What do i need for safe solar observing with 90mm refractor? -Puzzled by range of available filters

[ONIKKINEN]

I want to observe the sun with a 90mm aperture refractor, what is the way to go? I see there are foil filters, full aperture glass filters, masked partial aperture glass filters, Herschel wedge diagonals, blocking filters at the eyepiece side and so on. As i understand it no kind of eyepiece threaded filter only will do the trick but some kind of full aperture thing (or the wedge?) is needed.

Looking to not spend a fortune but dont have set in stone budget, but around a couple hundred euros or thereabouts would have to do the trick. I see there are a number of options with this kind of budget but have no clue what is the best way to go.

[Paz]

The simplest and cheapest way to go is a foil filter like this...

Astrozap Baader Solar Filter | First Light Optics

You can also get glass ones but either way this kind of filter goes over the front of the telescope so everything behind it is safe. What you need to avoid, as you have noted, is any "eyepiece filters" that attach at the eyepiece end of the scope. The problem with them is they attempt to do their job right where the heat would be concentrated so are likely to fail. 

At higher cost you could get a Herschel wedge that provides a slightly better quality image and allows you to vary the brightness if you put a polarising filter on the eyepiece.

Lunt White Light Herschel/Solar Wedge | First Light Optics

Blocking filters are I think more to do with hydrogen alpha observing which is very expensive in comparison (it's over £1k for a hydrogen alpha filter).

[Elp]

Option 1: Baader or Seymour Solar film is the cheapest for white light, the Baader comes in two ND types one for viewing and one for imaging. The Seymour gives a yellow colour to the image. You can make the housing yourself out of cardboard, make sure the film of the filter is cut out large enough to completely cover the aperture.

Option 2: a Herschel wedge, Lacerta make an affordable one, there's also the Baader ceramic one which has a ceramic plate on the bottom which absorbs heat a bit better if youre inclined to touch the bottom of the wedge whilst observing.

I also tend to always use a 1.25 inch UV/ir filter on the bottom of my eyepieces just for that extra piece of mind.

A baader solar continuum filter will provide slightly better contrast though I use a green (54/58? Forget the number) as it's similar.

You can use a Televue solar finder mounted on the scope to better find the sun, or make one out of cardboard.

Option 3: Daystar quark chromosphere, it's not cheap but will blow your mind seeing in hydrogen alpha, the larger aperture refractor the better as long as it works out to around f30 (scope f stop x 4.2 of the quark = working f stop), I've read conflicting information regarding a front mounted DERF filter, you won't need one for 90mm but anything 100mm front aperture plus it's wise to use one though they are not cheap. The received quality of the quark is also subjective.

Option 4: get a Lunt 40/Coronado PST/Daystar Solar scout, just listed the cheapest of the range.

Edited July 3, 2022 by Elp

[Zermelo]

There's also some discussion here:

 

[ONIKKINEN]

9 minutes ago, Paz said:

The simplest and cheapest way to go is a foil filter like this...

Astrozap Baader Solar Filter | First Light Optics

You can also get glass ones but either way this kind of filter goes over the front of the telescope so everything behind it is safe. What you need to avoid, as you have noted, is any "eyepiece filters" that attach at the eyepiece end of the scope. The problem with them is they attempt to do their job right where the heat would be concentrated so are likely to fail. 

At higher cost you could get a Herschel wedge that provides a slightly better quality image and allows you to vary the brightness if you put a polarising filter on the eyepiece.

Lunt White Light Herschel/Solar Wedge | First Light Optics

Blocking filters are I think more to do with hydrogen alpha observing which is very expensive in comparison (it's over £1k for a hydrogen alpha filter).

Why is there so much price difference between that Lunt wedge and say this one: https://www.teleskop-express.de/shop/product_info.php/info/p8732_Lacerta-1-25--Herschel-Prism-Set-with-ND3-Filter-and-Adapters.html

Just premium kit vs not so much premium kit or some other kind of difference in how they work?

6 minutes ago, Elp said:

You can use a Televue solar finder mounted on the scope to better find the sun, or make one out of cardboard.

Yep, what i had in mind. Couple of zipties to act as shadows and something to project that on. Easy to make and costs nothing at all.

[Elp]

Guessing it's just because Lunt is synonymous with solar equipment, a user with experience can offer more. 

Fair warning: Once you've done white light, you'll want to do ha...

[Mr Spock]

Film is certainly the cheapest route. But for image quality you can't beat a Herschel wedge.

This is my 102mm set up:

Wedge and continuum filter

In sunlight - doesn't get that hot in UK conditions.

The scope in action

And not forgetting, a safe for solar finder (remove any optical ones). This is a cute little Svbony.

[ONIKKINEN]

18 minutes ago, Zermelo said:

There's also some discussion here:

 

Hmm i had not considered the fragility of foil type filters discussed in that thread. Think ill rather go for a wedge then. I already have some eye damage from various stupid teenager things like watching magnesium burn and welding without goggles and would want to limit the damage to that. Nothing major, just a few extra floaters that pop up every now and then but still, lesson learned.

[ONIKKINEN]

4 minutes ago, Mr Spock said:

Film is certainly the cheapest route. But for image quality you can't beat a Herschel wedge.

This is my 102mm set up:

Wedge and continuum filter

In sunlight - doesn't get that hot in UK conditions.

The scope in action

And not forgetting, a safe for solar finder (remove any optical ones). This is a cute little Svbony.

Yes, this is what i will do. Convenient excuse to buy the solar continuum filter as i was already eyeing it for lunar photography with a mono camera to help with seeing.

For visual, its green though? Does it bother you at all or is the extra contrast clearly winning in this argument?

I reckon it would also help with chromatic aberration since the scope will be a 90mm ED F5.5 and will definitely have some chromatic aberration when viewed at high power.

[Mr Spock]

It is green - apple green! But does improve contrast quite a bit; you get used to the colour. My scope is a fp53 apo so doesn't need CA correction, but the green filter will take out most, if not all, CA from an achromat.

[Elp]

The film is not like aluminium foil which deforms easily, it's more like a plastic film and quite durable though yes you do need to store it correctly and check it before using is common sense. It's certainly worth it to try it as it doesn't cost much at all.

[ONIKKINEN]

1 minute ago, Elp said:

The film is not like aluminium foil which deforms easily, it's more like a plastic film and quite durable though yes you do need to store it correctly and check it before using is common sense. It's certainly worth it to try it as it doesn't cost much at all.

I am unfortunately sometimes a neanderthal when handling equipment. Many telescope shaped dents in my walls, corners, my car door 🙄 and so on... I trust the product but not myself with it.

[Paz]

5 hours ago, ONIKKINEN said:

Why is there so much price difference between that Lunt wedge and say this one: https://www.teleskop-express.de/shop/product_info.php/info/p8732_Lacerta-1-25--Herschel-Prism-Set-with-ND3-Filter-and-Adapters.html

Just premium kit vs not so much premium kit or some other kind of difference in how they work?

Yep, what i had in mind. Couple of zipties to act as shadows and something to project that on. Easy to make and costs nothing at all.

I don't know if the price difference has anything to do with quality. I have a 1.25" Lacerta wedge and I'm very happy with it and don't think I'm missing out on anything.

The Lacerta wedge is a shallower angle than the lunt which means it polarises more strongly and the eyepiece angle is more horizontal than a 90 degree lunt wedge  but I prefer the Lacerta's approach on both these points.

The lacerta wedge is built like a tank and should be able to cope with anything you might reasonably want to hang off it.