Public Lab Research note


How to tell if my filter is a Rosco 19

by shinnen | March 15, 2019 23:38 | 60 views | 8 comments | #18564 | 60 views | 8 comments | #18564 15 Mar 23:38

Read more: publiclab.org/n/18564


Hi,
I have a filter that 'appears' to be the same colour as the Rosco 19 filter, on the Rosco website. How can I tell if it is the same colour?
Thanks,
.... john


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8 Comments

A red filter used to convert a full spectrum camera (IR cut filter removed) to an NDVI camera must pass red light and NIR light but no blue light. Rosco publishes spectral transmission graphs of all of its filters, so we know the Rosco #19 meets these specifications. To learn the specifications of an unknown filter some type of spectrometer device is required.

You can also just try it and see if you get reasonable results.

Chris

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Hi Chris, I have two dedicated IR cameras, a Sony DSCV1 and a Sony F717. Should I be able to use these, and simply put the filter in front of the lens? When you say,'reasonable results' can you refer me to the location, presumably on the Publiclab site, that describes what 'reasonable results' are? Thanks, ....... john

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I don' t know what a "dedicated IR camera" is. You can use an appropriate red filter on a full spectrum camera to capture mostly NIR in the blue channel and mostly red in the red channel.

With an appropriate camera and filter, and with an appropriate calibration or custom white balance, NDVI values for healthy foliage in sunlight will be between 0.2 and 0.8 and NDVI values for non-foliage will be below 0.2.

Chris

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Hi Chris, I suppose 'dedicated IR camera' is not the best term. I simply have a DSCV1 and an F717, which are capable of 'normal colour photography, and infrared. "You can use an appropriate red filter on a full spectrum camera to capture mostly NIR in the blue channel and mostly red in the red channel." So, are you saying that any colour camera (not converted to IR) is good for NIR by placing the Rosco 19 filter in front of the lens? ... john

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A full spectrum camera is one that has been converted to capture NIR by removing the IR cut filter. This filter which is present in all standard cameras blocks NIR so must be removed before the camera can be used to capture NIR.

The basics of this process are described here: https://publiclab.org/wiki/ndvi-plots-ir-kit

Chris

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Hi Chris, Ah, I misunderstood the term 'full spectrum'. Now I get what your saying. So, a full spectrum camera does not have visible light block filter. That explains a lot. Thanks again for your help, and patience. .... john

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Hi, John, where did you get the filter? 

On Fri, Mar 15, 2019 at 7:39 PM \<notifications@publiclab.org> wrote:

Public Lab contributor shinnen just posted a new research note entitled ' How to tell if my filter is a Rosco 19':

Read and respond to the post here: https://publiclab.org/notes/shinnen/03-15-2019/how-to-tell-if-my-filter-is-a-rosco-19


Hi,
I have a filter that 'appears' to be the same colour as the Rosco 19 filter, on the Rosco website. How can I tell if it is the same colour?
Thanks,
.... john


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Hi Warren, I bought it a long time ago. It's square, and had "2A" with the '2' circled. I've tried to find out what that mean, but have not succeeded. ... john

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