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Pentax *ist DS Infrared Sensitivity


camera overview


 
Camera: Pentax *ist DS
Filter: none
Exposure time: 1/3200
F-stop: 2.8
ISO speed: 200
Focal length: 50mm
White balance: Automatic
EV: 13.6147

comments:
Camera: Pentax *ist DS
Filter: Heliopan 715nm IR pass filter
Exposure time: 1/30
F-stop: 2.8
ISO speed: 200
Focal length: 50mm
White Balance: Automatic
EV: 6.8777

comments:
The Pentax *ist DS is surprisingly sensitive to IR light, however, this is only in the red channel. The other channels are so insensitive that you can pretty much forget colour IR work unless you shoot RAW for IR work.


R: G: B:
These are the red/green/blue channels from the visible light shot above. You can see that the foliage is very dark even in the red channel.
R: G: B:
These are the red/green/blue channels from the IR shot above. It's very obvious that this is "real" IR, with white leaves and not "a bit beyond red". When IR sensitivity is concentrated in the red channel, this is a rather important question. The Pentax passed this test, too. Post-processing a "almost only red" image is difficult. I recommend RAW and have composed an introduction to RAW Conversion for IR images
 
The standard restrictions of dSLRs aside, like having to focus and frame through the almost opaque IR filter, the *ist DS is great as an IR camera. With a 715nm, you can frame through the filter and the Pentax' focus assist gives you a rather good clue whether you have focus or not. I haven't used AutoFocus lenses in IR yet, but I suspect that they would work - but no guarantee!
 



Shot handheld with a Heliopan 715nm IR pass filter over my Porst ColorReflex 50mm/1.7. Shot in RAW, converted with pixmantec's RawShooter Essentials . While I am no a RAW shooter for normal situations, I _strongly_ recommend using RAW for IR shots as I describe on my page about RAW Conversion for IR images. Stuff like WB and exposure compensation are really only possible with RAW. It may hurt your flash card memory, but it is worth it. Also, try bracketing focus distance with dSLRs and use the narrowest aperture you can manage to compensate misfocus.
Recently, Mike from the dpreview forum, myself and reader Ken Cho have found that AF on the Pentax *ist DS dSLR works well enough in IR with a mild 715/720nm filter.
You want to try first hand how much better RAW is suited to IR processing than JPEG? Please visit my post-processing page for cameras with almost all IR sensitivity in the red channel.





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