Originally posted by awaldram AA filter != IR Cut Filter
the K3 still has an IR cut filter
To get IR photos with the K-3, you need to block visible light while only allowing IR wavelengths to pass. This can be done by adding IR filters to your lens.
The IR filter covering the sensor will block much of this IR radiation. Thus, a long exposure is necessary to gather enough IR illumination after visible light has been excluded.
---------- Post added 03-21-14 at 09:27 AM ----------
Originally posted by blackcloudbrew Good question. I'm interested in the answer myself. One point is that AA filter or not, you can always put an IR filter on a DSLR and get IR images, it just takes a long exposure to get it, and then there is focusing issues etc. That's why IR converted cameras are more desirable. They are IR focus corrected and function like a normal camera.
IR converted and "full-spectrum" converted cameras are a different kind of beast from "normal" cameras.
Long exposures are still the norm, though not necessarily as long as an unaltered camera with a filter, so its mostly for landscapes.
Also, though I have not experienced any focusing issues, infinity focus is what I mostly use for landscapes.
IR converted cameras have an IR spectrum high-pass filter over the sensor. This allows IR light above the filter's rated wavelength to pass through the filter while blocking visible light. The result is a camera that takes dark pictures within a limited color spectrum. Focusing through the viewfinder is normal. Shorter wavelengths (650nm, nearer to visible light) are red. Longer wavelengths (900nm) appear purple to blue. You pick the filter at conversion time and can't change it. Color adjustment in post processing is more creative than corrective with these images. Auto-focus would work if the filter's thickness was corrected for the difference in wavelengths. Light metering is all over the place. If you know you only want to shoot in a certain spectrum, this is the way to go. Exposures are not as long as if you were using a regular camera with an IR filter, but you now have a dark filter over your sensor. Think of it as having a permanent ND6 filter on the sensor.
A "full-spectrum" camera has had its IR filter removed from the sensor and replaced with clear glass. Images without any added filter appear monochrome-pink. The sensor is really "hot", like ISO1600 when you set it to 100. Focusing happens first, before IR filters are added to the lens. This allows interchangeability of filters across the spectrum. IR-Cut "hot-mirror" filters can be added to the front of the lens to bring the camera back to the normal world. These are the same as the filter that was removed from the sensor, but they aren't as strong, so you would need two. Auto-focus works. Light metering is all over the place. Adding more than two filters to the end of the lens causes vignetting. The "hot-mirror" filters to correct back from the "full-spectrum" conversion cost as much as converting the camera in the first place. The additional IR filters range from $25 to $100 each.