It’s not totally accurate, but if you are close to overexposure you’ll see
small portions of your image blink in the LCD. Canon’s overexposure
threshold is relatively low, and any minor blinking areas should not be
a huge source of alarm. When you see major portions of your displayed
image blinking black to white you might want to reevaluate your
exposure strategy. Test your own equipment to determine limits you fi nd
acceptable, then dial in appropriate Exposure Compensation or adjust
your external light meter, if necessary.
Sensor Cleaning
It doesn’t matter that you take great pains to mount and dismount lenses
properly, or that your particular camera may have a weather seal, sooner
or later you will get dust on the sensor, and of a size large enough to
leave a shadow of itself on an image. When that happens, the sensor
must be carefully cleaned or the spot will probably stay forever.
Most dust is unnoticeable, especially at apertures larger than f22 and
against patterned backgrounds. Here’s what to do to fi nd out if your
sensor is dirty.
First, set your camera’s aperture to its maximum aperture (at least f22)
and the shooting Mode to Aperture Priority. You’ll want the smallest
aperture to provide enough depth of fi eld so even small spots will cast
a discernible shadow.
Take a picture of any clean, white background, such as a sheet of typing
paper. Because you’re using the camera’s meter on a pure white fi eld,
you may have to add Exposure Compensation to get a clean, but not
overexposed, white. Make sure the background is evenly lit. It won’t
matter if the image is in focus or not.
Download your image and open it in DPP or Photoshop. Enlarge it to
100% or 200%, scroll through it to look for crud. My test indicated some
small chunks of crud in the frame.
Canon recommends only one method of cleaning the sensor, rapidly
squeezing fresh air from an air bladder onto the sensor while holding the
camera upside down. Under no circumstances should you use canned air.
While the air may be clean, the propellant itself may spray out and land
on the sensor, drying immediately and seriously degrading image quality.
Using non-recommended methods may, in fact, void the warranty.
In a clean, relatively dust-free environment, hold the camera upside down
and remove the lens or body cap. If removing a lens, place a cap on the
mount before proceeding. This will keep airborne dust from landing on
the mount or the rear element of the lens. Continue to hold the camera
upside down, so loose particles will fall to the fl oor. Blow any dust off the
mirror and the interior assembly (FIG 4.50).
Find and select Sensor Cleaning in the Menu (FIG 4.51).
Your EOS-1 camera may want assurances that you’ll do the procedure
correctly. Assure it that you mean it no harm and select OK. Prosumer
bodies will tell you what to do when you’re done (FIGS 4.52 and 4.53).
With EOS-1 bodies, push the shutter button all the way down. Doing
so will lock the mirror to the top of the viewfi nder. With the prosumer
bodies, the mirror will fl ip up and lock a second or two after you choose
the Sensor Cleaning menu item.
Use the bladder to blow off the sensor, taking care not to touch the
surface of the chip with the end of the bladder. Be sure to blow air onto
the corners of the sensor as well as across the center. Dust likes to hide
out in the corners (FIG 4.54).
When you’re fi nished, and while still holding the camera upside down,
replace the lens or body cap. Turn off the power, returning the mirror to
its ready position.
As of this writing, both the Rebel XTi and the 1D Mark III feature
automatic sensor cleaning which eliminates most of the need for manual
sensor cleaning.
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