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UltravioletPhotography

Will this be enough? An IR blocking filter.


Andrea B.

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I found this at Edmund Optics: 675 OD4 Shortpass Filter

Here is its curve: Curve PDF

 

The curve does not show below 350nm, so I'd have to ask about that. Although one sort of assumes that shortpass means shortpass.

 

QUESTION: Is blocking IR to 1000nm enough for successful UV imaging if this shortpass filter were to be used over any of our UV-pass glass?

 

Thanks for any comments.

 

There are a number of other cuts besides 675nm, but that one seemed to have the most IR blocking range.

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Andrea, my picture the other day of that graffiti was with a filter that blocks to 1000nm. I don't know what the rolloff for that one was, but quite a lot of light gets recorded between 1000nm and 1100nm. I think 1100nm is probably the true cutoff for silicon so you'd better block out to that.
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It is not clear from this graph if the blocking extends far below 1 micron. I suspect it does not terminate there. I have taken IR photos easily with filters such as the Rocolax-1K (~1 micron longpass. ) So the answer to the question is, in the abstract, no.
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I have been intrigued by these filter coatings for quite some time as well. Shame they are so thick, rather needless given a fused silica substrate.

 

I always thought it would be cool to see the transmittance of a filter with the coatings from the 400nm, 500nm, 600nm stacked onto one ~1mm thick fused silica substrate.

 

Beyond ~1100 nm silicon becomes transparent so there is not much to work with north of 1 micron but some of the long pass filters out there do not have extremely sharp cutoff.

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It looks like that if I want to have an IR blocker from 690 - 1100, then I'll have to get something made specially. :( :wacko: :blink:

 

Why is it so hard to find good IR blockers?

 

John, have you looked at Edmund Optics OD4 UV bandpass filters? The have some really cool ones. Pricey of course.

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Andrea, a whole lot of stuff is transparent to IR, so that may be one reason? It's even been looked into for airport inspections. I have had great fun using the 1000nm filter with berries, to look inside:

post-94-0-18139500-1454471580.jpg

(Chokeweed berry, no-name 1000nm filter, Nikon Coolpix 995, unknown and long forgotten exposure settings. Lighting was by incandescent flashlight.)

 

Visible (same camera, automatic wb, same light)

post-94-0-51598600-1454471847.jpg

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