Do it different

[Dieter Lefeling <lefeling@xxxxxxxxxxxx>]

Hi folks,

I joined this list some days ago. Nice to meet some other guys that are
interested in this special topic. I'm doing IR photography for about
eight years now, using a technique I haven't found mentionend yet. I'd
really like to know what you think about it:

1. I use Kodak HIE 2481 with Canon FD equipment in the 17-85mm range.
2. My standard filter is a "normal" #25 (R60) red filter.
3. I set my camera to 1600 ASA (repeat: one thousand six hundred),
   metering is done through the filter (standard TTL, average or spot).
3. No focus correction is applied, even when I do close-ups and the lens 
   is used wide open at f/2.8
4. I use D-76 (stock, undiluted) for 12 minutes.

Some of this may sound a bit strange, but it really works! Perfectly!
I told some friends of mine about this method, they tried it and, guess
what, they got the same perfect results with their Minoltas and Nikons,
AF and MF. Usually I suggest a 1000 ASA rating, but most of my friends
feel the resulting negatives still look somewhat overexposed, so they'll
end up somewhere around 2000. Obviously, they/we are doing something
right!?

Explanations:

The 1600 ASA rating also appears on W.J.'s homepage (for IR slides).
It's simple: With a #25, the camera usually "sees" two or three f/stops
less light compared to no filter at all. Others rate HIE at 400 without
any filter and a #25 with HIE needs a 2x factor (=200). Since the camera
records a 4x or 8x factor for this filter (depends on make and model),
you finally get the mentioned 800 to 1600. I used this rating in bright
sunlight, with artificial (tungsten) light and on cloudy, overcast days,
bracketing +/- 1 stop just to be sure. The results were always perfect.

I don't use focus compensation simply because I don't need it. Take a
look at your lens and see where you can find its IR index. At least in
the wide-angle to short tele range, it usually is somewhere at f/4 or
f/8 on the depth-of-field (DOF) scale. This means, at least with f/4 or
f/8 no focus compensation is needed because any deviations are covered
by the lens' DOF. Now remember that this IR-index shows the neccessary
focus shift when focusing is done with "white light" (usually equivalent
to 550 nm) and the film is exposed with 800 nm (HIE's peak sensitivity -
at least Canon's indexes are calibrated to 800 nm). That means, this
focus shift is just right when you focus without a filter and expose
your picture with a "black" #87 or at least #88A. But that's not what
most of us do: We use a #25 red filter, i.e.: we focus in the 600-700nm
range and the film records the 600-900nm range. This means, about one
third of the light that reaches the film is perfectly focused (okay,
that's a *very* quick and dirty explanation, but I think you'll get the
picture). The sharpness of the remanining 700-900nm portion depends on
your lenses' color correction. You can just fine-tune your focusing by
applying a very slight correction towards the IR-index. Say, half the
correction the index suggests. But such a slight correction would be
obsolete since it's covered by DOF already at f/2 or f/4 - so you really
can (well, usually) forget about it.

Okay, IR-Gurus - what do you say?

Dieter

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End of Infrared-Digest V0 #402
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