[MrB1]

The best option is to have a camera converted and use it with an IR filter. You can put an IR filter on a non-converted camera but if it work, you'll usually need to use a long exposure at large aperture to get enough IR light through the UV/IR blocking filter in the camera. Results will vary with camera type from so-so to unusable, but even so, you need an IR filter, and it's best to convert a mirrorless camera since you won't be able to see through an optical viewfinder (consider the K-01 a good choice for conversion).

Some of this seems not to be my experience. My converted DSLR camera doesn't need to be used with an IR filter. The conversion has installed the IR filter on the sensor, which allows only IR light to pass through from roughly where visible light ends, and hence it allows the sensor to see mainly the IR frequencies. As the filter doesn't affect the light path to the viewfinder, the scene looks just the same as through a normal camera's OVF. To see the IR image, it is available on the rear screen in Live-View mode.

Philip

[Digitalis]

My converted DSLR camera doesn't need to be used with an IR filter

From what I have seen modified cameras benefit from stronger IR filters such as the R90, which to my eyes seem to improve image contrast.

[stevebrot]

Not seeing a picture here JensE, keen to see! Can anyone else see JensE's image?

Nope and no reference to be found in the source either.


Steve

[JensE]

Not seeing a picture here JensE, keen to see! Can anyone else see JensE's image?

Lacking really suitable pictures, I didn't post one, just intending to give an idea of what exposure times will be.


There isn't too much of an interesting IR spectrum in fall, but here's one example. For the first, I disabled the camera-specific color profile (=straight-through values for RGB, but it doesn't really matter much) and converted the red channel to monochrome. It was windy, therefore the long branch looks blurred. The very bright small leaves in the middle are from visually dark green Pyracantha. Note how the shadows remain dark, because they're mostly lit by scattered light with a lot of blue.

During processing, I noticed that the FA31 LTD does create a mild hot spot, despite being listed as not doing so.

The 2nd picture is a crude test of the fashioned red-blue channel swap. It seems there is a lot more blue (rendered red) coming through the filter in the periphery than in the center. I'll try more in spring, winter is just not IR time.

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Last edited by JensE; 02-03-2020 at 06:15 PM.

[cpk]

From what I have seen modified cameras benefit from stronger IR filters such as the R90, which to my eyes seem to improve image contrast.

My K-7 was converted to 665nm because I wanted to do false colour IR. These can be converted to black and white IR in post-processing; but the purest B&W IR, however, is done with an 850nm filter which would improve image contrast. I can attain this by using a strong red IR filter, but would lose the false colour capabilities. As it is, my K-7 can be hand held but might need a tripod with the addition of an IR filter.

Some samples (which have been posted previously elsewhere in this forum): Barns in the County, Series 3

[PDL]

Well, my experience with shooting IR film was with Kodak B&W and Kodak Ektachrome IR (at the end of the film run it was labeled as Aero)

When shooting B&W I used a Kodak Wratten 87 filter, which is opaque for the most part. Meters do not work and focusing is shifted on the focal plane (which is what the red dot on film DOF scales are for. You had to change the film in a light tight changing bag that had to be checked to see if the cloth was really blocking IR or you could fog the film. The felt in the film canister was not good at blocking IR so you had to be careful and the foam sealing the mirror in a SLR's mirror box may not be a good IR block which would result in fogged film (IR leaks). I have the spec sheet for Kodak IR B&W film and there is an image of a cheap flower vase and flowers illuminated by a pair of cloth irons on full. That stuff was sensitive to heat and it was weird, useful in some contexts, but weird. It required a very different mindset to use. If you got the film canister hot you could fog the film.

When shooting Ektachrome IR (ASA 160) that was shot with a minus blue filter (Wratten #12 yellow) - no blue/UV light contacted the film. Colors were shifted where red was related to healthy plants i.e. chlorophyll content. The EROS data satellites used false color representation that looked a lot like Ektachrome. Some camera companies (Pentax Included) build special IR cameras for various purposes. Phase One has a package of two 150MP cameras sitting side by side, one with their B&W image system that has extended range into the IR part of the spectrum and a special color back with extended no IR filter. On the Phase One system, the two cameras are carried in tandem and they provide the user with a customized image processing server to merge the images together in real time. Pretty impressive stuff.

Now as for removing the IR filter from your sensor, does this mean you are shooting what I would call "real" IR. Yes and no. Yes you are using extended IR sensitivity on the sensor, but the sensor is just a run of the mill photographic sensor. It is not a specifically designed sensor where UV and blue wavelengths are ignored like back in the film days with specialized emulsions. The IR conversions used with current sensors do require filters, as cpk states above, to allow IR frequencies to be predominate in the imaging process. Having been a fan of Ektachrome IR film, I am really not all that impressed with digital "simulations" because the IR films were based on light wave frequency response - not channel swapping.

Now, this all begs the question of why do I think this? My first career was as a Archaeologist who was interested in using computers and photography in the field. This was before or as portable computers were just coming out (early 80's). I was shooting IR film and using the resulting images to find excavated human created features in the landscape. I can remember one of my professors in grad school saying that portable computers will never be used on an excavation site because "How are you going to keep the dirt/dust out of the floppy drive?". Now these guys are using drones to map sites in IR and visible frequencies, in stereo and processing the images on pretty powerful PC's in near real time. I also taught a "Scientific Photography" course to Archaeology students with an emphasis on IR and UV photography at the college level along with methods of documentation of museum specimens.

PS: I dug out my filter 75mm x 75mm Wratten no.87 (Kodak Cat 149 6256) and looked up the price today $185.00 - it was not that expensive back when I bought it, yikes that was almost my weekly income back in the day.

[JensE]

Having been a fan of Ektachrome IR film, I am really not all that impressed with digital "simulations" because the IR films were based on light wave frequency response - not channel swapping.

The picture, which Digitalis showed in the post above, used a filter on a converted photographic sensor, which is designed to approximate the spectral response to Ektachrome EIR very closely (as far as photographic use is concerned), see the article and comparison shots using a Canon sensor at Kolarivision.

[MrB1]

Now as for removing the IR filter from your sensor, does this mean you are shooting what I would call "real" IR. Yes and no. Yes you are using extended IR sensitivity on the sensor, but the sensor is just a run of the mill photographic sensor. It is not a specifically designed sensor where UV and blue wavelengths are ignored like back in the film days with specialized emulsions. The IR conversions used with current sensors do require filters, as cpk states above, to allow IR frequencies to be predominate in the imaging process.

Not necessarily. The conversion includes fitting an IR filter onto the sensor, so a filter on the lens is not essential but optional, as CPK implies. An extra filter can be used, depending on the desired effect and on the type of filter fitted to the sensor. CPK's conversion (665nm) transmits some of the longer wavelengths of the visible light spectrum along with the IR, so an extra 850nm filter would be needed to absorb all the visible light and let only IR pass through. However, there is a choice of different filters available for fitting during the sensor conversion, including the 830nm filter for those who want to capture only the IR spectrum.

Philip

[Prohibitiory]

Thank you, Aggy. Possibly not far away - it's at Weston Turville Reservoir, near Wendover.

Philip

Indeed very close! Wendover woods are gorgeous, need to go for some nice photoshoot there in Summer

[PDL]

The picture, which Digitalis showed in the post above, used a filter on a converted photographic sensor, which is designed to approximate the spectral response to Ektachrome EIR very closely (as far as photographic use is concerned), see the article and comparison shots using a Canon sensor at Kolarivision.

Yes, you have to modify the camera and its sensor (removing the build in IR cutoff filter) and use the additional filter to get the effect. But you are not getting the same levels of frequency response as the film. It is the specific response to the frequencies in Ektachrome IR (Aero in its last days because it was mostly used in aerial images) that back in the day I was interested in exploring. Infrared False Color photography is used extensively in Cultural Resource Management:
Infrared False Color photography (IRFC) - Cultural Heritage Science Open Source
Bulgaria, Archaeology Examination - Cultural Heritage Science Open Source
I was interested in using techniques such as these to find Pre-Columbian villages along the Middle Missouri River in the US. Unfortunately, I had to leave the field for medical reasons and nothing really developed.

---------- Post added 02-04-20 at 03:26 PM ----------

Not necessarily. The conversion includes fitting an IR filter onto the sensor, so a filter on the lens is not essential but optional, as CPK implies. An extra filter can be used, depending on the desired effect and on the type of filter fitted to the sensor. CPK's conversion (665nm) transmits some of the longer wavelengths of the visible light spectrum along with the IR, so an extra 850nm filter would be needed to absorb all the visible light and let only IR pass through. However, there is a choice of different filters available for fitting during the sensor conversion, including the 830nm filter for those who want to capture only the IR spectrum.

Philip

You also need to modify the sensor to remove the IR cutoff filter. Ideally, you would use a B&W sensor and cut off all visible light, just like the way the old B&W film used.

Now if you can show me a off the shelf B&W image of -- well anything -- that uses two cloths irons as the only means of illumination - then we can talk some more.

[JensE]

But you are not getting the same levels of frequency response as the film.

Therefore my carefully chosen words. Are there any spectral sensitivity curves published for Kodak EIR film?

[PDL]

Bingle is your friend:

https://125px.com/docs/film/kodak/f13-HIE.pdf

The source site "https://125px.com/docs/film/kodak" is a list of the latest spec sheets for Kodak films.

[JensE]

Bingle is your friend:

https://125px.com/docs/film/kodak/f13-HIE.pdf

The source site "https://125px.com/docs/film/kodak" is a list of the latest spec sheets for Kodak films.

... 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 https://125px.com/docs/unsorted/kodak2/ti2323.pdf. I didn't know that the site allowed browsing, so with the help of your remark I found it at https://125px.com/docs/unsorted/kodak2/ti2323.pdf, 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 ...

[PDL]

Well this site just ate my response.

[stevebrot]

Well this site just ate my response.

It's a sign! An ill omen! Flee pilgrim, Flee!


Steve