Difference between using no OLPF and a full spectrum OLPF?

[Will Turner]

I've got a shoot with some IR work coming up and I wanted to see if anyone knows what the visual difference would be between shooting with no OLPF installed in the camera and shooting with a full spectrum OLPF? From what I can tell the differences would be that the witness marks would be inaccurate and the chances of aliasing are higher. In terms of the image and the color that would come through in the R3D, would that be basically the same?

 

[Robert Hart]

Please take heed of better answers from better brains than mine. - I assume you will use IR filters to take out visible light, even if shooting in darkness. If you allow a mix of visible light and IR light at the same intensities, say from street lighting or other ambient visible light sources, your image will tend to be soft and out of focus or soft-haloed due to mixing of light sources which refract differently through a lens.

The witness marks will be inaccurate. I understand that a few older stills lenses also had an infrared scale inscribed on the lens barrels but I have not seen one myself.

An image formed from infrared light and focused for infrared will be sharp but the image formed with visible light will be out of focus. It can be difficult to find focus by viewing a screen if the light sources are mixed and of equal intensity. - Please experts, challenge these comments strongly. My own experience is drawn only from filming via a GenII intensifier, not direct-to-sensor, however I expect that the same issue will apply.

 

[Nick Morrison]

No OLPF will simply expose your sensor to a host of problems and is not a good idea - not only does it protect your sensor, and help control moire/aliasing, it's also a crucial part of the optical chain and color science.

For various flavors of IR, you will need to install custom olpfs that help filter these spectrums and direct them to your sensor.