With Digital cameras - by Chris Maddock
Infrared photography is not restricted to film users,
but can be possible for many digital camera users. This
article is intended to explain a little about how to take
digital IR photos, what equipment is needed and how to process
the images. I've split it into several sections for clarity;
Cameras and Lenses
Taking the images
Conventional Monochrome IR processing
False-colour IR Processing
Dealing with “Hotspots”
Not all digital cameras can take IR photos. To reduce
IR blooming in images the sensor assembly often includes
an infrared blocking filter, which rather restricts what
can be done if you do want IR. The first thing to do if
you want to try it is to find out if your camera can see
IR with any degree of success. The easiest is to look on
the Internet to see if anyone is already successfully doing
IR with the same model. If you have no luck there then you
can at least test to see if your camera can at least see
any IR light. All you need is a TV remote control – in a
darkened room point it at the camera (and the camera at
it) and take a photo whilst holding down one of the buttons
on the remote. If the resultant image shows a bright spot
then the camera can see IR light. Unfortunately, that is
all it will tell you. To test further you need an IR filter.
Lenses can also be a source of problems. Some lenses
have coatings that will cause a bright “hotspot” in the
middle of the image, which will render them unusable for
IR work. In some cases the hotspot is not excessive and
can be dealt with in Photoshop – I’ll cover how I deal with
this on my Canon G5 at the end of the article. A partial
list of Canon lenses that do and do not cause a hotspot
can be found here
There are quite a number of these on the market, the
principle difference being at what point in the light spectrum
they block light. Sometimes (but not always) the filters
have names based on the cut-off point, a higher number cuts
off more visible light, if the name doesn’t relate to the
cut-off point then a visit to the manufacturer’s specs will
give the answer. Some filters are available as screw-in
types in different sizes, others are gel type filters which
tend to be cheaper but harder to handle and less durable.
Many people use an R72 or Wratten 89B filter, which cuts
out light wavelengths under 720nm (nanometres), but these
tend to be expensive – especially when experimenting. A
49mm Hoya R72 filter is around £24, the price can increase
sharply for bigger sizes.
A cheaper alternative is the IR87 from the Lee technical
filters range. This cuts off at 730nm and is a gel filter.
A 100mm square will cost around £13 and can be cut to mount
in a Cokin P-series frame or cut to size to make several
for lenses that take rear mounted filters.
An even cheaper alternative if you can find it is Ilford’s
SFX filter, which is not always available since Ilford only
produce small amounts of the SFX film from time to time.
This is intended for use with SFX200 InfraRed film. Although
Ilford don’t state the cut-off point they do list the R72
and Wratten 89B as suitable alternatives. I reckon the cut-off
point is lower than those since I can just about see through
it (unlike the others) which means it is passing some visible
light. This is my personal preference since I like to produce
false-colour IR photos and some visible light is needed
for these. The SFX filter is a gel filter in Cokin A and
word of warning about gel filters; whilst these can be mounted
in Cokin type holders I found that the length of exposures
needed (anything up to 30 seconds) can allow sufficient
visible light to leak behind the filter and reflect off
the filter and any dust particles.
My solution is to sandwich a layer of the gel between two
screwin skylight filters. This stops the light leakage and
protects the filter.
Because of the IR blocking filter, most digital cameras
have a much lower sensitivity to IR light than they do to
visible light. The result of this is that exposures are
long – depending on the camera, subject, aperture and ISO
setting used they can be anything from 5-30 seconds – using
a tripod is strongly recommended, as is bracketing.
Correct white balance is important. The IR filter will
add a cast to the images, ranging from a strong magenta
to a strong red depending on the camera and filter used,
so it’s strongly recommended to set the camera to a custom
white balance. This is usually done by taking a shot of
a sheet of white paper (with the IR filter fitted) then
setting the camera to calculate and use the white balance
from that – check your camera manual for the exact method.
If you shoot RAW, then this can be dispensed with and the
white balance chosen when processing the images.
Framing the shot can be very difficult, especially when
using an R72 or Lee 87 filter, as there is hardly any visible
light transmitted. If you use screw-in filters then you
can set the framing up before fitting the filter. Drop-in
behind-the-lens filters are a real pain but pre-framing
can be done – but don’t forget to put the camera body-cap
on whilst fitting the filter, to prevent dust getting into
the mirror box whilst you’re doing it. The simplest solution
I’ve found is not to use an SLR – my Canon G5 can rather
*********** well through my preferred SFX filter, so I use
that and view it on the preview screen. As a committed SLR
user I knew I’d find a use for that screen eventually ;-)
Focussing is the final hurdle to overcome. IR light focuses
at a different point to visible light and most modern lenses
don’t have an IR depth of field scale – if they have a DOF
scale at all. Older lenses that had a proper DOF scale often
had an additional line for IR focussing. You can focus manually
using visible light then back it off a little although how
much requires practise. A reasonably small aperture (f8
or so) will help to correct any inaccuracy. If you have
an autofocus camera (thinks, are there any non-AF digitals?)
then your luck may be in. Provided that you don’t use too
dark a filter the camera may be able to autofocus successfully,
and that will take into account the required shift for IR
focussing. It’s worth a try, even my Canon D30 (not the
best of AF systems in the world) can focus most of the time
with a Lee IR87 filter.
OK, we now have some images to work with, so let’s get
Conventional Monochrome IR processing
We’ll start off processing an image for the traditional
infrared black & white look. I shot this one in RAW
so didn’t worry about the white balance. Here is how it
looks when opened in RawShooter, apart from the amount of
foliage it’s very Martian.
After selecting a grey area of the clouds to set the
whitebalance, things look far better, so I convert it and
open in Photoshop.
quick Desaturate and Curves adjustment to bring up the contrast
gives me the finished image, ready for framing.
An interesting variation on infrared is to use some colour
but partially reverse the colours by swapping the red and
blue channels. This can produce striking images but doesn’t
work for all scenes.
This is another shot which I took in RAW, so once again
we have a strong red cast when opened in RawShooter.
Again, I select the whitebalance from a grey area of
cloud and convert it before opening in Photoshop.
To perform the Channel Swap go to Image->Adjustments->Channel
With the Red Output Channel selected (default) change
the Source Channels – Red to 0% and Blue to 100%. Leave
Now select the Blue Output Channel and change the Source
Channels – Red to 100% and Blue to 0%. Again, don’t make
any change to the Green channel.
Once I’ve done this, the image looks like this;
quick application of Auto Contrast and Auto Color and this
one’s ready to be framed as well.
I’ve automated the Channel Swap using a Photoshop Action
which you can get here
As I said in the Cameras & Lenses section, the coatings
on some lenses can cause a bright hotspot in the middle
of the images. I found that my G5 does give a hotspot but
that it’s not too excessive, and most of the effect can
be edited out. If you look closely at the false colour image
you can see a patch in the middle of the image that is slightly
brighter and slightly yellowy, this is the hotspot.
It can’t be removed completely, but it can be reduced –
this is the method I use for my G5 images.
Once the image has been converted and opened in Photoshop
I make an oval selection somewhat larger than the hotspot,
and feather it by 200 pixels (Select->Feather)
then open Image->Adjustments->Hue/Saturation and tweak
the settings. Somewhere around Saturation –40 and Lightness-10
usually does the trick
Now remove the selection (Select->Deselect) and perform
the Channel Swap as above. Once again, a quick application
of Auto Contrast and Auto Color finishes it off.
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text and photos are copyright © Chris Maddock, 2007