KG3 IR Absorption vs IR Blocking filters? Same?

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KG3 IR Absorption vs IR Blocking filters? Same?

Post by MalVeauX » Wed Apr 11, 2018 4:59 pm

Hey all,

I broke a KG3 today. Looking to replace it for a DIY kit (the Skybender) that I use to image in 393nm and 540nm. Dunno how I broke it, but when I was tilt-tuning with the Skybender I heard a sound and looked in there and found the IR filter (KG3) with a total crack down the center. Only looking for 1.25" size.

Is a KG3 IR absorption filter the same as an IR blocking filter? I can readily find IR blocking filters. But IR absorption, like the KG3, is different maybe? It's only purpose is to reject heat and allow 393nm and 500~540nm pass.

Thanks!

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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by Merlin66 » Thu Apr 12, 2018 5:10 am

If you check out the KG3 transmission curve, you'll see it acts as a UV-IR blocker.
https://www.google.com.au/search?q=Kg3+filter&rlz
It looks a good match for 393nm (whereas "normal" UV-IR filters cut at around 400nm and effectively block the CaK.)
You probably should replace like with like. Adding just an IR filter won't cut the UV side.
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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by marktownley » Thu Apr 12, 2018 6:55 am

MalVeauX wrote:
Wed Apr 11, 2018 4:59 pm
Is a KG3 IR absorption filter the same as an IR blocking filter? I can readily find IR blocking filters. But IR absorption, like the KG3, is different maybe?
Hi Marty, KG3 blocks a lot further into the IR than a IR Blocker filter. I use KG3 in my CaK filter, also in a skybender (thanks Apollo!) I find it helps increase contrast when imaging,

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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by MalVeauX » Thu Apr 12, 2018 10:28 am

Thanks guys,

I just ordered a new KG3 from NewPort (same exact filter). Just was curious if there was a way to make it even better compared to absorption versus reflection, etc, regarding IR.

I'm mostly interested in 393nm with it, as an inexpensive way to play with near Calcium with a Skybender for now, rather than shell out for a Quark CA or Lunt CA (can't do the Lunt CA, if its limited to 100mm apertures, I don't want something that has a hard limit). Rarely see the Quark CA's used, or I'd get one. So until then, I'll fool with the Skybender. It does seem to work decently to show something significantly different from just white light. And I have a set of 532nm filters to use with it too, along with a 540nm filter, to play around in white light more and try to see if I can do better convection cells that way, as soon as the KG3 arrives to test it out.

Very best,

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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by Bob Yoesle » Thu Apr 12, 2018 1:41 pm

Remember that at 393 nm that 100 mm aperture is equivalent to about 166 mm of aperture at 656 nm. You can also go larger with more sophisticated ERF/blocking filter implementations.

viewtopic.php?t=16455
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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by MalVeauX » Sat Apr 14, 2018 3:32 am

Thanks Bob,

Experimenting with some older tech and older information, simply new to me! :)

Very best,

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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by MalVeauX » Mon Apr 16, 2018 4:22 pm

Hey guys,

Can't find it in any of the documentation, but does it matter which side of the KG3 is facing the heat source (sun)? I got it in today, but it's just the glass, and I have to put it in filter cell which I have, but just wanted to make sure it's not directional. One side has the KG3 printed on it plainly to see. But again, the documentation on the filter, and on the website, doesn't really cover whether it matters what direction or face the filter is used.

Ideas?

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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by marktownley » Mon Apr 16, 2018 4:52 pm

No it doesn't matter Marty
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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by MalVeauX » Mon Apr 16, 2018 8:07 pm

Thanks! Did the trick and took care of the heat, back in business.

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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by marktownley » Tue Apr 17, 2018 5:45 am

If you are using that with a 120mm scope on the nosepiece like that my money is that the heat will crack it.
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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by MalVeauX » Thu Apr 19, 2018 3:55 pm

I've been imaging this way for months and so far, no cracking. Granted, I image for maybe 30 minutes in the morning. I don't go for hours and hours all day with it.

What would your recommend?

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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by christian viladrich » Thu May 03, 2018 6:55 pm

A KG3 filter absorbs energy from the infrared.
In other words, the energy received is accumulated in the KG3. So the temperature of the filter increases untill an equilibrum is reached when the energy radiated by the filter equals the energy received.
But .. because an increase of temperature means dilation of the glass, and because the temperature is not uniform accros the filter, the dilations are not uniform accord the filter.... which means ... the filter breaks...

A dielectric (multicoated) IR blocking filter is a different beast. The substrate is transparent, which means it doesn't accumulate heat. This is the work of the coating to reflect IR. This is done with some energy losses, which means a very small amount of energy is transfered to the subtrate. This is very minimal. So, no dilation and no filter breaking (unless you use a large scope).

So, a dielectric filter is the way to go. But ... dielectric filters do not cut IR beyond about 1100 nm. This might be an issue or not, depending on the size of the scope.

Depending on the optical setup, the use of a red multicoated filter could also be a good option.
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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by TheSkyBurner » Sun May 06, 2018 12:10 am

beloptik sells an IR cut dielectric coated kg3 glass... I use it with a 120mm objective similar to yours, near the focus and it has yet to break :) I think sometimes it is just a case of bad luck with humidity from your area adding to the equation.

That skybender is a great piece of hardware, very useful ( i have seen several people posting images with it lately with admirable results) I have one too but cannot thank the person who gave them out for free, he doesnt answer questions anymore.

https://beloptik.de/de/uv-ircut-on-kg3-sperrfilter/

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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by christian viladrich » Sun May 06, 2018 8:52 pm

As you said, the Beloptik filter is a dielectric filter. The coating reduces the heat load on the substrate. That would be a different story with a KG3 with no coating.
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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by MalVeauX » Sat May 26, 2018 2:49 am

Thanks all,

I broke the KG3 already. It spent a lot of time in my 120mm refractor eating full sun and succame after a 3 hour session and broke.

So, that means I need to either look into this dielectric IR cut KG3 filter you're all mentioning, or I need to look into some kind of ERF. Gotta compare some stuff.

Would appreciate links to any of this stuff (USA here, if it matters). That link above to Beloptik is a filter that blocks UV, which means, it blocks the 393nm wavelength, and would not be useful for a Calcium set.... right?

I'm starting to really think about the Quark CaH and Lunt CaK at this point. Ugh.

Very best,

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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by Merlin66 » Sat May 26, 2018 3:18 am

I think you'll find the UV-IR cut excludes the 393nm.....
The Baader CCD Blue filter could be an alternative worth looking at. (# 2458470B)
I've just acquired one for testing on my Omega CaK stack.
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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by TheSkyBurner » Sat May 26, 2018 11:07 am

You gonna fry any filter that close to focus, you just need to move the erf away from the close focus. If you look at the lunt cak system, the first filter is like 100mm inside the focuser, this means heat is always an issue with calcium. Ithe iruv cut filter won do anything if you put it on the nosepiece. I think the skybender was just using it as a secondary erf and you just didnt get the memo for a primary erf,
You definitly need a prefilter well before the kg3 or have the kg3 mounted inside the focuser. Im assuming it was placed there at the noseto just prevent the more expensive 393 filters from popping first

I think

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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by TheSkyBurner » Sat May 26, 2018 11:08 am

That baader b ccd filter is definitly good, but its still gonna pop at the eyepeice in a 120mm scope. You need to put it on your first extension tube.

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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by TheSkyBurner » Sat May 26, 2018 11:08 am

That baader b ccd filter is definitly good, but its still gonna pop at the eyepeice in a 120mm scope. You need to put it on your first extension tube.

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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by TheSkyBurner » Sat May 26, 2018 11:12 am

One more note, i have a beloptik kg3 and it substantially worsens the kline imag, quite noticably on the computer screen inFact. Ive personally determined that a b&w ir uv cut filter works best, especially when combined with a b&w 010 filter.

Put that b&w combo on your b ccd filter and you got a perfecte kline erf

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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by TheSkyBurner » Sat May 26, 2018 11:25 am

Hey i was just looking at your other posts, you already have the erf filter you just got it placed in the wrong section of the skybender. That 395 filter is the erf and the kg3 is suppsed to go behind it. One of the 393filters go on the tilt module and the second one goes on your camera

That is a prefilter you got and the kg3 was the secondary, .

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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by MalVeauX » Sat May 26, 2018 1:03 pm

TheSkyBurner wrote:
Sat May 26, 2018 11:25 am
Hey i was just looking at your other posts, you already have the erf filter you just got it placed in the wrong section of the skybender. That 395 filter is the erf and the kg3 is suppsed to go behind it. One of the 393filters go on the tilt module and the second one goes on your camera

That is a prefilter you got and the kg3 was the secondary, .
Interesting,

That's not what Apollo (the guy that made this) said to do... I have it in the configuration he said it was supposed to be in when he gave it to me. But, I don't know any better honestly, so for all I know maybe it is wrong.

I'm at the point where I need to just pony up on a Lunt Cak or Quark CaH. :(

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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by TheSkyBurner » Sat May 26, 2018 1:16 pm

people do make mistakes, and judging by this erf lens he gave me I would say he had a helluv an erf system that isnt posted publically.

Maybe he intended for you to break the kg3 filters to show people that they are fallible, making the erf I have more popular?

Anybodies guess at this point, but you definitly have an ERF, just place it further up the focuser. You probably wont even need the kg3 filter anymore. Lunt systems dont use ir/uv cut filters; they just have a single UV bandpass filter according to another post in the mod section. And from the looks of the image, its super wide band .


Here is the post but sadly the user didnt upload the images on this forum it looks like and now they are gone.
viewtopic.php?f=9&t=24205

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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by TheSkyBurner » Sat May 26, 2018 1:31 pm

I just ordered the last 2" b-ccd filter from agena. Gonna install it in my skybender and test this thing out to see what kind of heat comes out the back of it. For 156$ is way cheaper than any semrock option and seemsto already have UV/IR cut applied to it according to the transmission spectra.

https://agenaastro.com/baader-2in-b-ccd ... 8475b.html

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Re: KG3 IR Absorption vs IR Blocking filters? Same?

Post by MalVeauX » Sat May 26, 2018 1:38 pm

Hrm,

So maybe, I could use something like this (2" to 1.25" adapter):

https://agenaastro.com/blue-fireball-m4 ... gJlDvD_BwE

Put the 395 filter I have on the nose of the extension tube, and put that into the focuser. Then, put the skybender (or any train with the 393nm filters) back towards the camera side.

I wonder if it would vignette big time.

Alternatively, I wonder if I can find a way to make an ERF for this in general, such as a 2" filter of some kind (like the blue filters?) and put that first, then the 395nm, then the 393nm?

Very best,

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