The Effect of Near-Infrared Filters on Visible Spectrum

[timor]

And for deeper penetration of the subject additional info about actions of filters (by Wratten number) here:
Frequently Used Filters for Black & White
Not all is, what seems to be.

 

[petrochemist]

Thanks Snowbear. In the absence of any other information I opened up Photoshop to look at their B&W photo tool which has presets for different color filters, incl. an infrared setting. When you look at the color slider settings (reds,yellows,greens,cyans,blues,magentas), for the High Contrast Red and Infrared presets there's a disparity with the reds. The High Contrast Red preset increases the brightness of red 120% whereas the infrared filter reduces it -50%. I know these are just an approximation to mimic the behaviour of filters on analog film but it's confusing none the less.

Photoshop filter tools are very different to actual physical filters.
The 'infra red' filter is trying to mimic the results you would get shooting with infra red film.
Like all such fake infra red treatments, It doesn't do it very well. Not surprising as there is NO information in a standard shot showing the infrared reflectance of objects. I suspect it's main function is to assume things that are green are foliage and to brighten them (Healthy foliage reflects very high amounts of infra red). Items painted the same shade of green as a tree will often be difficult to pick out in a visible light photo yet very obvious in infra red. What it's trying to do is similar to estimating the red channel by looking at the blue and green channels.

FWIW many visible light filters transmit significant infra red (including a blue filter I got recently) which can give interesting effects if the camera has been modified to record infra red.

 

[timor]

Quick check by experiment: Rollei Retro 80S and red or even orange filter and voila.