Constructing Solar Filters.

[LukeSkywatcher]

Hi all.

I am just seeking advice from you guys and gals who spend much of your time observing the Sun.

Here's the thing:

I just bought myself a sheet of Baader AstroSolar film (thanks FLO) with the intention of constructing a pair of solar filters (or a box filter) for my 20X90 bins (and with the leftovers...........another filter for my 75-300mm camera lens).

However....it has just dawned on me that with the magnification of the bins(20x), i dont stand much chance of actually being able to see any sunspots.

Do i ?

I have a solar filter for my 90mm (f/l 1000) scope and when observing with that scope i used a 9mm EP................giving me a magnification of..................a lot more then 20X.

So 20X simply aint gonna cut the mustard.

Soooooooooo NOW i am thinking that i may be better off constructing a solar filter for my SW Heritage 130P Flextube Dob.

Is that even possible?

I mean the scope is an open truss scope so surely even if i just cover the front of the scope (up around the secondary mirror) ..........stray sunlight will spill in through the open truss' and either crack the primary mirror or be transmitted through the EP and fry my eyeball..........................OR BOTH.

Would a shroud stop this from happening in the same way it stops stray light at night?

Sorry for ALL the questions.

If ANYONE can point me in the direction of a site where i can find out how to build a solar filter for such a scope that would be FANTASTIC and much appriciated.

However if you feel that i will be able to see sunspots through my 20X90 bins (however small they may appear) then please let me know so i can go ahead and start constuction.

At €20 euro a pop..................i dont wanna waste the Baader film

[Merlin66]

IMHO I'd give the Bino's and the Dobbie a miss and just stick with the 90mm refractor.

A combination of the Solar film and either a Baader Continuum filter or a green "standard" filter will give you very good views of the sun's surface.

The larger aperture of the dobbie may be nice to think about, but generally the seeing conditions etc etc will probably dissappoint you.

I use a Baader +continuum on my ED80 with magnifications up to x120 and believe me there's plenty of detail!

[LukeSkywatcher]

Thanks Merlin. I see where you are going with this. For solar observing forget the bins with 20x mag and forget the Dob.

The 90EQ scope is a pain in the *** at night to move and set up but during the day it is so much easier so i should use that as my own PST.

[russ]

Ken,

Which # wratten green filter do you recommend?

Paul, i have the Celestron Astromaster 90 as my white light solar scope and it works beautifully with the Baader Solar Film. Although i cheated and bought it ready mounted in a cell.

[NickH]

90mm refractor will work fine... the sun is a massive object

White light filters on their own are okay but add the Continuum filter (green or actual continuum one) and the granulation leaps out.

[russ]

I have a #56 Green filter, so will give that a try when i get home.

[Merlin66]

That should do the trick!

I've used various green filters; Celestron, Meade, green from RGB sets etc etc before commiting to the Baader Continuum.

Ken

[russ]

Ken, is the Baader Solar Continuum a big improvement on the green filters?

[brianb]

is the Baader Solar Continuum a big improvement on the green filters?

It's an improvement but it's one of those that is an expensive small increment rather than a cheap big one. If you have a green glass filter with poor optical surfaces then you will notice a significant improvement. The improvement will be more marked with cheap short focal ratio "achromats" with poor colour correction.

I used to attempt to image in white light with Baader solar film & the solar contiunuum filter. One day I decided to try without the continuum filer & haven't looked back. This was taken with just an IR/UV blocker in conjunction with the "visual" ND5.0 Baader solar film. With a good quality fluorite triplet apochromat though!

2010 Apr 12, 1104 UT. WO FLT 110, Baader solar film, x2 barlow, DMK21.

The extra light helps beat the seeing by keeping exposures short. Not having a "thick" filter is especially helpful when the seeing is "rapid" as it was yesterday. A small loss of contrast resulting from not using the continuum filter is easily "fixed" in processing; a blurred image is impossible to compensate for properly.

Visually IMO a filter is more about controlling the light level for comfort than anything else ... assuming your scope has minimal chromatic aberration ... if it does, then try a minus violet filter, it may work just as well as an expensive green! But, if you need some light level reduction, the Baader solar continuum filter is about as good a product as exists, if you don't mind the "weird" coloration and especially if you have chromatic aberration to cope with.

[russ]

Many thanks Brian, that's a great explanation and a huge help.

Beautiful image by the way.

I won't be using an Apo but the f11.11 Achro is quite well corrected showing minimal CA. I'll have a play around with some filters, i still have a Lumicon #56 green which is off good quality and a darker green Antares filter.

Have you imaged that huge prom today?

[brianb]

Have you imaged that huge prom today?

Sorry my sky is full of grey gloop.

[russ]

That's a shame Brian.

[Merlin66]

IMHO, I think the Continuum has the edge over the green filter...FOR VISUAL observing.

For imaging, then I tend to agree with Brian, a UV-IR cut-off is usually enough.

[LukeSkywatcher]

90mm refractor will work fine... the sun is a massive object

White light filters on their own are okay but add the Continuum filter (green or actual continuum one) and the granulation leaps out.

Thanks Nick. I know the 90EQ works fine. Today i used it with the Baader filter i made 2 yrs ago and the filter is still GOOD (i was worried about dust on it)

The only green filter i have is a Celestron No.56 but i have never used the green filter for observing the sun.