Great Mistery solved :)

[AlexMax]

Hi

I had some stock of old Kodak HIE, which i went on to shoot with an M6, a Biogon 35mm, and a Skopar 21mm f4.

I handed the film to a lab, it is a reputable one, and they returned the film to me, two rolls of it completely unexposed.

( No, it is not the proverbial Cap on Lens mishap.. )

The filter I used was the IR 95 ( 950nm ), and the ASA was set to 100.

I figured out what happened :

Despite the fact that the meter in the M6 is sensitive to wave lengths above 950nm ( heck, in summer days at noon I was shooting handheld,at 1/60, 1/125, 1/250... ) the film IS_NOT :bang: . so, two entire rolls were unexposed.

Which leads me to this question :

In an AE film camera, how can i be sure of which proportion of light measured by the meter is actually used by the film ??

I guess that the film was not "unexposed", it was severely under exposed, to the point that no image was recoverable, so, if instead of shooting hand held, i would have added some extra stops, i would probably have some keepers...😡

Best regards

Alex

 

[sevo]

Infrared film cannot be exposed by meter, unless you calibrate the meter to the film, filter and illumination (location, time of day, time of year, atmospheric conditions).

TTL metering through the filter will not even eliminate the filter from that equation - the spectral sensitivity of meter cells is not the same as that of film. The native response of photo diodes and transistors increases with wave length, while the sensitivity of film decreases in the same direction. And the "blue cell" filters integrated in the meter to correct the spectral response for the visual range may mess that up even further.

In general, if you can expose IR handheld, you ought to know something is wrong - this was only possible with fresh HIE in particular situations...

 

[AlexMax]

In general, if you can expose IR handheld, you ought to know something is wrong - this was only possible with fresh HIE in particular situations...

Hi Sevo,

Thanks for the hint, but, i have used Ilford SFX 200, and in Bright summer days, i managed to shoot handheld with fast lenses wide open...

Best regs

Alex

 

[sevo]

Hi Sevo,

Thanks for the hint, but, i have used Ilford SFX 200, and in Bright summer days, i managed to shoot handheld with fast lenses wide open...

As a film designed to photograph the drivers in passing cars with a non-blinding dark red/not quite infrared flash, SFX is very fast in that spectral range - and uses a subset of the visual range light meters are corrected for. Unfortunately, that is not really infrared - can't be if the film is to fit its intended application, as the thermo insulating glass in cars is fairly opaque to genuine infrared.

 

[elmarman]

Are you SURE that the Lab to which you gave the IR film processed it in proper B&W Chemicals and NOT C41 Colour chemicals ? If they did then the bleach would dissolve all the silver leaving a CLEAR film looking as though it was not exposed.