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[OM] Re: cleaning sensors

Subject: [OM] Re: cleaning sensors
From: Moose <olymoose@xxxxxxxxx>
Date: Thu, 22 Feb 2007 13:40:43 -0800
Scott Peden wrote:
> Wow, I didn't even recognize the parts you were talking about. Obviously I
> don't know the parts names.
>   
Doesn't sound like you quite understand how it works. Take a look here 
<http://en.wikipedia.org/wiki/Single_lens_reflex>. (Note the example 
camera shown is an OM.)
> I have an E-500 and I keep hearing about bulbs, but I think all I have is an
> electronic timer and a remote.
>   
The reference to bulb is an archaic one, but still in use. The first 
shutters after photographic emulsions got fast enough to need something 
other than just taking the lens cap off for a while, then putting it 
back on, were activated by air pressure from a rubber bulb. The 
photographer would squeeze the bulb, count or watch a clock/watch, then 
release.

When shutters with shorter, mechanically timed exposures were designed, 
they retained the "bulb" setting, although it was by then mechanically 
activated, for exposures longer than those provided by the timing 
mechanism in the shutter. The label persists to this day with a setting 
labeled "B" on many cameras which opens the shutter for as long as the 
shutter release is pressed.
> When you take the lens off, there is a small mirror, when I looked up from
> there, there is another reflective surface and that is what has all the
> hairs and lint on it, and how it got there beats me.
>   
Take a look at the diagram in the above link. The mirror you see 
directly ahead is #2. The reflective surface directly above it is #5, 
the viewscreen. What you see through the viewfinder is the image 
projected on this screen by the lens via the mirror. The sensor, #4, is 
hidden behind the shutter, #3.

Hair, dust, etc on the mirror is not in focus through the viewfinder. 
What you are seeing is on the viewscreen. As you can see, the optical 
path with the mirror down is different from that when a picture is being 
taken with the mirror up, and the viewscreen is not a part of it then. 
So stuff on the viewscreen has no effect whatsoever on the images taken.

If the stuff bugs you, you may try blowing it off with an ear syringe or 
a more expensive device which does exactly the same thing bought from a 
photo supplier. Don't use "canned air", for various reasons. The 
viewscreen is made of softish plastic, so attempts to brush dust off 
must be done with care. They tend to be counter-productive anyway, as 
the brush puts a static charge on the plastic, thus quickly attracting 
more dust.

Some (D)SLRs have interchangeable viewscreens, so one may take them out 
for easier cleaning. That is not true of the E-500
> The vibration thingy apparently isn't powerful enough to clean the crap off
> of it.
>   
The vibration thingie is behind the shutter and in front of the sensor. 
It's job is to keep dust out of the light path for image making, not the 
one for viewing. It's not 100% effective, and I forgot to mention that 
you appear to have, or have had, something on yours in the shots you 
posted. P5112584, 85, 87 and  93 all show a blob that is likely 
something on the front of the sensor assembly.

They are most visible against a light, blank area like sky and at 
physically small ( numerically large) apertures.

Moose

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