Baader ND3.8 Photo Film.

[JamieW]

Thinking of taking the plunge and getting a Baader CaK filter for imaging which comes supplied with some ND3.8 photo film. What I'd like to know is can this film be used safely for visual white light observing by using an additional ND filter? And if so which one? (It would be used with a 6" reflector)

Thanks in advance,

Jamie

[Naemeth]

Thinking of taking the plunge and getting a Baader CaK filter for imaging which comes supplied with some ND3.8 photo film. What I'd like to know is can this film be used safely for visual white light observing by using an additional ND filter? And if so which one? (It would be used with a 6" reflector)

Thanks in advance,

Jamie

The Baader CaK Filter + 3.8ND Solar Film is only suitable for imaging. You need ND5.0 for visual use.

[JamieW]

Thanks Naemeth, but can an additional ND filter be attatched to the eyepiece? If not then it's two lots of film and some colour coding to make sure I don't mix them up!

[Naemeth]

Thanks Naemeth, but can an additional ND filter be attatched to the eyepiece? If not then it's two lots of film and some colour coding to make sure I don't mix them up!

I don't believe so. The two 3.8ND filters may either filter out too much light, or not quite enough. It's much safer to go with one ND5.0 and one ND3.8 for imaging.

[JamieW]

Cheers mate. Better to be safe than sorry.

[JamesF]

ND3.8 solar film attenuates light by a factor of something like 6,300, AFAIR. ND5.0 attenuates it by a factor of 100,000. An eyepiece filter such as used for viewing the moon would do little to prevent harm to your eye when combined with ND3.8, and two layers of ND3.8 would cut out far too much altogether. A sheet of ND5.0 is hardly expensive. Do the sensible thing.

James

[RikM]

You can image quite successfully through the ND5.0 film in white light. I am not use how it would work with the CaK though.

[JamieW]

ND3.8 solar film attenuates light by a factor of something like 6,300, AFAIR. ND5.0 attenuates it by a factor of 100,000. An eyepiece filter such as used for viewing the moon would do little to prevent harm to your eye when combined with ND3.8, and two layers of ND3.8 would cut out far too much altogether. A sheet of ND5.0 is hardly expensive. Do the sensible thing.

James

Now that's why I love this forum. The difference between 3.8 and 5.0 doesn't convey the difference between x6,300 and x100,000 (well not to me at least).

It goes to show that a little knowledge is a dangerous thing.

You can image quite successfully through the ND5.0 film in white light. I am not use how it would work with the CaK though.

That's what I intend to do now. I'd much rather have over-exposed images than fried eyeballs.

[JamesF]

Now that's why I love this forum. The difference between 3.8 and 5.0 doesn't convey the difference between x6,300 and x100,000 (well not to me at least).

It goes to show that a little knowledge is a dangerous thing.

For reasons that are probably meaningful to someone but not clear to me, the numbers represent the attenuation on a logarithmic scale. 10^5 is 100,000, 10^3.8 is a smidge over 6,300.

James

[johninderby]

Here's a quote from Telescope Service regarding their solar filters with Baader film.

Photography or visual observation? With your order, you can decide whether you want the filter with visual (ND 5) or photographical (ND 3.8) version. The latter one has 10x more transmission and allows short exposure times. When you want to use this version for visual purposes, a strong neutral density and UV/IR cut filter is necessary.

John

[GreatAttractor]

Precisely speaking, ND 5 attenuates light by factor 10^-5 and ND 3.8 by 10^-3.8, so the latter is 10^-3.8/10^-5 or about 16x brighter. I've read suggestions that ND 3.8 can be used visually with "dark" filters like Solar Continuum, but never tried it. To me ND 5 + Solar Continuum in a F/10 scope was bright enough.