How to test for front focusing ?

Erik Dasque said:

just received my 1D (from stock at Delta and shipped overnight) and
it seems like there is no banding (# over 8xxxx). I was wondering
how I should test the focus issue and what it really is ? I just
want to eliminate all possible issues while I am still
conditionning the batteries and before I go on and start using it
outside my studio.

Click to expand...

DavidP said:

The red box is where the AF sensor was located. The blue line is
the plane of focus. The green line is what I'd hoped to focus on.

Can't argue with the results. The plane of focus was inside the
red AF sensor box.

Basically, grab a ruler, and lay it out flat. Then shoot it (on a
tripod) by moving a few yards away, and being above it by a few
feet. Then focus on a point, and shoot. Be sure to use RAW format.

In the TWAIN driver, when you convert, you can see where the AF box
was located. Very handy.

Erik Dasque said:

just received my 1D (from stock at Delta and shipped overnight) and
it seems like there is no banding (# over 8xxxx). I was wondering
how I should test the focus issue and what it really is ? I just
want to eliminate all possible issues while I am still
conditionning the batteries and before I go on and start using it
outside my studio.

Click to expand...

--
The Unofficial Photographer of The Wilkinsons
http://thewilkinsons.crosswinds.net
Photography -- just another word for compromise

Click to expand...

Erik Dasque said:

What do you think ? Do I have a Front Focus problem ? I took a 400
pictures at the Red sox opening game with my 100-400 on a Monopod
(with IS) and they all seemed a little out of focus, which might be
caused by front focus I guess but also a lot of other things. How
would front focus affect sport pictures taken with my 100-400 (and
1.4x extender, sometime).

If I do have a Front Focus issue with my 1D what is the best way to
proceed ?

TIA,

Ed.

DavidP said:

The red box is where the AF sensor was located. The blue line is
the plane of focus. The green line is what I'd hoped to focus on.

Can't argue with the results. The plane of focus was inside the
red AF sensor box.

Basically, grab a ruler, and lay it out flat. Then shoot it (on a
tripod) by moving a few yards away, and being above it by a few
feet. Then focus on a point, and shoot. Be sure to use RAW format.

In the TWAIN driver, when you convert, you can see where the AF box
was located. Very handy.

Erik Dasque said:

just received my 1D (from stock at Delta and shipped overnight) and
it seems like there is no banding (# over 8xxxx). I was wondering
how I should test the focus issue and what it really is ? I just
want to eliminate all possible issues while I am still
conditionning the batteries and before I go on and start using it
outside my studio.

Click to expand...

--
The Unofficial Photographer of The Wilkinsons
http://thewilkinsons.crosswinds.net
Photography -- just another word for compromise

Click to expand...

Click to expand...

David James Miller said:

shoot a chart at 300mm and 400mm

DJM

Erik Dasque said:

What do you think ? Do I have a Front Focus problem ? I took a 400
pictures at the Red sox opening game with my 100-400 on a Monopod
(with IS) and they all seemed a little out of focus, which might be
caused by front focus I guess but also a lot of other things. How
would front focus affect sport pictures taken with my 100-400 (and
1.4x extender, sometime).

If I do have a Front Focus issue with my 1D what is the best way to
proceed ?

TIA,

Ed.

DavidP said:

The red box is where the AF sensor was located. The blue line is
the plane of focus. The green line is what I'd hoped to focus on.

Can't argue with the results. The plane of focus was inside the
red AF sensor box.

Basically, grab a ruler, and lay it out flat. Then shoot it (on a
tripod) by moving a few yards away, and being above it by a few
feet. Then focus on a point, and shoot. Be sure to use RAW format.

In the TWAIN driver, when you convert, you can see where the AF box
was located. Very handy.

Erik Dasque said:

just received my 1D (from stock at Delta and shipped overnight) and
it seems like there is no banding (# over 8xxxx). I was wondering
how I should test the focus issue and what it really is ? I just
want to eliminate all possible issues while I am still
conditionning the batteries and before I go on and start using it
outside my studio.

Click to expand...

--
The Unofficial Photographer of The Wilkinsons
http://thewilkinsons.crosswinds.net
Photography -- just another word for compromise

Click to expand...

Click to expand...

Click to expand...

Jim Leonard said:

I can forsee a significant problem with most of the tests that I'm
seeing. Most of the tests are shot with the focus point on
something severely canted. Since the AF sensor is not a point (or
even a line) but rather a plane there is a continuum of valid
positions for the lens to be in. Furthermore the AF sensor is not
necessarily completely enclosed by the rectangle overlayed on the
image. Can I suggest a slightly modified test. Have a high
contrast planar object parallel to the focal plane that you focus
on and have your ruler intersect it. The following were taken with
my d30 and are 1:1 crops. The ruler intersects the card at 16.5
inches. In the first I am focusing on the card about a half inch
to the left of the ruler and it appears that the in focus plane is
somewhere inbetween the 16.5 line and the 16.375 line.



on this next picture, I focused on the ruler with the focus point
centered on the 16.5 line. After hunting and failing to find focus
a couple of times it finally gave a focus lock for this. In this
case the 17 line was outside of the AF box etched on the focus
screen.



I repeated these tests a few times and got similar results. When
the AF sensor was over the card it would always be about a 1/16th
of an inch front focused. When the AF sensor was pointed at the
ruler I never got consistent AF although it would sometimes snap
into position as though it new exactly where to go.

All of the above was done in my basement with a 50mm f/1.4 on my
d30 at about 20 inches from the target. The camera was set at
1/160 sec f/1.4 ISO 100 (from which you can calculate an
approximate light intensity if you know how (which I don't off the
top of my head)) in one shot AF mode and the center focus point set.

As I'm going away for the weekend I won't be able to respond to
comments or criticisms so please feel free to trash my name

jim

Click to expand...

Jim Leonard said:

I can forsee a significant problem with most of the tests that I'm
seeing. Most of the tests are shot with the focus point on
something severely canted. Since the AF sensor is not a point (or
even a line) but rather a plane there is a continuum of valid
positions for the lens to be in. Furthermore the AF sensor is not
necessarily completely enclosed by the rectangle overlayed on the
image. Can I suggest a slightly modified test. Have a high
contrast planar object parallel to the focal plane that you focus
on and have your ruler intersect it. The following were taken with
my d30 and are 1:1 crops. The ruler intersects the card at 16.5
inches. In the first I am focusing on the card about a half inch
to the left of the ruler and it appears that the in focus plane is
somewhere inbetween the 16.5 line and the 16.375 line.



on this next picture, I focused on the ruler with the focus point
centered on the 16.5 line. After hunting and failing to find focus
a couple of times it finally gave a focus lock for this. In this
case the 17 line was outside of the AF box etched on the focus
screen.



I repeated these tests a few times and got similar results. When
the AF sensor was over the card it would always be about a 1/16th
of an inch front focused. When the AF sensor was pointed at the
ruler I never got consistent AF although it would sometimes snap
into position as though it new exactly where to go.

All of the above was done in my basement with a 50mm f/1.4 on my
d30 at about 20 inches from the target. The camera was set at
1/160 sec f/1.4 ISO 100 (from which you can calculate an
approximate light intensity if you know how (which I don't off the
top of my head)) in one shot AF mode and the center focus point set.

As I'm going away for the weekend I won't be able to respond to
comments or criticisms so please feel free to trash my name

jim

Click to expand...

Jim Leonard said:

I can forsee a significant problem with most of the tests that I'm
seeing. Most of the tests are shot with the focus point on
something severely canted. Since the AF sensor is not a point (or
even a line) but rather a plane there is a continuum of valid
positions for the lens to be in. Furthermore the AF sensor is not
necessarily completely enclosed by the rectangle overlayed on the
image. Can I suggest a slightly modified test. Have a high
contrast planar object parallel to the focal plane that you focus
on and have your ruler intersect it. The following were taken with
my d30 and are 1:1 crops. The ruler intersects the card at 16.5
inches. In the first I am focusing on the card about a half inch
to the left of the ruler and it appears that the in focus plane is
somewhere inbetween the 16.5 line and the 16.375 line.



on this next picture, I focused on the ruler with the focus point
centered on the 16.5 line. After hunting and failing to find focus
a couple of times it finally gave a focus lock for this. In this
case the 17 line was outside of the AF box etched on the focus
screen.



I repeated these tests a few times and got similar results. When
the AF sensor was over the card it would always be about a 1/16th
of an inch front focused. When the AF sensor was pointed at the
ruler I never got consistent AF although it would sometimes snap
into position as though it new exactly where to go.

All of the above was done in my basement with a 50mm f/1.4 on my
d30 at about 20 inches from the target. The camera was set at
1/160 sec f/1.4 ISO 100 (from which you can calculate an
approximate light intensity if you know how (which I don't off the
top of my head)) in one shot AF mode and the center focus point set.

As I'm going away for the weekend I won't be able to respond to
comments or criticisms so please feel free to trash my name

jim

Click to expand...