I'd like to add something to this... (may I say correct?)
The problem with the pressure plate hole and real IR film (like Kodak HIE) is
not that some IR radiation is passing through the back cover and exposes the
film. Remember that the presure plate only covers a bit more than the 24x36
rectangle at the back of the shutter hole. If that was the case, the whole film
*WILL* be fogged because the film will be exposed to those non-metalic areas.
What's going on then?
Well... those films lack of a anti-halation layer. That means that the radiation
can pass though them. That's also why you have to load them in complete
darkness. The light can sneak inside the film cartridge by entering through the
piece of film that's outside (much like light traveling in an optical glass
fiber). (this effect also causes the typical 'halos' arround highlights in IR
photography)
In the case of the pressure plate, the metalic surface is not fully opaque and
it will absorb but also reflect some of the IR passing through the film. The
bouced IR will hit the film again, exposing it a bit more. At the hole, there's
no bounced IR, and the density of the image formed at that point will be a bit
less than the surroundings, making a AWFUL mark in EACH exposed frame. (it won't
be very noticeable in dark areas, given the lesser amount of light coming in)
I wouldn't recommend the aluminium foil tip given there. It reflects different
amounts of radiation than the black, metallic pressure plate. You can take a
piece of fully exposed film or unexposed and developed slide (such as the tab
that you get sometimes back from the lab) [the point is that it must be black!],
cut a size enough to cover the plate and stick it with some removable double
sided mounting tape.
The homepage of our 'ListMaster' has very interesting info about IR...
http://www.a1.nl/phomepag/markerink/mainpage.htm
Enjoy!,
Gerard.
BTW: my EOS50E has the damn hole and it used to cause more problems than the IR
sprocket counter. You can crop the little fogged area of the IR counter, but the
"shadow" (it's just the oposite, but I need a name ;-) of the hole is in the
lower right corner... a nice place for composition to bring the eye back to the
picture.
Rafal Walas wrote:
> <snip>
> > Hi Rafal,
> >
> > Do you know what is the source of the "small problem" with IR film
> > in the EOS 1000 and 1000N series cameras? As far as I know, they
> > have a sprocket film drive. Where does the fogging originate?
>
> Yes I (or rather EOS Magazine) have an answer for you:
>
> "All EOS models have a pressure plate on the inside of the camera that holds
> the film flat during exposure. The prssure plate used for EOS 1000 series
> models has a rectangular hole in it. This is to accomodate the tiny LEDs
> that Quartz Date versions of the cameras use to print data onto the film.
> The same plate was used in non-Quartz Date models to keep costs down.
> Infrared radiation can pass through thin plastic, such as the back of the
> camera. The hole in the metal plate allows this radiation to reach the film,
> causing a small rectangular area of fogging in the bottom right hand corner
> of the picture. However, you can easily alleviate this problem by:
> - taping a piece small square of aluminium foil on the back of the camera
> over the position of the hole, IR radiation cannot penetrate metal; or
> - composing your photographs carefully so that the small patch of fogging
> can be cropped."
>
> So now everything seems to be clear. EOS Magazine is really valuable source
> of EOS info.
> Try www.eos-magazine.com !
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