Filter/Speed/Meter & DON'T meter using a Nikon Camera

["Rolland Elliott" <rolland_elliott@xxxxxxxxxxx>]

You may be lucky, but that still doesn't change the fact that Nikon installs 
IR blocking filters in all their 35mm cameras I know of dating back at least 
as far as the FG.  (this includes the F3 for the person who asked). (And as 
a side note, every other major 35mm camera manufacturer I know of uses SPD 
[silicon photo diodes] for their expsure meters and probably uses IR block 
filters).

You can still meter though an infrared filter on a Nikon camera, but the 
meter is not picking up lots IR light, it is picking up traces of other 
wavelengths, probably in the deep red area of the spectrum. Which exact 
wavelengths doesn't really matter that much. If it works for you, keep doing 
it. But don't imply to people that the camera is metering IR light because 
it isn't.

Would someone do the following?:
1.  Load a camera with color film (sensitive to visible light).
2.  Attatch an opque IR filter over the camera lens.
3.  Take an exposure reading through the filter and adjust the camera ISO to 
give you a good picturs on this color film.
4. Remove the filter and then take the picture.

Someone could do this (and given the range of latitude of color film ) and 
probably get well exposed shots most of the time.  However, they are not 
really figuring the exposure in a very logical way.

The exact same analogy holds for IR photography. Except for the fact that 
the IR block filter is permanently attatched right above the exposure meter. 
  You can try to meter IR light through a filter that BLOCKS IR light, but 
it's not very logical to do so.

Given the wide lattitude of IR Black and white film, and the fact that many 
people bracket their exposures, and the fact that there is a good 
corrolation between visible light and IR light in outdoor scenes. it does 
not surprise me that people have had success doing this.

Just trying to explain the science behind the art.

If anyone is attending college or has access to a spectrometer, I'll gladly 
ship the small IR blocking filter I removed from the Nikon N90s camera I 
have for testing.  It would be interesting to get a curve of this filter's 
spectral response. It is 1/4 the size of a penny. For being so small it sure 
does cause a lot of problems for us IR photographers.

Peace, Rolland


- --- Rolland Elliott <rolland_elliott@xxxxxxxxxxx> wrote:
>And I’ve used my N90s camera for about 5 years with many good results with
>IR photography. However, you are fooling yourself if you think you are
>metering IR light. You are metering visible light and it is just a
>coincidence the IR exposure is fairly close to the level of vislble light.

Well, I'd rather be lucky than good.  As I said, experience has me adjust 
for
the scene, but this coincidence has been fortunate for me for the past 
hundred
or so rolls of HIE, so hopefully the luck will continue.  I do post my 
pictures
on my Web site (below), so people can judge for themselves whether or not my
advice will work for their own personal style.

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