Focus Confirmation
Eugene
In Canon DSLR, there is a Focus Confirmation
dot in the viewfinder. Supposed you are using
Manual Focus. Does this Focus Confirmation
works by Phase-Difference Sensor with
AF lights or does it use Contrast Detection
like in those models with Live View Mode?
(or other mechanisms that doesn't use
the two?
E
John Passaneau
It uses the same sensor that is used for auto focus. The
Phase-Difference method is used in the live view mode because the
mirror is up in live view and the auto focus sensor is blocked. In
manual focus the mirror is down and the auto focus sensor is active.
John Passaneau
Eugene
But how could that be. In manual focus, no infrared light is
sent to the subject to gauge distance because it is
manual focus in the first place where you are the one
to adjust the distance. Also I'm talking about the focus
confirmation in other Canon without Live View like
the 20D, etc.
E
Hans Kruse
subject. Read the explanation of phase detection auto focus here
http://en.wikipedia.org/wiki/Autofocus
--
Med venlig hilsen/Kind regards,
Hans Kruse www.hanskrusephotography.com, www.hanskruse.com
John Passaneau
That is because Canon DSLR's don't use infrared light to auto focus.
It's auto focus sensors are passive. This is why in low light the auto
focus becomes slow or doesn't work.
John Passaneau
Eugene
>
> - Show quoted text -
Why come point&shoot digicam doesn't use phase detection
autofocusing. If it is costly. How come the DSLR doesn't
use the cheaper Active Autofocus used in point&shoot
which emits light and use reflections to gauge distance.
Both are equally fast and accurate.
E
nospam
<765c2bff-e250-4b4f...@d2g2000pra.googlegroups.com>,
Eugene <eugen...@gmail.com> wrote:
> Why come point&shoot digicam doesn't use phase detection
> autofocusing.
where would you put the phase detect sensors and mirror?
> If it is costly. How come the DSLR doesn't
> use the cheaper Active Autofocus used in point&shoot
> which emits light and use reflections to gauge distance.
> Both are equally fast and accurate.
cameras haven't used autofocus systems that emit light or sound for a
*long* time. they also don't work very well.
Eugene
> In article
> <765c2bff-e250-4b4f-bbe3-0de0c9bed...@d2g2000pra.googlegroups.com>,
>
> Eugene <eugenhug...@gmail.com> wrote:
> > Why come point&shoot digicam doesn't use phase detection
> > autofocusing.
>
> where would you put the phase detect sensors and mirror?
Beside the CCD.
>
> > If it is costly. How come the DSLR doesn't
> > use the cheaper Active Autofocus used in point&shoot
> > which emits light and use reflections to gauge distance.
> > Both are equally fast and accurate.
>
> cameras haven't used autofocus systems that emit light or sound for a
> *long* time. they also don't work very well.
I had Sony point&shoot digicam before like T1 and others where
it can send red light beam to the subject. If it doesn't detect
focus by calculating the reflections. What method then
does it use to autofocus? Maybe the red light is just to
make better the contrast and so contrast autofocus
can work??
In Canon DSLR, why doesn't it emit red light too but
the flash itself for Phase Detection Autofocus. If
flash is brighter, why doesn't point and shoot digicam
uses flash to highlight contrast for autofocus?
E
nospam
<dd49428f-f9c6-45cb...@r31g2000prh.googlegroups.com>,
Eugene <eugen...@gmail.com> wrote:
> I had Sony point&shoot digicam before like T1 and others where
> it can send red light beam to the subject. If it doesn't detect
> focus by calculating the reflections. What method then
> does it use to autofocus? Maybe the red light is just to
> make better the contrast and so contrast autofocus
> can work??
that's a focus assist light so that the actual autofocus system can
find something on which to focus.
> In Canon DSLR, why doesn't it emit red light too but
> the flash itself for Phase Detection Autofocus. If
> flash is brighter, why doesn't point and shoot digicam
> uses flash to highlight contrast for autofocus?
some cameras use flash for autotfocus assist and others use infrared
(and sometimes just red) light. i find the ones that use repeating
flash to be annoying as hell.
Ray Fischer
>On Apr 23, 7:29 am, nospam <nos...@nospam.invalid> wrote:
>> In article
>> <765c2bff-e250-4b4f-bbe3-0de0c9bed...@d2g2000pra.googlegroups.com>,
>>
>> Eugene <eugenhug...@gmail.com> wrote:
>> > Why come point&shoot digicam doesn't use phase detection
>> > autofocusing.
>>
>> where would you put the phase detect sensors and mirror?
>
>Beside the CCD.
It isn't useful to focus on objects outside of the field of view.
>> > If it is costly. How come the DSLR doesn't
>> > use the cheaper Active Autofocus used in point&shoot
>> > which emits light and use reflections to gauge distance.
>> > Both are equally fast and accurate.
>>
>> cameras haven't used autofocus systems that emit light or sound for a
>> *long* time. they also don't work very well.
>
>I had Sony point&shoot digicam before like T1 and others where
>it can send red light beam to the subject. If it doesn't detect
>focus by calculating the reflections. What method then
>does it use to autofocus?
It uses the light to provide illumination for the usual contrast or
phase-detect autofocus.
> Maybe the red light is just to
>make better the contrast and so contrast autofocus
>can work??
Yep.
>In Canon DSLR, why doesn't it emit red light too but
>the flash itself for Phase Detection Autofocus.
Because the flash works and is cheaper than providing an additional
red light. When you put on an external flash like the 430EX it
actually does emit red light.
> If
>flash is brighter, why doesn't point and shoot digicam
>uses flash to highlight contrast for autofocus?
Probably because battery power is scarcer for P&S cameras.
--
Ray Fischer
rfis...@sonic.net
Bob Larter
Rubbish.
--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------
Jürgen Exner
>Why come point&shoot digicam doesn't use phase detection
>autofocusing.
Is this a question? Usually people end a question with a question mark
to avoid confusion.
>If it is costly.
Is this a statement? Or a question? Somehow that sentence seems to be
rather incomplete.
>How come the DSLR doesn't
>use the cheaper Active Autofocus used in point&shoot
>which emits light and use reflections to gauge distance.
>Both are equally fast and accurate.
That must be a record amount of misinformation mixed into a single
sentence.
- Active Autofocus is not cheap but quite expensive because you need an
additional transmitter and receiver
- to the best of my knowledge there is not a single P&S camera using
active autofocus. It was the big hype some 20+ years ago but is very
much obsolete today
- active autofocus is neither as fast nor as as accurate as phase
detection for various reasons. You cannot focus the beam very narrow.
You cannot aim the beam precisely. You are not focussing through the
actual lens. And although it is faster than contrast optimization it is
still not as accurate for pretty much the same reasons as compared to
phase detection.
And dSLRs don't use the the P&S method of contrast optimization because
phase detection is much faster and it can be done without raising the
mirror to expose the sensor.
jue