Solar UV/IR Rejection Filter

[Eris (Gerard)]

Hi everyone my question is can I use an Astronomik CLS CCD as an IR energy rejection filter in front of my Quark for Solar observing. I’ve been told that I must use some kind of IR energy rejection on my 120/900 f7.5 scope. The Bader UV/IR Cut filter has been suggested as well. The short of it is that I already have the 1.25 CLS CCD filter and the transmission curves look better than the Baader filter.
Can any of you experienced Solar Observers please advise if the CLS CCD will do the job?

[Merlin66 (Ken)]

Gerard,
As you say the filter curve for the Astronomik looks as capable as the Baader UV-IR filter - I would agree with you.
I would look an either of these filters as a minimum for your Quark and 125mm aperture.
A Baader Ha 30nm CCD filter would be a more versatile filter and even more safe.
Just my opinion-I don’t have or use a Quark but have many other solar scopes.

[Eris (Gerard)]

Thanks for the info Ken. I also have an Astronomik Ha 6nm filter. How would that go? Is it too narrow?

[Merlin66 (Ken)]

Gerard,
The curve for the 6nm filter looks good.
Worth trialling.

[Dave882 (David)]

I’m fairly new to the solar game but last year picked up a second hand quantum SE (similar to quark) that I’m running on a 127mm refractor with 4x extender. I’m using the optolong CCD Red filter as erf. Visual only at this point.
It’s just stunning on the prominences but probably a bit too bright so that the surface detail is difficult to enjoy. Also my eyes feel a bit overworked (dry and sore) after a session of a couple hours. I think the narrower Ha filter would be better but I’ve not tried it yet to confirm if it makes the image dimmer. Would love to know your findings if you do try it.

[iborg (Philip)]

Hi David


Would a neutral density filter be useful? I assume after most of the energy has been removed from the system!


Or a simple disk with a hole to reduce the aperture somewhat?



Philip

[Eris (Gerard)]

Thanks again Ken. This approach is only for imaging anyway. The scope is 120 mm so I’m hoping it’s under the limit of extreme. There’s only one way to find out given the cautious ok’s I’m hearing from everyone.

[Eris (Gerard)]

Hi Philip and David. Thanks for your input.
Re ND filters, I would be wary of them unless I saw a reliable transmission curve but even then it would need to block out the Ultraviolet and Infrared ends of the spectrum. Stopping down would help with lowering brightness but would not block out UV/IR.
David if visual observing may I suggest that your red filter does have an efficient UV/IR block.
I am going to go with Ken’s suggestions and use the Ha 6nm filter as an ERF and see what the outcome will be as most people I've contacted are thinking the same way.
I’ll let you know what happens but wouldn’t you know the weather forecast here isn’t looking too promising over the next few days.
Thanks for your ideas and suggestions.

[Dave882 (David)]

Originally Posted by Eris

Hi Philip and David. Thanks for your input.
Re ND filters, I would be wary of them unless I saw a reliable transmission curve but even then it would need to block out the Ultraviolet and Infrared ends of the spectrum. Stopping down would help with lowering brightness but would not block out UV/IR.
David if visual observing may I suggest that your red filter does have an efficient UV/IR block.
I am going to go with Ken’s suggestions and use the Ha 6nm filter as an ERF and see what the outcome will be as most people I've contacted are thinking the same way.
I’ll let you know what happens but wouldn’t you know the weather forecast here isn’t looking too promising over the next few days.
Thanks for your ideas and suggestions.

Hi Gerard- yes you’re 100% correct I don’t think Philip was suggesting using a ND filter instead of the Red but in addition too. Red filters CCD (not planetary) and Ha filters are recommended due to the fact that they inherently have the Uv/IR blocked due to only passing the designated wavelengths. The rest is reflected back up the tube.

[Eris (Gerard)]

Hi again David. Thanks for your comments.
Yes, it is an interesting challenge to get things
right and stay safe. I’m looking forward to
a positive outcome to this project.

[Merlin66 (Ken)]

Bottom line with any effective energy rejection filter (ERF) is to pass the wavelength of interest (in this case H alpha which is only 2A wide) and block at effective ND5 all other wavelengths from UV though to NIR (and beyond if possible)
Ha Narrow band filters (Baader, Astronomik etc) can have bandwidths from 3nm (30A) to 30nm (300A) which more than cover the Ha line. They also have very good blocking - at least up to 1100nm. The available transmission curves rarely go beyond this limit.



This is the response limit for silicon based chips ie CCD and Cmos. There is still some solar IR beyond that point but not visible to the eye but in some limited professions -glass blowing, furnace work etc long exposure can be a concern.


(I had headaches - figuratively! making an ERF for CaK wavelengths. Normal UV-IR filters cut at 400nm whereas I needed to get down to 393nm. In the end the ERF was a combo of four filters which gave a narrow bandwidth coverage of CaK and blocking all the way through to NIR)
With the SHG for imaging visual wavelengths, a Baader ND0.9 and a Astronomik L1 UV-IR filter combo does the job.

[iborg (Philip)]

Hi All


Just for clarification - the suggestion of an ND filter was definitely as an additional filter, after UV/IR etc blocked.


Philip

[Eris (Gerard)]

Thanks Ken and Phillip for your replies and clarification. It obviously makes sense.
Ken that’s a very interesting combo re the CaK side of things. This where the whole question got started with looking for my L filter as a UV/IR block in my old RGB filter set, which I couldn’t find. I think that L filter equates to today’s L2.
Its been an interesting journey which has revealed a number of options. Thanks for your ideas and views.