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10-13-2021, 12:37 PM   #1
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Frequency Range of K-1ii (IR Sensitivity?)

I've been really enjoying my Pentax K-1ii. I recently took a cave/forest picture and decided to print it B&W. The shot looked really good and I noticed that the leaves in the trees were practically glowing. I've seen a bunch of IR photography and that's often the effect I see (and like). Does the K-1ii have any IR sensitivity? I don't seems to be able to find the spectral response of the K-1ii sensor. Does anyone know where it cuts off and is it sensitive to IR light?

When I chased thunderstorms in college, I used a video camera that after we drowned it, it somehow gained some IR sensitivity. The videos near sunset showed the trees practically glowing. I liked that look. So I wonder if I can take some IR shots with the K-1ii.

10-13-2021, 01:47 PM   #2
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I've not tried (or owned) a K-1, but would anticipate it's infra-red response would be much the same as the other Pentax CMOS-sensor cameras, usable, if a little slow, with an R72 (very dark red) filter, around 750nm, but virtually no response with an 87 filter at around 780-800nm.
I like b&w i/r images, but usually use my old 6Mpixel *istDL2 with it's CCD sensor which has greater i/r sensitivity than my newer cameras.
I'm not taken with the "false-colour" effect so have no experience of it.
As i/r filters are not cheap, I'd suggest buying an R72 to fit the lens with the smallest diameter filter thread that you own, or even acquiring an old manual focus 28mm or similar and a filter to suit, rather than lashing out on a large-diameter filter to fit a wizz-bang full-frame zoom, only to find you don't get on with it
The image in the viewfinder will be very dark, so you'll probably end up using LiveView … a luxury I don't have on my *istDL2
Good luck
10-13-2021, 02:48 PM   #3
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The K-1's IR sensitivity is dismal. I tried mine with a 720nm filter and found that I could get an image with the lens wide open (f2.8) and a relatively long exposure but for shooting anything that moves, forget it. It's not the sensor, but a UV/IR cutoff filter in front of it which greatly reduces the amount of IR getting to the sensor. Focusing is difficult because there's not enough light for the LCD display to give a clear image nor the AF system to work. Ordinarily, a smaller aperture would be used to make use of depth of field for sharper images, but a smaller aperture works against you to require even longer exposures.

On the bright side, infrared has little effect producing off colors in an image which can happen if a good UV/IR cutoff filter is not used on a solid state sensor. For my IR photography, I choose the K-01 (no optical VF which is useless for IR anyway) and had it converted to full-spectrum. Not quite as high a resolution sensor as the K-1 but plenty good enough for great IR shots. With conversion, the AF works the way it would for visible, and with an external UV/IR cutoff filter, the camera can be used for normal use. Converting a K-1 seems indecent to me in a way since it's such a great camera otherwise and gutting it for IR use precludes the use of its viewfinder (for IR) and risks a high cost instrument. If you want to try IR with the K-1 be prepared to use a tripod, fast lenses, and low shutter speeds.

Your glowing foliage might be due to the way you converted to B&W. If the green channel was accentuated, it would lighten leaves and green foliage considerably, possibly giving it a glowing appearance. The K-1 actually has a B&W conversion (in its filters mode) which simulates IR by making use of this, however this is just a simulation and doesn't make use of any actual infrared light. That filter might be useful for your purposes, however.

Last edited by Bob 256; 10-13-2021 at 09:43 PM.
10-13-2021, 05:09 PM - 1 Like   #4
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I can't comment regarding the K-1, but I have had reasonably good results with a Hoya R72 and my K-3. The sensor's IR sensitivity is rather poor, but not non-existent.



Even under bright summer sun, the exposure was quite long (160s) at f/8. I found that different color effects might be had by applying various white balance in post, in this case tungsten.

FWIW, I also have some el cheapo Zomei filters that claim a 720nm cut-off; but in actuality, they very badly bleed visible light and are unsuitable for use with other than IR-specific capture media.


Steve


Last edited by stevebrot; 10-13-2021 at 07:53 PM. Reason: Completeness
10-13-2021, 09:41 PM   #5
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There is an IR cutoff filter in front of the sensor. If you really want control, you need to remove this filter first. Afterwards you need to control what light hits your RGB+IR sensor. Just using a deep red filter will let a small band with of light pass through - deep red to IR cutoff wavelengths. Creating that „glow“ intentionally will be difficult.
10-14-2021, 01:10 AM   #6
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ISO 1250, f2,5, 1/25s, tripod. Old picture. IIRC I used deep red filter, not IR720. But converted camera would be much much better (second image, K-5 with 640 nm filter on the sensor, with usable viewfinder)


10-14-2021, 08:23 AM   #7
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QuoteOriginally posted by Bob 256 Quote
Your glowing foliage might be due to the way you converted to B&W. If the green channel was accentuated, it would lighten leaves and green foliage considerably, possibly giving it a glowing appearance. The K-1 actually has a B&W conversion (in its filters mode) which simulates IR by making use of this, however this is just a simulation and doesn't make use of any actual infrared light. That filter might be useful for your purposes, however.
Thanks. I didn't think of that. I live in the South, so the primary color is GREEN. I'll try the B&W setting on the camera to see what I get.

---------- Post added 10-14-21 at 08:25 AM ----------

QuoteOriginally posted by stevebrot Quote
I can't comment regarding the K-1, but I have had reasonably good results with a Hoya R72 and my K-3. The sensor's IR sensitivity is rather poor, but not non-existent.

Even under bright summer sun, the exposure was quite long (160s) at f/8. I found that different color effects might be had by applying various white balance in post, in this case tungsten.
That's a great shot! I'll see what I can find in the way of IR filters. That's they type of shot I'd like to make. Obviously, I'll use a tripod as even the shake reduction can't do 160s....

---------- Post added 10-14-21 at 08:27 AM ----------

QuoteOriginally posted by Medex Quote
ISO 1250, f2,5, 1/25s, tripod. Old picture. IIRC I used deep red filter, not IR720. But converted camera would be much much better (second image, K-5 with 640 nm filter on the sensor, with usable viewfinder)
Those are also really nice.

Now y'all have given me some cool things to try....

I know that my older Pentax P&S had IR sensitivity because I remember being able to see an IR remote LED flash on/off in the Pentax "live view" viewfinder.


Last edited by dmach47; 10-14-2021 at 08:30 AM. Reason: I can't speel...
10-14-2021, 10:39 AM   #8
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QuoteOriginally posted by dmach47 Quote
That's a great shot! I'll see what I can find in the way of IR filters. That's they type of shot I'd like to make.
I can recommend the Hoya R72. It is a bit expensive, but has a strong cut-off at 720nm.


Steve
1 Day Ago   #9
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QuoteOriginally posted by Bob 256 Quote
Your glowing foliage might be due to the way you converted to B&W. If the green channel was accentuated, it would lighten leaves and green foliage considerably, possibly giving it a glowing appearance. The K-1 actually has a B&W conversion (in its filters mode) which simulates IR by making use of this, however this is just a simulation and doesn't make use of any actual infrared light. That filter might be useful for your purposes, however.
I know I can take B&W photos with the K-1, but the switch from full color to B&W and then back to full color is not trivial. Too bad I can't reassign one of the "custom" buttons to "toggle between B&W and Color Images".
1 Day Ago   #10
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QuoteOriginally posted by dmach47 Quote
I know I can take B&W photos with the K-1, but the switch from full color to B&W and then back to full color is not trivial. Too bad I can't reassign one of the "custom" buttons to "toggle between B&W and Color Images".
I'm not using them myself, but from my understanding this should be possible with accordingly set up user modes? So you could switch between B&W and color with a flick of the mode dial?
23 Hours Ago   #11
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If you want to seriously do IR, have the IR blocking (hot mirror) filter removed. Spencer's & Kohlari will work on K-1's. LifePixel unfortunately won't. I'd go with Kohlari over Spencer's personally (I've had problems with them). If you have the hot mirror removed, exposure times would be pretty much the same as regular photography as the hot mirror blocks the frequencies of light you're trying to use.
18 Hours Ago   #12
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QuoteOriginally posted by dmach47 Quote
I know I can take B&W photos with the K-1, but the switch from full color to B&W and then back to full color is not trivial. Too bad I can't reassign one of the "custom" buttons to "toggle between B&W and Color Images".
Normally, an "infrared" photo is a black and white image (example 1), since there are no "colors" in the infrared spectrum. If you shoot through an infrared filter, most Pentax cameras will render a reddish image because the red Bayer filter passes more IR than the blue or green sections. You then process this to a black and white image, removing the red cast. The image can then be rendered as a "tinted" image with software (duotones and tritones), as in example 2.

If a camera is converted to full spectrum, then any visible light coming through the lens will be processed as always, giving a color image but superimposed on that is an IR image. By placing the right filter (orange, medium red, yellow, etc.) on the lens, the amount of visible light is modified and you get a hybrid of visible and IR which can produce some interesting color images (as with the great examples Medex provided). These aren't true "infrared" images and might be called "false color" images though that term more correctly applies to a specific type of visible/IR image in which green and red substitute for blue and green respectively, and IR substitutes for red. This latter type of image requires visible + IR images which are manipulated in post processing (or with Kodak Aero IR film which is no longer made), However, "false color" lends itself to an image produced this way.

In shooting an infrared image with the K-1 by putting an IR filter over the lens, you should only try for the first case I mentioned, that of a B&W final result. You can get this by using the K-1's ability to generate a B&W image from a given file (which will remove the reddish color cast), or it can be done in post processing with a software of your choice. The best practice is to aim for the right exposure and shoot away, and worry about the conversion to B&W later. But, as previously mentioned, the K-1 is not the best choice unless its UV/IR blocking filter is removed (even then, I wouldn't consider it to be a "best" choice - the K-01 is far better).

Even with a converted camera, you'll get the red cast through an IR filter (720nm or higher) which has to be removed later. However, with a FS converted camera, you can get some interesting (and pleasing) full color images by using a colored filter which passes visible light below 720nm, with not much post processing needed.

I had my conversion done by Isaac Szabo who did a great job and has an informative site about the subject where you can get a better idea of the different types of IR images (no personal connection to Isaac Szabo).

Isaac Szabo

Note: both the attached images were shot through a Hoya RM90 filter which cuts on mostly beyond 900nm. I was using a full spectrum converted K-01 camera and a Pentax 18-55mm lens at f9.5 and about a 1/125 second exposure.
Attached Images
   

Last edited by Bob 256; 17 Hours Ago at 04:19 PM.
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