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02-05-2020, 07:48 PM   #31

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QuoteOriginally posted by JensE Quote
... except that the one you found was for HIE, not EIR and several search hits on EIR, which I checked, were all not accessible anymore. That included I didn't know that the site allowed browsing, so with the help of your remark I found it at, must have been moved after indexing. Looking at the diagram on page 7, the spectral sensitivity of the IR sensitive cyan layer extends to 900nm, but never drops very far in the visible spectrum - similar to a monochrome IR film, just with another sensitive peak at around 530nm, where HIR drops. All of the colors layers have blue sensitivity. That is indeed not exactly possible to replicate with a color sensor which mixing channels. Kodak writes: "As indicated in Figure 2, all three layers are inherently sensitive to blue radiation. To limit the exposure of each layer of color infrared film to only its intended spectral region, a yellow filter (minus blue), such as a KODAK WRATTEN Gelatin Filter No. 12 (or equivalent), is always used over the camera lens. With the yellow filter in place, the layers act as though they are sensitive only to green, red, and infrared (all blue radiation is absorbed by the filter)."

Color filters in front of sensors have overlapping sensitivities in order to achieve a good balance between luminosity and color sensitivity. (OT: Just by chance, one of my first hits while searching for sensor curves is a scientific article by DxOlabs - published in the proceedings of Electronic Imaging 2009 and is made available as an electronic reprint (preprint) with permission of SPIE - discussing this very topic.). A few measurements, which compare a unmodified cameras with 'full-spectrum' converted ones, can be found on JMC Scientific Consulting Ltd | Cosmetic science consulting, see e.g. Camera sensor sensitivity measurement UV to IR | JMC Scientific Consulting Ltd for a Canon 5DSR or Project Mirrorless ? Part 2, the camera conversion | JMC Scientific Consulting Ltd for a Sony sensor. So camera sensors do extend to 800nm, but lose quite a bit of channel separation. Tweaking a filter to work with the built-in color matrix in camera must result in a technically fairly rough approximation, tuned for the look to be similar for 'typical' subjects. In fact, given the dissimilarities, it's amazing how close they got. With a different filter and a custom color profile (fairly skewed), one could get a lot closer to the actual EIR spectral response, but it would always require external raw image processing.

I'm feeling an itch to have my rarely used K-5 converted, but I already have enough toys which I rarely find the time to play with ...
To summarize:
Two documents from the same site and different years: Kodak Docurment 1996 Kodak Document 2005

This does bring back memories for me. The pertinent paragraph relating to what I was looking for from the 2005 document is:
"Aerial / Technical Ground Photography
KODAK EKTACHROME Professional Infrared EIR Film is suitable in agriculture and forest surveys for the detection of crop yields, crop and tree diseases, insect infestations, and identification of tree species. Photographs of foliage made with color infrared-sensitive films often show great variations in infrared reflectivity when leaves visually show just small variations in shades of green. Healthy trees have a much higher infrared reflectance than diseased trees, so infrared results can distinguish between them. Healthy deciduous trees photograph magenta or red in spring and summer, while diseased trees may photograph from dark red to green or even yellow. In any given vegetation, the season, water or mineral content of the soil, or age may affect the results."

The bold text is why I was looking to use this emulsion back in the day. I would, however, change the word "trees" to leafy plants. It was demonstrated early on with false color photography, that plants growing in thin soils (think buried walls) did were not as robust as plants growing in deeper soils. In the Midwest US the Pre-Columbian villages had houses that were dug down into the ground and had structures of wood and soil built over the depression.
As simulated here: Mitchell Prehistoric Indian Village - Views of the Village (Yeah I worked there for a summer while I was in grad school it was just down the road from my in-laws) The house depressions were a darker green than the surrounding areas due to the depth and organic content of the soils. Interesting stuff - no I did not take any EIR images of the site - I did not have my cameras nor did I have and EIR film. (Grad students are really poor - shocking huh..)

Anyway, all of this talk has also made me interested in converting one of my older camera bodies into a "full spectrum" system. I have a Wratten #12 filter that would screw into my FA 50mm and I have a Wratten #87 filter, but I need to get a gel holder for it. I am sure that converting a older body and starting to shoot stuff with weird "looks" would drive my better half up the wall. Now, where did I put that unused box of "roundtoits".

---------- Post added 02-05-20 at 06:51 PM ----------

QuoteOriginally posted by stevebrot Quote
It's a sign! An ill omen! Flee pilgrim, Flee!

No problem, I recreated the best stuff.

Now all you converter people, have Kodak's spec/tech sheets on IR films. Now you can see if you are really technically replicating the film or are you just going for a different look.

02-05-2020, 09:49 PM   #32
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Some lenses suffer from hot spotting, a persistent flare that appears in the middle of images taken in IR this thread will tell you the lenses that are prone to this effect*. That thread probably needs to be updated for lenses on the K-1. [ Which brings up another question, Anyone ever had their K-1 adapted for full spectrum imaging yet?]

Kolarivision have their own list of lenses suitable for IR, It appears to be more up-to-date [2018] and they have information on lenses from other brands too. I'm not surprised at all to see all 3 of the FA limited lenses show up on the good IR performers list.

* It is said to be an undesirable effect of visible light coatings propagating Internal IR reflections, and this effect can be influenced by lens aperture.

Last edited by Digitalis; 02-05-2020 at 09:59 PM.
02-06-2020, 07:07 AM   #33
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QuoteOriginally posted by Digitalis Quote
I'm not surprised at all to see all 3 of the FA limited lenses show up on the good IR performers list.
I need to do more tests with more filters at different settings, but so far I have reservations about the FA 31 LTD on the (non-converted) K-1.
02-06-2020, 07:22 AM   #34
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If that is the case I may have to find my IR filter set and do some testing of my own. Personally, I have had few issues with the FA31 in IR.

02-06-2020, 01:41 PM   #35
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A quick synthetic test: I lit my white office door using a 100W warming lamp and a diffuse reflector - reasonably even, angled a bit (to avoid any danger of direct reflections), resulting in a slight gradient. The lamp produces a deep red light with supposedly a lot of near-IR light. Focused the lenses at infinity, but took pictures from ~1m distance. Lenses set at f/5.6, exp. -0.3, ISO800 - resulting in about 25s in aperture priority mode with the filter on. I took one shot with and one without filter (~1/5 s). I loaded the IR DNGs in Rawtherapee with the 'Neutral' profile and, after a short inspection making sure everything is in range, selected the unfiltered DNG as flat-field exposure. Then desaturated for B&W and saved the below. If anything is visible in the fairly flat "Neutral" profile, it may become relevant visually, starting from Neutral, most pictures need more contrast, making a hot spot more obvious.

The first one is from the FA31, the 2nd from FA77. I'd say with my cheap shiny 720nm Neewer filter, I need to be a little careful with the FA31, but it is still very usable. The hot spot is not stronger than the vignetting at wider apertures, just a lot more central and steep. Outdoors I observed some color shift. The FA77's is likely barely noticeable in practice. The faint contours at the top of the FA31 exposure btw. result from a piece of paper taped there and the softening of the flat field exposure (set to 100px here).

In conclusion, I'll read up on IR filters of different manufacturers to see what's worth buying in addition.
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02-06-2020, 05:31 PM   #36
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I don't know if those are real hot spots. Here's my example:
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