Canon 30D autofocus weirdness explained

Lawrence Glickman wrote:
Chris Savage wrote:
Lawrence Glickman wrote:
lid wrote:
Lawrence Glickman wrote:

But don't forget, there are, at least on
my camera, 2 switches that have to be thrown: one on the lens, and,
one on the camera body. All this takes time, and in an opportunistic
shooting situation, this won't come without a bit of practice.

Not if you're talking of using your D80. You only need switch the lens
to manual focus. But if your lens has an A/M setting you get the best of
both worlds -- you can use the focus ring and the camera will accept
that you're the boss and just let you focus.

You mean, I can leave the Camera switch on auto-focus, and just switch
the LENS switch to manual, and the unit will go into manual mode.

Let me try this, hold on a minute....

You are CORRECT Sir, I stand corrected. But prey tell, WTF is the
AF/M switch on the camera for then?

I never touch the switch on the lens. On the D200 the switch is easy to
flick with my left 'ring' finger while looking through the viewfinder.
Often I'll use AF to get in the ballpark and if I want to do manual,
flick it off & finish in manual. This is for AF-S lenses where you can
manual override even without switching but putting it in manual makes
the focus stay put rather than having the lens twitch back to where I
didn't want it again :-)

On Sun, 20 Apr 2008 01:22:28 GMT, Paul Furman
wrote:

Lawrence Glickman wrote:
Chris Savage wrote:
Lawrence Glickman wrote:
lid wrote:
Lawrence Glickman wrote:

But don't forget, there are, at least on
my camera, 2 switches that have to be thrown: one on the lens, and,
one on the camera body. All this takes time, and in an opportunistic
shooting situation, this won't come without a bit of practice.

Not if you're talking of using your D80. You only need switch the lens
to manual focus. But if your lens has an A/M setting you get the best of
both worlds -- you can use the focus ring and the camera will accept
that you're the boss and just let you focus.

You mean, I can leave the Camera switch on auto-focus, and just switch
the LENS switch to manual, and the unit will go into manual mode.

Let me try this, hold on a minute....

You are CORRECT Sir, I stand corrected. But prey tell, WTF is the
AF/M switch on the camera for then?

I never touch the switch on the lens. On the D200 the switch is easy to
flick with my left 'ring' finger while looking through the viewfinder.
Often I'll use AF to get in the ballpark and if I want to do manual,
flick it off & finish in manual. This is for AF-S lenses where you can
manual override even without switching but putting it in manual makes
the focus stay put rather than having the lens twitch back to where I
didn't want it again :-)

Clever, Paul. Very clever. My *old* procedure, before electronic
cameras came about, would be to focus 1/3rd of the way into the image
I wanted to capture, knowing that 2/3rds DOF would go behind it, and
1/3rd in front. But there IS one thing I have yet to try on an
*electronic* camera, and that is HYPERFOCAL setting.

With the lens set at HYPERFOCAL, as the name suggests, everything is
in focus from right in front of the lens out to infinity. Of course,
this can't be achieved with a *normal* electronic lens. And I don't
know of anyone besides myself, who has actually ever USED the
hyperfocal setting.

IMO, one of the shortcomings of P&S cameras is that they don't allow
the photographer to control DOF for selective focus, and annoyingly,
all too often, the background pulls your attention away from the
intended subject, be that a person's face, a bird, or whatever. IOW,
having everything in focus can be a terrible distraction, and *ruin*
an otherwise good photo. IMO of course.

So, I am a fan of selective focus. If it is done properly. IOW, I
wouldn't want to see a portrait where the only parts of the model that
were in focus were the nose, eyes, and mouth. Otoh, I've seen some
women where the ENTIRE image should be as out of focus as the camera
is capable of ;-|

Lg

On Sat, 19 Apr 2008 23:20:28 +0000, Roy G wrote:

"Lawrence Glickman" wrote in message
news
On Sat, 19 Apr 2008 14:38:41 -0500, lid wrote:


I performed a similar *experiment* with my D80. I set it to spot meter
at the center of the viewing field, and *autofocused* on a number of
objects set about on a large table. Each time, the autofocus *nailed*
the subject of interest, even though they were separated by only
inches. This tells me I'm going to have to be careful if I use spot
metering in scenic situations. In fact, this tells me NOT to use
single-spot-metering in scenic situations, otherwise I loose the
foreground or the background, or both, depending on where the
single-spot-metering icon appears.

Fortunately, I can just rotate the button to scenic mode, and IIRC, up
to 5 or 11 sensors will evaluate the composition and decide on a focal
plane and f/stop.

So, in summary, one setting does not fit all situations. I am against
manual focus, because the camera motors can make this adjustment much
faster than I can manually.

Now if you want Selective Focus, and intentionally want a *soft*
forground/background, of course use spot metering and/or manual focus.
Portraiture comes to mind.

Lg


Hi

I do hope you will excuse me, but exactly what does Spot Metering have
to do with Focussing??

Roy G
They are just confusing themselves - was going to let them play.
--
Neil
reverse ra and delete l
Linux user 335851

On Sat, 19 Apr 2008 14:38:41 -0500, lid wrote:
: Some time ago I complained about the autofocus behavior of my Canon 30D.
:
: So today I ran some tests.
:
: I created a page entirely filled with close-spaced 10 point
: bold type. I also made a small patch, about 1/2 inch square,
: from the same text, and mounted it out 1/2 inch from the page
: so the mount did not show.
:
: I was three to five feet from this. I tried two lenses,
: a 100 mm f/2.8 macro, and a 70-300 f/4.5-5.6 IS tele zoom,
: at 70-150 mm. I tried the center focusing spot of the camera
: as well as the right hand one, using only one spot.
:
: The results were clear and the same: The little raised square
: has to be big enough that its corners essentially touch the
: circle in the viewfinder for it to be the focus target. This
: is the same for the two different focus areas. Alternatively
: stated, the focus area, assuming that they are square, which I
: have not yet tested, is four times the linear dimension of the
: little squares. It will take harder tests to tell if they are
: square.
:
: This essentially explains all that ever bothered me about the
: erratic autofocus of this camera. I had assumed, based on nothing,
: that the size of the squares meant that they represented the
: autofocus areas. Apparently they do not. Canon would not tell me
: anything about the size of these areas, apparently it is a
: secret.
:
: So, in the future, I will know that if my subject is not that large,
: to use manual focus.
:
: Actually, this is pretty crappy performance. That large an
: area covers far too large a spot.

Does the autofocus mechanism actively try to identify targets, or does it just
go with what it sees at the focus point? IOW, would you have gotten the same
results if the color of the target had been different from that of the
background? The fact that you seem to have identified a lower limit on the
size of the target suggests to me that some form of target identification is
being used.

Bob

On Sat, 19 Apr 2008 19:38:27 -0500, Lawrence Glickman
wrote:
: On Sun, 20 Apr 2008 00:30:48 +0100, Chris Savage
: wrote:
:
: On 2008-04-19, Lawrence Glickman wrote:
: On Sat, 19 Apr 2008 15:04:49 -0500, lid wrote:
:
: Lawrence Glickman wrote:
:
: So, in summary, one setting does not fit all situations.
: I am against manual focus, because the camera motors can make this
: adjustment much faster than I can manually.
:
: True, it's faster. But if you want to focus on an object smaller than
: the autofocus sensor covers, you've got to use manual. Unless,
: of course, it's at the same distance as everything else
: around it.
:
: No doubt. Absolutely true. But don't forget, there are, at least on
: my camera, 2 switches that have to be thrown: one on the lens, and,
: one on the camera body. All this takes time, and in an opportunistic
: shooting situation, this won't come without a bit of practice.
:
:
: Not if you're talking of using your D80. You only need switch the lens
: to manual focus. But if your lens has an A/M setting you get the best of
: both worlds -- you can use the focus ring and the camera will accept
: that you're the boss and just let you focus.
:
: You mean, I can leave the Camera switch on auto-focus, and just switch
: the LENS switch to manual, and the unit will go into manual mode.
:
: Let me try this, hold on a minute....
:
: You are CORRECT Sir, I stand corrected. But prey tell, WTF is the
: AF/M switch on the camera for then?

So that you don't have to re-focus for every shot?

Bob

On Sun, 20 Apr 2008 08:38:19 -0400, Robert Coe wrote:

: You are CORRECT Sir, I stand corrected. But prey tell, WTF is the
: AF/M switch on the camera for then?

So that you don't have to re-focus for every shot?

Bob

I am pleased to discover this *feature*

I never have had this option on my other electronic cameras. This is
very thoughtful of Nikon.

Lg

"Neil Ellwood" wrote in message
...
On Sat, 19 Apr 2008 23:20:28 +0000, Roy G wrote:

"Lawrence Glickman" wrote in message
news
On Sat, 19 Apr 2008 14:38:41 -0500, lid wrote:


I performed a similar *experiment* with my D80. I set it to spot meter
at the center of the viewing field, and *autofocused* on a number of
objects set about on a large table. Each time, the autofocus *nailed*
the subject of interest, even though they were separated by only
inches. This tells me I'm going to have to be careful if I use spot
metering in scenic situations. In fact, this tells me NOT to use
single-spot-metering in scenic situations, otherwise I loose the
foreground or the background, or both, depending on where the
single-spot-metering icon appears.

Fortunately, I can just rotate the button to scenic mode, and IIRC, up
to 5 or 11 sensors will evaluate the composition and decide on a focal
plane and f/stop.

So, in summary, one setting does not fit all situations. I am against
manual focus, because the camera motors can make this adjustment much
faster than I can manually.

Now if you want Selective Focus, and intentionally want a *soft*
forground/background, of course use spot metering and/or manual focus.
Portraiture comes to mind.

Lg


Hi

I do hope you will excuse me, but exactly what does Spot Metering have
to do with Focussing??

Roy G
They are just confusing themselves - was going to let them play.
--
Neil
reverse ra and delete l
Linux user 335851

After 50 years of SLR & DSLR use, I think I have a fair knowledge of camera
settings, but this lot seem to be inventing a whole new set of upside down
rules.

Roy G