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Forum: Photographic Technique 03-27-2009, 01:07 AM  
*istD IR conversion
Posted By PentaxOldtimer
Replies: 6
Views: 3,263
Hi, new on the forum and this infrared thread caught my attention so I'm making my first post here. Sharing my experience with IR may prove useful here.

I have an un-modified *istD but I use it to shoot B/W infrared. (I don't want it modified, I don't really like the look of color IR that much and I can still use it as a "normal" camera.) I used to work with IR film back in the day so I'm partial to the look of traditional B/W IR.

With an R72 filter on the *istD the camera still meters accurately and autofocus works fine. That's a good thing since you can't see anything through that filter. I typically use the filter on my 18-35 for landscapes and set aperture between 11 and 16. I shoot RAW at ISO 200 and use aperture priority mode for this work instead of manual, which is my normal shooting mode. I also normally prefer manually focusing but it's impossible when you can't see through the filter.

With the filter off I compose the scene with the camera on a tripod. After the composition is good I attach the filter. It's imortant at this point to activate the autofocus because even if it was in focus without the filter the autofocus will now refocus correctly at the longer wavelength of the IR light. (Does anyone remember using the IR shift indicator on manual focus lenses back in the good ol' days? Nice that the autofocus takes care of that now.)

The other important thing to remember at this point is that the camera will also meter at this time if the autofocus is activated via the shutter button. I don't have my eye to the viewfinder because I can't see anything in there anyway with that virtually black filter attached but stray light will get in there and cause big metering errors if it isn't covered up. I use the eyepiece cover that came with camera. If I don't have that with me then I very gently place my thumb over the eyepiece during the metering and exposure.

Depending on the brightness of the scene the exposures generally vary from 1 to 6 seconds long. The resulting RAW image is actually black and red, black being the darkest elements in the scene and red representing the middle and bright tones. If I see any white in the preview image then I know the white areas are overexposed and I dial in a bit of EV compensation if necessary. (Doesn't happen that often though.)

I take the black and red image and desaturate when post-processing to render the resulting B/W image. When desaturated the images typically need a bit of exposure boost to look right. I then tweak the image to taste as I would any other.

As I said I personally like the look of B/W IR and using this method with the *istD means no camera mod is necessary and when the filter comes off I'm shooting normally again. This doesn't work on my K10D though because of the IR filtration on it's sensor. I have accidentally screwed the filter on when using that body and then stood there scratching my head for a minute wondering why it wouldn't work.

A portfolio of my *istD IR images is here: Portfolio

Jim
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