Depth of Field is Enough to Negate Parallel Issues??????

"Nicholas O. Lindan" wrote in message thlink.net...

I will lay odds something is seriously wrong with this man's camera or
his setup: things aren't parallel.


Here's another reason i don't think it's a parallel issue when i'm
taking pictures of my flat, 2-D paintings. Look at this:


http://www.outsight.com/hyperfocal.html


From this website, i got this:

Calulation for 4x5, 150mm focal length, at a focus distance of
50".

f-stop Depth of Field (in inches)

5.6 4.6"
11 8.3"
16 12.1"
22 16.9"
32 25.3"


This calculator bases the DOF on 8"x10" prints, so this will be
a factor.


My point is that at f16 or f22, the painting could have been +/- 6
inches from the focal plane (at 50"), and it still would have been in
focus.
What the tolerance for the film is (+/- of the 64T film focal
plane), i don't know. I have yet to compare the depth of the fresnel
lens to the depth of the film plane in the film holders, but they look
pretty close to me. And as i have said, the Xenar was perfectly sharp
in the center of the pics.

And i've got a good eye for making things nice and straight, so i
don't think the parallelism is the problem. There is a sort of
"parallax distortion" (i don't know what else to call it), whereby the
edges of the paintings will not be parallel to the edges of the
fresnel focusing screen if they are not facing each other perfectly.
You can use this to align the camera to the painting, when you don't
have a copy-stand.

So i don't know why my f32 exposure (using Schneider sironar-N
150mm) seemed a tiny bit sharper than my f22 and f16 ones. Maybe it
was a fluke, i'll try it again this weekend with my recently acquired
used sironar-N.

Thank you for any input you could give.


Slick

My point is that at f16 or f22, the painting could have been +/- 6
inches from the focal plane (at 50"), and it still would have been in
focus.

No, it wouldn't have been in focus. The only thing in focus would have been
the plane on which you were focused. What I think you mean to say is that
depth of field should have covered up the focusing error. You base that on
the table you quoted. However, depth of field tables make certain
assumptions about the acceptable size of the circle of confusion, the size
of the print, the viewing distance from the print, etc. Perhaps your
standards are higher than those of the person who constructed the table, or
perhaps you made a larger print, or perhaps you were looking at the print
from a closer distance than the tables contemplated. Or perhaps lots of
other things that can cause areas of a print to not look "sharp" (e.g. the
film flatness issue you mention).

So i don't know why my f32 exposure (using Schneider sironar-N
150mm) seemed a tiny bit sharper than my f22 and f16 ones. Maybe it
was a fluke, i'll try it again this weekend with my recently acquired
used sironar-N.

As you stop down a lens aberrations decrease. Diffraction increases.
However, at F32 diffraction isn't much of a problem with a 4x5 negative and
a magnification factor of only 2x - 4x. So maybe by stopping down to F32
you reduced some aberrations that were affecting the print without
noticeably increasing the adverse effects of diffraction? Just a thought,
I'm not sure the aberrations reduced by stopping down would have affected
the "sharpness" of the print,. As I recently demonstrated, I'm not an optics
expert. : - )

"Dr. Slick" wrote in message
m...
"Nicholas O. Lindan" wrote in message
thlink.net...

I will lay odds something is seriously wrong with this man's camera or
his setup: things aren't parallel.


Here's another reason i don't think it's a parallel issue when i'm
taking pictures of my flat, 2-D paintings. Look at this:


http://www.outsight.com/hyperfocal.html


From this website, i got this:

Calulation for 4x5, 150mm focal length, at a focus distance of
50".

f-stop Depth of Field (in inches)

5.6 4.6"
11 8.3"
16 12.1"
22 16.9"
32 25.3"


This calculator bases the DOF on 8"x10" prints, so this will be
a factor.


My point is that at f16 or f22, the painting could have been +/- 6
inches from the focal plane (at 50"), and it still would have been in
focus.
What the tolerance for the film is (+/- of the 64T film focal
plane), i don't know. I have yet to compare the depth of the fresnel
lens to the depth of the film plane in the film holders, but they look
pretty close to me. And as i have said, the Xenar was perfectly sharp
in the center of the pics.

And i've got a good eye for making things nice and straight, so i
don't think the parallelism is the problem. There is a sort of
"parallax distortion" (i don't know what else to call it), whereby the
edges of the paintings will not be parallel to the edges of the
fresnel focusing screen if they are not facing each other perfectly.
You can use this to align the camera to the painting, when you don't
have a copy-stand.

So i don't know why my f32 exposure (using Schneider sironar-N
150mm) seemed a tiny bit sharper than my f22 and f16 ones. Maybe it
was a fluke, i'll try it again this weekend with my recently acquired
used sironar-N.

Thank you for any input you could give.


Slick

"Dr. Slick" wrote in message
m...
"Nicholas O. Lindan" wrote in message
thlink.net...

Here's another reason i don't think it's a parallel issue when i'm
taking pictures of my flat, 2-D paintings. Look at this:

Calulation for 4x5, 150mm focal length, at a focus distance of
50".

f-stop Depth of Field (in inches)

5.6 4.6"
11 8.3"
16 12.1"
22 16.9"
32 25.3"

My point is that at f16 or f22, the painting could have been +/- 6
inches from the focal plane (at 50"), and it still would have been in
focus.

there are 2 DoF, one is depth of field and the other is depth of focus, the
latter is less forgiving, for object at infinity it is "c*N" where c =
circle of confusion and N = aperture. Assuming 0.1mm CoC for 4x5 and an
aperture of f/342, you would have a deph of cous of 3.2mm in front and back
of the image plane. For objects closer than infinity it becomes a bit
greater, for 50" for instance, is 3.6mm. So your problem could still be
paralellism.

Guillermo

f/256 wrote:
"Dr. Slick" wrote in message
m...

"Nicholas O. Lindan" wrote in message

thlink.net...

Here's another reason i don't think it's a parallel issue when i'm
taking pictures of my flat, 2-D paintings. Look at this:

Calulation for 4x5, 150mm focal length, at a focus distance of
50".

f-stop Depth of Field (in inches)

5.6 4.6"
11 8.3"
16 12.1"
22 16.9"
32 25.3"

My point is that at f16 or f22, the painting could have been +/- 6
inches from the focal plane (at 50"), and it still would have been in
focus.


there are 2 DoF, one is depth of field and the other is depth of focus, the
latter is less forgiving, for object at infinity it is "c*N" where c =
circle of confusion and N = aperture.

Your analysis is correct, but let me quibble about this since it took me
a while to figure it out after reading a variety of books and articles
on photographic optics. I don't think the matter is well understood.

There are well known formulas relating what happens on the subject side
of the lens to what happens on the film side of the lens. It is a
matter of terminology how you describe it all, and either can be used.
For example, the usual considerations associated with depth of field,
and choosing the proper aperture to have what you want in focus, can all
be accomplished using the focus spread method described at
www.largeformatphotography.info
These involve measurements made along the rail or bed on the film side
of the lens. The formula you quote plays an important role in this method.

The difference between depth of field and depth of focus lies in how you
intend to use the formulas and measurements.

When you consider depth of field, you envision that the film plane is
exactly where you want it and you want to know what out in subject space
will be adequately in focus. This can be specified as distances to
different parts of the scene as in conventional depth of field tables.
It also can be specified in terms of how far from the film plane the
exact images of the extremes of the depth of field region lie.

When you consider depth of focus, you envision that you are focusing on
a single plane in the scene, and you ask how far off the film plane can
be from the exact image plane without the image in the film being out of
perceptible focus. That could also be specified in terms of distances
in the scene, using those well known formulas, but it wouldn't be too
useful to do that.

In reality, these two concerns can't be separated. If you have a
problem with depth of focus because the film plane isn't where you want
it to be, then the whole range of what is in adequate focus will shift.
You will generally gain depth of field in the near and lose it in the
far, or vice-versa.

Fortunately, in a well adjusted camera, the error in film placement is
small compared to the focus spread at apertures that one normally uses
in large format photography. If it isn't, then the camera is not going
to perform adequately. You would notice this by seeing that in some
parts of the scene, the foreground or background is being favored
compared to what you intended. But the very act of focusing introduces
a related depth of focus issue. You focus wide open at a relatively
large aperture and stop down to actually take the picture. In the
formula 2Nc, the N that is more relevant for focusing errors is usually
the wide open aperture, while the N in 2Nc for focus spread (depth of
field) calculations is the taking aperture. (The c's may also be
different, but that is another matter.)

Assuming 0.1mm CoC for 4x5 and an
aperture of f/342, you would have a deph of cous of 3.2mm in front and back
of the image plane. For objects closer than infinity it becomes a bit
greater, for 50" for instance, is 3.6mm. So your problem could still be
paralellism.

Guillermo

"Dr. Slick" Garvin Yee wrote:

I rented this lens [G-Claron 150mm] and shutter, and
took pics at f16, they turned out terribly fuzzy.

This is getting to be farce.

Would the good Mr. Yee please post a few examples of "terribly fuzzy" to
his website:

http://www.drslick.org/


--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer: Electronics; Informatics; Photonics.

"Reciprocity Failure" wrote in message t.com...

No, it wouldn't have been in focus. The only thing in focus would have been
the plane on which you were focused. What I think you mean to say is that
depth of field should have covered up the focusing error. You base that on
the table you quoted. However, depth of field tables make certain
assumptions about the acceptable size of the circle of confusion, the size
of the print, the viewing distance from the print, etc. Perhaps your
standards are higher than those of the person who constructed the table, or
perhaps you made a larger print, or perhaps you were looking at the print
from a closer distance than the tables contemplated. Or perhaps lots of
other things that can cause areas of a print to not look "sharp" (e.g. the
film flatness issue you mention).


That's why i stated the calculator was based on an 8"x10" print,
and
my standards will be a bit higher, as i expect to make them up to 30"
or so.

I'll be very careful about the parallelism tonight.

BTW, could someone explain to me what the "circle of confusion"
means? It's confusing!

:^O


Slick

On 2/29/2004 4:42 AM Reciprocity Failure spake thus:

My point is that at f16 or f22, the painting could have been +/- 6
inches from the focal plane (at 50"), and it still would have been in
focus.

No, it wouldn't have been in focus. The only thing in focus would have been
the plane on which you were focused. What I think you mean to say is that
depth of field should have covered up the focusing error. You base that on
the table you quoted. However, depth of field tables make certain
assumptions about the acceptable size of the circle of confusion, the size
of the print, the viewing distance from the print, etc. Perhaps your
standards are higher than those of the person who constructed the table, or
perhaps you made a larger print, or perhaps you were looking at the print
from a closer distance than the tables contemplated. Or perhaps lots of
other things that can cause areas of a print to not look "sharp" (e.g. the
film flatness issue you mention).

Come on, let's be reasonable here. Perhaps you forgot what he was shooting:
flat artwork. According to the table he posted, the depth of field at the
aperture he was using (f/22) is more than 16 inches. Even if the constructor
of the table was too forgiving (accepting of out-of-focus images) by a factor
of two or even three, that's still plenty enough room to cover whatever small
error in alignment he had. We're talking a couple of inches *at most* here.


--
It's fun to demonize the neo-cons and rejoice in their discomfiture, but
don't make the mistake of thinking US foreign policy was set by Norman
Podhoretz or William Kristol. They're the clowns capering about in front of
the donkey and the elephant. The donkey says the UN should clean up after
them, and the elephant now says the donkey may have a point. Somebody has
come out with a dustpan and broom.

- Alexander Cockburn, _CounterPunch_
(http://www.counterpunch.org), 9/17/03

On 2/29/2004 1:29 PM Dr. Slick spake thus:

BTW, could someone explain to me what the "circle of confusion"
means? It's confusing!

It's supposed to be confusing.

But really: the CoC, in lay terms, is the circle made on the image plane (film
plane in this case) by a point of light from the subject. As the focus on that
point is improved, the CoC gets smaller and smaller, as it approaches (but
never quite reaches) a perfect point on the film plane.

Others can give lots more detailed and technical explanations of this basic
optical phenomonon. This is all you need to know for LF103.


--
It's fun to demonize the neo-cons and rejoice in their discomfiture, but
don't make the mistake of thinking US foreign policy was set by Norman
Podhoretz or William Kristol. They're the clowns capering about in front of
the donkey and the elephant. The donkey says the UN should clean up after
them, and the elephant now says the donkey may have a point. Somebody has
come out with a dustpan and broom.

- Alexander Cockburn, _CounterPunch_
(http://www.counterpunch.org), 9/17/03

On 2/29/2004 1:29 PM Dr. Slick spake thus:

BTW, could someone explain to me what the "circle of confusion"
means? It's confusing!

Here's kind of a dumbass explanation from one of the Web "encyclopedias":

http://en.wikipedia.org/wiki/Circle_of_confusion


--
It's fun to demonize the neo-cons and rejoice in their discomfiture, but
don't make the mistake of thinking US foreign policy was set by Norman
Podhoretz or William Kristol. They're the clowns capering about in front of
the donkey and the elephant. The donkey says the UN should clean up after
them, and the elephant now says the donkey may have a point. Somebody has
come out with a dustpan and broom.

- Alexander Cockburn, _CounterPunch_
(http://www.counterpunch.org), 9/17/03

David Nebenzahl wrote:
On 2/29/2004 1:29 PM Dr. Slick spake thus:

BTW, could someone explain to me what the "circle of confusion"
means? It's confusing!


Here's kind of a dumbass explanation from one of the Web "encyclopedias":

http://en.wikipedia.org/wiki/Circle_of_confusion

But it is wrong. The maximal acceptable circle of confusion is usually
significantly larger than film grain. It is based on what would appear
as a point in a final print viewed in a specified way.