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Solar filters: film or glass? Recommendations for a 6" refractor

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#1 angelsp

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Posted 16 March 2023 - 07:37 AM

Hi,

Planning for the 2024 solar eclipse, I'd like to buy the filter to use with my 6" (1200mm, f/8) refractor. So asking the wise guys on this forum, what do they recommend without breaking the bank?

 

Thank you!


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#2 Diana N

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Posted 16 March 2023 - 08:03 AM

Either type of filter will work and is safe, provided you buy it from a reputable manufacturer. You will find that the film filters are less expensive and also lighter weight (so they won’t throw your telescope out of balance). Both types are fragile and must be handled carefully and stored carefully, and very carefully checked for defects before placing on the end of your telescope.  You want to make sure to check the filter every time you use it.

 

Another nice way to cut cost is to just buy the film and make your own cell to hold it in. There are lots of instructions online for how to do it; the important part is just making sure that the cell fits very tightly onto the end of your telescope so there is no possibility of it coming off while you are actually observing.


Edited by Diana N, 16 March 2023 - 10:07 AM.

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#3 dghundt

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Posted 16 March 2023 - 09:03 AM

I bought film in a premade holder for my 600mm f4 camera lens for 2017.  That was lost (aka stolen) during my flight.

I got some spare solar film, went to Dollar Tree, and built my own holder.  It wouldn't hold up with heavy use, but the material costs were much less and it worked just fine.


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#4 Seldom

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Posted 16 March 2023 - 11:31 AM

Hi,

Planning for the 2024 solar eclipse, I'd like to buy the filter to use with my 6" (1200mm, f/8) refractor. So asking the wise guys on this forum, what do they recommend without breaking the bank?

 

Thank you!

In 2017 I used a Baader ASTF 100 on my 100mm scope.  It gave good color rendition for proms.  The 100 in the product name is the scope diameter.  The ASTF come with a holder that makes it easy to install and remove when your software warns you to take it off and put it on.  Something to keep in mind if you are planning to build you own holder and buy solar film separately.


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#5 angelsp

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Posted 16 March 2023 - 12:58 PM

Thank you very much for all the responses!


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#6 foxwoodastronomy

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Posted 16 March 2023 - 10:26 PM

angelsp, is this your first time trying to image an eclipse?  Your answer will help determine my recommendation.  Thanks.



#7 jrussell

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Posted 29 March 2023 - 11:02 AM

I'm glad somebody asked this. I came here for the very same reason lol.



#8 Napp

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Posted 29 March 2023 - 11:26 AM

Baader Solar safety film provides a better image than other films and glass. Optically flat glass is very expensive. I’m not aware of any of the glass filters using it. These type filters are good for seeing photosphere features like sunspots. If you want to see proms and other chromosphere features you will need to spend $$$ for hydrogen alpha equipment.
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#9 foxwoodastronomy

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Posted 29 March 2023 - 07:24 PM

I have a response to this question directed specifically to NEW eclipse photographers who will shoot manually, not try to computer script. If 2024 is your first eclipse and you want to image it, I know that you are going to worry about what exposure settings to use for the Diamond ring, Baily's beads, and then the corona. I get it! I also did at my first eclipse in 2001, and that was way before YouTube and all of these helpful forums, so we had to learn from books and struggle with exposure tables. And we were using slide film with a fixed ISO back then. In 2017 I read thread after thread from people trying to figure out what to do before the eclipse. I recently gave Zoom lectures to two big astronomy clubs in New Mexico and New York. Many members admitted they struggled in 2017 and felt like they were taking their best guesses at exposures and wished they had known my plan before 2017. But this is why I recommended metalized glass filters: it's because I understand the light transmission characteristics of glass. I have successfully used them at five eclipses and analyzed my results to give new eclipse photographers a plan. I know that for your camera and lens system, with the f/stop of your system and the ISO you choose to use (usually between 200 to 800), if you select a shutter speed to expose a full solar disk image properly, that means a bright center but with preserving natural limb darkening, that same shutter speed with expose inner corona when you glass filter is off. That is powerful information to know about your gear, and you can know it right now. Then I can tell you that two stops faster in shutter speed will be a suitable shutter speed for the diamond ring and Baily's beads going into C2 with the filter off. Then you just slow the shutter speed by third stops or half stops up to 1, 2 or 3-second exposure time depending on if you are guiding or not. This takes the mystery out of eclipse photography! If you are a "newbie," these four steps will allow you to be successful. Then the only thing you need to worry about is anticipating C2 and C3, don't be late, and don't forget to remove your solar filter. For guys who read this and have experience with a few eclipses, I know you have your routines, and that's cool; this is for first-timers in 2024 or people who messed up in 2017 who are not going to script. The images attached are from one of my lectures and contain some relevant pages from my eclipse book.

Attached Thumbnails

  • 1 CN full disks.jpg
  • 2  CN last crescent.jpg
  • 3  CN inner corona.jpg
  • 4  CN ring beads.jpg
  • 5 CN corona.jpg

Edited by foxwoodastronomy, 29 March 2023 - 07:31 PM.

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#10 wdavidsmc

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Posted 03 April 2023 - 03:52 PM

Thank you for your book information. I'm definitely a beginner astrophotographer and have a question:

Could  solar film and a cellphone also work? 
I'm thinking of doing video with my 4SE so I could also enjoy watching the eclipse.

Does your book cover this?



#11 foxwoodastronomy

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Posted 03 April 2023 - 09:56 PM

Hi, thanks for your comment.  I do not get into using cell phones in the book.  But to answer, your question, sure it would work!  You can cut the film out of a pair of solar glasses and just tape it over the lens on the back of the phone.  I've tested it some and it works.  It would be helpful if you download some that allow your phone's camera to make exposure adjustments.  Remember to remove the film for totality!  My app makes those announcements for you. Above I posted pages from my book about detailed photography.  But know that my book has dozens and dozens of pages on eclipse observation techniques.   I have written a lot about the science of the partial phase phenomena.  More than any other eclipse book available. You might find that interesting.



#12 BlueTrane2028

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Posted 03 April 2023 - 10:15 PM

I'm in the "use a Herschel Wedge" camp for refractor solar...

https://www.highpoin...-case-ls2hw?utm


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#13 SteveInNZ

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Posted 04 April 2023 - 05:02 AM

I'm in the "use a Herschel Wedge" camp for refractor solar...
 

Great for normal white light solar viewing but not the best option for an eclipse where you want to swap it out for a normal diagonal during totality. 

 

Steve.



#14 KMH

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Posted 04 April 2023 - 05:41 PM

Based on my experience, I would not recommend glass filters.  The ones I've tried have given rather soft images.  I haven't tried the Baader films, but everything I've read suggests the image quality is much better than glass.

Good luck!

Kevin



#15 Look at the sky 101

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Posted 04 April 2023 - 05:49 PM

Great for normal white light solar viewing but not the best option for an eclipse where you want to swap it out for a normal diagonal during totality. 

 

Steve.

Can you please explain why?



#16 SteveInNZ

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Posted 04 April 2023 - 10:20 PM

Can you please explain why?

Sure. It all happens at C2, when the last little bits of the photosphere disappear (Baily's Beads), the pink photosphere dominates the rim and the corona starts to become visible. It's the Wow moment that you don't want to miss.

If you have a front mounted filter, you pick your moment and remove the filter. There's no change in focus or anything else to change. If you have a wedge or a Quark, you are removing something between the eyepiece or camera and the telescope and replacing it with something else. So that's three things you need to hold and swap around without dropping them, in the (pseudo) dark and then you have to refocus. All at the Wow moment.

 

I say pseudo-dark because you have inevitably looked up at that moment and it wasn't quite dark enough so you have that "starred into headlight" experience. Even if you haven't, it's just got dark quicker than you can dark adapt and you want to

 

Steve.


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#17 foxwoodastronomy

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Posted 05 April 2023 - 05:17 AM

Based on my experience, I would not recommend glass filters.  The ones I've tried have given rather soft images.  I haven't tried the Baader films, but everything I've read suggests the image quality is much better than glass.

Good luck!

Kevin

Hi KMH, some of the best eclipse photographers in the world use glass filters for the partial phases, like Fred Espenak.  You say that the images are "soft", but we are talking about the partial phases with the filter on, at 600 to 1,000 mm focal length, and the only thing to be worried about is imaging sunspots which are tiny at the focal length anyway.  But the partial phases are not where crucial eclipse photography happens.  The real imaging occurs when you remove the solar filter at C2.

There are some eclipse photographers that swear by Baader film and I am fine with that.  But you said you haven't used Baader film.

So, I am wondering what you recommend and why?  Thanks, Gordon



#18 foxwoodastronomy

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Posted 05 April 2023 - 05:18 AM

Sure. It all happens at C2, when the last little bits of the photosphere disappear (Baily's Beads), the pink photosphere dominates the rim and the corona starts to become visible. It's the Wow moment that you don't want to miss.

If you have a front mounted filter, you pick your moment and remove the filter. There's no change in focus or anything else to change. If you have a wedge or a Quark, you are removing something between the eyepiece or camera and the telescope and replacing it with something else. So that's three things you need to hold and swap around without dropping them, in the (pseudo) dark and then you have to refocus. All at the Wow moment.

 

I say pseudo-dark because you have inevitably looked up at that moment and it wasn't quite dark enough so you have that "starred into headlight" experience. Even if you haven't, it's just got dark quicker than you can dark adapt and you want to

 

Steve.

Steve, great answer, but I think you meant to write "pink chromosphere."

Gordon



#19 angelsp

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Posted 05 April 2023 - 11:48 AM

angelsp, is this your first time trying to image an eclipse?  Your answer will help determine my recommendation.  Thanks.

Yes, it is.

Thanks!



#20 angelsp

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Posted 05 April 2023 - 11:55 AM

A lot of helpful information!

Thank you all!



#21 Look at the sky 101

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Posted 05 April 2023 - 12:00 PM

Sure. It all happens at C2, when the last little bits of the photosphere disappear (Baily's Beads), the pink photosphere dominates the rim and the corona starts to become visible. It's the Wow moment that you don't want to miss.

If you have a front mounted filter, you pick your moment and remove the filter. There's no change in focus or anything else to change. If you have a wedge or a Quark, you are removing something between the eyepiece or camera and the telescope and replacing it with something else. So that's three things you need to hold and swap around without dropping them, in the (pseudo) dark and then you have to refocus. All at the Wow moment.

 

I say pseudo-dark because you have inevitably looked up at that moment and it wasn't quite dark enough so you have that "starred into headlight" experience. Even if you haven't, it's just got dark quicker than you can dark adapt and you want to

 

Steve.

OK thanks. 



#22 KMH

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Posted 05 April 2023 - 02:28 PM

Hi KMH, some of the best eclipse photographers in the world use glass filters for the partial phases, like Fred Espenak.  You say that the images are "soft", but we are talking about the partial phases with the filter on, at 600 to 1,000 mm focal length, and the only thing to be worried about is imaging sunspots which are tiny at the focal length anyway.  But the partial phases are not where crucial eclipse photography happens.  The real imaging occurs when you remove the solar filter at C2.

There are some eclipse photographers that swear by Baader film and I am fine with that.  But you said you haven't used Baader film.

So, I am wondering what you recommend and why?  Thanks, Gordon

Gordon,

 

I was thinking mostly of my experience with Mercury and Venus transits, where the planetary discs were decidedly soft (although they weren't soft with my H-alpha scope).  But also higher resolution imaging of sunspots is problematic.  It's of course quite possible that I did not chose my filter wisely!  Definitely I would like to know what Fred Espenak uses.

I think I will try the Baader film for the annular eclipse coming up in October, and maybe do a side-by-side comparison.

 

Kevin

 

edit - it looks like Fred recommends Questar or Thousand Oaks - I think mine is Meade or Orion.


Edited by KMH, 05 April 2023 - 03:48 PM.


#23 SteveInNZ

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Posted 05 April 2023 - 04:14 PM

Steve, great answer, but I think you meant to write "pink chromosphere."

Gordon

D'oh!. Indeed I did.

 

I may as well share my thoughts and experiences with solar filters. I've used a few.

 

I haven't personally used a glass one but it is a common assertion that they have lower contrast from the reflection off the second surface of the glass. The same reason we use first surface mirrors in telescopes.

For me, it comes down to Murphy's Law. If there's a chance I might drop it, the consequences between a glass and mylar filter are quite different.

 

As an aside - Consider what you are going to do with the filter when you remove it. Will you or someone stand on it ? Will it blow away if there's a breeze ? Can you find it when you need it at C3 ? I have a plastic bag taped to the tripod leg if I'm using a removable filter.

 

For the filter material, there are two general types - black polymer or metalized mylar. My recommendation is to use the black polymer in cases where there will be light reaching the back side of the filter. Things like eclipse glasses, filters in a holder on the front of a lens (Cokin style) and probably phones. The reflection on the back of the mylar filters makes it difficult for your eyes to pick what to focus on and reduces the contrast in your photos. They're still quite usable but the black just improves the experience. If the filter is a good fit on the end of a telescope, binoculars, etc that's not an issue. Pick the image color you prefer.

 

And my really simple method for no computer eclipse imaging. Get a simple remote/cable release for your camera. If you want to, you can work out what your maximum exposure time is for your mount (tracking or not) and how many stops you want to bracket each shot. But you don't have to.

 

Put the remote in one hand and with the other, adjust the shutter speed dial. So during the eclipse, you don't even have to look at the camera. Press the shutter release, rotate the dial two clicks, press the shutter release, rotate two clicks, repeat. As the exposures get longer, you'll hear it getting in to the one potato, two potato, times and then you start rotating the dial in the other direction.

 

You may (or may not) want to use the 2 second shutter delay to let any camera shake dissipate.

 

I highly recommend the use of a tracking mount for visual as well as photography. If it turns cloudy, you want the scope to be pointing at the Sun so that if there's a tiny break, you don't have to go searching for it.

 

Steve.



#24 foxwoodastronomy

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Posted 05 April 2023 - 08:17 PM

Gordon,

 

I was thinking mostly of my experience with Mercury and Venus transits, where the planetary discs were decidedly soft (although they weren't soft with my H-alpha scope).  But also higher resolution imaging of sunspots is problematic.  It's of course quite possible that I did not chose my filter wisely!  Definitely I would like to know what Fred Espenak uses.

I think I will try the Baader film for the annular eclipse coming up in October, and maybe do a side-by-side comparison.

 

Kevin

 

edit - it looks like Fred recommends Questar or Thousand Oaks - I think mine is Meade or Orion.

So, I know from talking to the owner of Seymour Solar that are very few places that actually supply the glass that goes into the solar filters that all of these different companies use.  So, the bulk supply comes from the same manufacturer. At, least around 2017, it did.  Thousand Oaks has been out of the glass business for some time, opting to sell its Solarlite film.  I have a number of old Thousand Oaks glass filters that I like.  I also have a couple from Seymour Solar that I like. I did talk to Thousand Oaks last year and they told me they got a shipment of glass that they were going to test to see if it met their specifications.  I don't know what has become of that.  So, your Mead or Orion most like has glass that originated form the same place.  Questar stuff maybe better, I don't know.

 

I don't like SolarLite film because its optical light transmission is about 3 stops less than glass.

 

I have a section in my book that is called "filters that are not glass."  The two pages I attached have three images all taken with the same gear at the same setting.  A balanced full disk exposure of the Sun with glass, then SolarLite, then Baader.

 

There is a post above that talks about using black polymer film.  Regular black polymer is not good enough optical quality for imaging I would not recommend it.  In fact, Thousand Oaks sells SolarLite which they say has the optical quality of glass.  They also have a new product called Silver Black Polymer, which I think is their old black polymer with a silver surface on one side.  And with the Silver Black Polymer, they DO NOT recommend it for long focal length photography, only wide-angle images.  And that makes sense if it is based on black polymer.  I only use black polymer for finder scopes or binoculars, never on my imaging gear.

 

I've tested glass versus other filters.  Not for scientific specifications, but side by side on the same system, at the same setting.  Glass has a nice flat spectrum distribution. SolarLite film took three times the sample time to "almost" get to the exposure of glass.  Black polymer has a redshift.  And Baader film passes WAY MORE light with a big blue shift.

 

When shopping for Baader film be aware that it comes in optical density 5 (OD 5) and optical density 3 (OD 3).  OD 3 is NOT for visual use, just imaging.  OD 5 is for both, visual and imaging.  However, I find that Baader film even at OD 5 passes too much light, I can't imagine using OD 3.

 

I just like, and trust glass.

 

Gordon

Attached Thumbnails

  • glass and solar lite.jpg
  • baader.jpg
  • 4 spectrums labeled with copyright 800px.jpg

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#25 angelsp

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Posted 06 April 2023 - 04:32 PM

Based on all the information, I think that glass is the option I'll choose. 

I like the first image with the Seymour Solar glass filter, and they have in stock.

 

My refractor is 6 inches, but with the dew shield is 8 inches. I can remove the shield, but I'd rather to keep it. Is there any problem?





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