Steaphany
Well-Known Member
Question: How do you shoot IR photos with a SD14 ?
Answer: Put a Hot Mirror Filter over the lens.
As counter intuitive as this sounds, it's turning out to be what it takes. The reason is the Foveon imager is just too sensitive to the IR spectrum. Shooting with out the SD14's internal Hot Mirror filter opens up the IR spectrum, but the sensitivity over whelms anything recorded by the Green and Blue channels.
Prior to purchasing a LDP X-Nite CC1 filter to easily switch between IR and natural color photography, I tried a Tiffen Standard Hot Mirror. It turns out that the Tiffen filter is not strong enough to put the SD14 back into normal color balance, but IR is attenuated sufficiently so not to over whelm the imager. The result being images with the expected visible light colors plus an IR bias to the Red.
Here are some X-Rite Color Checker images demonstrating:
This is an image shot with the SD14's internal Hot Mirror filter installed, (that I shot prior to breaking it):
View attachment 1718
When the internal Hot Mirror filter is removed, this is the result:
View attachment 1719
Everything is some shade of Red and there is little Blue and no Green. This image is so far from the ideal that you can't correct the color by referencing a white or neutral grey.
Now, with the internal Hot Mirror filter removed and a Tiffen Standard Hot Mirror on the lens, here is the result:
View attachment 1720
and when color corrected:
View attachment 1721
Note that only some of the hues towards the Red end of the spectrum are off from their expected values.
When shooting a photo with this configuration, the resulting image is:
View attachment 1722
Color corrected:
View attachment 1723
Note that this is far from being a perfect photo, my goal was to see what I could get with a scene which included live plants which reflect a lot of IR along with soil and inorganic materials.
This highlights another issue, as the angle through the Tiffen Standard Hot Mirror deviates from perpendicular, more IR becomes attenuated leaving the IR effect greatest in the center and it diminishes towards the edges of the frame. This explains why the Sigma internal How Mirror is so thin and fragile. They need to minimize the effect of edge of frame light being color shifted.
I still have to run more tests and see about achieving a uniform IR effect across a whole frame, but at least I have things a lot closer.
Answer: Put a Hot Mirror Filter over the lens.
As counter intuitive as this sounds, it's turning out to be what it takes. The reason is the Foveon imager is just too sensitive to the IR spectrum. Shooting with out the SD14's internal Hot Mirror filter opens up the IR spectrum, but the sensitivity over whelms anything recorded by the Green and Blue channels.
Prior to purchasing a LDP X-Nite CC1 filter to easily switch between IR and natural color photography, I tried a Tiffen Standard Hot Mirror. It turns out that the Tiffen filter is not strong enough to put the SD14 back into normal color balance, but IR is attenuated sufficiently so not to over whelm the imager. The result being images with the expected visible light colors plus an IR bias to the Red.
Here are some X-Rite Color Checker images demonstrating:
This is an image shot with the SD14's internal Hot Mirror filter installed, (that I shot prior to breaking it):
View attachment 1718
When the internal Hot Mirror filter is removed, this is the result:
View attachment 1719
Everything is some shade of Red and there is little Blue and no Green. This image is so far from the ideal that you can't correct the color by referencing a white or neutral grey.
Now, with the internal Hot Mirror filter removed and a Tiffen Standard Hot Mirror on the lens, here is the result:
View attachment 1720
and when color corrected:
View attachment 1721
Note that only some of the hues towards the Red end of the spectrum are off from their expected values.
When shooting a photo with this configuration, the resulting image is:
View attachment 1722
Color corrected:
View attachment 1723
Note that this is far from being a perfect photo, my goal was to see what I could get with a scene which included live plants which reflect a lot of IR along with soil and inorganic materials.
This highlights another issue, as the angle through the Tiffen Standard Hot Mirror deviates from perpendicular, more IR becomes attenuated leaving the IR effect greatest in the center and it diminishes towards the edges of the frame. This explains why the Sigma internal How Mirror is so thin and fragile. They need to minimize the effect of edge of frame light being color shifted.
I still have to run more tests and see about achieving a uniform IR effect across a whole frame, but at least I have things a lot closer.