|
Canon 300D IR Filter Removal Mod. |
|
|
|
Written by Dave Grennan
|
Having spent the last year refining my astrophotography
techniques. I have now come to the conclusion that the major
factor limiting my results was the IR blocking filter installed in
front of the CMOS sensor by Canon. As I live in a city suburb, I need
to use broadband LPRs for much of my imaging although LPR filters are
great for passing some wavelenghts of light, they do absorb some light
so I was being hit by a double whammy. In order for photons to
reach my sensor, the little fellers need to fight through two selective
filters. I knew I could get better results than I had been
acheiving.
Why do the Mod?
The stock filter installed by Canon is designed to absorb UV and IR
wavelenghts and give the optimum colour balance for normal daytime
photography. The filter does a great job on ordinary shots
but has serious shortcomings when it comes to astrophotography.
The reason is that the stock filter as well as blocking the IR
wavelenghts also blocks some other wavelenghts which are a major
component of some astronomical objects. Particularly important is
the hydrogen alpha wavelenght. This forms a major component of
the light from many nebulae and other astronomical objects. A popular
mode of astrophotography is narrowband imaging. The inbuilt
filter pretty much prohibits this as it blocks most of the lines imaged
with narrowband filters. SInce I live in a light polluted suburbm
Barrowband imaging is definitely something I want to do. A while
back I did a test. I took a shot of M27 with an OIII filter in
place. Although I could visually see M27 through the cameras view
finder, no length of exposure would record the nebula. Nada, not
a thing!! The only conclusion I could reach was that the internal
filter was blocking all of the lines which my OIII filter transmitted.
The
down side of doing the mod is that normal daytime shots will not have
the correct colour balance once you carry out the mod. All photos
will look very decidedly pink due to the extra sensitivity to red
light. There are two ways to correct this
1 - Use the custom white balance on the camera. The downside of
this is that you need to take a photo of a white target every time your
lighting changes. Also I think the results even when this is done
is not entirely satisfactory.
1- Use a colour correcting filter. For me this is the way to
go. No need to mess with white balance and the results look far
more satisfactory than with the CWB. European modders note:
The only filter I can find which does a satisfactory job is the XNite CC1 filter.
The shipping charges outside of the US are more than the cost of the
camera. Cost me 82USD shipping and handling for a filter that
costs 76USD!!
Who should do the Mod?
My experience doing this mod was made a lot more enjoyable by following
Gary Honis's procedure to the letter. However this mod is not for
everyone. You must understand that as soon as you open the camera
you immediately void your warranty. Not a problem for me as my
camera is out of warranty anyway! Although I am not an electrical
engineer by profession, I have quite a bit of experience at this kind
of thing, including modifying several webcams for long exposures and
replacing the CCD sensirs in these cameras. Although the canon
300D procedure is quite straightforward you need to be comfortable with
working with small scale electronics, understand electrostatic safety
measures to protect your camera from damage. If having read
Gary's mod and you are not absolutely happy with carrying out the
instructions, I highly recommend you leave your camera alone or get
someone else to do it! Saying all of that, I found the mod posed
no major issues and I feel most people with a basic understanding of
such matters will have no problems at all.
So your still reading eh?
Good, Good!
I do not intend on repeating Gary's excellent procedure
as I have nothing really to add to it. I will outline some of the
difficulties I faced and how I resolved them and present some photos I
took along the way.
Disassembly of the camera was fairly routine. I just
followed the steps as outlined by Gary. A couple of notes
here. It is vital that you label all of the screws as you take
them out. I simply taped them to a piece of white paper and wrote
beside them where they came from. If you dont do this you havent
a breeze of putting them back where they are supposed to go.
As for cutting the replacement glass. I used the 3mm glass which
Gary recommended in his mod procedure (from edmund optical). I decided to cut the glass
with the protective film still in place. I used a (brand new)
rotary cutter to scribe the break line on the glass. The glass
broke perfectly straight with just moderate finger pressure. Once
I installed the glass I managed to get finger marks on it when
installing it in the filter frame. After trying to clean it, I
decided to cut a fresh piece as I could see micro scratches all over it
from cleaning it.
The spacer shims required to bring the autofocus point back to its
pre-mod position were cut from a 0.1mm 'feeler gauge' finger.
This was taped to a piece of wood and drilled with holes the same size
as the CMOS assembly mounting screws and then cut to size with a
scissors.
The other problems I faced were more unexpected. It seems than
Canon had used an awful ot of glue to stick the filter in place. After
an hour of prodding poking and chipping the old filter, it simply would
not budge. I came to the conclusion that I was past the point of
no return anyway. So drastic action was called for. I took
a hammer and a screwdriver to it breaking the glass right in the
middle. That sorted it out pretty quickly!! A side issue of
all the glue used in the filter holder was that some of the glue had
bled out an stuck the thin black gasket which surrounds the
filter. I broke this gasket a couple of times trying to carefully
pry it off. This wasn't a big issue. When I had replaced
the filter, I simply glued the pieces back in place and painted over it
with some flat black modelling paint.
Some photos showing my camera at various stages of modification.
The above shows the camera with the back removed exposing the circuit board and the metal shield still in place.
Now the shield has been removed exposing all the ribbon cables which need to be disconnected.
The circuit board has now been removed uncovering the CMOS assembly itself. Now the real fun begins!!
The circuit board has been removed. Note you need to take extra
care hadling this. Use proper ESD safety measures and store the
board in an anti-static bag if possible. The last thing you want to do
is fry one of those ICs with static from your body!
The CMOS assembly now awaits the filter replacement. Take great
care not to get finder marks on your filter when installing it. I
noticed a small finger mark on my clear glass replacement after the mod
had been completed. Thankfully its on the outside so I can clean
it later.
Since I wrote this report I've now had a chance to test the newly
modded camera under the stars. My first light image of the
horsehead nebula (B33) pleased me no end.
The value of modifying the camera is now patently clear to
me. You may ask, what did the pre-mod horsehead look like?
Let me put it simply. There was no pre-mod horsehead shot because
I simply couldnt record it with my camera in its pre-mod state. A
whole new world of imaging is now open to me including narrowband
imaging, (when I can afford the 2inch narrowband filters).
Normal Daylight Color Correction.
I purchased an XNite CC1 colour correcting filter so that I may
continue to use the camera for normal daytime shots. Here are
some images taken with and without the filter to show just how well it
works. All images were taken in "Auto" mode with flash.
First is a shot without the camera. "Pretty in Pink" eh?
Now the same shot with the XNite CC1 filter
Another shot without the filter
and again the same shot with the filter.
I'm very pleased with the colour balance now that the CC1 is in
place. In fact I think I prefer the colour balance than in the
pre mod state. The colours certainly strike me as being richer
than before the mod.
Well now I have the best of both worlds. A capable astro camera
which doesnt cost the earth and a decent camera to take normal shots
with. Now who could argue with that!
Clear Skies,
Dave.
|
Articles 
