Canon 350D IR Filter Modification

Canon 350D IR Filter Modification


Page 1: Introduction and Camera disassembly
Page 2: Filter Replacement
Page 3: Camera reassembly

Introduction

The Canon EOS range of digital SLR cameras are well known in the field of astronomy for their use as deep sky imagers. Whilst they are great for imaging star clusters, galaxies and reflection nebulae, there comes a problem with other types of nebulae.

Inside the camera, in front of the CMOS sensor is a 'low pass' IR filter which blocks out the IR light that the sensor is sensitive too. Unfortunately it also cuts down two important wavelengths of red light used to image nebulae. One is the crucial Hydrogen-Alpha wavelength, of which only 25% is transmitted. The other is the Sulphur-II wavelength, used in tri-colour emission line imaging along with Oxygen-III, only around 15% of S-II light is transmitted.

There is only one real solution to this; remove it. Some people just remove it, others replace it with anti-reflection glass. I have chosen to replace it with the Baader ACF filter, which blocks out IR and UV light, but much more steeply. This allows it to still be used normally for daytime photography yet transmits around 97% of both H-alpha and S-II light.


It's not an easy task, but hopefully worth it. Over the next few pages I will show you how it's done.
First, things you will need:
A grounded wrist strap is recommended at all times when handling the electronics and CMOS sensor.


It's also a good idea to keep everything in containers, with screws separated depending on which stage they were removed.


Warning
Needless to say, opening up your camera and messing with the insides will void its warranty. There is a possibility that you will destroy your camera if you do not perform the modification correctly. Do not attempt this if you have no experience with electronics, or do not want to risk breaking your camera. By continuing reading, you accept these risks as your own responsibility.

Camera Disassembly

The camera, pre-mod... let's get started.



1) Before starting, remove the battery and CF card.



2) First, remove the 2 screws on the side with the 3 jack sockets.



3) Remove the 5 screws from the bottom.



4) Open the CF card compartment and remove these 3 screws.



5) The back of the camera can now be detached with the help of a flat-headed screwdriver or similar.



Gently tease it away from the body. Note there is a small clip near the On/Off switch.



Be careful when removing the back, as it is still attached by two ribbon cables at the bottom.



6) The ribbon cables do not simply slide out, but have a hinged lock that must be undone first.
To unlock it, use a thin flat-headed screwdriver to raise the black bar to a vertical position, approaching from the side with the ribbon cable.
It should then be able to slide out.



7) The other cable is similar, except the black bar needs to be raised from the opposite side from the cable.
The back is now separate and can be set aside, preferably in a bag to keep out dust.



8) The connector with 3 red wires can be removed. It does not slide out but simply pops out, with some levering from beneath.



9) Remove the left side cover. Start from the bottom as it is clipped at the top.



10) You must now remove the centre metal shield to gain access to two ribbon cables underneath.
It is attached by 5 soldered tabs (red), the tabs circled in yellow were not actually soldered down on mine.
Use a soldering iron and some solder wick, carefully remove the solder from, and lift up each of the tabs so that the shield lifts away.
Be careful to keep the soldering iron away from the delicate components, and any plastic parts.





11) You'll need to remove a screw that's behind a piece of the plastic cover, you may wish to use the soldering iron to melt a hole to get to it.
I just cut away a chunk of the plastic with a knife. It won't be visible after reassembly, so it doesn't need to be neat.





12) There are now 9 ribbon cables to be disconnected (red). Go around each one, and lift up the tab.
I have suggested the order that I found easiest to do this in. Also remove the 4 screws circled in blue.



13) Slide this piece of metal from the CF compartment. With some teasing it should come away.



14) Pull each of the ribbon cables out of their sockets, you can use a pointed object to poke into the small holes to help.
When they are all detached, lift the circuit board away from the bottom.



15 ) The board is still connected by one set of black wires near the top left corner. This is simply pulled out.



16) The board can now be set aside, preferably in an anti-static bag to keep dust and static away.



17) The CMOS sensor is now exposed. Unscrew the 5 circled screws and carefully lift away the assembly.



Make sure the 3 copper spacers above the holes with the 3 longer screws are still in place.
Put the body away, protected from dust, keeping it facing down to prevent any of the spacers from falling out
(there are also some behind the metal that can't be seen, so don't shake it about)


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