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Infra Red Blocking

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#1 Tel

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Posted 03 March 2013 - 06:12 AM

Hi Folks,

I'm trying to get to grips with the use/need for infra red blocking but still remain somewhat confused. I hope therefore you can help me understand its purpose more fully.

For example: some years ago, I bought a Mk.1 Meade DSI, just after they hit the market, which possessed an IR filter below the nose piece adapter and which I understood to be necessary in preventing star "blobbing" in the image.

By the same token, I understand that I need, and indeed use an IR blocking filter attached to my Phillips' webcam, (SPC900NC), for planetary and lunar imaging.

Again: my standard Canon 350D has an in-built IR filter in order, (as I understand it), to produce accurate colour reproduction in terrestrial images.

However, my last year's acquired Atik 314L+ does not appear to have any IR filtration/blocking at all.

Furthermore, I understand that if (as I wish to do), combine this monochrome camera with RGB filters, these in themselves should be purchased with integral IR blocking, (e.g. Baader series), as opposed to those "run of the mill" colour filters designed purely for visual use.

Could anyone, therefore, please clarify where IR blocking fits into the scheme of things and whether the Atik, when used in monochrome only, would benefit from such.

I would be grateful for any responses you may care to provide,

Best regards,
Tel

#2 D_talley

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Posted 03 March 2013 - 11:46 AM

You are mixing apples and oranges. The IR filter in the DSI , SPC900 and Atik is to reduce star bloat.

The IR filter in the DSLR is to correct the color in normal photos. This filter also stops Ha which we want. This filter is normally removed for astro photos.

You would add a different IR filter to the DSLR if you take photos with a refractors telescope to reduce star bloat.

Visual filters do not block the IR since the eye cant see it. You cant use visual filter for imaging because of this. Normal imaging filters block all except the color they are made for. That is why your mono camera did not come with a filter, they expect you would be using LRGB filters with it.

#3 Tel

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Posted 03 March 2013 - 01:25 PM

Hi Dwight,

Many thanks for the input. my apologies though: maybe I mislead you by not having make myself clear in the above post, but you're only confirming that which I already knew or assumed, via, I hoped, through the examples I gave.

What I was trying to ask was, whether IR blocking IS essential to the removal or at least reduction of star bloating, (as I assumed it to be), and therefore whether my Atik 314L+, which apparently does not possess such a blocker, would benefit from the use of one ?

If this is so, it's surprising, at least to me, that these relatively cheap filters are not included in the price of such a CCD camera costing £1000 ($1600) here in the UK.

Many thanks once again and best regards,
Tel

#4 Charlie B

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Posted 03 March 2013 - 02:04 PM

Tel,

I believe that IR blocking is needed in refractors, but not in reflectors. The star bloating, I think, is caused because the refractors don't focus IR tightly and, while your eye can't see it, the ccd is sensitive to IR. Generally, refractors don't have this kind of color dispersion. However, I suggest that you always want to use an IR blocking filter on the nosepiece of your camera.

Regards,

Charlie B

#5 neptun2

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Posted 03 March 2013 - 05:25 PM

As Charlie says the IR and UV blocking is needed if you use refractor as telescope because even the APO refractors are corrected only for the visual spectrum and not for UV/IR. The cameras are sensitive to UV/IR plus the visible spectrum so such filter is needed for refractors if you don't want to see star blobbing. The photographic LRGB filters include UV/IR blocking so if you use such with your Atik you should not worry about such problems.

#6 Tel

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Posted 04 March 2013 - 04:41 AM

Hi Dwight, Charlie B and Neptun 2 !

The need for an IR filter application to my Atik 314L+ was as I suspected but many thanks for the more detailed explanations and reasons of which I wasn't aware ! You have more than answered my question ! :bow::bow:

Best regards,
Tel

#7 Rick J

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Posted 04 March 2013 - 03:16 PM

The photographic LRGB filters include UV/IR blocking so if you use such with your Atik you should not worry about such problems.


True but if you have a CRGB filter set the C (Clear) filter has no IR block. The debate rages on whether it is advisable to use C or L with reflecting telescopes with reasonable arguments on both sides depending on your goals.

I bought my first filter set used and the seller had no idea if his was a clear or luminance filter. Simple to test -- if your IR TV remote works through the filter it is a clear filter if it doesn't it is luminance. Turned out his set was LRGB.

Rick

#8 Konihlav

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Posted 05 March 2013 - 03:41 AM

lot of good stuff was already said, I only add what I just wrote in a related thread:
www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5713775/page/0/view...

hungerford:

- if you are using an achromatic refractor (or anything other, just very low-end type (cheap) telescope) than that's pretty normal

- even an ED refractor is not perfect in UV, i.e. namely in Blue channel the UV leaks in and makes really bigger B-channel stars then it should (on one side, the B-stars are normal to be bigger as stars are either yellowish or bluish and that color must be shown somehow, on the other side, using e.g. IDAS LPS-P2 that cuts out UV or Baader UV/IR Block that blocks from 420nm to 6xx something really helps! - I am using it with my ED).

- CCD filters - are you using dedicated LRGB CCD filters for CCD imaging? they are supposed to cut UV/IR. But that's not completely true. The Astronomik or Baader or OrionUSA filters are far from perfect, they all leak. On the other side Astrodons are "perfect" but have other problem - in the Blue color they pass 100% (have 100% transmittance) already before 400nm wavelength (like from 380nm up) and this is problem for all refracting optics (lenses...) while this is perfect for mirror systems (reflecting optics). I am using Astrodons with IDAS LPS-P2 or with Baader UV/IR when I do LRGB imaging with my only ED-like telescope. For Newtonian I do not need to.

what I describe are common issues that took me 2-3 years to understand and discover and resolve :)

good luck!



#9 cn register 5

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Posted 05 March 2013 - 03:29 PM

I'm interested in your statement that the Baader UVIR filter is leaky. From what I can see from the published data http://www.alpineast...r_cut_specs.htm there's no leakage in UV or IR - at least not until you are at a wavelength of more than 1100nm and AIUI the CCD comeras are not sensitive to that wavelength.

Where is the leakage coming from?

Chris

#10 Konihlav

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Posted 05 March 2013 - 03:39 PM

you understood it wrong or I was not precise in my description. In any case, I use Baader UV/IR filter for cutting out the UV and IR and this one works great. This one is perfect no leakage...

#11 Konihlav

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Posted 05 March 2013 - 04:15 PM

other Baaders are also most probably safe, I can't really tell on that one as I did not measure this brand on a spectrometer myself (I am believer who like to test himself to see who is fair (e.g. Astrodon) and who is not (e.g. Astronomik)). The IDAS LPS P2 and V4 and Baader UV/IR are filters I really like to use on my ED lens.

#12 cn register 5

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Posted 05 March 2013 - 04:53 PM

Thanks for the clarification.

I know the Baader Visual OIII filter leaks because the TV remote works through it but the CCD filters seem OK. That's a pretty crude test but I don't have a spectrophotometer handy.

Chris

#13 andysea

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Posted 06 March 2013 - 12:32 AM

Hi Pavel
If I understand this correctly you are worried that the Astrodon might leak some light in the UV range and therefore create issues withe refractive optics. Is that correct? I am interested because I use the same filters.
Is some UV really a big issue?

Thanks
Andy

#14 Konihlav

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Posted 06 March 2013 - 02:18 AM

Chris - that's correct. Visual filters obviously pass/leak out of band spectrum.

Andy - that is not correctly put. It is not leakage (in terms where it means something BAD), it is in-band transmittance that is very high and this both is a very GOOD thing! So Astrodons are top-notch best filters though a bit pricy (but we know why, quality, coatings, durability, ...). I have only pointed out that both I-series and E-series Blue filters from LRGB set from Astrodon are so very good filters that they pass even around 400nm spectrum (this is all superb for reflecting optics and astrographs) and this is not good for refracting optics (ED lens, for instance). Therefore I strongly recommend for refracting optics to use either the Baader UVIR 420-6xx blocker or IDAS LPS-P2. That's for LRGB imaging with "poor" ED lens :) may you experiment yourself and see...

#15 Konihlav

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Posted 06 March 2013 - 02:23 AM

to put it the other way - it's not about filters (in case of Astrodons), it's about the quality of optics you use with them (the same BTW holds true for so called parfocality, it's something not related to your filters, but to the optical system you are using). I have point out that cutting the 20nm more from 400nm in UV-Blue part is really not a bad thing when using refractive optics :) that's the whole point.

#16 Konihlav

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Posted 06 March 2013 - 02:28 AM

Hi Pavel

Is some UV really a big issue?

Thanks
Andy


yes and no (this answer can be given to any astrophotography related question as it always depends on conditions - and not a single one, but a raw of variables).
YES for CCD chips that are more sensitive in B range (like e.g. KAI-4022, KAI-11000, ICX285, ICX694/674) and NO for CCD chips that have a peak QE curve shifted towards R range (like e.g. KAF-3200, KAF-1603, KAF-6303). The common KAF-8300 is kinda in between.

#17 Tel

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Posted 07 March 2013 - 03:18 AM

The photographic LRGB filters include UV/IR blocking so if you use such with your Atik you should not worry about such problems.

True but if you have a CRGB filter set the C (Clear) filter has no IR block. The debate rages on whether it is advisable to use C or L with reflecting telescopes with reasonable arguments on both sides depending on your goals.

I bought my first filter set used and the seller had no idea if his was a clear or luminance filter. Simple to test -- if your IR TV remote works through the filter it is a clear filter if it doesn't it is luminance. Turned out his set was LRGB. Rick


Hi Rick,

Many thanks for the input. I was aware of the difference between "clear" and "luminance" but wouldn't have known how to tell 'em apart unless there was some description. That test however, with the TV remote, is brilliant ! I've got a reasonable technical background but would never of thought of that one ! :bow::bow:

Many thanks and best regards,
Tel

#18 Tel

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Posted 07 March 2013 - 05:43 AM

A last question on this topic, guys, if I may ?

In the UK here, we have a supplier offering a set of unblocked LRGB filters for £85 while the Baader blocked set comes at over twice the price.

However, given that an all singing, all dancing IR blocking filter can be bought singly at relatively low cost, what is the advantage in using an expensive set of individually IR blocked filters rather than merely placing a single IR blocking filter either directly on the nose-piece of the camera or before each cheaper, unblocked colour filter contained, for example, in a filter wheel ?

There has to be a sound reason why this is not, seemingly, a viable route to simple, and at the same time, all encompassing IR blocking in LRGB imaging.

Best regards,
Tel

#19 Charlie B

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Posted 07 March 2013 - 07:32 AM

I use a single IR blocker on the nosepiece. The disadvantage is the it requires an extra filter and you are passing the light through more glass.

The advantage is that it is cheaper and a little more flexible to use by combining with a clear and RGB in a filter wheel or with an unblocked light pollution filter.

Charlie B






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