Instruction manual

5
Note: Some lenses don’t produce even edge-to-edge sharpness across their
range, so experiment with your lens to determine if there is any falloff in
sharpness at particular focal lengths.
Vignetting
Add-on lenses such as a telephoto lens can help improve your photos.
However, because these lenses are long they may cause vignetting. Vignetting is
what happens when the lens barrel itself gets into a picture, causing the frame to
lose its square shape. Subtle vignetting may cause the corners of you photo to be
dark, blurry or rounded; extreme vignetting can produce a round image (in this
case, the edge of the lens itself is included in the photo).
A digital camera converter lens may require an adapter so it mounts correctly
on the camera. In order to prevent vignetting, adapters may have to be removed
when the lens is no longer attached.
If you find that your camera with its add-on lens is prone to vignetting, keep
an eye on the camera’s LCD screen. If your see vignetting, try zooming farther
into the telephoto range and see if this eliminates the problem. As a last resort,
you can crop the darkened corners out of your photo using photo editing software.
1.1.2 Viewfinders
A. Optical Viewfinder
A camera’s optical viewfinder is normally positioned above the actual lens,
and there is also a horizontal offset. So what you see through the optical
viewfinder is different from what the camera’s lens projects onto its sensor. This
"parallax error" is most obvious at relatively small subject distances. Digital SLR
cameras have no parallax error, and exact focus can be confirmed by eye.
Optical viewfinders only allow you to see a percentage (80 to 95%) of what
the sensor will capture. Additionally, the viewfinder normally shows a lower
percentage (e.g., 85%) of the final image area at telephoto range (this percentage
increases to 89 - 95% at wide angle settings). So don’t be surprised if an
aircraft’s wheel, strut or wingtip shows up in your picture, even when you didn’t
see it in the viewfinder while you were framing the shot. With practice you can
anticipate this effect when framing your shot.
Note
This condition will be further complicated if the customer wants data imprinted
on the photos, such as time and/or date stamps or watermarking. This data is
usually superimposed at the bottom of the photo, so you will have to adjust
your framing to ensure this data doesn’t interfere with a clear view of the
target.