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05-24-2011, 04:00 AM   #1
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Is IR filter suitable for K-r?

As per title, appreciate your kind inputs

05-25-2011, 09:54 AM   #2
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I tried a 760nm filter in bright daylight. Light loss was at least 6, maybe 8 stops.
With an 850nm filter loss was 8 stops or more.

The K-r seems to have a very good internal IR block filter.
With that much loss a point and shoot does much better for IR.
05-26-2011, 03:36 AM   #3
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does it mean it is not suitable?
05-26-2011, 04:24 AM   #4
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QuoteOriginally posted by Shingkyo Quote
does it mean it is not suitable?
The K-r is suitable to make good IR photos within some constraints:

The exposures will be long. About 200-400x longer than with no filter. Therefore the scene must not move during exposure.

Therefore you will need a tripod or other means to hold the camera steady and will have to frame the scene before putting the filter on.


Last edited by newarts; 05-26-2011 at 05:39 AM.
05-26-2011, 05:02 AM   #5
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there's another thread on Ir here https://www.pentaxforums.com/forums/pentax-beginners-corner-q/93743-k-x-infra...otography.html you might like to check out.
05-26-2011, 04:41 PM   #6
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Yes, the KR can take true IR photos through a filter. The longer the pass wavelength of the filter the less visible light gets through. In bright daylight a 720 lets some red through and can be used but true IR effect in daylight starts at about 850nm. Unless you get a high quality IR filter the image results will look grainy due to poor filter purity. Cheap filters can be found on ebay to experiment with. Of the various cameras I have tried, the K-r cuts the most IR I have ever seen (about 6 to 7 stops). The FZ Panasonic point and shoot super zooms I have lose about 4 to 5 stops, even cheaper 5mp pocket cameras are better at about 3 to 4 stops. If you find a camera that you can read a book with a TV remote, then that's IR response Have fun.
05-27-2011, 05:14 AM   #7
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I have a relatively cheap IR 720nm IR filter I got to just experiment. Yes, the images are fairly grainy, but some aren't bad. I have not been able to get any of the great odd colors that I see in some IR photos online, my images look best in just black and white. I wonder if a better filter would make a difference or if the K-r is just not going to produce those kinds of IR photos unless it's modified?

I've found that you can use live view with the filter on to at least compose the image, which is nice.
05-28-2011, 04:18 AM   #8
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Is this brand "Massa" good to start with?

58mm 4 pcs Infra-Red IR Filter 720 760 850 950nm set - eBay (item 250818887441 end time Jun-10-11 20:05:50 PDT)

05-28-2011, 04:37 AM   #9
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QuoteOriginally posted by Shingkyo Quote
The filters do not appear to be coated so may cause flare and their low cost implies (but does not prove) lower optical quality.

But their cost is sufficiently low that you won't lose much and at the very least will see (and can tell us) if there is significant practical difference between the various cut-off wavelengths. I hope you buy them and tell us the results!
06-01-2011, 06:38 AM   #10
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how about the HOYA 72 IR? is this good?
06-01-2011, 07:42 AM   #11
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QuoteOriginally posted by wed7 Quote
how about the HOYA 72 IR? is this good?

I can testify that it is good with my K-x & K100D. It will admit the most IR (compared to any higher cut-off) and not admit significant red (compared to any lower cut-off).
06-01-2011, 08:07 AM   #12
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QuoteOriginally posted by loco Quote
I have a relatively cheap IR 720nm IR filter I got to just experiment. Yes, the images are fairly grainy, but some aren't bad. I have not been able to get any of the great odd colors that I see in some IR photos online, my images look best in just black and white. I wonder if a better filter would make a difference or if the K-r is just not going to produce those kinds of IR photos unless it's modified?
.....
There are "colors" in the IR if you use filters with cut-offs shorter than about 825nm. Here's an example photo (720nm+ pass):


The colors you see in the photo are there because the sensor's color channels respond differently to IR wavelengths. Here's a graph showing the wavelength response of a typical Bayer filter:


The black line is total normalized response. Notice that the sensor's red channel passes all the IR while blue and green channels pass IR selectively above about 700nm.

With this graph it is possible to interpret the IR reflectivity corresponding to the various "colors" in the photo. The blue shade of the sunglasses indicate they are highly reflective in the long IR and absorb at shorter wavelengths.

While the photo may not "look like" a typical IR photo, that's only a result of our being conditioned as to how an IR photo "should look". That's not to say I know how to exploit these false IR colors

If one wants a classical IR photo look it is an easy task to turn the above into B&W or to do further color channel manipulation by swapping channels, subtracting blue from green to isolate the band between 720-800nm etc..

You might as well use a 720nm filter because it is a trivial matter to exclude the photo's red channel thereby ignoring wavelengths shorter than 800 or so.

Notice that above about 825nm each color filter's sensitivity to IR wavelengths is about the same hence the photo will look essentially monochrome (ie. "B&W").

Last edited by newarts; 06-01-2011 at 08:38 AM.
06-01-2011, 08:36 AM   #13
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Thanks newarts. I'm not getting those kinds of cool colors in my photos. I have tried following some online tutorials for post processing and channel swapping, but have had little luck. I'm guessing my filter (a Zykkor) is just not very good? The black and white converted photos look OK. I was just hoping for the dramatic look I've seen in some online photos.

Thanks again!
06-01-2011, 10:18 AM   #14
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QuoteOriginally posted by loco Quote
Thanks newarts. I'm not getting those kinds of cool colors in my photos. I have tried following some online tutorials for post processing and channel swapping, but have had little luck. I'm guessing my filter (a Zykkor) is just not very good? The black and white converted photos look OK. I was just hoping for the dramatic look I've seen in some online photos.

Thanks again!
How are you setting your white balance before shooting? That can have a big effect on your results.

Try using manual white balance while pointing your camera at the grass or a green tree.

Can you post one of your photos?

Does your filter look red or black when you look through it? Perhaps it is passing too much visible light? - If so see how things look by getting rid of the red channel in post processing.
06-01-2011, 11:19 AM   #15
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QuoteOriginally posted by newarts Quote
How are you setting your white balance before shooting? That can have a big effect on your results.

Try using manual white balance while pointing your camera at the grass or a green tree.

Can you post one of your photos?

Does your filter look red or black when you look through it? Perhaps it is passing too much visible light? - If so see how things look by getting rid of the red channel in post processing.
Thank you, newarts. Here is one I took today. It's actually the best one I've gotten so far, but still not what I was hoping for.




My filter looks very dark red. I was using auto white balance, so perhaps manually white balancing would help a lot. Thank you, next time I'm out, I will give that a try.

What I've been doing is setting white balance to 2000 in Gimp (2000 is the lowest setting available), which seems to give a better effect than doing the same in Lightroom. Not sure why. Then, I finish processing in LR.

The effect I really like in photos I've seen is a very dark sky. I have not been able to achieve that one at all.

I appreciate your help!
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