A "VERY RARE" macro lens?

Started Feb 17, 2013 | Discussions thread
wfektar
Contributing MemberPosts: 689
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Re: !!! MORE TESTS !!!
In reply to igoriginal, May 2, 2013

igoriginal wrote:

In today's most current digital cameras, there are actually several filters that are "sandwiched" together, to become called - collectively speaking - the camera "sensor" array.

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Instead, once a camera is "full spectrum" converted, the photographer can then decide which specific bandwidth that they want to create an exposure with, limited only by their imagination and the specific cut / band-pass filter that they then screw on to the front of a lens (which is tuned to pass through whatever wavelengths / bandwidths the externally mounted filter was designed for).
Of course, the photographer can also mount an externally threaded-on "hot mirror" filter, if and when they want to force their camera's color-interpretive sensory input back to "normal" (human range only) functioning.

All well and fine, but there's nothing sacred about the bandpass behavior in the Bayer array, and (in principle, at least) if the array were replaced with one that had red elements with much longer tails in the IR and blue with longer tails into the UV you'd have a "full spectrum" conversion that matches the native sensor response and still give you good daylight behavior.

It does make one wonder about the actual spectral behavior about the dyes used. One can go nuts and have the dyes also have differing bandpasses in the UV and IR tails, allowing some spectral discrimination there as well, just as they do in the visible. In principle, anyway: such dyes might not actually exist.

Although, admittedly, IR "faux color" itself, is interpretive in the end, and up to the artist.

So why does most vegetation (which is actually green) appear in an off-white or pure white color, when making an INFRARED exposure? Because most green vegetation REFLECTS all IR energy (while absorbing some UV-A energy). It's "luminescent" or "shimmering white" appears, hence, is consequently caused by all IR energy bandwidths being reflected by the plant and then sent to the full-spectrum sensor. Recall how I said that "color" frequencies repeat, at other multiples of our own, human perceptions of color (infinite "octaves"). And since most green vegetation reflects IR radiation (from sunlight), then it looks WHITE to a full-spectrum camera because it is yet another broad range of "white light" (violet through red, combined), only at a different bandwidth.

However, since Wratten #25 filter still permits the tail-end of the "human visible" bandwidth to pass through the it (deep red, and then all IR energy above it) ... then this is why the green vegetation appears as an "off-white" color, with a slightly reddish color cast (remaining red-end light mixed with full IR reflectance).

So, we cannot call this image so much "false color", as much as call it "color shift."
It may look surreal, but that doesn't mean its not there. It just proves that we humans are really NOT as special as we THINK we are, because there is a much broader world of energy out there that is invisible to our human eyes, although is visible to the eyes of some other life-forms.

Hopefully, all of the stuff I covered in this response made sense.

Again, all well and fine, but what you're really referring to is luminance, as there is no spectral discrimination in the IR (that we've characterized, at any rate). But this does make me wonder what the IR (and UV) behavior of the RGB dyes used in the array look like. We don't actually know that "it is yet another broad range of "white light" only at a different bandwidth" at the sensor, only at the Bayer array.

Thanks so much, for this!

No problem. Actually many of the technical guides there might be of interest.

Also, have you tested the apochromaticity of the lens? Do you ever see UV or IR bloat (that is, light at those wavelengths not quite coming to the same focus)?

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