9 point focus or focus-recompose

[SFishy]

Brian,

You are right, and in my "thirds" example, I did have to alter the point somewhat to fit. But would it work the same way? In other words, If I pick one of the red points, the quadrent I'm selecting the red quadrent as the area to be used for focusing?

The points actually are closer to the ideal spots for the Golden
Section intersections. (The "Rule" of Thirds itself is just a
simplification of Golden Section lines). Whether this was
intentional on Canon's part I have no idea.

Kind Regards,
Brian

 

[SFishy]

Brian,

You are right, and in my "thirds" example, I did have to alter the position of the points slightly to somewhat fit. But would it work the same way as I illustrated? In other words, If I pick one of the red points, the quadrent I'm selecting is the red quadrent as the focusing area to be used for focusing?

The points actually are closer to the ideal spots for the Golden
Section intersections. (The "Rule" of Thirds itself is just a
simplification of Golden Section lines). Whether this was
intentional on Canon's part I have no idea.

Kind Regards,
Brian

 

[SFishy]

Susan,

Thanks for the 15 feet guideline. That's helpful.

Also, I understand what you're saying about using the point closes to the object you want to focus on. But I'm still a bit confused about what the points themselves represent (because obviously, you won't always have an object right under one of those points exactly, so they must represent a larger area.

As illustrated in an earlier reply, would you agree they follow the "rules of thirds" or the "Golden Section" rule?



Amy

For objects greater than 15 feet away, using the centre point and
recomposing seems to work just fine for focus (the fifteen foot
figure comes from the Canon literature - although aimed at the 1
series cameras rather than the 20 or 10D) - separating the exposure
and focus functions as described in other posts may help under some
circumstances where final composition is critical to get the
exposure right.

Closer distances and wide apertures can be more problematic - head
shots taken at f1.8 can lead to a nose tip rather than an eye being
in focus, and if possible I use the focus point that gives the
least possible shift in recomposition.Using the joystick on the 20D
is pretty quick (I have the custom function enabled that gives me
instant control over the focus points by using the joystick) For
realy close up work manual focus and a tripod is best - although
I'd love a focussing aid on the focus screen.

The only time I use multipoint focus with all the points turned on
is AI servo mode. Here locking on to the object with the centre
point and then letting all the points track seems to work
brilliantly, in conjuntion with burst mode shooting. I took over
100 shots of my daugher body surfing, using a 90-300mm lens at
300mm and every single one of them was acceptably sharp straight
out of the camera, despite the speed she was moving at and the
possibility of locking on to other people or waves in the water.

 

[Susan S.]

Susan,

Thanks for the 15 feet guideline. That's helpful.

Also, I understand what you're saying about using the point closes
to the object you want to focus on. But I'm still a bit confused
about what the points themselves represent (because obviously, you
won't always have an object right under one of those points
exactly, so they must represent a larger area.

As illustrated in an earlier reply, would you agree they follow the
"rules of thirds" or the "Golden Section" rule?

Fifteen foot guideline is what Canon say for their series 1 cameras, so I assumed it applies for the 20 and 10D too, and as an ad hoc rule it seems to work.

I always just assumed that the focus points were a scattering of more or less likely places in a frame that people are likely to want to focus on - - given that Canon haven't seen fit to make an infintely moveable focus point (my G3 has a single focus point that I can move just about anywhere in the frame which is pretty useful. Another of the P&S features that I wouldn't mind seeing moved to the DSLRS!) I never noticed that the spread conformed roughly to a rule of thirds until you pointed that out, and it is quite likely that this is the reasoning behind the choice of positions in the frame that the camera can focus on. I still haven't quite got to grips (in terms of knowing instinctively when I am shooting!) with which of them rely on horizontal and which on vertical contrast and exactly how big they are yet -I know that they are somewhat bigger than the little squares on the screen.

 

[Susan S.]

Doesnt the metering link to the selected focusing point? So by
using an offcenter focusing point you're weighting that more
heavily....

Yes - that's one advantage of it if the off center point is on your subject as you take the photo - but if you focus and recompose in one shot AF mode, then both the exposure and the focus are locked on the half press of the shutter button while the subject is covered by the focus point so recomposing will make a bit, but not a huge difference in exposure relative to the 'ideal".

I'm not sure I understand the advantage of switching to having the
focusing button separate from the shutter......If you do this, when
is the metering locked?

With default settings of the camera, using the AE lock ( ) button will lock the exposure, with the focus being set on half press of the shutter button - useful for backlit subjects - especially in partial metering mode. (see page 86 of the 20D manual). You can use custom functions to switch these 2 functions around - a lot of people like to use CFn 04 in setting 1 to have focus on the * button as you only have to press it once and not hold it down and then the exposure is set on half press of the shutter button. I must confess to not having tried it.

If you use an IS lens, are you saving battery power by focusing
w/the * button because you're not engaging the IS till you hit the
shutter?
I do find that I drain the battery fast w/my IS l100-400... I may
have a (stationary) bird or animal in my sights and hold the
shutter button down a while waiting for the right moment..

I don't know about that - could well be true. The IS is a bit of a battery guzzler! I have the 17-85IS.

Quite frankly, the one thing I miss since moving to the 20D is the
eye control .... it really worked for me esp when shooting
wildlife. The joystick isnt much help, I find that it's too far
toward the center...my finger hits the rim of my glasses(sure I
know I can take them off and use the diopter).

The main reason I switched to a DSLR is so that I didn't have to take my reading glassses around to look at an LCD screen in my P&S (but I still have to get my kids to tell me what settings I'm using sometimes if I forget my glasses!). I've got used to the joystick, but the eyecontrol does sound attractive.

I'm using the rear
dial to set the focusing point but still trying to find the most
comfortable method.

tx

 

[Hoang Pham]

Susan,

Thanks for the 15 feet guideline. That's helpful.

Also, I understand what you're saying about using the point closes
to the object you want to focus on. But I'm still a bit confused
about what the points themselves represent (because obviously, you
won't always have an object right under one of those points
exactly, so they must represent a larger area.

As illustrated in an earlier reply, would you agree they follow the
"rules of thirds" or the "Golden Section" rule?

Fifteen foot guideline is what Canon say for their series 1
cameras, so I assumed it applies for the 20 and 10D too, and as an
ad hoc rule it seems to work.

I always just assumed that the focus points were a scattering of
more or less likely places in a frame that people are likely to
want to focus on - - given that Canon haven't seen fit to make an
infintely moveable focus point (my G3 has a single focus point that
I can move just about anywhere in the frame which is pretty useful.
Another of the P&S features that I wouldn't mind seeing moved to
the DSLRS!) I never noticed that the spread conformed roughly to a
rule of thirds until you pointed that out, and it is quite likely
that this is the reasoning behind the choice of positions in the
frame that the camera can focus on. I still haven't quite got to
grips (in terms of knowing instinctively when I am shooting!) with
which of them rely on horizontal and which on vertical contrast and
exactly how big they are yet -I know that they are somewhat bigger
than the little squares on the screen.

--
photoblog http://www.xanga.com/nviati
proud new owner of a Canon EOS 20D as of my birthday > 12/19/2004

 

[BlackSMP]

For me it is mostly added control over AF in action shots or an quick way to override AF.

I've CFn4.2 set which means that the camera cease to AF when I press the -button.

I use to quickly get the camera in MF mode without using the MF/AF switch. Focus manually, press the " " button to disable AF, press the shutter button to take the picture.

It is also used to control AF in action shots when tracking subjects and to make sure that the AF isn't fooled by other movements in the frame.

--jalle

I'm not sure I understand the advantage of switching to having the
focusing button separate from the shutter......If you do this, when
is the metering locked?

If you use an IS lens, are you saving battery power by focusing
w/the * button because you're not engaging the IS till you hit the
shutter?
I do find that I drain the battery fast w/my IS l100-400... I may
have a (stationary) bird or animal in my sights and hold the
shutter button down a while waiting for the right moment..

Quite frankly, the one thing I miss since moving to the 20D is the
eye control .... it really worked for me esp when shooting
wildlife. The joystick isnt much help, I find that it's too far
toward the center...my finger hits the rim of my glasses(sure I
know I can take them off and use the diopter). I'm using the rear
dial to set the focusing point but still trying to find the most
comfortable method.

tx

Coming from the Sony 707 I am VERY used-to the focus-recompose
technique. I would use it all the time.

In reading around here, and on the web, "focus-recompose" doesn't
appear to be the best method with the 20D (or other dSLRs),
especially at wider apertures. I've been reading about the 9-point
focusing, and how to select the best point.

So I have some questions

First -- do a lot of you still use center-point focus and then do
focus-recompose, and how are your results?

Second -- for those of you using the 9-point focus... do you find
you can do so quickly? Was it just a matter of getting used to
doing it?

For objects greater than 15 feet away, using the centre point and
recomposing seems to work just fine for focus (the fifteen foot
figure comes from the Canon literature - although aimed at the 1
series cameras rather than the 20 or 10D) - separating the exposure
and focus functions as described in other posts may help under some
circumstances where final composition is critical to get the
exposure right.

Closer distances and wide apertures can be more problematic - head
shots taken at f1.8 can lead to a nose tip rather than an eye being
in focus, and if possible I use the focus point that gives the
least possible shift in recomposition.Using the joystick on the 20D
is pretty quick (I have the custom function enabled that gives me
instant control over the focus points by using the joystick) For
realy close up work manual focus and a tripod is best - although
I'd love a focussing aid on the focus screen.

The only time I use multipoint focus with all the points turned on
is AI servo mode. Here locking on to the object with the centre
point and then letting all the points track seems to work
brilliantly, in conjuntion with burst mode shooting. I took over
100 shots of my daugher body surfing, using a 90-300mm lens at
300mm and every single one of them was acceptably sharp straight
out of the camera, despite the speed she was moving at and the
possibility of locking on to other people or waves in the water.

 

[KJbruin]

I used to think the same but now shoot with all AF points enabled quite often (especially when shooting at wide aperatures). If the wrong point is selected then I use the joystick to choose the correct one. I find that AF tends to be more accurate by selecting your AF point compared to focus lock and recomposing. And enabling all AF points is simply quickest way of getting this done.

Ben_Egbert wrote:
[snip]
I just dont get why you would want to shoot with all AF points
enabled - Other than AI- Servo which probably works better that way.

For normal shooting, I would find it rather pointless and annoying.
--
http://www.pbase.com/timothyo

 

[samkatz]

susan,
tx.

I didnt realize you only had to press the * once to achieve focus and you don't have to hold it down like the shutter button This sounds better than switching to manual focus when you know you have to reposition the subject a lot

will try playing around w/this setting

If you use an IS lens, are you saving battery power by focusing
w/the * button because you're not engaging the IS till you hit the
shutter?
I do find that I drain the battery fast w/my IS l100-400... I may
have a (stationary) bird or animal in my sights and hold the
shutter button down a while waiting for the right moment..

I don't know about that - could well be true. The IS is a bit of a
battery guzzler! I have the 17-85IS.

Quite frankly, the one thing I miss since moving to the 20D is the
eye control .... it really worked for me esp when shooting
wildlife. The joystick isnt much help, I find that it's too far
toward the center...my finger hits the rim of my glasses(sure I
know I can take them off and use the diopter).

The main reason I switched to a DSLR is so that I didn't have to
take my reading glassses around to look at an LCD screen in my P&S
(but I still have to get my kids to tell me what settings I'm using
sometimes if I forget my glasses!). I've got used to the joystick,
but the eyecontrol does sound attractive.

I'm using the rear
dial to set the focusing point but still trying to find the most
comfortable method.

tx

 

[RDKirk]

Brian,

You are right, and in my "thirds" example, I did have to alter the
point somewhat to fit. But would it work the same way? In other
words, If I pick one of the red points, the quadrent I'm selecting
the red quadrent as the area to be used for focusing?

You said "quadrant as the area to be used for focusing." To clarify, you still want to use the AF mark itself for focusing. Although the sensitive areas are larger than the marks, you still want to use the marks themselves.

--
RDKirk
'TANSTAAFL: The only unbreakable rule in photography.'

 

[RDKirk]

I always just assumed that the focus points were a scattering of
more or less likely places in a frame that people are likely to
want to focus on - - given that Canon haven't seen fit to make an
infintely moveable focus point (my G3 has a single focus point that
I can move just about anywhere in the frame which is pretty useful.
Another of the P&S features that I wouldn't mind seeing moved to
the DSLRS!)

This is possible on P&S cameras because they're using the actual imaging sensor as a viewing/focusing sensor. DSLRs use a different set of discrete sensors focusing sensors. The trade off is increased accuracy and significantly increased focusing sensitivity and speed for DSLRs.

I still haven't quite got to
grips (in terms of knowing instinctively when I am shooting!) with
which of them rely on horizontal and which on vertical contrast and
exactly how big they are yet -I know that they are somewhat bigger
than the little squares on the screen.

The rectangles are actually three times longer than indicated by the marks. The sensitive portions extend to each end of the mark as much farther as the mark itself is long. The sensitive portion of the center area extends vertically and horizontally from the square as much farther as the dimensions of the square itself. In other words, the center sensitive area is shaped like the Red Cross with the square at the center.

The central area is sensitive to linear contrasts running either vertically or horizontally. The rectangular marks, however, are sensitive to linear contrast running perpendicular to the rectangle, but blind to linear contrasts running parallel to the rectangle. This feature is useful in discriminating the focus when you have background contrasts competing with your intended subject.

If you're having a difficult time getting the camera to focus on your subject, take note of whether the background or the subject has linear contrasts (it's amazing how oftent that is the case). If so, then activate a rectangle and turn the camera so that the rectangle is either parallel to th contrast you want to ignore or parallel to the contrast you want to focus on. In this way, the rectangles are frequently superior to the central square.

--
RDKirk
'TANSTAAFL: The only unbreakable rule in photography.'

 

[Steven Sterne]

This link will take you to my earlier post, which shows the actual sizes as RD Kirk has explained:

http://forums.dpreview.com/forums/read.asp?forum=1019&message=11863244

 

[Mark Gillett]

..I also have the 1d2 and its no problem changing focus points. You rsubject invariably falls in on of two or three areas and to switch is not slower than recomposing. You also have the added problem of the wrong exposure when you recompose if you re using evaluative metering.

Mark

there's an artical by Chuck Westfall of Canon that recommends using
the focus points not Focus Lock and Recompose. Especially at wide
open apertures under a distance of 15'.

the reasoning is that they focus plain is then moved and as a
result increases the chance of Front or Back Focus.

folks here will debate the issue to death, but I'm on the side of
Chuck and believe him as an engineer for the Cameras. I've had
absolutely no focus issues with the 20D and I have switched
techniques to using the focus points as a result of his artical.
The artical is based on the 45pt AF system of the 1D bodies, but
the same is going to apply to the rest of the EOS systems too.

I too am a firm believer in selecting AF points manually mainly
because earlier EOS cameras including the 10D placed a huge bias on
exposure and flash metering on the selected AF point.

But good luck to the 1-series users with no AF joystick to move
those 45 AF points around. You have to press a button and rotate 2
dials to dial in the AF point you want. Try doing it in Servo mode.
Impossible. A serious flaw in design in my opinion. Kudos to Canon
for planting a Joystick on the 20D. Now you can even switch AF
points while tracking a moving subject.

--
http://www.pbase.com/markgillett

 

[Diane B]

RDKirk wrote:
snip

The rectangles are actually three times longer than indicated by
the marks. The sensitive portions extend to each end of the mark
as much farther as the mark itself is long. The sensitive portion
of the center area extends vertically and horizontally from the
square as much farther as the dimensions of the square itself. In
other words, the center sensitive area is shaped like the Red Cross
with the square at the center.

The central area is sensitive to linear contrasts running either
vertically or horizontally. The rectangular marks, however, are
sensitive to linear contrast running perpendicular to the
rectangle, but blind to linear contrasts running parallel to the
rectangle. This feature is useful in discriminating the focus when
you have background contrasts competing with your intended subject.

If you're having a difficult time getting the camera to focus on
your subject, take note of whether the background or the subject
has linear contrasts (it's amazing how oftent that is the case).
If so, then activate a rectangle and turn the camera so that the
rectangle is either parallel to th contrast you want to ignore or
parallel to the contrast you want to focus on. In this way, the
rectangles are frequently superior to the central square.

--
RDKirk
'TANSTAAFL: The only unbreakable rule in photography.'

I remembered I had the link to the diagram Chuck Westfall (head of technical marketing I believe)made for the Rob Galbraith forum of the 10D's AF coverage. This could be related to the 20D I assume.



http://www.pbase.com/chuckwestfall/image/18920257

There is also one for teh 1D/1DS that may be interesting.
http://www.pbase.com/chuckwestfall/image/18921414

Diane
--
Diane B
black and white lover, but color is seducing me
http://www.pbase.com/picnic/galleries

 

[SFishy]

So what happens in these cases, as I asked originally... do I have my focus points selected correctly in the first two? and what about the third? Which would you pick?







This illustrates why I think it's possible the point represent a MUCH larger area, but not sure where or how much.

Amy

You said "quadrant as the area to be used for focusing." To
clarify, you still want to use the AF mark itself for focusing.
Although the sensitive areas are larger than the marks, you still
want to use the marks themselves.

 

[RDKirk]

I remembered I had the link to the diagram Chuck Westfall (head of
technical marketing I believe)made for the Rob Galbraith forum of
the 10D's AF coverage. This could be related to the 20D I assume.



http://www.pbase.com/chuckwestfall/image/18920257

There is also one for teh 1D/1DS that may be interesting.
http://www.pbase.com/chuckwestfall/image/18921414

The difference between the 10D and the 20D, besides the layout of the rectangles, is that the center square area has real 2D dimensionality.

That is, although the points are marked as though they are rectangles and squares, in fact they are lines (no 2nd dimension). In the 10D, the central cross is also two crossed lines of sensitivity.

However, on the 20D with an f2.8 lens, the central square actually has two effective dimensions because of the additional sensors that come into play with an f2.8 lens. The Canon sources I've seen differ as to whether the 20D has both an additional vertical sensor and an additional horizontal sensor, or just an additional horizontal sensor (the rather garbled explanation in the manual suggests only an additional horizontal sensor, which would provide twice the accuracy against vertical contrasts).

--
RDKirk
'TANSTAAFL: The only unbreakable rule in photography.'

 

[Ed Rotberg]

While I primarily use the center point for most of my static shooting, and for wildlife (other than birds in flight), I almost alwasy select a point when photographing people. The reason is that I'm almost certainly closer when doing this, and the resultant DOF, especially at wide apertures, is narrower. When you Focus-Recompose, you tilt that narrow plane of focus (it's actually a sphere) away from where it was correctly focused, causing your subject to almost certainly be out of focus.

For birds in flight, I use all 9 AF points, unless it's against a very busy background. Then I will revert center point AF.

The joystick on the 20D makes this so much easier than the 10D was. IMHO, it's worth practicing to learn this technique.

= Ed =

there's an artical by Chuck Westfall of Canon that recommends using
the focus points not Focus Lock and Recompose. Especially at wide
open apertures under a distance of 15'.

the reasoning is that they focus plain is then moved and as a
result increases the chance of Front or Back Focus.

folks here will debate the issue to death, but I'm on the side of
Chuck and believe him as an engineer for the Cameras. I've had
absolutely no focus issues with the 20D and I have switched
techniques to using the focus points as a result of his artical.
The artical is based on the 45pt AF system of the 1D bodies, but
the same is going to apply to the rest of the EOS systems too.

I too am a firm believer in selecting AF points manually mainly
because earlier EOS cameras including the 10D placed a huge bias on
exposure and flash metering on the selected AF point.

But good luck to the 1-series users with no AF joystick to move
those 45 AF points around. You have to press a button and rotate 2
dials to dial in the AF point you want. Try doing it in Servo mode.
Impossible. A serious flaw in design in my opinion. Kudos to Canon
for planting a Joystick on the 20D. Now you can even switch AF
points while tracking a moving subject.

--
= Ed Rotberg =

'A waist is a terrible thing to mind'
http://www.edrotberg.org/gallery

 

[Ben_Egbert]

RDKirk wrote:
snip

That explains my problem, when shooting birds in flight, they usually small enough in the viewfinder to fit bewteen the active focus areas.

--
http://www.pbase.com/roserus

Ben

 

[SFishy]

Which is part of what I don't understand.

Did Canon not intend for these point to represent a larger area??? (Rule of thinds or golden section rule?)

Amy

RDKirk wrote:
snip

That explains my problem, when shooting birds in flight, they
usually small enough in the viewfinder to fit bewteen the active
focus areas.

--
http://www.pbase.com/roserus

Ben

--

Creativity is allowing yourself to make mistakes. Art is knowing which ones to keep.
http://www.something-fishy.com/photography

 

[RDKirk]

Which is part of what I don't understand.

Did Canon not intend for these point to represent a larger area???
(Rule of thinds or golden section rule?)

A DSLR doesn't use the imaging sensor to determine focus by contrast, as a P&S does. It uses discrete linear sensors that make passive phase detection readings (not contrast, actually) and estimations. The system looks once, determines what direction and how far the lens must move to get correct focus, then commands the lens to make that movement.

This means there isn't any "area" measurement to speak of, because the phase detection arrays are short lines of pixels that don't have any width to speak of. The center point is a vertical/horizontal cross of pixels (the 20D has either a second cross or just another horizontal line of pixels that come into play with an f2.8 lens).

So we're talking about short segments of detection, not area detection. The segments at the 1:30, 4:30, 7:30, and 10:30 points in the 20D viewscreen are almost--but not quite--at the Golden Mean intersections.

There appear to be limits to how far from the lens axis the sensor arrays can be located (see that even in the 1D series, all 45 of them are clustered fairly close to the center). I think Canon got as far out as they could within the intended 20D price point, but they aren't claiming to have put them on the Golden Mean intersections (as the Contax digital did).

--
RDKirk
'TANSTAAFL: The only unbreakable rule in photography.'