Glory Hallelujah - Softball Time - A FOCUS technical question - NEED GURUS!

SHAMELESS PLUG:
Softball tournament images of my daughter's team, all shot
with a D50 
and Sigma 70-300 f4-5.6 APO at:
http://www.flickr.com/photos/chemisti/sets/72157594
556255669/

OPENING STATEMENT:
I do not like any of the dynamic focus methods because I
want the 
camera to focus on what I point it at (control freak).  I
have on 
occassion used all 5 of the focus sensors for creative
framing, but 
generally use the center focus indicator/sensor.

OBSERVATIONS:
1.  I have noticed in low light that the autofocus likes
sharp 
contrast lines.  If you attempt to focus on a face in low
light it 
may have a problem.  However, you may easily focus on a
stripe on the 
person's shirt under the same light conditions.  I have used
this to 
take images or to use the focus lock function and then
recompose 
prior to releasing the shutter.
2.  I have noticed that the D50 really likes to focus on the
fencing 
behind batters when shooting softball (lots of high
contrast, sharply 
defined lines or edges).  
3.  I have read in lens reviews about lenses that
"front focus" 
or "back focus" which indicates that a flaw exists
which prevents 
exact, precise, and accurate focusing.

MUSINGS:  
The observations make me wonder exactly how the autofocus
system 
works.  I assumed that the autofocus sensor adjusts the lens
until it 
somehow returns a "in focus" signal, at which
point it stops either 
(a) powering the lens motor or (b) turning the focus screw
drive.  
When it can't find something "sharp" to focus on,
it may hunt from 
minimum focus to infinity searching for something to
"lock on to".

FINALLY, THE QUESTIONS:

1.  Does anyone other than Nikon engineers really understand
how the 
autofocus mechanism works?  Why, you ask?  Well, I am a
hopelessly 
analytical person (engineer) who is under the illusion that
what I 
understand, I can control or at least compensate for. 
Insight into 
the mechanism might help me control focus better.

2.  If the camera controls the focus (the sensors are in the
camera 
and not the lens, right?), how can a lens "front
focus" or "back 
focus"?  It seems that the camera adjusts until it
thinks the subject 
is in focus - how can the lens mess this up?

3.  Am I using improper technique?  Tips on keeping the lens
focused 
on the batter/catcher rather than the backstop are
appreciated.  It 
doesn't happen on all shots, but happens with some
regularity.

4.  I have tried one of the dynamic focus settings and I
found that 
it is hard to control extraneous stuff entering the frame
during 
sports/action shooting and drawing the focus away from the
intended 
subject.  Do I misunderstand how it is to be used? 
(Remember the 
restrictions on vantage point for sports - you can't always
get to 
the spot for the best image) 
It is a feeling thing, it seems that given the chance, the
D50 
would "prefer" to focus on the backstop rather
than the intended 
subject - hard to explain...

If any of this makes sense to you and you have (a)
experience which 
can be useful to help, or (b) understanding of how the
autofocus 
mechanism works, your guidance/wisdom/experience is valued.

If my question doesn't make sense, thanks in advance for
wasting 15 
minutes to get to this point...

D50 ROCKS!





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Hey Chemisti   Frustrations abound in this our chosen
hobby.

as to Question #2 Lag time will result in focusing beyond or
just 
short of the intended point.The Camera  stops the focus
motor at the 
perfect focus range but the motor continues to travel until
residual 
energy is overcome by the resistance . there is a time delay
between 
stop and end of motion.This is likely to vary between
different 
lenses and definitely between the body AF Motor and the SWM
motor in 
the lens. 
as to #4  the backstop provide a gridwork of intersecting
lines all 
close to the same distance and will likely fill the focus
area 
whereas the batter or catcher will not. 
 Focusing on a snow Leopard across the street the other day
was quite 
frustrating at times . I had to very carefully place the
head right 
in a specific portion of the Focus area otherwise AF would
choose the 
chain link fence about 15 feet closer to me.


Personally i'd be tempted to stay with manual focus .
Figuring 150 
feet from the plate f4 at 300mm will yield 8 feet DOF. Most
batters 
tend to stay in the same part of the box so focusing on them
when 
they go into their crouch should provide descent referance
and cover 
most of the batter's box; that should do for her turn at
bat. 
Focusing on the catcher might place the batter out of focus
during 
the swing. though 5.6 for aperture should provide about 17
feet DOF 
and allow for this too.

The ball has to enter the focus area as well so there is
potential 
for the AF to pick up on this and readjust during the play
if Dynamic 
focus is in use. a strong reflection from the spinning ball
will 
likely catch it at some point.


Man with all the great shots you posted last season i'm
surprised 
that you are looking for advice.

Good Shooting

Mike

--- In Nikon-D50@yahoogroups.com, "chemisti"
<chemisti...> wrote:
>
> SHAMELESS PLUG:
> Softball tournament images of my daughter's team, all
shot with a 
D50 
> and Sigma 70-300 f4-5.6 APO at:
> http://www.flickr.com/photos/chemisti/sets/72157594
556255669/
> 
> OPENING STATEMENT:
> I do not like any of the dynamic focus methods because
I want the 
> camera to focus on what I point it at (control freak). 
I have on 
> occassion used all 5 of the focus sensors for creative
framing, but 
> generally use the center focus indicator/sensor.
> 
> OBSERVATIONS:
> 1.  I have noticed in low light that the autofocus
likes sharp 
> contrast lines.  If you attempt to focus on a face in
low light it 
> may have a problem.  However, you may easily focus on a
stripe on 
the 
> person's shirt under the same light conditions.  I have
used this 
to 
> take images or to use the focus lock function and then
recompose 
> prior to releasing the shutter.
> 2.  I have noticed that the D50 really likes to focus
on the 
fencing 
> behind batters when shooting softball (lots of high
contrast, 
sharply 
> defined lines or edges).  
> 3.  I have read in lens reviews about lenses that
"front focus" 
> or "back focus" which indicates that a flaw
exists which prevents 
> exact, precise, and accurate focusing.
> 
> MUSINGS:  
> The observations make me wonder exactly how the
autofocus system 
> works.  I assumed that the autofocus sensor adjusts the
lens until 
it 
> somehow returns a "in focus" signal, at which
point it stops either 
> (a) powering the lens motor or (b) turning the focus
screw drive.  
> When it can't find something "sharp" to focus
on, it may hunt from 
> minimum focus to infinity searching for something to
"lock on to".
> 
> FINALLY, THE QUESTIONS:
> 
> 1.  Does anyone other than Nikon engineers really
understand how 
the 
> autofocus mechanism works?  Why, you ask?  Well, I am a
hopelessly 
> analytical person (engineer) who is under the illusion
that what I 
> understand, I can control or at least compensate for. 
Insight into 
> the mechanism might help me control focus better.
> 
> 2.  If the camera controls the focus (the sensors are
in the camera 
> and not the lens, right?), how can a lens "front
focus" or "back 
> focus"?  It seems that the camera adjusts until it
thinks the 
subject 
> is in focus - how can the lens mess this up?
> 
> 3.  Am I using improper technique?  Tips on keeping the
lens 
focused 
> on the batter/catcher rather than the backstop are
appreciated.  It 
> doesn't happen on all shots, but happens with some
regularity.
> 
> 4.  I have tried one of the dynamic focus settings and
I found that 
> it is hard to control extraneous stuff entering the
frame during 
> sports/action shooting and drawing the focus away from
the intended 
> subject.  Do I misunderstand how it is to be used? 
(Remember the 
> restrictions on vantage point for sports - you can't
always get to 
> the spot for the best image) 
> It is a feeling thing, it seems that given the chance,
the D50 
> would "prefer" to focus on the backstop
rather than the intended 
> subject - hard to explain...
> 
> If any of this makes sense to you and you have (a)
experience which 
> can be useful to help, or (b) understanding of how the
autofocus 
> mechanism works, your guidance/wisdom/experience is
valued.
> 
> If my question doesn't make sense, thanks in advance
for wasting 15 
> minutes to get to this point...
> 
> D50 ROCKS!
>




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--- In Nikon-D50@yahoogroups.com, "chemisti"
<chemisti...> wrote:
>
> SHAMELESS PLUG:
> Softball tournament images of my daughter's team, all
shot with a D50 
> and Sigma 70-300 f4-5.6 APO at:
> http://www.flickr.com/photos/chemisti/sets/72157594
556255669/

Good stuff!

> OPENING STATEMENT:
> I do not like any of the dynamic focus methods because
I want the 
> camera to focus on what I point it at (control freak). 


Then MF, AF will always hunt for best contrast focus and
often 
overshoots as well, with some longer lenses I've had real
issues with 
false focusing out of focus (nothing in focus at all). When
I tried a 
D80 it coped much better.

Niel



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First - thanks for the replies from my esteemed colleagues
and mentors!

Second - your personal observations let me know that it is
something
that I am not the only one who has challenges.

I have just noticed that I get home and review images and am
surprised
to find shots (say at f8) where I would have SWORN that
everything was
in focus only to find out that the players are slightly out
and the
backstop is drop-dead-gorgeous-sharp.  

I am evidently not the sharpest tool in the shed and it has
just
finally occurred to me that I might be able to overcome it. 
Hey, at
some point I should be getting a better "hit"
ratio.  Other aspects of
my shooting have improved and so should this.

I have noticed from time to time that if I intentionally
make the
camera focus on something at a significantly different
distance and
then refocus on the desire subject, the camera seems to do
better.

I have looked (with wild, lustful eyes and shaking hands) at
a D80 and
even... dare I say it... at a D200 and admired the bright,
beautiful
viewfinders and the much more sophisticated AF system.  I
caressed her
beautiful curves and admired her stately repose... oops,
this is a
family forum ;-D

Quite frankly, I had assumed that if I couldn't get my
trusty D50 to
focus well with only 5 simple points, how could I master 11
or 13 or
27 or however many it is - pretty blinking AF points dancing
all over
the viewfinder?  GOOD GOD MAN, I NEED IT SIMPLE...

After reading Thom Hogan's essay, it seems that all that
stuff might
actually be useful!  It now also makes sense that with all
those
straight, sharp lines filling the frame, the camera would
actually
"prefer" to focus there if it loses focus in one
of the sensors for
even a split second - which is actually pretty easy with all
the
movement.  Also makes me wonder how the D40 does in these
situations
with only 3 AF points - (gotta do something to keep feeling
superior...)

Well, when in doubt, it seems that there is ONLY one thing
to do -
show this problem to my wife and explain in intimate detail
how the
only true cure for this complex technical issue is to
replace the D50
with a D80 and a complete assortment of pro glass - 
YES, THAT SHOULD DO THE TRICK!  After all, the D50 has over
66000
shutter releases on it - nearly "over the
hill"...

D50 ROCKS!  (But a D80 could get me by in a pinch - he he
he.)



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