Friday, November 9, 2018

My History: Re-Inventing the Digital IR Ektachrome

Over the years, I have done shoots for music bands using one of my full spectrum converted cameras with vis-infrared filters to create faux color spectrum photos. I use my own proprietary filters to achieve different effects.






The infrared appeal comes from early work in infrared film of artists such as U2, Jimmy Hendrix, and many photos by Elliott Landy.


Dylan taken by Elliott Landy using Kodak IR Ektachrome


U2 B&W infrared film for "The Unforgettable Fire" album


Jimmy Hendrix album, probably the first to use IR Ektachrome film

In around 1997, I used a version of Kodak IR Ektachrome (EIR) film for work in environmental sensing, to examine agriculture health using the Normalized Difference Vegetation Index, and other Indices of similar nature.  The Kodak IR Film allowed one to calculate how "red" vegetation was in order to determine early crop failure, it other applications of interest to the USGS or government.




The process was tedious. You manually exposed the Kodak IR Aerochrome (the film for aerial platforms), developed it at specialized labs, or with specific chemical processes, and used ancient optical scanners to get values through photodosimetry; and finally calculating values by the NDVI, or other algorithms we had developed.

 In late 1999, acquiring my first digital camera at work, and promptly dropping it, I took the broken device apart in a clean room, and found the infrared cut filter ("hot mirror") had been cracked.  I carefully stripped the glue and removed the filter.  After putting it back together, I found the camera had strange coloration.  It didn't take long for me to realize that it was sensing the near infrared, and knowing a little about silicon materials for detectors, I began experimenting.

I wanted to reproduce the near-infrared color film we used in remote sensing, and gather the data digitally, so I could avoid the tedious scanning and dosimetry processes.  Then I could easily gather data and more whichqu prices, analyze and exploit the techniques I was refining.

That camera, and every camera I've converted since is a full spectrum camera from near UV, visible to near infrared.  I modulate the transmitted spectrum with filters over the lens or between the back of the lens and the detector.

My first attempts, using sea-green filters, gave pale pink vegetation, not the rich red one sees in EIR film, where a military object appears greenish, but the vegetation stands in contrast with it.  While I've created and patented techniques that work even better than the EIR film for multispectral and hyperspectral imaging applications, I still pursued the digital equivalent to EIR film.




Scenes like the one below, created with the EIR film, are iconic.  And I realized a few years later, the vegetation , while having the same hue, was more saturated and darker--indicating, EIR film was less sensitive to the near infrared than the converted digital camera using a deep sea green filter.


Photo by lomography.com

I grabbed my sample packs of gel filters and examined each under the LCD of my converted digital camera with an R72 filter, again over full spectrum camera, to see which of the filters appeared darkest in the infrared.  Most were highly transparent in the IR, but two stood out: Lee Gel Medium Blue Green and Lee Scuba Blue.


R72 photo of gel filters


Admittedly, nearly 20 years ago, I had a far more limited palette of gels to try, and today, the ones I'm discussing are closest to what I found worked then.  I've since tried both of the Lee filters mentioned, and the scuba blue, darker than the other, provides a much closer feel to the original EIR film, when custom white balancing off of a grey card.


Photos taken in my neighborhood.  Scuba Blue Gel filter only


Scuba Blue Gel filter only

As close as it is, I wanted to get a more faithful reproduction of the famous remote sensing EIR film. You'll note the above photos have slightly lighter vegetation, and the street is also pink.  The sky is dark (but blue).  The scuba blue still passed a little too much near infrared.  I added a Schott KG3 glass in front of the lens.


Schott KG3 + Lee Scuba Blue


Schott KG3 + Lee Scuba Blue

The above photos, combining an inefficient hot mirror with a Scuba Blue gel, was taken with custom white balance on a grey card, and exposed normally.   There is no post processing or color tweaking.  This is out of camera.  For all intents and purposes, it appears like the original EIR film.

You can get the Scuba Blue in a sheet for less than $10.  The Schott KG3 glass is a little more pricey and rare.  However, Rosco (another gel maker) sells a cheap inefficient hot-mirror glass, called the Permacolor #8000 which can be had for $12-30, depending on the size--and you can get it cut to your filter size, as needed.

The following were taken with only the Scuba Blue gel filter behind a cropped fisheye.  In one, the water is a very dark tone, just as it is with EIR film.














UPDATE on Feb 22, 2019:  I found out a company is selling a filter claiming to mimic the EIR film, but they sell them (pre order as of now) for substantially more than the few dollars I paid to create my personal filter.


16 comments:

  1. Hi David, I was trying to make this work. What thickness of KG3 are you using? Thanks. Steve

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  2. Hi David,
    Very nice article and information. I'm Yann the one behind the creation of KolariVision's IRChrome filter. Indeed the filter is more expensive than the solution you found. But keep in mind that the filter is glass only and doesn't use any gel. Gels are inexpensive by nature and create a lot of chromatic aberrations in the corner of the images even with high quality lenses. On the other hand, glass allow to keep the image as it bests quality... And high quality glass allowing such range of wavelengths to pass through is expensive. Your results are really good, keep up the good work !

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  4. Last, when I see the transmittance of the Scuba Blue, I assume that the gel is really dimming the light entering the lens and hitting the sensor resulting in far longer shutter speeds or higher isos than with a gel that allows more light in, isn't it ? Could you please share the EXIFS of your test shots ?

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  5. With the gels you used, when I compare Medium Blue-Green and Scuba Blue, I'm a bit confused because the transmission curves doesn't show what happens beyond 700 nm. Did you measured it in order to know of much IR light is passing ?
    http://www.leefilters.com/lighting/colour-details.html#116

    In my early researchs for IRChrome filter, I tested Wratten 38A. As you can see in the curve, IR are passing through this gel :
    http://sweiller.free.fr/spectro/filters/Wratten/Filter%2036-38-38a.jpg

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  6. Hello Yann. I will respond to your comments in a single comment. First of all, if you felt I disparaged your work, I apologize. It is great to find other like-minded individuals that pay attention to light and filter spectra. I agree, a glass filter provides more durability, quality and ease of use.

    On to your questions:

    I added a zoom in on the Scuba and Med Blue-green spectral transmissions on the gel-pack cards. It is here: https://3.bp.blogspot.com/-4ViP2uF3Elw/XJN5VhwF9kI/AAAAAAAABz0/ebY0-w0uFVkiOJME1QPqT3aBnEeUmBkTACLcBGAs/s1600/20190321_074408.jpg

    As you can see, the Med Blue-Green has an NIR transmission beginning at around 720nm and rising to about 50% at 800nm. The Scuba Blue has a transmission starting at 750nm and rising to about 50% probably at ~820nm. I have not done more spectral measurements. When combined with the KG3 glass, the transmission dies quickly after about 820nm.


    The EXIF that you want I looked up for the above image linked at https://4.bp.blogspot.com/-ZITIVgT35PM/XHGQU6bx4KI/AAAAAAAABxo/bq0gpd9MF-MQqCvOlAfG4cBdlzGf38aigCLcBGAs/s1600/20190223_132309.jpg

    This was taken with a 7artisans f/2.8 7.5mm, with the aperture set to ~f6 (it is a manual non-click ring) shutter of 0.002s and ISO 100. WB was custom set to gray card.

    I would like to note, that I never found any spectra of your IR Chrome filter when I looked there this morning. I only learned about it a month ago.

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  7. David, Thank you for the 400nm to 800 graphs. Just so people know, the graphs in the Lee swatch books have 250nm to 800nm graphs, where as their online graphs are only 400nm to 700nm.
    Have you also tried the Lee 116 for this? That was why I came here now to ask, because I had seen that graph in the swatch book, and it looks similar but with higher peak amplitude, so it might get better exposure time. Of course, I was still using the f/11 setting... so...
    I had no problems with exposure outside using the #729 filter, but inside it required some higher ISO.
    For example, for a typical outdoor shot here are the setting: ISO 200, f/11, 1/30s.
    Not sure if that is similar to yours.

    Do you know of any glass that works the way the Scuba Blue does?
    I am quite happy with how the Scuba Blue #729 is working for me.
    It looks like the "Chrome" to me.
    I believe Lee filters are polyester, and there optical adhesives made to bond polyester to glass, Schott did it with their KV filters (no longer made), so if someone wanted to make any of the Lee filters more convenient or combine them with something else, like a KG filter... then it is doable.

    Here is a link showing the progress of test I and others have done based on your stack you shared here.
    If you want to remove this link, that is fine, I don't know your feeling on that sort of thing.
    I mostly just wanted you to see it, and find out of you have any ideas or suggestions.
    Is there any way to contact you privately?
    Thanks again for your help and for posting this stack. Brilliant!
    Steve

    http://www.ultravioletphotography.com/content/index.php/topic/3179-lee-blue-filter-test-to-get-the-aerochrome-red-in-camera/









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    1. Steve,
      Thanks for your message. Yes, I tried Lee116 (see my comments in the blog about Medium Blue Green, not giving as true of a red). As for a glass filter, the one sold by Kolari might be your best option. I think Yann pointed out the reasons why it could be more expensive.

      Using an index matched optical adhesive (such as UV curing glues) one could fashion together a Scuba Blue gel sandwiched between 1mm thick KG3 glass. The edges would have to have gel clearance to allow the glass adhesive contact withouth the gel in the way. I've made holographic notch filters this way coating dichromated gelatin film on glass. Durability is ~10 years in my experience. Not nearly as great as doped glass.

      Another option, in glass, to try (I haven't) is the combo of the Schott BG3/BG4 or BG25 + KG3 type cut off filter. The BG3/4/25 have a similar profile to the Scuba and Med-Blue Green in the visible, but transmit more NIR than the IR Ektrachrome. Once upon a time, I had a BG3. I will see if it is still in an old box and give it a try.

      I don't mind the link. Thanks for the plug. As for contacting me, I believe my profile here allows that. I'll check and see if I turned that on.

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    2. I will also comment on my experience with Rosco Permacolor glass filters. They are surface thin-film coated dichroic glass filters (for heat-endurance light strobes). Optically, they are fine, but you can't use them with wide angle lenses. Thin film filters will have an angular spectral shift at wide angle (longer optical path length). For narrow FOV applications, they are fine. There is a Sea Green and a Teal Permacolor filter. My memory says, they are close as well, in the visible. The NIR transmission is high though. I have the plots on my computer at work...

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  8. Thanks David. I like knowing how things work, making things, I tend not to ever buy anything that doesn't come with a graph, or doesn't say what it is...
    I have some Norland #75 adhesive (like you say, UV curing). I will give it a try soon.
    I have tested BG3, BG25, B-410, not BG4 however, but a few others, and none worked like the #729.
    However, I was doing white balance from RAW at first (using C-NX2).
    Then when I did a custom white balance in the camera, the results became much better, which is unusual in my experience, I always get better white balance from RAW.
    Usually I can't do an in camera white balance with my Nikons, unless the filter is in the visual range, so I seldom even try anymore.
    Some of those filters you mention I show examples of in the link I posted, but those tests were all white balanced from RAW.
    There is one there using BG25 2mm + KG3 2mm I think. It might look a little better using custom white balance in camera, but it has a little different look, darker, almost a UV/EIR look.
    Thanks again for your help.
    Steve

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  9. David, If you can't find your BG3, let me know, I have a few, I can send you one, same goes for BG25, etc... Free! :-)
    Thanks.
    Steve

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  10. Yann, It isn't the B-410 is it, of course that would be a secret, but you have B-410, so just wondering, because the color of it looks a little like B-410, but my results using B-410 are too orange for my taste.

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    1. I just purchase IR chrome filter from Yann and Kolari and the results are ORANGE... very disappointing... I have tried both on FS converyed SONY a7R and also on a FS converted Fuji x100f...
      Best are orange!! not REd at all with custom white balance.. very disappointing..

      Best results I ever got was with the sigma foveon sensors! I have used both the do merrills = darker reds, and the new foveon mirrorless quattro with great results with x1 green hoy and FLD filters.

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    2. Hi, you could send me your RAWs. As stated on Kolari website, WB and RAW development is MANDATORY for IRChrome to work. Sensor tech differs from one manufacturer to another so the hue can slightly shift to a more warm (orange) or cool (magenta) rendition.
      Yann PHILIPPE

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  11. Is it possible to buy the Kolari filter within EU. Purchase from USA results in a doubling of cost due to taxes, VAT, shipping agent fees, etc. If Yann Phillipe was able to supply a 77mm filter then I would be very happy.

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