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Forums Lobby MASTER YOUR VISION Infrared & Ultraviolet (Public) topic #2965
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Subject: "950nm???" Previous topic | Next topic
slothead Gold Member Donor Ribbon awarded for his generous support to the Fundraising Campaign 2014   Frederick, US  Nikonian since 12th Aug 2009 Wed 03-Apr-13 10:42 PM
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"950nm???"



I placed an order last month (coming from the Orient - will be awhile!) for some IR filters and one of them appears on my order form as as a 950nm filter. I didn't order that, but before I cancel it - please!! - tell me what it is! I could understand something less than 720 or even less than 850nm, but 950nm? What will this do for me?

Tom
http://tjmanson.smugmug.com
D800, D750, and a handful of lenses.

  

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kds315 Moderator Awarded for his in depth knowledge and skills in a variety of subjects, most notably in Macro and Close-Up, Infrared and Ultraviolet Photography   Weinheim, DE  Nikonian since 15th Nov 2007 Wed 03-Apr-13 11:43 PM
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#1. "RE: 950nm???"
In response to Reply # 0



Allow you to have considerably longer exposure times (the positive way to put it) and purely b/w images.

For scientific use it makes sense (deciphering ink traces etc.) as was used for the Qumran rolls...

Cheers, Klaus
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Link(s) to the lens database (macro, UV, IR) as well as to my UV BLOG, plus many UV images here:
http://photographyoftheinvisibleworld.blogspot.de/
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NanoMeter   US  Registered since 17th May 2012 Thu 04-Apr-13 11:12 PM
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#2. "RE: 950nm???"
In response to Reply # 0
Thu 04-Apr-13 11:16 PM by NanoMeter


Hi Tom, The higher nanometer(nm) absorption type IR longpass filters tend to have more gradual tapered curves than the lower nm versions. Since the nanometer rating often denotes the 50% transmission point, this means that the filter may transmit lower than the actual rated nm (especially with more gradually sloped transmission curves). Take a look at the Schott longpass filters, they don't have the exact nm filter you describe, but you will see what I mean about the transmission curve taper, which is generally the case with other filters in the high range.

http://www.us.schott.com/advanced_optics/media/img/filteroverview_longpass_view.jpg

Schott doesn't have as many filter glasses in that range. Schott longpass filter glass jumps from RG850 to RG1000 (denoting 50% transmission).

You will also find that the equivalent Wratten numbers, 87B and 87A are in that same range and have slower more gentle sloped curves than the lower Wratten versions.

Now, keep in mind that some filters can be a combination of absorption glass with interference surface coatings.
Such filters often times have quite steep slopes, but can also tend to have uneven center to side color or anomalies in the resulting photos. An example of this is the Peca 908 (#87B), which although it is generically marked as an "87B" it has a much steeper slope than a Wratten 87B, and if you look at a graph of the 908 you will see an uneven transmission graph which often times will cause anomalies in the photos.
http://www.ir-uv.com/peca_94.jpg

However, Peca's 906 (#87A) is a class act, and is a quite true glass version of the stereotypical Wratten 87A type filter.
http://www.ir-uv.com/peca_93.jpg

NOTE: Peca makes excellent filters, and I believe they only have a couple filters that use such added coatings that can cause such anomalies.

Also I should mention Hoya has several filter glasses in that range.
Here is a list comparing Schott and Hoya longpass IR glass offerings:

Schott ~ Hoya
RG-830 ~ IR-83
RG-850 ~ IR-85
none ~ RM-86
none ~ RM-90
RG-1000 ~ RM-100

Without an actual transmission curve or a spectrometer to test the filter with there is no way to know what kind of animal you have.
However, if the pics look good, then I will be happy.


  

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swampwizard   Atlanta, US  Registered since 04th Nov 2012 Fri 05-Apr-13 01:38 PM
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#3. "RE: 950nm???"
In response to Reply # 2



Thanks, I've always wondered about the different NM's.I have a 950nm filter. Why is this filter good for color only?

  

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Forums Lobby MASTER YOUR VISION Infrared & Ultraviolet (Public) topic #2965 Previous topic | Next topic