Seeing through a Hoya R72 IR filter

[iancoxleigh]

I've been shooting a fair bit of IR with a FM2n and HIE. I was using a old Nikon

swing-door gelatin filter holder so that I could easily swing the filter off for

composing/focusing and replace it for shooting. But, one day I left a needed

adapter ring at home and had to screw the filter directly onto the lens.

 

Well, I was able to see through the filter (after a second or two for my eyes to

adjust) well enough to compose the shots and could also see the white leaves

wood-effect clearly. In fact, having got the film back, I was able to see a

fairly good approximation of the the resulting image by looking through the

filter. I did most of the shooting in overcast skies. The one day it was bright

I could even see clearly enough to roughly focus.

 

I know I'm not really seeing the IR and that the Hoya lens lets in a fair bit of

the lowest red range. But, I've never heard anyone else mention being able to

see and compose through a Hoya R72 (or see the IR 'wood-effect'). So, I thought

I'd ask around and see if I am a bizarre freak or if this is fairly normal.

[vivek iyer]

Yes, this is fairly normal.

 

depends on your vision though.

 

Try a stronger filter and you won't see a thing.

[oskar_ojala]

Yes, it's actually mentioned somewhere. I can see a faint image through my #89B equivalent Heliopan. One should be careful, though, not to look at anything like the sun using the filter.

[hagay_friedmann]

Yep, I too can see through my R72... though it's really very dark reddish - possible...for some unknown reason... its spectrum range suppose to be from 720-800 nanometer

and our human vision range is approximately: 450-650 nanometer

well - what does it mean?

that the Hoya starts to work from 630-640 nanometer and not 720...

my guess anyway...

[bjørn rørslett]

The "72" refers to the 50% transmission point, at 720 nm. There is a significant transmission lower than this, and the eye can readily detect say 5% transmission in the deep red < 700 nm allowing us to observe visually through the filter. Still, what we see is not *pure* IR, but rays in the borderline between deep red and near IR.