# Cleaning the focusing screen.



## tecboy (May 8, 2012)

I have some dirt and lints on my focusing screen.  I watched in youtube about cleaning it.  It looked easy but I have a Canon T3i, and I don't know how to take the focusing screen off.  Tips anyone?


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## 480sparky (May 8, 2012)

Check the manual.  Search YouTube for a video.


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## tecboy (May 8, 2012)

There is nothing in the manual about taking focusing screen off.  Also, I can't find anything in youtube.


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## 480sparky (May 8, 2012)

Perhaps the screen is non-removable.


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## KmH (May 8, 2012)

It's usually the side of the focusing screen you can get to just by removing the lens that gets stuff stuck to it.

Use a blower/brush to keep your camera's mirror box dust free.

Use good technique when you change lenses to minimize the chance of dust and whatnot getting into the mirror box area of your camera.

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Adorama Camel Hair Cleaning Brush, 1"


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## tecboy (May 8, 2012)

Is it okay or not okay to use a cotton swap and a cleaning fluid to clean the focusing screen and reflex mirror?


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## KmH (May 8, 2012)

It is not ok to use a cotton swab, because it will likely leave more lint than it picks up.

The mirror mechanism is pretty delicate, because it has to be light-weight so it can move so fast.

There is no good reason for using any kind of cleaning fluid inside the mirror box.

Something is seriously amiss if the mirror has more than just a very light amount of dust on it.


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## imagemaker46 (May 8, 2012)

KmH said:


> It is not ok to use a cotton swab, because it will likely leave more lint than it picks up.
> 
> The mirror mechanism is pretty delicate, because it has to be light-weight so it can move so fast.
> 
> ...



I just use the same cloth I use to clean eye glasses, using a can of air can blow the dust deeper into the camera, unless you are really careful with it. There should be no need to remove the mirror.  Follow what KmH has suggested.


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## tecboy (May 8, 2012)

I think it is a debating issue.  I read in some other forums, and one guy said he uses cotton swab with isopropyl alcohol without any problem to clean mirror.  I saw in youtube that he uses square swabs in individual wraps with cleaning solution to clean the mirror.
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## dxqcanada (May 8, 2012)

From what I recall the ground screen should never be "cleaned" as it is a finely etched surface. Blower Ok. Any rubbing/scrubbing device NO.

I have seen (in the past) many damaged ground screens from people who have cleaned it with a qtip, cloth or other ... only to leave permanent marks.


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## Josh66 (May 8, 2012)

Be very careful.  The internet is full of stories about focusing screens getting destroyed from 'cleaning'.  IMO - if a bulb blower doesn't do the trick, learn to live with it.

Anything you can see on the focusing screen will never show in the pictures - it's just annoying having to see it all the time.

When the exposure is being made, the mirror and focusing screen are out of the light path.


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## tecboy (May 9, 2012)

Got it.  It is good to hear from you guys.


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## tecboy (May 9, 2012)

Is there anything I can read about reflex mirror on the internet?  How does it works?


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## tecboy (May 9, 2012)

I found info on how to take the focusing screen off.  Does anyone knows where I can buy a good thin tweezers?  
Canon EOS 600D Focusing screen installation


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## dxqcanada (May 9, 2012)

Tweezers


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## tecboy (May 9, 2012)

dxqcanada said:


> Tweezers


Thanks.
What do you guys think of these? Visible Dust Focusing Screen Swab


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## KmH (May 10, 2012)

tecboy said:


> Is there anything I can read about reflex mirror on the internet?  How does it works?


You could look on Wikipedia and use an Internet search engine to discover other online resources.

Digital single-lens reflex camera - Wikipedia, the free encyclopedia


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## Garbz (May 11, 2012)

tecboy said:


> Is there anything I can read about reflex mirror on the internet?  How does it works?



The wikipedia page KmH linked to will give you half the story. Basically the mirror reflects light upwards to the viewfinder through a focusing screen. When you press the shutter it moves out of the way and the shutter goes off. 

Here's an ultraslowmo:
https://www.youtube.com/watch?v=7Ovar4tjRSY&feature=fvwrel

Worth mentioning is the missing part of the information is that there's actually TWO mirrors. The main one you can see is semitransparent. Some light gets through this mirror and is reflected by a second mirror behind the main towards the BOTTOM of the camera. The bottom is where the autofocus system is installed.


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## tecboy (May 11, 2012)

Garbz said:


> tecboy said:
> 
> 
> > Is there anything I can read about reflex mirror on the internet?  How does it works?
> ...



I always wonder what the 2 mirrors are for. Thanks


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