Re: I need advice on the test for focus.
- From: "Peter Jason" <pj@xxxxxxxxxx>
- Date: Wed, 30 May 2007 12:02:46 +1000
At the moment I photograph buildings in town
which benefit from very sharp focus. I use a
zoom 7-14mm wide angle Zuiko lens.
The wide-angle properties are very good but
the focus is variable, which is strange
because wide-angle lenses have a focus
infinity point past about 3 feet, and I
always use a tripod.
Up until now I have not been using the "focus
bracketing" because this takes up too much
time & memory.
I am using 1/4 compressed jpgs, and
sometimes in the gloomy early mornings I need
exposures of many seconds.
"Happy Traveler" <happy_traveler@xxxxxxx>
wrote in message
news:07qdnYV74vw9TMHbnZ2dnUVZ_t6qnZ2d@xxxxxxxxxxxxxx
"Actual pixels" means what it says -- one
pixel in the image is one pixel on the
monitor. No interpolation taking place, so
a good way to judge an image.
But what do you mean by "efficiency"?
Whether the camera focuses correctly or how
sharp is a correctly focused image? The
latter is a very complex topic, and not
something that you can easily measure at
home. Results will depend on the lens
quality, aperture setting, the low pass
filter in front of your sensor and the
camera's image processing.
Unless you are taking a picture of a flat
object, there is only one distance that's
in focus, and the rest is, by necessity,
blurred to some degree. How much depends on
the focal length, the distance to the
object and the aperture (f #) setting.
A simple test for correct focusing is to
arrange three cereal boxes (or similar flat
objects with fine print and some color),
with the one on the left 1" in front of the
one of the center, and the one on the right
1" behind. Open the aperture to the maximum
(lowest f #), zoom or position the camera
to have all three boxes in the image,
select a single point center focus and
place it on the center box. In the image
you should see the center box sharp and the
other two blurred. If the left or the right
box is the one in focus, the focusing
mechanism needs adjustment. Make sure your
camera is set to its highest resolution and
lowest compression (if you are using JPG).
"Peter Jason" <pj@xxxxxxxxxx> wrote in
message
news:f3igvv$150m$1@xxxxxxxxxxxxxxxxxxxxxxx
I have a digital camera and I want to
monitor the focus efficiency.
In Photoshop CS2 there is an "actual
pixels" facility which, presumably,
enlarges the picture up to a constant
size.
Is this a good way to monitor the focusing
of the camera?
Peter
.
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