Photographic Benefits of UV/IR Blocking Filter

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Christopher
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Photographic Benefits of UV/IR Blocking Filter

Post by Christopher » Wed Apr 24, 2019 4:28 pm

When solar photographers specify their hydrogen-alpha light path I often see a UV/IR blocking filter listed and I'm curious to know what specific benefits are derived particularly as it relates to the quality of the image (heat energy management considerations aside). Is there a placement requirement in order to achieve those benefits?
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Re: Photographic Benefits of UV/IR Blocking Filter

Post by marktownley » Thu Apr 25, 2019 6:49 am

Maybe it's a belt and braces approach from me - I have a few UV/IR filters I use in conjunction with solar. One sits ahead of my BF15 on my coronado 90 as there is no ERF I can see on this scope, so is predominantly the blocker (and etalon) dealing with out of band light, the UV/IR just turns back some of this energy off my blocker and will hopefully through reduced thermal cycling extend the life of my recently replaced ITF filter. I also use one ahead of my Quarks for the same reason. Currently in the process of sourcing a suitable UV/IR filter that passes CaK so I can use as a more efficient sub aperture ERF in CaK - Baader Blue doesn't let a huge amount of light through.


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Re: Photographic Benefits of UV/IR Blocking Filter

Post by Christopher » Thu Apr 25, 2019 3:50 pm

Hi Mark,
Thanks for responding. So it sounds like your usage is strictly for managing thermal energy. I think I understand those considerations. I'm also wondering about the impact on data collected during imaging and how that might affect the image quality (for better or worse). The PGR implementation of the IMX174, for example, has a spectral response curve from 380 to 1100nm and so is capable of registering some of the near IR energy. Assuming that energy makes it through a narrowband solar H-alpha light path (which the use of UV/IR filters would suggest is true) in measurable amounts and assuming it registers on the image histogram (also not sure) is the data of any benefit or detriment at that point in rendering an image? Stated differently, with the Baader filter eliminating data below 400 and above 700 is there any measurable data being lost and if so, what is its impact on the image?
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Re: Photographic Benefits of UV/IR Blocking Filter

Post by Montana » Fri Apr 26, 2019 7:09 am

Christopher, I always use a UV/IR filter when I image with my Solarscope. As cameras are so sensitive these days they pick up on the far infrared that many blocking filters do not block. I think the difference is extremely subtle but I get higher contrast by eliminating that far infra red. Just test and see, you will soon notice if it is a waste of time or not. Not all blocking filters are the same.

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Re: Photographic Benefits of UV/IR Blocking Filter

Post by pedro » Fri Apr 26, 2019 7:37 pm

I also use a UV/IR all the time, WL imaging mainly. It is important to block the far infrared as Alexandra mentions

For H-alpha imaging I use a Baader 35nm or 7nm filter (fitted to the nose of the camera) that are infrared blocked as well



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Re: Photographic Benefits of UV/IR Blocking Filter

Post by robert » Sat Apr 27, 2019 8:48 am

I use a Baader UV/IR filter for Ha and it definitely cuts out a slight foggy blur from far red light getting in the camera. When I first started CaK imaging with a Lunt B600 I used it and was very disappointed until I realised that it cuts out most of the CaK line! Only a very faint blurred image left.

I replaced it with an IR cut filter and that was a massive improvement for CaK. (Stupid!)

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Re: Photographic Benefits of UV/IR Blocking Filter

Post by skyhawk » Sat Apr 27, 2019 9:00 am

Do they make any difference for visual, thanks


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Re: Photographic Benefits of UV/IR Blocking Filter

Post by Montana » Sat Apr 27, 2019 3:10 pm

Skyhawk, no, because the eye cannot register these wavelengths. Eye health? no idea?

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Re: Photographic Benefits of UV/IR Blocking Filter

Post by Bob Yoesle » Sun Apr 28, 2019 11:52 am

I have seen first hand that if something can go wrong, it will eventually actually go wrong - at least for someone. So when it comes to safety, I'm pretty conservative. I also believe there is a reason most solar telescope OEM's incorporate IR blocking as a safety AND liability issue. Here's a slide I put together for my presentations on solar observing and equipment:

PPT eye safety.jpg
PPT eye safety.jpg (429.04 KiB) Viewed 916 times

From the solar irradiance at sea level curve, you can see there are potential eye health issues for both UV/IR A and UV/IR B for the cornea, lens, and retina, and this will increase proportionally with the area of the objective. Back when the aperture of H alpha systems were relatively small, the energy levels were not as significant as they are today with much larger apertures being employed, and the Macgyvered PST mods, etc. being put together. One therefore needs to take this into account with appropriate filtering, especially as telescope aperture increases. The ERFs employed by Daystar and Coronado - typically C/O/RG glasses - absorb very little IR:

Scott glasses.jpg
Scott glasses.jpg (90.82 KiB) Viewed 916 times

Secondary IR blocking is therefore needed, and is sometimes added via IR coatings to these absorptive glasses (Lunt, BeloptiK). Even so, some OEM filters can let a bit of IR through, as seen here as out-of-focus continuum in the top image, and corrected with additional IR filtering on the bottom:

IR leak.jpg
IR leak.jpg (218.44 KiB) Viewed 916 times

Additional IR Blocking can therefore be employed for both IR A - the typical DERF or UV/IR blocking filter, and IR B - a KG 3 type filter.

SS v Badr ERF.jpg
SS v Badr ERF.jpg (189.03 KiB) Viewed 916 times

This gives me a bit of security from both an eye safety and filter longevity (ITF, etc.) perspective.

Filter IR damage.jpg
Filter IR damage.jpg (288.86 KiB) Viewed 916 times

Just my 2 cents worth - as in my experience a little prevention is worth a lot of cure.


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Re: Photographic Benefits of UV/IR Blocking Filter

Post by skyhawk » Sun Apr 28, 2019 12:30 pm

Montana wrote:
Sat Apr 27, 2019 3:10 pm
Skyhawk, no, because the eye cannot register these wavelengths. Eye health? no idea?

Alexandra


thank you


Just for info, if I ever come over as "blunt" or upset it is not intentional, I am AUTISTIC, I have Aspergers, and ADHD, Autism, so my apologies if I ever sound, unintentionally confrontational. Thank you

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Re: Photographic Benefits of UV/IR Blocking Filter

Post by Christopher » Mon Apr 29, 2019 3:41 pm

Thanks to all who chimed in. It has cleared some things up for me (excuse the pun :P ). I can see how they benefit the image through narrowing the wavelength the camera is recording. Seems that this results in better contrast and structural details. No one indicated that they found the extra data useful or desirable. Seems a 1.25" could be quite useful. There are also some configurations where a 2" would be nice too, such as when a barlow or reducer is used on the nosepiece. I see where this is going :lol:


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