33 replies to this topic

[Quark-Coder]

Hello everyone. For quite a while, I’ve been using a homemade solar filter made from a CD-RW disc  to image the Sun. Yes, it works, but the quality is bad.

I’ve decided it’s time to get a proper solar filter.

 

There are two options:
1. Buy solar film
2. Buy an ND filter

 

Why doesn’t the first option quite work for me? Because I don’t have access to high-quality film — only some unclear Baader copy from AliExpress.

ND filters are easier to buy. I’ve already found one with 20 stops. However, I came across information stating that ND filters do not block infrared radiation, which can fry my camera sensor.

So it turns out that with an ND filter, i also need a UV/IR cut filter — and things aren’t so straightforward there.

For example, there’s the KG3 filter with the following transmission curve:

And there’s the QB21 BG38 filter, which has a narrower transmission curve:

Which filter is better for protecting the camera, and do I even need one at all?

Edited by Quark-Coder, 24 April 2025 - 06:19 AM.

[UKnewbie1729]

Out of the two, the QB21, the 23 looks like it goes pretty far into the infrared, and I'd say yes, you do need one.

[alanturner]

A third option for white light solar is Thousand Oaks

 

https://thousandoaksoptical.com/

[Quark-Coder]

A third option for white light solar is Thousand Oaks

 

https://thousandoaksoptical.com/

Well... I didn't just write "I don't have access to high-quality film" for no reason.
My country is not on the delivery list at all.

[Quark-Coder]

Out of the two, the QB21, the 23 looks like it goes pretty far into the infrared, and I'd say yes, you do need one.

Maybe you meant that KG3 captures more infrared?
And KG3 transmits less light due to the lack of anti-reflective coating.
But I still haven't figured out which filter to take =)

[Traveler]

In your case a welding glass with Shade factor 12, 13 or 14 is maybe possible for you to buy.
Factor >15 is getting to dark/dim.

 

And if i may say so: do stop messing with a CD, it is not safe!

[Quark-Coder]

In your case a welding glass with Shade factor 12, 13 or 14 is maybe possible for you to buy.
Factor >15 is getting to dark/dim.

 

And if i may say so: do stop messing with a CD, it is not safe!

Well... no. I’ve already tried welding glass. The quality is worse than with my CD-RW filter.

[KLWalsh]

I tried the Thousand Oaks film and was unimpressed. The rough texture one one side of the film caused my images of the Sun to be slightly fuzzy.
The Baader solar film is far superior, imho. My images of the Sun were sharp. I also prefer the more natural white color of the Baader film, vs the odd murky yellow color of the Thousand Oaks film, but that’s my personal preference.
The Baader film is inexpensive.
You should be able to find ‘universal’ filters made with the film on a frame that attaches/clips onto your camera lens.
But if not, it’s easy enough to buy the film and attach it to a cylinder made from an empty plastic soda water bottle. Then slide the cylinder over your camera lens and hold it in place with some painter’s tape.

[BQ Octantis]

For the oblivious:

 

DO NOT LOOK AT THE SUN WITH YOUR EYES THROUGH ANYTHING BUT ISO 12312-2:2015-CERTIFIED FILMS. ANYTHING ELSE MAY ALLOW TOO MUCH UV THROUGH, WHICH YOU WON'T NOTICE AS YOU STARE AT THE SUN AND BURN OUT YOUR EYES!!!

 

With that disclaimer, I've had great luck IMAGING through a mylar emergency blanket, which are prolifically available on AliExpress:

 

 

But when I suggested that in a post over in solar, you'd think I posted the plans to a dirty bomb!

BQ

Edited by BQ Octantis, 26 April 2025 - 07:30 AM.

[Quark-Coder]

I tried the Thousand Oaks film and was unimpressed. The rough texture one one side of the film caused my images of the Sun to be slightly fuzzy.
The Baader solar film is far superior, imho. My images of the Sun were sharp. I also prefer the more natural white color of the Baader film, vs the odd murky yellow color of the Thousand Oaks film, but that’s my personal preference.
The Baader film is inexpensive.
You should be able to find ‘universal’ filters made with the film on a frame that attaches/clips onto your camera lens.
But if not, it’s easy enough to buy the film and attach it to a cylinder made from an empty plastic soda water bottle. Then slide the cylinder over your camera lens and hold it in place with some painter’s tape.

No. In my location, purchasing proper solar film is not possible. I already mentioned this at the very beginning of this thread. If I could buy something like that, this topic wouldn’t even exist.

[Marcus1]

What about the good old fashioned pinhole camera obscura projecting onto white card.

Edited by Marcus1, 25 April 2025 - 04:57 PM.

[Quark-Coder]

What about the good old fashioned pinhole camera obscura projecting onto white card.

Having a telephoto lens and a camera of the required parameters, I can't even imagine why such a device should be built, considering that the quality will drop significantly.
This is a fun experiment, but not for solar imaging.

[KLWalsh]

No. In my location, purchasing proper solar film is not possible. I already mentioned this at the very beginning of this thread. If I could buy something like that, this topic wouldn’t even exist.

I saw your original comment, but-
Amazon (dot) com carries it, and Baader Planetarium sells it directly. As do various astro retailers, including Agena Astro.
I thought perhaps if you searched more, you’d find a place that sells it.

Edited by KLWalsh, 25 April 2025 - 10:01 PM.

[bignerdguy]

Well... I didn't just write "I don't have access to high-quality film" for no reason.
My country is not on the delivery list at all.

Can you get Celestron accessories in your country anywhere?  If so try buying this from a local vendor:

 

https://www.celestro...VnTNDAPSZRUGCo6

 

I use it on my Canon 60D (FS Modded) and it works great.

 

 

I will ay that focusing on the sun with the tiny screen on my camera is a pain in the rear but if you can use a PC with a bigger screen its far easier to achieve focus.

Edited by bignerdguy, 25 April 2025 - 08:31 PM.

[Quark-Coder]

I saw your original comment, but-
Amazon (dot) com carries it, and Baader Planetarium sells it directly. As do various astro retailers, including Agena Astro.
I thought perhaps if you searched more, you’d find a place that sells it.

Amazon does not ship to my country, baader planetarium does not ship to my country and Agena astro does not ship to my country either. I repeat - if I could buy normal quality solar film, I would do it and not start a thread.
My country is sanctioned and there is practically nothing related to astrophotography.

[Quark-Coder]

Can you get Celestron accessories in your country anywhere?  If so try buying this from a local vendor:

 

https://www.celestro...VnTNDAPSZRUGCo6

 

I use it on my Canon 60D (FS Modded) and it works great.

 

Sun 5-27-2024.jpg

 

I will ay that focusing on the sun with the tiny screen on my camera is a pain in the rear but if you can use a PC with a bigger screen its far easier to achieve focus.

Only some Sky-Watcher filters are available. But they’re too big for my lens.

Focusing is not a problem - I’m using autofocus on my lens, and with NINA’s Lens Focusing plugin, I can move it very precisely.

[UKnewbie1729]

Maybe you meant that KG3 captures more infrared?
And KG3 transmits less light due to the lack of anti-reflective coating.
But I still haven't figured out which filter to take =)

Yes, infrared starts at 780 nm wavelength, this is where the BG38 / QB21 cuts off completely so no infrared gets through at all, the KG3 / GRB3 transmits all the way up to 900nm, this is very deep into the infrared, you -really- don't want to focus those wavelengths on your sensor.

Edited by UKnewbie1729, 26 April 2025 - 07:18 AM.

[BQ Octantis]

ND filters work great. I use an ND 100K filter with my camera all the time.

 

 

The sensor temperature does not rise much at all.

 

BQ

Edited by BQ Octantis, 26 April 2025 - 06:57 AM.

[Quark-Coder]

ND filters work great. I use an ND 100K filter with my camera all the time.

 

 

The sensor temperature does not rise much at all.

 

BQ

Wouldn't ND 1000k be too dark then?

[Quark-Coder]

Yes, infrared starts at 780 nm wavelength, this is where the BG38 / QB21 cuts off completely so no infrared gets through at all, the KG3 / GRB3 transmits all the way up to 900nm, this is very deep into the infrared, you -really- don't want to focus those wavelengths on your sensor.

Got it. Then I'll take QB21, thanks.

Edited by Quark-Coder, 26 April 2025 - 08:48 AM.

[BQ Octantis]

Wouldn't ND 1000k be too dark then?

The ND 100K at ISO100 f/2.8 requires subs of ~1/2000 sec to not clip. So an ND 1000K would clip at anything below ~1/200 sec.

 

The nice thing about the ND 100K is that it leaves enough light to use a dual-band energy reduction filter to isolate Ca-K and Ha.

 

BQ

[BQ Octantis]

I forgot to ask what camera you're using. The reason my stock Canon 600D/T3i doesn't care about the IR passed through the ND filter is because the built-in LPF-2 filter is itself an IR cut filter.

[UKnewbie1729]

Got it. Then I'll take QB21, thanks.

To be honest, I'd say you'd be better off following BQ_Octantis' suggestion of an ND filter, it will give a more even reduction in intensity across all colours, the QB21 filter starts to decrease at 600nm (orange) so it would remove infrared but you would also loose some deeper red signal compared to the other colours, if that matters to you?

 

  As BQ_Octantis pointed out, this does depend on what sort of camera you are using, you may need to add extra infrared blocking such as the QB21 even with an ND 100.  I have the same model of camera myself (Canon 600) and I've shot the sun unfiltered at 200mm - 1/2000sec - ISO100 - f22 with no sensor damage

 

Considering what you mentioned about how difficult it is for you to get hold of anything internationally though, go with whatever you can get

Edited by UKnewbie1729, 26 April 2025 - 10:36 AM.

[Quark-Coder]

I forgot to ask what camera you're using. The reason my stock Canon 600D/T3i doesn't care about the IR passed through the ND filter is because the built-in LPF-2 filter is itself an IR cut filter.

I have two cameras: stock Canon 550D and Ha modified Canon 60D without LPF-2.

[UKnewbie1729]

My advice would be use the 550D for solar and save the 60D for those faint Ha nebulae after solar isn't an option