色之不同

同一個相機， 如果沒有內置濾光鏡， 就可以拍出4種不同“色”來：

普通： + 紅外濾鏡（去掉紅外）S8612

紫外:  +紅外濾鏡S8612+ 可見濾鏡（去掉可見）UG11

紅外： +可見濾鏡UG11

全波段： 無濾鏡。 因為相機的紫外靈敏度比較差（我算了一下， 與可見光差10EV， 就是如果可見是曝光為1/400秒， UV為 （3秒左右）， UV的量應該是可見的1/1024），所以基本上是紅外+可見, 紫外太少了。

 

A play of colors under various light conditions.
Acronyms: UV=ultraviolet, VIS=visible light, IR=infrared.

Method：
Camera: Panasonic DMC G5 full spectrum converted.
IR: camera + UG11 (no VIS, UV is negligible)
UV: camera + UG11 + S8612 (no VIS, no IR, only UV allowed)
VIS: camera + S8612 (no IR, UV is negligible)
Full Spectrum: camera only (all light allowed in, but CCD sensitivity is low to UV so most of the time UV negligible, mainly IR+VIS).

UV and VIS shots are white balanced in camera, IR is either converted to black and white or using Kelvin scale in side the camera. Full spectrum photos are simply balanced with automatic.  Exposure adjusted by photoshop but no other changes.

1. I took four petals, each from one color, all flowers are begonias. Under infrared light, you cannot really tell which flower has what: they are supposed to be white, yellow, pink and red.  Can you guess which one is white and which is red, at least? I think not.


2. This is under UV. Now we see something more interesting. The top one is nearly black while the lower one is light blue. Still I would have guessed that the top one is red which would be wrong.


3. Now we see which is which! I am a bit surprised that red is　lighter than yellow under UV. If I desaturate this photo to make it black and white, red will be slightly darker than yellow.  


4. Under full spectrum (with visible light + IR +UV, although UV is really at very low levels), the color more or less the same as normal (what we see) with a pinkish tint to everything. I have not tried white balance this with a Teflon to see if it would look better.

5. now we play with some real flowers. Under IR, they all looked the same -- we cannot tell what color they will be.


6. Under UV, the geranium is blue, evening primrose retained its yellow (but remember since the true yellow is blocked by UG11, this yellow is a false color with certain wavelength of UVA).  The three types of asters all are highly UV absorptive.


7. Now we can see the asters, one is a tick-seed (Coreopsis), a daisy (Chrysanthemum), and a flee-bane (Erigeron sp).　They are either yellow or white, of course, since there is no such a thing as a black aster (with the exception of some dahlias so deep purple they can be almost black).

8. Full Spectrum shot of the same flowers.