# How (not) to clean the phase af array & vf screen?



## Marsu42 (Apr 23, 2014)

I'm shooting outdoors a lot and my 6d has gotten quite dirty - as I just learned this might be the reason why the outer points have such a mediocre performance. I clean my sensor all the time, but have never have done this with the af array and vf screen (shows a lot of dust specs).

My first idea would be the rocket blower, but if that doesn't help is there anything I should *not* do to clean these? I faintly remember someone writing the matte vf screen is very sensitive and improper cleaning can ruin it...


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## Mt Spokane Photography (Apr 23, 2014)

The Focus screen is made of a easily scratched plastic that also takes and retains fingerprints. I don't recommend touching it unless you are ready to buy a replacement.

Blowing gently is OK, but you are just moving dust from one place to another.

I've never heard of anyone cleaning the AF sensor, dust on it does not show in the images, and is very unlikely to affect exposure, so the risk versus improvement ratio is pretty high. Same for the sub mirror.


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## tolusina (Apr 24, 2014)

Thanks, your post inspired me to get out the garden sprayer and the EG-S box and tool, finally blow that chunk that's been annoying me away to somewhere else.

I've heard/read same like Mt Spokane, the focusing screen is a never ever touch item, so I use the Canon focus screen tool and box that came with the EG-S screen. The box has a slot for holding one screen while you take the other out of the box.
There was a visible spec on the screen, blew that off, still had a chunk in the finder so I blew off the focusing sensor/bottom of the prism, chunk is now gone.
My imagination fails to see a wet clean method of cleaning the focus sensor, access is pretty odd.

As Mt Spokane commented, stuff blows from one place to another, that's why I've adopted/adapted a garden sprayer.

My thorough cleaning procedure goes something like this;
Remove lens, blow off the rear element and mount.
Blow out the mirror box with the mirror down.
Using mirror lock up, NOT yet manual sensor clean, blow out the mirror box again being very careful not to full blast the shutter blades.
Release the mirror to its rest position, remove the focusing screen, place the screen in the screen (tool) box, blow off both sides of the screen, blow off the bottom of the prism, re-install the focusing screen.

Now I'm ready for the manual sensor clean mode, assuming I've already determined the need to do so.

For those that don't yet know, here's how to check your camera's sensor for crud.
Set ISO to minimum, aperture preferred, stopped down all the way, focus on infinity, jpg is ok, but I'd sure want the largest, finest .jpg.
Shoot a totally plain scene, a cloudless daytime sky works, I usually use either a blank sheet of paper or my PC's screen with notepad open and full screen. Indoors, you'll likely have a long shutter speed and camera movement, no worries, it doesn't matter for this test as the sensor cannot move relative to itself, you'll see. 
Review your .jpg at full size, scroll around the whole thing looking for anomalies.
Dust, grit, fibers and the like will have well defined contours, hopefully, these will blow off with whatever blower you use.
Spots from liquids, grease and such will be more like blobs, these will need wet cleaning. Do blow off the sensor prior to wet cleaning, even if no dust is visible in your test photo.

I use Photographic Solutions Inc., photosol.com Sensor Swabs and Eclipse cleaning solution for wet cleaning the sensor, follow the P.S. instructions. I usually cheat on the instructions a bit, I'll swab a couple of passes with each swab.

I've never been able to see any contaminants on the sensor with naked eyes, nor with a 4x(?) loupe, sensor just dazzles me like a flat kaleidoscope.

Garden sprayer, I know, sounds like it might be extreme, it's not.
I just measured pressure developed by a hearty squeeze of an ear syringe, found 15 psi and a burst of less than a second.
Garden sprayer pumped until it gets pretty stiff develops 25 psi, sprays continuously for about 12 seconds, pressure drops very rapidly.
Haven't yet tested canned air, it's now on my pretty immediate list.

I mentioned “full blast” and the shutter blades above, I did that very briefly once, blades shook and rattled quite a bit, scared myself. Got lucky, no damage occurred, still, I won't be doing that again. Garden sprayer will blast something else for 5 seconds or so before it gets aimed at the shutter blades again.

Of course, everything in there is delicate, no touch, no scratch, shutter blades seemed to be the most fragile of all, also good places to trap dust.

Wet sensor cleaning is a tedious process, I've never gotten satisfactory results with the first pass, several passes are usually required.
Clean, take and review a test shot, repeat until satisfied. 
It takes a while, don't leave it to 5 minutes before you head out to a shoot, night before is better.

Careful as I was (or thought I was anyway), last cleaning left some dried cleaner spots, barely visible at f22, couldn't see them at all at f11 or larger so I left them as I rarely shoot smaller than f8.


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## philmoz (Apr 24, 2014)

tolusina said:


> Haven't yet tested canned air, it's now on my pretty immediate list.



Be careful, the chemicals in the propellant in some canned air products can make things much much worse.

Phil.


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## tolusina (Apr 24, 2014)

philmoz said:


> tolusina said:
> 
> 
> > Haven't yet tested canned air, it's now on my pretty immediate list.
> ...


Sure yeah, good you brought that up, that's why I don't have any around to test. I'ma buying one can only, and that just to measure its pressure.


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## Marsu42 (Apr 24, 2014)

Mt Spokane Photography said:


> I've never heard of anyone cleaning the AF sensor, dust on it does not show in the images, and is very unlikely to affect exposure, so the risk versus improvement ratio is pretty high. Same for the sub mirror.



I've recently heard that non-cross sensors might have bad performance when dust particles are on the af sensor, and as my 6d's outer points are abysmal I think I should try to remove dust if there's any. Alas, I have absolutely no idea how the af sensor is built physically and how to clean it.

Btw for the sensor, I use the lensrentals method though w/o the expensive butterfly, works fine and is a dry method:

DSLR Sensor Cleaning (The LensRentals.com Method)


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## Sporgon (Apr 24, 2014)

Mt Spokane Photography said:


> I've never heard of anyone cleaning the AF sensor, dust on it does not show in the images, and is very unlikely to affect exposure, so the risk versus improvement ratio is pretty high. Same for the sub mirror.



Marsu42 was referring to the AF accuracy. 

@ marsu42; you have to raise the mirror to expose the AF module, so I have to do it as per the camera sensor cleaning operation. 

Agreed you are blowing dust from one place to another, but on a number of occasions I have had an outer point that seems to have failed altogether. I give the AF module and sensor a good blow with a rocket blower and that outer point that seems to have failed works fine again. 

Remember that with zoom lenses that alter their physical length such as the 24-105, 24-70, 70-300, 100-400 etc, their zoom action is constantly pumping air in and out of the camera. Although the weather sealed lenses do have a brush 'seal' around the inner barrel it sure as hell aint a good dust seal after a fair amount of use. So someone who uses these types of lenses a lot are going to get more dust issues than someone who just uses primes, even though they may be changing lenses more. 

A tip for you on focusing on 'naked' horses - I am presuming you are shooting wild ones without any head collars or tack on - try using Servo AF with the centre points expanded, and unless very close have all AF points activated. I know this sounds contrary to 'single shot AF' and centre point being more accurate, but I have found that when trying to focus an an animal with very flat fur such as a horse, the aformentioned method is much more successful with the 5DII and 6D.


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## Marsu42 (Apr 24, 2014)

Sporgon said:


> A tip for you on focusing on 'naked' horses - I am presuming you are shooting wild ones without any head collars or tack on - try using Servo AF with the centre points expanded, and unless very close have all AF points activated. I know this sounds contrary to 'single shot AF' and centre point being more accurate, but I have found that when trying to focus an an animal with very flat fur such as a horse, the aformentioned method is much more successful with the 5DII and 6D.



Alas, the 6d has no af pt expansion, so it's "center" or "all" or "single outer" (non-cross). The problem with outer pts has been described in length, I hope the rocket blower did the trick and there's at least some improvement. "Center" results in a big loss of resolution since I have to crop a lot.

Least and least "all" is extremely unreliable with my 70-300L, the 6d simply cannot decide where to af and keeps shunting around the place once 1-2 outer pts are not on the object. I often feel a real pity for my 6d baby, it's not the camera's fault Canon did such a botch job on the fw and the poor thing has to struggle like this. If I manage to have all pts on the object, the 6d in my experience still doesn't focus on the front, but somewhere else in a totally unpredictable manner - though I didn't try all af options with "all".


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