# 5D3 Focus Screen Cleaning Lesson



## celltech (Apr 30, 2013)

Was feeling spunky the other night and decided to clean the dust from my mirror. Was using a cotton swab and 90% isopropyl alcohol (1st mistake). Thought what the hell, I would clean the focus screen as well (2nd mistake).

For reasons I still don't understand the focus screen ended up with "milky" stains in 2 areas. It kinda reminded me of hard water deposits on shower glass. I am not sure if the tiny water component in the alcohol stained it or if the swab damaged the etching on the screen. Whichever it was, it was not coming off.

Of course the screen is not supposed to be user replaceable (and just why not Canon??? the 5D2 was...) and finding a OEM replacement was proving hard. Then I found a service manual, got the part number and found they are only $11. Part number is CY3-1655-000 FYI...

It's not that hard to actually replace. Be sure you have the right sized screwdriver as the screw heads are soft and seem to be harder to find than the screen. When you are putting the retaining spring back **do not touch the screen with anything**...that plastic is as soft as putty.

So now I have a rocket blower, PecPads and 99% alcohol to clean the mirror. But I am never going near that screen again...


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## cpsico (Apr 30, 2013)

celltech said:


> Was feeling spunky the other night and decided to clean the dust from my mirror. Was using a cotton swab and 90% isopropyl alcohol (1st mistake). Thought what the hell, I would clean the focus screen as well (2nd mistake).
> 
> For reasons I still don't understand the focus screen ended up with "milky" stains in 2 areas. It kinda reminded me of hard water deposits on shower glass. I am not sure if the tiny water component in the alcohol stained it or if the swab damaged the etching on the screen. Whichever it was, it was not coming off.
> 
> ...


Sometimes doing it yourself just isn't worth it!


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## celltech (Apr 30, 2013)

Well...yes and no. Had I realized how soft the focus screen plastic is, it would have changed things. If it's truly dirty and has dust you just can't blow off I will say that it's not hard to remove and clean with a soft brush if you are careful.

I only wish I had read up more on what it was made of and how it was made. I truly thought it was glass when I started...

And now that I know it's only $11 I feel a lot better about messing with it.


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## neuroanatomist (Apr 30, 2013)

celltech said:


> It's not that hard to actually replace.



Of course, there's replaced...and there's _properly_ replaced. During camera assembly, one of the steps performed by an actual human being is the horizontal and vertical alignment of the focus screen, which is done using a variable number of tiny shims (for bodies with a user-replaceable focus screen, it's the holding bracket that's carefully shimmed into alignment). That alignment ensures that the focus screen provides a flat field in the same plane as the image sensor. If you only use autofocus and not manual focus through the viewfinder, you don't really need to worry about it, but if you frequently MF, a misaligned focus screen can result in missing critical focus depending on where your subject is in the frame.


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## Mt Spokane Photography (Apr 30, 2013)

neuroanatomist said:


> celltech said:
> 
> 
> > It's not that hard to actually replace.
> ...


 
Canon will sell the shims, assuming you know which ones you need. Some 3rd party focus screens include the shims matched to the screen.

Another common error is using a Phillips head screwdriver rather than a JIS. Its easy to damage screw heads if you use the wrong tool. (Speaking from experience)


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## celltech (Apr 30, 2013)

As I was looking around for a new screen I kept coming across the $92 versions from focusingscreen.com and was worried about the shimming. But once I found the OEM part I was hoping that it was built with the same dimensions and accuracy as before.

I did notice my camera had 4 shims. 3 looked to be brass and the last one was something painted black. As I think about it I wonder why they even need them. If they never intended for the screen to be replaced I would think things could be manufactured with better tolerances. My stack of shims is 1/2 the thickness of the screen.

I never use MF so it's no biggie for me. I have not taken a critical eye to it but when the camera locks focus it looks good in the viewfinder. My vision kinda sucks anyway...time to get lasik again.


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## awinphoto (Apr 30, 2013)

QUICK... while the camera is in warranty, send it to canon, they will replace the screen under warranty. I had a similar problem... dirt on my screen and I tried to self clean it.... screwed the pooch... I sent it to canon and they replaced the screen free of charge (minus shipping charges)... send it in before the warranty expires.


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