Making a screw-in Solar Filter

[hollis_f]

Originally Posted by PM01

I spoke to a person that works at Astro Physics, one of the distributors of the Baader Solar film. When I mentioned the method of the screw in filter, the person said "VERY dangerous to do this as the edges will more than likely have pinholes that will let in harmful light and IR". .

Any holes will be detected in the test image.

[PM01]

Hollis_f,

Just relaying the message from the pros at AP. They're very cautious about the construction of the filter. I'm only about an hour away from them so I get to visit them quite often. If the filter works, more power to you!

Have glassless versions ready. Then a/b compare them. Anything more than 200mm, you should be able to pick out differences. Well worth the effort.

Event is coming up! Best of luck to all that are viewing in that it will be clear for you!

[hollis_f]

Originally Posted by PM01

Hollis_f,

Just relaying the message from the pros at AP. They're very cautious about the construction of the filter. I'm only about an hour away from them so I get to visit them quite often. If the filter works, more power to you!

Handheld this afternoon through thin cloud. I would try making one without the glass, but the clouds are already rolling in, and the forecast don't look great for tomorrow. I reckon there's enough detail in this image to satisfy me that your "It could mean the difference from seeing blurry blotches to high detail" is proven wrong in this case.

[PM01]

Hollis,

What focal length? As I mentioned, above 200mm you would start to see a difference. I'm shooting with 1200mm so it's very obvious.

As for the pinholes being detected in the final image, remember that any type of pinholes are not at the focus plane. If we take the inverse situation, say, dust on the lens, you won't be able to pick off dust on the lens due to it's proximity relative to the focal plane. But IR will definitely get through if the holes are big enough.

I'd rather play it safe, but that's me.

Hope the weather works out for you!

[PM01]

And from the AP website...

"Unlike commercial film and glass filters, Baader's AstroSolar™ will not significantly degrade the imaging capabilities of your telescope. Roland Christen of Astro-Physics has checked out samples of this material on a double-pass interferometer and measured a 94% Strehl Ratio when placed flat over a 6" test optic. Compare this to Strehl ratios of 45% for aluminized Mylar and less than 24% for inexpensive glass solar filters. "

Also worth a read...

http://www.clarkvision.com/articles/...ity/index.html

[pwm2]

Originally Posted by PM01

Hollis,

What focal length? As I mentioned, above 200mm you would start to see a difference. I'm shooting with 1200mm so it's very obvious.

As for the pinholes being detected in the final image, remember that any type of pinholes are not at the focus plane. If we take the inverse situation, say, dust on the lens, you won't be able to pick off dust on the lens due to it's proximity relative to the focal plane. But IR will definitely get through if the holes are big enough.

I'd rather play it safe, but that's me.

Hope the weather works out for you!

A narrow beam from a hole in the film is only dangerous if it is focused - it's the focusing created by a big camera lens that makes it so very dangerous to play with the sun because of the large magnification in power density. The sun itself can manage 1kW/m2 but with a lens the result can be much higher power densities.

A tiny hole in the film at the front of the lens means that the amount of energy that gets through the hole is still quite small - it is not the same as having a large glass of a magnifier focus at a single spot.

Next thing is that a tiny point in the eye has good water cooling.

So a tiny hole that isn't visible in normal test images, should not be able to project energy densities high enough to damage the eye.

[hollis_f]

Originally Posted by PM01

What focal length? As I mentioned, above 200mm you would start to see a difference. I'm shooting with 1200mm so it's very obvious.

That image was with my 100-400, which is what I'm planning on using tomorrow.

Originally Posted by PM01

As for the pinholes being detected in the final image, remember that any type of pinholes are not at the focus plane.

So what? If there's a hole large enough to let in enough light to damage eyes or sensors then it's going to let in enough light to show in the test image.

Originally Posted by PM01

But IR will definitely get through if the holes are big enough.

What? What possible influence can the size of any pinholes have on the wavelength of the light that gets through?*




*Edit: Yes, for those that know some physics, the hole size can have some influence. But it will make IR less likely to get through than visible light. And there will be no detectable effect from enormous pinholes.

[PM01]

hollis - are you focusing through the liveview or through the optical finder? If it's liveview then the pinholes become a no issue. Optical finder - be careful.

I always err on the side of caution since I'm in charge of a university observatory. We get lots of people going through there and I always have to think about liability so I always have to cover all the bases, especially with solar work.

Switched from the solar film material since it doesn't really like being stored outside in the observatory - no temp or humidity regulation. Lots of moisture attack, thus pinholes. The H-alpha scopes were much more expensive but work out nicely. Baader ceramic wedge is still my favorite.

[dolina]

Hollis is the home made filter inserted into the filter holder? I was thinking of covering the front (where the lens hood mounts) of the lens with the solar filter you recommended. Wish I took the foresight to photograph this. I was expecting cloudy whether in Manila today.. )

[Jay-Bird]

IMG_2798 by zeroedinphoto, on Flickr

And as a bonus, I am not blind.

[PM01]

Did anyone get first contact pics? Also, the backlit atmosphere of venus was incredible!!!

[pwm2]

Originally Posted by dolina

Hollis is the home made filter inserted into the filter holder? I was thinking of covering the front (where the lens hood mounts) of the lens with the solar filter you recommended. Wish I took the foresight to photograph this. I was expecting cloudy whether in Manila today.. )

What filter holder? His design is having the film between two screw-on filters, so he screws this dual-filter (now triple-filter) combo onto his lens like you do with a normal, round, UV filter. Since the combo is used with a 100-400 tele lens, there isn't any vignetting issues with using stacked filters.

And since he kept the original filter glass, the solar film is protected from finger prints or mechanical abuse that may damage it and create holes in the film. With unprotected film, you get big problems how to store a home-made design so the film will still be intact when it's time to use it.

[hollis_f]

Rotten Bloody weather.

[dolina]

Originally Posted by pwm2

What filter holder? His design is having the film between two screw-on filters, so he screws this dual-filter (now triple-filter) combo onto his lens like you do with a normal, round, UV filter. Since the combo is used with a 100-400 tele lens, there isn't any vignetting issues with using stacked filters.

And since he kept the original filter glass, the solar film is protected from finger prints or mechanical abuse that may damage it and create holes in the film. With unprotected film, you get big problems how to store a home-made design so the film will still be intact when it's time to use it.

My mistake. I read that he was going to use it with a 300mm f/2.8 lens.