otherwise definitely stick to the safe options.

[DRT]

22 minutes ago, Macavity said:

It does indeed help! Interesting to learn Baader do allow *various* ND Filters. 
 

The Baader comes in two packages:

"Visual" - Wedge + ND3.0 + Continuum

"Photographic" - All of the above + NN0.6 + ND0.9 + ND1.8 filters for "further dimming", so are intended to be used in addition to the ND3.0  not in place of it.

I'm not entirely sure that taking a Lunt wedge apart is a good idea as it could be permanently damaged and returning it to visual use would carry a risk. If you tried the experiment with a Baader you could do so by swapping the ND3.0 for the ND1.8 and, as Stu says, the worst that can happen is you fry your camera.

 

[Macavity]

Thanks Derek. I have ALL the answers I need! But indeed, without a "thesis"
on such things (my albeit safe) ideas are often open to misinterpretation? 

I'm not suggesting "taking apart" a Lunt Wedge. But there are two schools
of thought re. Solar Safety? Such things would be doubtless resolved in any
(probably fun) F2F meeting! And perhaps such idea are not for SGL fora... 

Maybe a moderator should quietly dispose of both THIS and my CaK thread?
Without anger or malice, I would not object -- I may even worry rather less!

Aside: I mostly buy BAADER stuff. The hardware I TRUST the most! But in
trying to find answers, I remain "circumspect" of some of their claims. Often
even their technical "papers": "Buy more Baader... The Rest are rubbish"?

I do worry about filters... I swear some are "more accident than design"!  

[DRT]

Apologies for the mis-interpretation,  Chris. The only Lunt wedge I have owned had no visible means of being safely dismantled in order to remove the in-built ND3.0 so I couldn't understand how you were going to do that without damaging something. 

From what you say you seem to have safety covered off

[ronin]

Interesting question but I note that no one has pointed out the the scope will be collecting whatever apertures worth of light and heat. wedges and such like reduce and directs what goes where but the IR collected has to go somwhere. If if it directed from the eye then it is directed towards something else (heatsink hopefully), and whatever that something else is will get warm/hot.

The ND3 filter will absorb a lot of the IR and so get hot, it is not that far removed from a much disliked sloar eyepiece glass filter, they tend to be about 10-5 and you are talking of 10-3.

The 5% that the herschel wedge passes is sort of low, not really, but where does the other 95% get directed to and so heat up.

These things still obey the laws (present) of physics and conservation of energy is one of them.

[Stu]

15 minutes ago, ronin said:

Interesting question but I note that no one has pointed out the the scope will be collecting whatever apertures worth of light and heat. wedges and such like reduce and directs what goes where but the IR collected has to go somwhere. If if it directed from the eye then it is directed towards something else (heatsink hopefully), and whatever that something else is will get warm/hot.

The ND3 filter will absorb a lot of the IR and so get hot, it is not that far removed from a much disliked sloar eyepiece glass filter, they tend to be about 10-5 and you are talking of 10-3.

The 5% that the herschel wedge passes is sort of low, not really, but where does the other 95% get directed to and so heat up.

These things still obey the laws (present) of physics and conservation of energy is one of them.

Ronin, there is no comparison between a solar eyepiece filter which is inherently dangerous and a properly setup Herschel Wedge. Many people safely use wedges and I think it is wrong to put incorrect doubts into people's minds.

By all means encourage safety, but not false rumours.

[DRT]

31 minutes ago, ronin said:

Interesting question but I note that no one has pointed out the the scope will be collecting whatever apertures worth of light and heat. wedges and such like reduce and directs what goes where but the IR collected has to go somwhere. If if it directed from the eye then it is directed towards something else (heatsink hopefully), and whatever that something else is will get warm/hot.

The ND3 filter will absorb a lot of the IR and so get hot, it is not that far removed from a much disliked sloar eyepiece glass filter, they tend to be about 10-5 and you are talking of 10-3.

The 5% that the herschel wedge passes is sort of low, not really, but where does the other 95% get directed to and so heat up.

These things still obey the laws (present) of physics and conservation of energy is one of them.

 

From FLO...

Quote

 

Baader CoolCeramic Heat Cage! 

The Solar light enters into the prism body and falls onto a 45° inclined prism surface. Approx 4.6% of Solar light is reflected into the eyepiece or camera respectively. The much larger percentage of light (95.4%) is fed into a separate “heat cage” which includes a special heat-absorbing ceramic tile. Like on a space shuttle the ceramic tile traps the radiant energy without overheating its surroundings. The body of the Baader Safety Herschel-Prism is closed on all sides which prevents any danger of contacting direct Sunlight, making it safe for educational work. Since the “heat cage” is separated from the prism body and connected only with four screws, there is virtually no heat distribution extended into the prism itself.

 

I have used my Baader wedge for hours on end on a hot summer day with a 6" refractor on a tracking mount and have never felt it being hot or even warm to the touch.

The Lunt wedge transfers the heat to a red metal plate on the back end of the wedge and the heat disperses into the air. The red plate has a warning to that effect stamped on it. having touched the plate a few times I can confirm they get hot.

Whilst I agree that anything placed in sunlight will heat up my experience is that the ND3.0 does not seem retain any perceptible amount of heat when in use.

[Macavity]

33 minutes ago, DRT said:

Whilst I agree that anything placed in sunlight will heat up my experience is that the ND3.0 does not seem retain any perceptible amount of heat when in use.

Well, maybe the subject does merit discussion / understanding.
Hey, I learned something here! Possibly more than... (randomly):
http://www.alpineastro.com/Solar_Observation/HerschelWedge.htm

Maybe I'm being a overly fussy? But even *I* struggled a bit?  

It's clear that (WL) photo-filters produce significantly more light
variation than I might have imagined. Nothing is ever "trivial"?

[Macavity]

Someone who actually measured the temp of a FRONT ERF (Went off scale at 50 deg)! 
http://www.astrosurf.com/viladrich/astro/instrument/intrumentCaK/instrumentCak.html
He also uses a "Stopped down" TAK - Albeit for CaK imaging. Worthwhile perusing much
of his stuff for various plots of various things though... 

One derives some comfort from the notion that it's (maybe) 50 deg not say 500 deg!
Accurate calculations are quasi-impossible? But I would expect an ND 3.0 filter after the
(4.5%) glass reflector to be perhaps a few degrees at most? I might even measure it!

Even Schott (Glass) seem to acknowlege calculations are difficult (only "ball park"?):
http://www.schott.com/d/advanced_optics/768b0d65-8838-4021-b7a9-5c06647d055c/1.1/schott_tie-32_thermal_loads_on_optical_glassus.pdf
The problem for glass is doubtless poor thermal conductivity, differential heating etc. 

[DRT]

Presumably a lot depends on where on Earth the scope is. I doubt very much that my Derbyshire set-up would ever experience the intensity of an Arizona based equivalent?

[Merlin66]

Guys,

The European and International standards (for solar radiation protection) recommend a MINIMUM of ND5 attenuation for safe operation across the whole spectrum. (I have a detailed write-up available on the various standards - too big to post here but could supply a copy to interested members)

This is achieved with the combination of the Herschel Wedge and a ND3 filter.

For imaging it's a different matter.....it's not the possible heat build up (minimal) but the camera response and performance - completely different issue - that's why Baader supply two types of Solar filter - an ND5 for "maximum" visual safety and an ND3.8 for imaging (more light, shorter exposures).

I've used many different solar telescopes in the summer heat of Australia - white light with Wedge, Ha etc. and never had any issues/ concerns with heat (after the wedge/ filters/ ERF) or safety.

(The ONLY problem I had was getting Daystar to confirm that the Quark would successfully work (come on band) in ambients greater than 40 deg C..........)

 

 

[Stu]

6 hours ago, Merlin66 said:

Guys,

The European and International standards (for solar radiation protection) recommend a MINIMUM of ND5 attenuation for safe operation across the whole spectrum. (I have a detailed write-up available on the various standards - too big to post here but could supply a copy to interested members)

This is achieved with the combination of the Herschel Wedge and a ND3 filter.

For imaging it's a different matter.....it's not the possible heat build up (minimal) but the camera response and performance - completely different issue - that's why Baader supply two types of Solar filter - an ND5 for "maximum" visual safety and an ND3.8 for imaging (more light, shorter exposures).

I've used many different solar telescopes in the summer heat of Australia - white light with Wedge, Ha etc. and never had any issues/ concerns with heat (after the wedge/ filters/ ERF) or safety.

(The ONLY problem I had was getting Daystar to confirm that the Quark would successfully work (come on band) in ambients greater than 40 deg C..........)

 

 

Thanks as always Ken.

Where does aperture feature in this, or doesn't it? Presumably a 150mm frac delivers more energy to the eye than a 60mm? Is it ever necessary to add more filtering with a larger scope?

[Macavity]

6 hours ago, Merlin66 said:

The European and International standards (for solar radiation protection) recommend a MINIMUM of ND5 attenuation for safe operation across the whole spectrum. (I have a detailed write-up available on the various standards - too big to post here but could supply a copy to interested members)

This is achieved with the combination of the Herschel Wedge and a ND3 filter.

Thanks for that, Ken! I think you have summarised the *essence* of this...
As a GENERAL thought, maybe we need more "Stickies" (Here as well!) re.
Solar Wedges? Add "Photo" ND3.8 versus "Visual" ND5.0 filters etc. etc.

As far as I can see, what I am proposing (soon to have done) is clone what
Baader market as their "Photo Edition" of their Ceramic Herschel Wedge! 

In fairness, but not mitigation, I note even in the VISUAL edition, it SEEMS 
easily possible to remove both ND 3.0 and the Solar Continuum Filter and
substitute with others (even none)? And not just an "I told you so" thing.

I HAVE NO ANSWER to an implied question: Should we openly discuss safety
issues? Or do we assume someone, somewhere will *misunderstand* things!
The alternative is to not mention such stuff I suppose? At *this* level better?

I was still intrigued that Baader apparently put the *mirrored* surface of the
Continuum Filter in FRONT of the ND 3.0 Filter... I was not going to risk my
(far too expensive!) double stacked CaK filter in that particular situation!

Here's some thought provoking "IR" data re. (assumed) Neutral Filters:
http://www.sonnen-filter.de/
As sometimes mentioned various filters are known to "leak" Infra Red.

ASIDE:

***********************************************************
"Macavity" has been chided for being "thoroughly incomprehensible" (lol).
Jokes aside, I'd STILL PREFER this thread (+ my Cak one) be simply deleted!
***********************************************************

[Macavity]

1 hour ago, Stu said:

Thanks as always Ken.

Where does aperture feature in this, or doesn't it? Presumably a 150mm frac delivers more energy to the eye than a 60mm? Is it ever necessary to add more filtering with a larger scope?

Clearly (but not always!) people add Energy Reduction Filters (ERFs) to
solar scopes... Recommended as well, particularly re. larger apertures.
But again, something one has to "know about" and consider carefully?

Maybe one can make do with quite modest apertures? Resolution is a
consideration? Brightness (shorter exposures!) might be too though?
There is a lot of erudite / creditable information out there re. "Solar"!  

That said, it takes a bit of finding? We do seem one of the
more "experimental" (and complex!) areas of Astronomy?
But (arguably) one of the more friendly and interactive!  

[Stu]

15 minutes ago, Macavity said:

Clearly (but not always!) people add Energy Reduction Filters (ERFs) to
solar scopes... Recommended as well, particularly re. larger apertures.
But again, something one has to "know about" and consider carefully?

ERFs are used for Ha but not for white light as far as I'm aware....?

[Macavity]

13 minutes ago, Stu said:

ERFs are used for Ha but not for white light as far as I'm aware....?

Fair point! H-Alpha certainly have dedicated (carefully designed) ones.
Currently had (DS) CaK filters on my mind... ERFs are more "ad hoc". lol
But again, an incentive do LOTS of research re. safety of such stuff...   

[Peter Drew]

2 hours ago, Stu said:

Thanks as always Ken.

Where does aperture feature in this, or doesn't it? Presumably a 150mm frac delivers more energy to the eye than a 60mm? Is it ever necessary to add more filtering with a larger scope?

I think filtering depends a lot on the type of filter, where it's placed and what wavelength of light is being observed. It seems for white light (the full Monty) much heavier filtering is necessary for safety, full aperture solar film before the objective appears to be adequate regardless of the aperture though fast focal ratios can provide an overbright final image. Ha on the other hand has far more filtering elements in the optical train to deal with a very narrow band of the available white light. I have been using and experimenting with Ha long before the PST came on the scene, probably pushing the bounds of safety on early,less informed trials and so far have had no noticeable side effects other than wallet damage.  

[Merlin66]

OK, what answers do you want.....

The ND5 filter rating applies to all telescopes independent of aperture (think of a Baader ND5 front filter on a C14 etc.)

Your CaK application - well an easy solution is to use a Baader CCD Blue filter as a suitable ERF - this cuts all wavelengths above 4000A ie visible light.

IR leakage above 1100A has no real impact on CCD's as the effective sensitivity has reduce almost to zero. Leakage above 1500A has no impact on visual. 

3 hours ago, Macavity said:

I was still intrigued that Baader apparently put the *mirrored* surface of the
Continuum Filter in FRONT of the ND 3.0 Filter... I was not going to risk my
(far too expensive!) double stacked CaK filter in that particular situation!

I don't know why you should be surprised (or concerned) - the residual energy after the wedge is already very low........it will have no negative impact on the Continuum filter.

2 hours ago, Stu said:

ERFs are used for Ha but not for white light as far as I'm aware....?

You are correct, but sometimes I forget to remove the upfront D-ERF on the PST mod when changing back to white light with the wedge........the only impact is you are then viewing the solar surface (continuum) in the 30nm region around Ha.

[Macavity]

Guys, I'm "happy"! Or STILL wishing I hadn't asked?
No case of wanting further answers - I have all I need.
I also have found a load of references I can consult...

As I said, I was intrigued (sic) re. Baader's placement of 
mirror surface of the Solar Continuum. It may help!
I AM more wary about putting *my* DS CaK filter in
that position. It is much my "pride & joy" (money). lol

I have no doubt you are RIGHT re. heat / light levels.
Sometimes there is a point in asking semi-rhetorical
questions! I quite like the shared experience thing? 
AND it helped to hear of a personal experience (DRT).
More questions??? Hey, you answered them anyway. 

You have made a good point about safety. But we seem 
to be going round in circles. I don't feel it ALL my doing.
Your post re. "European & International standards" (plus
my reponse? ) seemed a rather good place to END this?
I sense some is about the evocative issue  of Safety. 

Apologies for any potential misunderstanding originating
from my posts. But THAT is the main reason I felt I ought
to persist with this. In fairness the thread has drifted. It is
a bit of a dialogue too? I will (belatedly) leave it there!!!

P.S. Forgive me for the little bit of levity above? I find it
frustrating too! Aside from "Physicist", I used to do THIS
as a JOB every day. Users can be VERY frustrating. But
I had to be *nice* to them! "Never got half this grief"?