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Ilford SFX filter


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I am about to try Ilford SFX in 120 for the first time but am not sure which filter gives nearest to true IR results. From various places on the web it seems Hoya R72 is the best option but this is generally a screw on filter. I will be using various lenses/bodies so really wanted a 100mm x 100mm filter I could use on everything.  Lee filters do a 87c but from what I have learnt, one blocks light above 720nm and the other above about 850nm. Does anyone know if that makes a difference, what the extra filter factor would be, or better still has anyone used either, or both?

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I've shot a lot of Ilford SFX 200 in the 120 format through a IR720 filter. The filter came from China via eBay at a remarkably cheap price compared to the famous brands. I selected a 82mm diameter screw-in filter with a variety of inexpensive step-down adapter rings so that I can securely attach it to any of my lenses.

Because this filter blocks nearly 100% of visible light and transmits wavelengths of 720 nanometres and longer it enables SFX to display infrared image with a visible Wood effect for most green vegetation. Skies and water surfaces tend to go black and clouds stand out dramatically. The filter factor I use is 5 stops which means SFX has an effective infrared speed of E.I. = 6.

SFX is sensitive to wavelengths only up to about 760nm so it cannot see through a IR850 filter and no images will result however long the exposure.

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I believe last time I tried, I could almost see the brightest highlights through a 720nm filter.

Enough to know where to aim the camera.

 

But yes, the spectral area between that and the film cutoff is small. 

And yes I have one of the Chinese filters.

 

Note that you can also have fun with DSLRs, though again the sensitivity is low.

(And older ones are better than newer ones.)

 

It doesn't take many tries to find out the exposure needed.

-- glen

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