I want to buy a solar filter, which one?

[Louis D]

1 hour ago, DarkAntimatter said:

Regarding wedges, is there any danger to the scope in having the filter at the eyepiced end?  With an aperature filter, the light intensity is attenuated before it gets into the scope at all.  With filters at the other end, do we need to worry about heating of secondary mirrors, etc?

Even with a refractor, I'd be concerned about not keeping the sun centered as with an unattended alt-az mount.  As such, I always cap my frac when walking away from it with a wedge in place.  I have no idea what all that solar energy would do to the side of the interior of the focuser, and I'm not about to find out.

[Louis D]

I had a Thousand Oaks glass solar filter years ago, but because the coating is just on the surface, not throughout the glass, it's super susceptible to pinhole damage.  I eventually trashed it and went with BSF.  I can't say that the image was any better with the BSF, just white instead of orange as with the TO filter.

[saac]

Here's a review of the two types of filter , taken from the Baader web site.  The author considered that the Baader filter provided a better performance over the glass filter. 

Jim 

 

 

Baader White Light Filter Review by William Paolini.pdf

[Louis D]

2 hours ago, Ags said:

The most common one is a Herschel Wedge, which looks like a telescope diagonal, but it only reflects tiny percentage of the light to the eyepiece

Not true.  It actually reflects about 4.6% of the light impinging on it.  You still need about an ND5 filter equivalent in the upper part of the wedge to bring the light down to a safe level visually.  An ND3 is sufficient for astrophotography, though.  As such, most wedges are sold with an ND3 permanently mounted in the upper section to allow for photography and require you to use either a polarizing filter or ND2 filter to bring the light level down for visual use.  I've found an ND3 is too much and cannot locate a low cost ~ND2 filter.  If anyone knows of one, let me know.  I only know of the Baader ND1.8 for $49.  At that price, I'll just keep using my variable polarizing filter which is more flexible anyway.

[Ags]

Thanks for the correction. I'll edit the original post to avoid causing any confusion.

Edited July 6, 2021 by Ags

[Tiny Clanger]

20 minutes ago, saac said:

I wonder if the ripple thing is to ensure you don't stress the film by trying to have a totally flat installment.  Stressing it mechanically would introduce the possibility of damage . 

Jim 

That was what I guessed

3 hours ago, Tiny Clanger said:

In the instruction sheet on how to make your own Baader film filter they explicitly say it should be wrinkled, not flat. I'd guess this is to avoid any mechanical damage done to the carrier layer by stretching it. 

Heather

I've absolutely no idea about the merits of glass vs film in terms of quality, Baader reckon film is better, but they would say that ,  wouldn't they 🙂 I'll be interested to see the results of your investigations

Heather

[Stu]

16 minutes ago, Louis D said:

Not true.  It actually reflects about 4.6% of the light impinging on it.  You still need about an ND5 filter equivalent in the upper part of the wedge to bring the light down to a safe level visually.  An ND3 is sufficient for astrophotography, though.  As such, most wedges are sold with an ND3 permanently mounted in the upper section to allow for photography and require you to use either a polarizing filter or ND2 filter to bring the light level down for visual use.  I've found an ND3 is too much and cannot locate a low cost ~ND2 filter.  If anyone knows of one, let me know.  I only know of the Baader ND1.8 for $49.  At that price, I'll just keep using my variable polarizing filter which is more flexible anyway.

I use a Baader Coolwedge with a ND3.0 filter and continuum filter visually. ND3.0 is safe for visual, no need for ND5.0. A continuum filter knocks the brightness back to comfortable levels and also enhances the contrast on faculae and granulation.

Quote from FLO website about the two versions available:

Baader offers two versions of their Herschel Wedge: 

Visual V

The Version-V for visual use comes with a pre-installed ND=3.0 (required for safe viewing) filter and a 2" Continuum Filter.

Photographic P

The Version-P for photographic use is essentially the Version-V with three additional Baader ND filters (ND1.8, ND0.9 and ND0.6). The additional filters are handy for further dimming the image for white light viewing, or attaching to eyepieces or a T2-15 Reducer, and are particularly useful for imaging.

[Stu]

Note that I’ve just hidden a post suggesting that an ND3.0 filter is not safety critical with a Herschel Wedge. This is NOT correct. The ND3.0 must ALWAYS be fitted to the eyepiece side of the wedge to bring light levels down to safe limits. This will still be too bright for comfortable viewing so a continuum or polarising filter are also needed.

Please always make sure you follow manufacturer advice when using these wedges, and educate yourself about how to use them safely. Don’t post advice for others if you are not experienced and sure of your facts.

Many thanks

[John]

I'm not a frequent solar observer but when I do it's with a refractor and I use a 1.25 inch Lunt Herschel Wedge fitted with an integral ND 3.0 filter (at the bottom of the eyepiece drawtube of the wedge) and a single polarising filter which goes onto the eyepiece to give fine control of final image brightness.

If I observed the Sun more I would probably invest in a Solar Continuum filter and use that in place of the polarising filter.

I've been very pleased with the white light solar views that the above delivers with refractors from 100mm to 120mm in aperture. I find a 7.2mm - 21.5mm zoom eyepiece very effective for this type of observing.

The rig also works very well for outreach sessions. I feel that it is safer than an "over the front end" filter because, if the wedge falls off the back of the scope, the eyepiece goes with it and all the solar energy will just exit the back of the scope tube. I guess a singed crotch is a remote possibility but, so far, so good

Handing you back to the solar experts now

Edited July 6, 2021 by John

[Louis D]

1 hour ago, John said:

The rig also works very well for outreach sessions. I feel that it is safer than an "over the front end" filter because, if the wedge falls off the back of the scope, the eyepiece goes with it and all the solar energy will just exit the back of the scope tube. I guess a singed crotch is a remote possibility but, so far, so good

Probably not an issue because the light cone will spread out again on the other side of the image circle.

[Louis D]

2 hours ago, Stu said:

I use a Baader Coolwedge with a ND3.0 filter and continuum filter visually. ND3.0 is safe for visual, no need for ND5.0. A continuum filter knocks the brightness back to comfortable levels and also enhances the contrast on faculae and granulation.

Quote from FLO website about the two versions available:

Baader offers two versions of their Herschel Wedge: 

Visual V

The Version-V for visual use comes with a pre-installed ND=3.0 (required for safe viewing) filter and a 2" Continuum Filter.

Photographic P

The Version-P for photographic use is essentially the Version-V with three additional Baader ND filters (ND1.8, ND0.9 and ND0.6). The additional filters are handy for further dimming the image for white light viewing, or attaching to eyepieces or a T2-15 Reducer, and are particularly useful for imaging.

I suppose it's safe with just the ND3, but it's insanely uncomfortable for more than a quick glance.

I've used some of my Optica b/c color notch filters with my wedge and agree that they sufficiently knock down the brightness such than no additional ND filters are necessary beyond the built-in ND3.

My Hercules wedge came with a variable polarizing filter.  It works well to set a base brightness.  I can then spin the eyepiece in the holder to adjust it further thanks to the polarized light coming from the wedge.

The variable iris, though, seems useless.  I don't know why the designer wasted money adding it.  It's incredibly nice with lots of curved blades and a smooth action, but still unnecessary.

[Stu]

3 hours ago, Louis D said:

I suppose it's safe with just the ND3, but it's insanely uncomfortable for more than a quick glance.

I've used some of my Optica b/c color notch filters with my wedge and agree that they sufficiently knock down the brightness such than no additional ND filters are necessary beyond the built-in ND3.

My Hercules wedge came with a variable polarizing filter.  It works well to set a base brightness.  I can then spin the eyepiece in the holder to adjust it further thanks to the polarized light coming from the wedge.

The variable iris, though, seems useless.  I don't know why the designer wasted money adding it.  It's incredibly nice with lots of curved blades and a smooth action, but still unnecessary.

Yep, my point was that an ND5 is not needed, but just ND3 is still too bright for comfort. ND3 plus Continuum works well, or you can even use a continuum plus a polariser to dim the image further if it’s still too bright. Personally I prefer the extra brightness with just ND3 plus Confinuum but everyone’s eyes are different so it makes sense to use what is comfortable.

I use binoviewers so unfortunately can’t easily benefit from being able to rotate a  polarising filter to adjust brightness in the same way you can with a single eyepiece. Perhaps also the splitting of the light means that further dimming is not required as the brightness is shared between eyes? That said, even with mono viewing I still just use ND3 plus C.

[Lotinsh]

Hello, I was wondering, once I get my sheet of filter, does it matter how I put the filter, like do I just cover the whole front with it or does it need a smaller hole?

This is what I mean just in case:

Edit: My thought process why I'm worried is because if the aparature is really wide won't it collect more light so to not damage my eyes I will have to make the hole smaller? Or am I wrong?

Edited July 7, 2021 by Lotinsh

[Stu]

11 minutes ago, Lotinsh said:

Hello, I was wondering, once I get my sheet of filter, does it matter how I put the filter, like do I just cover the whole front with it or does it need a smaller hole?

This is what I mean just in case:

Edit: My thought process why I'm worried is because if the aparature is really wide won't it collect more light so to not damage my eyes I will have to make the hole smaller? Or am I wrong?

I would go for the full aperture. The film is perfectly safe provided you make the filter holder correctly, it covers the whole aperture without gaps and can’t fall off. Making it full aperture rather than a small sub aperture is no less safe.

[JamesF]

I agree with Stu.  If you feel the need for a smaller aperture having made the full-size mask, you could always make a disc with a hole to place over the top of the filter, perhaps even in several different sizes to see what works best.

James

[Lotinsh]

Thanks again for wonderful advice, my hopefully last question, which one of these should I buy?

https://www.astroshop.eu/solar-filters/baader-sun-filter-foil-a4-210x297mm/p,2718

or

https://www.astroshop.eu/solar-filters/baader-sun-filter-foil-astrosolarr-eco-size-od-5-0-140x155mm/p,54593

[Louis D]

It depends on your aperture.  You want about an extra inch or so all around for secure mounting.  Add 50mm to your aperture diameter and that's the minimum size you need.

[Stu]

I would probably get the A4 sheet so you have some spare depending on the size of your scope. If you have an optical finder you could cover that too.

[Tiny Clanger]

1 hour ago, Lotinsh said:

Hello, I was wondering, once I get my sheet of filter, does it matter how I put the filter, like do I just cover the whole front with it or does it need a smaller hole?

This is what I mean just in case:

Edit: My thought process why I'm worried is because if the aparature is really wide won't it collect more light so to not damage my eyes I will have to make the hole smaller? Or am I wrong?

I had very similar  concerns, after absorbing a lifetime's worth of 'never look directly at the Sun ' warnings.

So, I started by making a small aperture mask for my little ST80, which has a similar hole in the lens cap arrangement . That worked fine, after observing  for several minutes I could still see ! Reassured , I made a full aperture filter for the ST80. Again , the 'scope and my eyes survived unscathed, so  I got really bold and made a full aperture (just enough film left, I'd been careful to use the area as sensibly as I could) for my 127 mak.  They all work fine, but as you'd  expect there's more detail when using the higher aperture instruments .

Before each use I hold the filter up and check it for tears or holes,  then fit the little solar finder I bought in place of whatever optical night time finder I had on the 'scope before removing the cap and putting the solar filter on in its place. The eyepiece goes in last. I feel having a set routine makes it less likely I'll be distracted and do something daft one day !

Heather

[Stu]

2 minutes ago, Tiny Clanger said:

I feel having a set routine makes it less likely I'll be distracted and do something daft one day !

That part is very important, it’s easy to get slack about things and make a mistake so having a routine helps avoid that. Make a checklist if it helps too.

I removed my wedge not long ago with the scope pointing at the sun uncapped. No harm done, just got a warm hand, but it was a reminder not to do stupid stuff!

[saac]

1 hour ago, Lotinsh said:

Thanks again for wonderful advice, my hopefully last question, which one of these should I buy?

https://www.astroshop.eu/solar-filters/baader-sun-filter-foil-a4-210x297mm/p,2718

or

https://www.astroshop.eu/solar-filters/baader-sun-filter-foil-astrosolarr-eco-size-od-5-0-140x155mm/p,54593

You may also want to consider a solar finder , easy to make diy version, or look up positioning routine.  Oh, I think it may already have been said but make sure your finder is also covered . 

Jim 

[johninderby]

Or just get a solar filter for your regular finder. Works great and with a 9x50 finder you can use just the finder on it’s own to check the sun for sunspots bedore setting up your scope.

Edited July 7, 2021 by johninderby

[Lotinsh]

I have a laser dot finder so I'm not sure if that can work for sun, but I'm pretty sure there is no need of a finder, as you can point your scope towards the sun until the shadow makes perfect circle (hard to describe). Still, thanks for advice, I can't wait to get my solar filter!

[johninderby]

So much easier and quicker to use a solar finder. The old shadow method is still useful to get you somewhere near then switch to the solar finder to zero in on the sun. 

[saac]

Solar film arrived today, thanks FLO    100% clouded over here at the moment , forecast not looking good through to the weekend.  I'll content myself with making the  holder . It's an A4 sheet so I have enough to make a filter for the finder as well - thanks for the idea Johninderby  

Jim