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08-10-2007, 10:17 AM - 1 Like   #1
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Infrared With The *ist D

I decided to get an infrared filter this week to give me an option for mid-afternoon shooting. I'm interested to see if the *ist D, *ist DS, or K10D are equally sensitive to IR light.

Here are a couple quick shots of the park near my house.

Both are taken with a *ist D and 31mm Limited with a Hoya R72 IR filter. I used auto-focus (it works in IR light). I composed these blind (because we can't see through the R72 filter!) and shot hand-held at ISO 400. I was surprised at the relatively fast shutter speeds, although these did require +2 or more Ev bump in ACR. Post-processing limited to RAW conversion and resizing only - these are the colors as they come out of ACR. Details on the RAW conversion are below the photos. Click on the photos for a bigger version on my Pbase site.


1/30s f/6.3 at 31.0mm iso400 + Hoya R72 IR Filter


1/50s f/4.5 at 31.0mm iso400 + Hoya R72 IR Filter

ACR color adjustments:
Temperature: 2000
Tint: -50

Calibration Tab:
Red Hue: 0
Red Saturation: +15
Green Hue: -55
Green Saturation: -55
Blue Hue: +65
Blue Saturation: -25


08-10-2007, 12:36 PM   #2
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Nice pics, especially considering the 'no can see to compose' factor. Think i'll give this a shot on the k10d and see what falls out. looked over the larger images and really like the effect. enjoy it.
08-10-2007, 01:37 PM   #3
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good job, sir. been interested in IR photography for a while, but went to buy a filter n the guy in the shop was like "nah it wont work very well on a K10D" so i was put off. He seemed pretty certain lol. Anyway I'll look into it a bit more. I dont fancy opening up my camera and removing the IR screen.
08-10-2007, 02:30 PM   #4
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I just took a quick couple snaps with the K10D and...black. I know it is possible to take IR photos with the K10D, but it looks like the *ist D is much more sensitive to it.

See:
"PENTAX *istDS IR" vs. "PENTAX K10D"

08-10-2007, 05:38 PM   #5
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This time color corrected...

I decided to do some false coloring on this one...this is a 3-image panoramic taken with my Super-Multi-Coated Takumar 24/3.5 at f/5.6. I composed without the IR filter on and used a tripod for this set...


(Click for much bigger version.)
08-10-2007, 06:27 PM   #6
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If I remember right, either PopPhoto or Shutterbug had an article about IR photo; the relation of the efficiency of the sensor filter to the camera's IR capability. It showed that since the K100D had a relatively ineffcient filter, it was the best camera currently on the market for IR photography, whereas the K10D was just "okay".
08-11-2007, 07:03 AM   #7
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Nice one, Carpents.
08-14-2007, 08:14 PM   #8
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Here's a shot with my K100D. Just my desk lamp on the keyboard.



ISO 800 for 6sec. I forgot the aperture..lol. But its with my XR 28/3.5 and 3 linear polarizers stacked. (62+62+77). No post processing. Just resized to 640x480.

I used to be able to get colour infrared straight out of my K100D with just 2 polarizers but later found out that the two polarizers couldn't totally cancel out the light coming in and so you would get colour shifts from visible to near IR and then back to visible as you reach the corners.

I just ordered a 720nm OEC branded IR filter (~$40CAN on ebay) to take a stab at the Hoya R72 IR everyone's been enjoying..lol. Stacking polarizers was fun but it seems to block out alot more of the specturm than the common R72 type filters and required longer exposures to get an image.

08-15-2007, 05:17 AM   #9
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QuoteOriginally posted by FotoPete Quote
I used to be able to get colour infrared straight out of my K100D with just 2 polarizers but later found out that the two polarizers couldn't totally cancel out the light coming in and so you would get colour shifts from visible to near IR and then back to visible as you reach the corners.

I just ordered a 720nm OEC branded IR filter (~$40CAN on ebay) to take a stab at the Hoya R72 IR everyone's been enjoying..lol. Stacking polarizers was fun but it seems to block out alot more of the specturm than the common R72 type filters and required longer exposures to get an image.
That's a cool idea, I'm going to try two polarizers over my Hoya R72. There is still the teeny-tiniest bit of visible light coming through the Hoya (but not enough to really impact the final image).

Report back what kind of shutter speeds you get with the K100D. The K10D is extremely insensitive to IR light - probably 5 or 6 times less sensitive than either the *ist D or *ist DS. I haven't done the calculations, but both the *ist cameras look to be about the same as one another for IR sensitivity. (An additional note - the Konica-Minolta 7D is very insensitive to IR light, similar to the K10.)

So, it will be interesting to see if the K100 shares the same IR cut filter as the K10 or *ist cameras.

One more picture, because in visible light this is a really boring shot:

Pentax *ist D, 31/1.8 Limited + Hoya R72 IR Filter, 1/25s, f/4.0, iso400
08-15-2007, 10:54 AM   #10
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I've read a few IR photography web sites and they refer to the istD as a great IR camera. The internal filter is "weak" and passes more IR.

We have three Pentax DSLRs and the Hoya R72 filter. A rough estimate from memory (I should do some side by side testing) follows.

Same subject in bright Sun:

K100D - 1/4 second
My wife's istD - 1/120 second
My filterless K110D - 1/1000 second

You might look into extracting only the Red channel from the Bayer encoding, the blue and green channels don't add to the image and can detract. The resulting photo will be 1.5 Megapixel but sharper.

Here is an example from the modified K110D at 1/3000 second.

P.S. I removed the internal filter for astrophotos, IR was a side benefit.
Attached Images
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PENTAX K110D  Photo 
08-16-2007, 08:41 PM   #11
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This is from my K100D + XR 28/3.5 + two 62mm linear polarizers. No pp. Circulars may behave differently I'm not sure.

ISO 400 - 3 sec. Probably f5.6 or f8 I don't remember. See the trees all come out in citrus but the diagonal colour shifts kinda spoil the photo.
08-19-2007, 02:35 PM   #12
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I posted earlier some estimates of relative sensitivity of Pentax cameras to IR and mentioned I should do some side by side testing. Today I tested my K1x0Ds and my wife's istD. The estimates for my cameras were pretty good, but the estimate for the istD, which was based on my wife's observation and reports I've read on line, was way off. I ran the test again and got similar results.

This is not a scientific test, just a casual compare of three cameras. I took photos of the same scene, with a tripod, same 50mm Pentax manual f2 lens, set at f2.8, and ASA 400, Hoya R72 filter. I adjusted the exposure so that each histogram had the peak in the center. Each camera had a different histogram shape (broad, narrow, lopsided), so I centered the main peak. On a computer they look similar in the ballpark for saturation, perhaps +- 1 stop.

istD 1/10 second
K100D 1/10 second
K110D 1/3000 second (no internal filter)

The surprise was the istD came out close to the K100D which contradicts what everyone says about the older model being more IR sensitive. Perhaps, the reports about the istD being great for IR were comparing to non Pentax DSLRs and not newer Pentax cameras. Perhaps my testing skewed the results but I tried to keep the conditions equal.

As expected the filterless K110D was several magnitudes more sensitive than the other two cameras.

Perhaps the histogram is a poor indicator for IR exposure, but if so all cameras should be affected equally.

Last edited by LeoTaylor; 08-19-2007 at 02:49 PM. Reason: Added sentence
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