Canon 550D Mirror Removal



Warning:
This page describes a modification I performed on my own camera. If you attempt this (or anything similar) yourself then you do so entirely at your own risk.



Why remove the mirror of a DSLR?


Here is a picture of a 600D mid-exposure with lens removed:



Notice how close the folded mirror is to the path of light rays going to the top of the sensor. This causes problems for fast F-ratio telescopes such as the f/2.8 Takahashi Epsilon 180ED and telescopes using the f/2 Starizona Hyperstar attachment. It causes additional vignetting at the bottom of the image (the image bottom comes from the top of the sensor because a lens turns an image upside down). It also causes a vertical diffraction spike on bright stars at the bottom of an image because the light paths have been interrupted by the straight edge of the mirror.

Here is a flat field taken with a Canon 350D on the Takahashi Epsilon (the scale has been exaggerated to clarify the effect):



Notice that the bottom strip is more vignetted than the corresponding strip at the top.

Here is the same flat field taken with a mirrorless Canon 550D:





Description of Removal Procedure:



There are 2 choices. Either strip the camera right down to gain access to the mirror box - this is a very complicated procedure, removing all the circuit boards and could easily cause permanent damage to the camera. Or attempt to remove the mirror without dismantling the camera. I opted for the second approach but it does damage the mirror hinges and so it's an irreversible procedure. It will be very expensive to have a mirror refitted!


Remove the battery so the camera cannot be accidently operated. Then remove the camera lens and this is what you see:




The mirror can be manually pushed up against pressure of the spring and taped into place:




Next step is to identify the hinges - one each side. Here is the right hand one:




Here is the precision screwdriver I used to melt through the plastic hinge. Alternatively a small soldering with a small bit could potentially be used. The advantage of melting the plastic is that no pieces of rubbish or dust is created




Heat the tip in a flame until it is just on the verge of glowing red:




The next part is very delicate. Gently press the hot tip into the plastic hinge to sever it. Be extremely careful not to go too close to the delicate shutter mechanism. Also be careful not to allow the tip to touch the side wall or rear wall of the mirror enclosure. You may need to reheat the tip 2 or 3 times and "cut" further each time until the hinge is severed or weakened sufficiently to easily break off. A steady hand and great care is required. Below is a picture of the severed hinge but it is difficult to see. Note the track in which another pin runs.




I was unable to remove the mirror because of the pin that runs in the track:




Here is the second hinge that needs to be severed in the same way:




After severing the second hinge, the mirror could be held and twisted with tweezers to allow the pin to come out of the track. Be very careful to hold the mirror away from the delicate shutter mechanism:



Don't forget to remove the remains of the hinges!! You don't want them floating around inside the camera!


There is no further need for the "spongy" section. Grab with tweezers and cut it away with a scalpel:




Here are all the pieces removed. Mirror assembly with two severed pins and the spongy bit. Sorry about the messy thumbprint on the mirror:




Here we have the final product - a mirrorless Canon 550D. Note how there is plenty of room for the lightpaths now.



Obviously the viewfinder can no longer be used and it should be blacked out or taped up to prevent light leaks during astrophotography. As far as I can tell the camera seems to behave normally when used in liveview mode. It appears to autofocus and autoexpose quite normally for daylight photography. However I haven't tried out every camera function because this one will be exclusively used for astro-work.

Feel free to contact me with comments or suggestions: astro@shelleyz.co.uk