I am puzzled about the behavior of camera sensor to the infrared spectrum.
I have heard that the you must remove the internal infrared filter to capture infrared pictures. So, I removed it and used a 760 nm infrared pass filter took some pictures. It looks like this (from Pentax point and shot):
Now, if I am going to put the same 760 nm infrared pass filter to another camera (without removing its internal infrared filter), it also takes the infrared pictures albeit with higher exposure time. Images in this case look like this (from Canon point and shot):
In both of cases, a 760 nm infrared filter was places before the lens of two cameras. The white balance is different but it will give an idea about what is happening. First image is blurry because no glass replacement is done yet to compensate for the internal infrared filter that I removed.
So, first camera is with infrared pass filter and second camera is with infrared pass + infrared cut filter.
My question is: If camera can take infrared pictures without removing internal infrared filter what is changing in these two scenarios? Change in the sensitivity of sensor to the particular wavelength or the overall sensitivity in infrared spectrum? Is the remove of internal infrared filter only reduces the exposure time? What is the overall logic in these two cases?!