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UltravioletPhotography

Anybody Know this Filter Please ?


colinbm

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I have found a reference to a filter I have been looking for....

It is similar to a BG3, but with a longer bandpass...

TransmissionCurve.jpg

 

http://droneyard.com/wp-content/uploads/2013/08/SchottBG3.gif

 

The only clue I have is it was used for plant stress detection & they called it an NGB filter, I am guessing that means......No red, Green + Blue.

I would love to have a piece of this glass :)

Cheers

Col

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Yes I appreciate that Bjorn, I'll have to deal with that, but it is the UV, Blue & Green, I want.

It is between the BG3 & S8612 that I have been looking for.

s8612.gif

Cheers

Col

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enricosavazzi

I believe NGB means Near-infrared, Green, Blue. Basically, it suppresses much of the red and transmits the rest of VIS and NIR. It also happens to transmit UVA, but this band is hopelessly swamped by the VIS and NIR transmission if daylight or a similar artificial source is used.

 

The NGB filter is/was used in some converted cameras, to record the blue of the sky and some of the green of vegetation together with NIR.

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Yes, that is what I am looking for Enrico.

Do you know where I can get some please.

52mm will be fine or even down to 1 1/4" astro is OK.

I can cut & mount any piece I can get :D

Cheers

Col

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The shape of the curve tells me it is a dichroic (not pigment-based) filter. Other than that, I can tell you little. Stacking on something like a 650SP would knock out the red and IR, in principle, though it were better this be something pigment-based (if that exists.) Stacking dichroics can do funny things sometimes.
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The transmission spectrum you posted appears to me to clearly be a dichroic type, with a considerable deep red pass band 690-770nm.

However, as you say an absorptive filter has advantages. I ordered one of the Public Lab "infrablue" DIY filters. It is likely just some type of blue gel.

I will post a transmittance spectrum once I have it in hand.

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enricosavazzi
For what is worth, I was not able to source any NGB glass of usable sizes for our typical purposes. It seems there is little demand for this type of filter.
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Editor's Note: I am moving this technical topic from the photo section to a technical section.
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I was just going to mention that!! ;)

That Ebay seller uviroptics might be able to tell you more about the filter or filter stack you are looking for. He has been investigating filters for some time now.

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