White Light front filter visual observing + IR/UV filter

[Mark at Beaufort]

I would interested if someone could explain the need to use a IR/UV filter whilst solar observing in white light. I understand that cameras need to have an IR/UV cut filter in place to improve the image taking. But why? If the front filter removes 99.99% of dangerous light/radiation which includes IR and UV - why the need for an extra filter?

So if a camera needs it would it be sensible to add this filter when visually observing.

It appears that 365 astronomy states that this is necessary even when using the Continuum filter.

I would welcome opinions. I would state that I have used an Orion glass filter, thousand oaks glass filter, several Baader filters and a Herschel Wedge so my eyes are still working but I just be happy to receive advice.

[vlaiv]

I think it has to do with UV rays.

Although solar filters remove a lot of light - Sun does emit a lot of light and using large scope also collects a lot of light. In the end there might be enough light left to do some damage.

Let's say that we are using 100mm scope and that normal pupil in daylight is about 1-2mm? Right? That is somewhere between x2500 to x10000 more light collected by the scope then by directly looking at the sun. Now we have Herschel wedge which leaves about 1/20th of the light (5% or so?) and ND filter - ND3 which gives 1/1000th of light - combined they give 1/20000th of the light.

That is only about 1/4 - 1/10 of what we would gather by naked eye - and looking directly at the sun. Image is magnified so it does not look as bright but same number of UV photons reach our eyes.

There are number of resources online about harmful effects of UV on eyesight.

As for Baader Continuum - it appears that Baader changed something in their manufacturing process as before their filter response curve looked like this:

There is a leak in UV part of spectrum.

So I guess it is all about avoiding cataract and other nasty things that can result from UV exposure.

[Mark at Beaufort]

Thanks @vlaivthat is useful - on that basis it would not hurt adding a IR/UV filter into the optical train even for standard visual observing.

[Merlin66]

I think also the NIR "leakage" is of concern to some people.

[Stu]

Interesting stuff. I've never used a UV/IR when observing over the years. I guess as a precaution it would not do any harm to add one so I may just do that. Thanks Mark.

[astro_al]

I had been wondering this myself. There is a good thread on Solar Chat on the current and previous version of the Continuum filter - https://solarchatforum.com/viewtopic.php?t=16944

As someone who bought the Baader Herschel Wedge this year I would expect to have the newer version of the Continuum filter and so no need for a UV/IR cut filter. Not sure if there is a definitive way to check though.

[Guest]

I always thought that a polarising filter protected against UV and IR. 

Am I incorrect in this belief? 

Edited March 12, 2020 by Guest

[johninderby]

Quote from Baader re their solar film.

”UV/IR cut filter gives additional safety even if the film blocks these dangerous wavelength very good in combination with additonal optics like telescope or binocular.”

Edited March 12, 2020 by johninderby

[vlaiv]

26 minutes ago, Grumpy Martian said:

I always thought that a polarising filter protected against UV and IR. 

Am I incorrect in this belief? 

Polarizing filter is selective in polarization and not wavelengths. This means it will pass some of UV and some of the IR in the same way it will pass some of the visible wavelength - depending on their polarization.

[Mark at Beaufort]

1 hour ago, johninderby said:

Quote from Baader re their solar film.

”UV/IR cut filter gives additional safety even if the film blocks these dangerous wavelength very good in combination with additonal optics like telescope or binocular.”

John that is very useful information. I have not seen this - have you a link?

[johninderby]

Here you go.

https://www.baader-planetarium.com/en/solar-observation/astrosolar-viewers-and-film/astrosolar-eco-size-safety-film-5.0-140x155-mm.html

A bit down the page in product questions.

[Merlin66]

Not all/any ND5 filters block all the UV through to IR (350nm to 2500nm) wavelengths.

 

[Mark at Beaufort]

26 minutes ago, Merlin66 said:

Not all/any ND5 filters block all the UV through to IR (350nm to 2500nm) wavelengths.

 

Ken on that basis it would be sensible, as an extra safety measure, to purchase a UV/IR filter - especially as they are not that expensive.

[Guest]

Baader UV/IR cut filter. 

Model No buvir-1

Part Number:  2459207A

The above details are taken from the FLO web site. 

Although in the description mentions IR, it does not seem to mention UV. But the advert title includes UV/IR. So would I be correct in the belief that this filter would bar both UV and IR radiation. 

[Mark at Beaufort]

57 minutes ago, Grumpy Martian said:

Baader UV/IR cut filter. 

Model No buvir-1

Part Number:  2459207A

The above details are taken from the FLO web site. 

Although in the description mentions IR, it does not seem to mention UV. But the advert title includes UV/IR. So would I be correct in the belief that this filter would bar both UV and IR radiation. 

 

I notice this statement on another website - I don't know how much below 400 nm it goes.

[johninderby]

https://www.baader-planetarium.com/en/downloads/dl/file/id/16/product/2974/baader_uv_ir_cut_filter.pdf

[Guest]

58 minutes ago, johninderby said:

https://www.baader-planetarium.com/en/downloads/dl/file/id/16/product/2974/baader_uv_ir_cut_filter.pdf

Thanks for that John. I do observe the sun from time to time through a wedge. But now at my age, I do concern myself with any threat to my eyesight. Poor as it is any way. It looks like the Baader UV/IR filter may well eliminate that threat. 

[johninderby]

I picked up one of these to test last week. 

https://www.amazon.co.uk/gp/product/B0744D3D91/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

[Merlin66]

Like many filter suppliers the transmission curves only show the wavelengths which would impact on CCD imaging -  around 370 - 1100nm. A silicon based CCD/CMOS is only sensitive up to 1100nm.

52% of the total solar energy is in the NIR - 700 - 2500nm.

For visual the whole NIR region needs to be considered - up to 2500nm.

Looking at the Baader UV-IR filter (and I'm sure others) you'll see significant leakage occurs beyond 1100nm. 

[Mark at Beaufort]

18 hours ago, johninderby said:

I picked up one of these to test last week. 

https://www.amazon.co.uk/gp/product/B0744D3D91/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

That is an interesting product and I notice its graph does not go beyond 1100nm as Ken mentions above.

To be honest I am now more confused at the safety aspect of viewing the Sun direct. If the front filter or Herschel Wedge does not stop IR radiation beyond 1100nm and this is also the case with UV/IR filters can this in the long term have an affect on the eye.

In saying this I have not read any cases where the eyesight has been ruined. Also, I cannot imagine that some major research has not taken place regarding safe direct viewing of the Sun.

[Merlin66]

Good question!

I think it's due to our lack of knowledge and limited time in visual observing.

 

[astro_al]

3 hours ago, Mark at Beaufort said:

To be honest I am now more confused at the safety aspect of viewing the Sun direct.

Me too. I thought that the Solar Continuum filter was enough but now I am not so sure. The Baader chart only shows up to 700nm, SolarChat shows up to 1100nm; but I guess up to 2500nm is unknown.

 

[Merlin66]

Guys,

The jury is still out on the effects of NIR beyond 1200nm.

The EU protection standards only address the UV-VIS-NIR up to 1400nm.....no recommendations for >1400nm.

 

More of a note of caution rather that a definitive risk.

 

 

[Moon-Monkey]

Well this was interesting to say the least . As someone relatively new to regular solar visual observation this does make me think about getting a UV/IR cut filter regardless we can buy a filter but not new eyeballs 👀!!!