| Our senses strongly shape our understanding
of the world, as every photographer well knows, but they sample only small
slices of the reality around us. What might we learn and think and feel
if we could hear beyond 20-20,000 Hz, as our dogs do, or see beyond the
narrow visible light band at 400-700 nm? One of the major principles of
"ghost photography" is that the energy of a "ghost"
is not seen in visible light, but lies instead in the invisible worlds
of infrared (IR) and the ultraviolet (UV) spectrums.
Digital
cameras are fitted with charged coupled devices (CCDs) which have an inherent
sensitivity to both infrared and ultraviolet radiation as well as the
visible spectrum. First generation digital cameras and the cheaper end
of the range of second generation cameras had poor or no infrared filters
built over the CCD. This led to them being too red in tungsten lighting
and were considered to be insufficient for normal photography.
So, digital camera manufacturers began including
effective infrared absorbing filters over the CCDs which make them effectively
a lot less sensitive to infrared. These filters are called "IR pass
filters" and are placed directly over the camera's CCD. this was
done to reduce IR contamination artifacts to acceptable levels in the
visible light images most camera buyers aim to take.
The focus of this article is to explain the process
in removing the IR cut filter and replacing it with optics that will allow
a greater transmission of infrared or ultraviolet light.
Caution!
Do
not attempt to perform the following procedures by yourself unless you
are familiar with optics and working with electrical components. It is
very easy to permanently damage your camera if you do
not know what you are doing. The process we are describing should only
be performed by a certified camera repair technician.
You have been warned!
We
will be demonstrating the procedure using a Sony Mavica (MVC-FD85). Other
cameras will vary in the disassembly but the process is basically the
same. All pictures are thumbnailed, so click on the images to see the
more detailed photos.
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Disassembly
Procedure
Step
1 : Remove the six screws that hold the two halves of the camera
together. After the screws have been removed, gently pry open the
two halves but use caution. The strap holder on the upper right
is screwed on the back half of the camera and slides through a slot
on the front half. It can be removed by gently pulling the rear
half straight back.
Step
2 : Locate the screws that secure the CCD to the optics housing.
this is located on the upper left of the front half of the camera. |
Watch
out for the strap holder
|
The
screws that hold the CCD in place
|
Step
3: Remove the two screws that hold the CCD to the optics housing. The
CCD can easily be removed out of the housing.
Remove
the screws
|
The
CCD pops free
|
Remove
the CCD from the housing
|
Remove
the filter cover |
Step
4: Carefully remove the cover for the IR cut filter. This can be
done by gently prying up on the corners. On this model two sides
appear to be composed of rubber. This rubber part is part of the
CCD and not the filter cover.
Step
5: Measure the IR cut filter. This is the light blue piece of glass
that sits on top of the CCD. The measurement here must be precise.
the IR cut filter must be replaced with another optic of the same
size that allows a greater transmission of either IR or UV light
(depending on how you want to modify the camera). This is important
because without it, the camera cannot focus properly.
Step
6: Now you need to purchase the new optic to replace the IR cut
filter. You can purchase them on-line from Optics-online.com
or Optolife.
Your local camera repair shop may or may not have these in stock
and may have to order them.
Step
7: After you have the new filter, you need to remove the old one.
Usually the filter is fixed to the CCD with some sort of bonding
material like optical silicone. Others have no bonding material
at all and are held in place by the filter cover. Gently remove
the IR cut filter and replace it with the new filter.
Step
8: Reattach the filter cover and reassemble the camera.
Article
by Cody Polston
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The
IR cut filter (light blue) |
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