This DOF thang

(The original thread was mistitled and I decided to take a new subject
anyway.) Refer to the original thread which posited that two cameras of
different film formats would have the same DO-Field if the lenses were of
equivalent focal length _and the prints were of equal size_.

I certainly do not mind being corrected, nor do I mind admitting when I am
wrong. It's more important to have the correct information out there.

So, my fundamental error in my example was in not having objects between the
focused foreground and the extreme (at infinity) background. Such objects
would have shown the loss of DOF more clearly in the large format image.
Correct, Brian?

In any event, it was an interesting thread because it showed a specific
example visually: mine with the picture shown and Brian's example.

Thanks all (except that Roland object whatever it realy is.)

(BTW - wasn't it rather daunting to see how poorly the Hasselblad did
compared to the 4X5? ) Bait. Don't take it.

dadiOH wrote:

1. Focal length has nothing to do with perspective. Near far
relationships will be identical no matter what FL on what format.

If you mean what you said above, I can only say "horse ****". A 50 MM lens
on a 35mm camera will certainly give a different perspective than a 135 MM
on that format or any other.

You seem to be mixing two concepts he perspective and field of view.
Perspective means "the appearance of things relative to one another as
determined by their distance from the viewer" (from a dictionary). Focal
length and size of film/sensor does NOT affect this at all. The
relationship remains the same no matter how you crop or zoom. Please,
try this before writing more. You can try this with pencil and paper.

Field of view, on the other hand, means the "the area that is visible"
and can be expressed as degrees, for example. Focal length and
film/sensor size affect this.

1. Perspective changes only when the camera moves in relation to the
subject(s).
2. FOV changes only when altering focal length or film/sensor size.

If, OTOH, you mean that lenses of the same FL will yield the same
perspective regardless od format, then that is what I said in the first
place so why bother replying?

Of course they will, but so will lenses of different focal length as
focal length only affects FOV, not perspective. See above. I replied
because your answer was both inaccurate and misleading.

What part of "the *apparent* DOF is different simply because of the
enlarging" and "It all has to do with the size of the circle of
confusion..." didn't you understand?

First you wrote: "the DOF will be the same" and then "the *apparent* DOF
is different". Obviously you don't understand the concept of DOF as
there are no "the DOF" and "the apparent DOF". There is only one DOF
which is purely subjective and allways defined also by the size of the
final print.

3. Please read: http://www.photo.net/learn/optics/dofdigital/

No need, I've known it for decades, probably before Mr. Atkins ever saw the
light of day

You are a typical "I have known these things for decades and I can't be
wrong" type of guy. I still suggest for you to read the above page. With
Google you can easily find pages which show the optical formulas. It's a
pity there are many misleading pages there also. I can find you the
formulas if you can't find them yourself.

Best Regards,
Severi Salminen

"David J. Littleboy" wrote in message
...

"jjs" wrote:

(BTW - wasn't it rather daunting to see how poorly the Hasselblad did
compared to the 4X5? )

I'm sure that the 4x5 is a _lot_ better than the Hassy, but presenting
Epson
3200 scans doesn't show that. You'd have to at least get some decent
high-res scans done. (And even that wouldn't satisfy Staceyg.)

But it was equally bad for each format. Oh no! Another argument?

"jjs" wrote:
"David J. Littleboy" wrote:
"jjs" wrote:

(BTW - wasn't it rather daunting to see how poorly the Hasselblad did
compared to the 4X5? )

I'm sure that the 4x5 is a _lot_ better than the Hassy, but presenting
Epson
3200 scans doesn't show that. You'd have to at least get some decent
high-res scans done. (And even that wouldn't satisfy Staceyg.)

But it was equally bad for each format. Oh no! Another argument?

Yesg. If you limit resolution to 20 lp/mm, then, for example, if the SWC
was actually resolving 66 lp/mm (likely) and the 4x5 was only doing 22
(unlikely, but assume for the sake of argument), you'd miss it. In that
case, the SWC would look better (well, slightly more detailed) at 16x16 than
the 4x5 would.

It's far more likely that the 4x5 is putting a lot more detail on the film,
even if it's not fully twice the linear resolution per frame height.

David J. Littleboy
Tokyo, Japan

"jjs" wrote in message
...

evil grin But _this_ 4x5 lens is not your father's 4x5 lens. Seriously,
it
is reputed to do 80lpmm wide open at F4.5. Stopped down to F16 couldn't be
hurting it too much.

Funny, but I thought my comment would have brought out Semi (Hemi?) with a
rebuttal. Lens resolution always goes down when one stops down. Right,
Hemi/Semi?

"jjs" wrote in message
...

evil grin But _this_ 4x5 lens is not your father's 4x5 lens. Seriously,
it
is reputed to do 80lpmm wide open at F4.5. Stopped down to F16 couldn't be
hurting it too much.

Funny, but I thought my comment would have brought out Semi (Hemi?) with a
rebuttal. Lens resolution always goes down when one stops down. Right,
Hemi/Semi?

Correct. Assuming constant field of view and constant f/#, the larger
format will have a shallower depth of field and a more distant
hyperfocal distance.

The catch here is the assumption that there is a "constant field of view."
In order to keep the field of view the same when using two different film
formats something else has to change - either the lens-to-subject distance
or the lens focal length must change to keep the field of view the same in
the film or the image magnfication factor must change to keep the field of
view the same in the print. Since lens focal length, distance from subject,
and image magnficiation all affect depth of field in the film or print I
believe it's the effect of one or more of these changes on depth of field
that you're seeing, not a change attributable to the change in film format.

"brian" wrote in message
m...
"jjs" wrote in message
...
(The original thread was mistitled and I decided to take a new subject
anyway.) Refer to the original thread which posited that two cameras of
different film formats would have the same DO-Field if the lenses were
of
equivalent focal length _and the prints were of equal size_.

I certainly do not mind being corrected, nor do I mind admitting when I
am
wrong. It's more important to have the correct information out there.

So, my fundamental error in my example was in not having objects between
the
focused foreground and the extreme (at infinity) background. Such
objects
would have shown the loss of DOF more clearly in the large format image.
Correct, Brian?

In any event, it was an interesting thread because it showed a specific
example visually: mine with the picture shown and Brian's example.

Thanks all (except that Roland object whatever it realy is.)

(BTW - wasn't it rather daunting to see how poorly the Hasselblad did
compared to the 4X5? ) Bait. Don't take it.


Correct. Assuming constant field of view and constant f/#, the larger
format will have a shallower depth of field and a more distant
hyperfocal distance. However, if the subject matter lies entirely
within the DOF for the larger format setup then you won't see any
difference in DOF between formats. Its only when you have sufficient
depth in the subject that the difference in DOF becomes obvious.

Brian
www.caldwellphotographic.com

But then that's the whole idea behind telephoto lenses,....is it not?
To flatten and compress distant subjects? Rather than making expansive
wide angle images.

"Telephoto lenses" (by which I assume you mean a long focal length lens, not
a true telephoto lens) don't compress and flatten distant subjects and wide
angle lenses (i.e. short focal length lenses) don't make "expansive" images.
The compression and "expansiveness" you observe when using these lenses is a
result of your camera position (farther from the subject with a long lens,
closer with a shorter lens), not the focal length of the lens.

"Gregory W Blank" wrote in message
...
In article ,
(brian) wrote:

Its only when you have sufficient
depth in the subject that the difference in DOF becomes obvious.

Brian
www.caldwellphotographic.com

But then that's the whole idea behind telephoto lenses,....is it not?
To flatten and compress distant subjects? Rather than making expansive
wide angle images.
--
LF Website @ http://members.verizon.net/~gregoryblank

"To announce that there must be no criticism of the President,
or that we are to stand by the President, right or wrong,
is not only unpatriotic and servile, but is morally treasonable
to the American public."--Theodore Roosevelt, May 7, 1918

Most pictures taken with wide angle
lenses DO have different perspective than pictures taken with long
lenses.

Lens focal length has no effect on perspective. Changes in perspective with
different focal length lenses result from changes in camera position, not
from changes in lens focal length. Take two photographs with two different
focal length lenses from the same camera postion. Print the one made with
the longer lens full frame, then enlarge and print a section of the one made
with the wider lens corresponding to the area covered by the print from the
longer lens. You'll see that perspective is exactly the same in the two
prints.

"Severi Salminen" wrote in message
...
Stacey wrote:

And then when you are going "across formats", you ussually aren't using
the
same optics. I've found different lenses perform better stopped down
than
others. i.e some 35mm lenses get pretty blurry at f16 while some medium
format lenses work fine at f22. A blanket statement like "the larger
format
has LESS DOF because of larger focal length" might be true mathmatically
but in my experience I've found the main drawback to larger formats
isn't
less DOF when viewing the same size prints, it's slower shutter speeds
to
use the smaller fstops needed to get there.

You are correct that there are many differences between various formats
that make this DOF conversation not that practical. But it is still
(IMHO) quite important to understand the facts behind the scene. The
same goes with perspective issue. Most pictures taken with wide angle
lenses DO have different perspective than pictures taken with long
lenses. Still one should understand that the reason is not the focal
length but the practical need to usually alter the shooting position
when changing focal length.

Regards,
Severi S.

It still think it is dangerously misleading to speak about "DOF in the
negative" and "acceptable sharpness" as being two different things.
There is no DOF in the negative, as the whole point in defining DOF
(either mathematically or just visually) is to define the region of
acceptable sharpness.

So we disagree. When discussing what causes changes in depth of field, which
I think was how this thread begin, I think it's misleading to speak of
apparent sharpness in the print since there are so many variables that enter
into that. I do agree that the ultimate point in discussing depth of field
from an aesthetic standpoint is the print or enlarged slide since we don't
normally view negatives or slides as final images. But when engaged in a
technical discussion such as this, I think it actually clarifies rather than
confuses to distinguish between depth of field in the negative as defined by
the size of the circles of confusion and depth of field in the print as
defined by circles of confusion in the film plus three variables
(enlargement, viewing distance, and personal standards of sharpness).

If I look at a 35mm slide from 10 meters, it will be 100% in DOF no
matter how hard I try to look: everything seems to be very sharp.

No, it won't be "100% in DOF " and everything won't "seem to be very sharp"
because your eye won't be able to resolve anything with an object that small
from that distance. All you'll see is a little square object with respect to
which the whole concept of depth of field will be meaningless. You're
confusing "seeing" something with "resolving" something. When something is
so far away that our eyes can't resolve it then speaking of depth of field
with respect to that thing is meaningless because our eyes can resolve
nothing about it. Just becasue we can't resolve something (i.e. the image in
the slide in your example) doesn't mean it has "100% depth of field" or
"seems to be very sharp." In fact just the opposite is true, it has no depth
of field and nothing about the image in the slide is very sharp.

Many people
would say that the DOF of the negative is allways constant regardless of
viewing distance. And that is obviously false statement if we understand
the meaning and purpose of DOF and how it is defined.

Circles of confusion in the negative are obviously always constant in the
negative so I don't know what you mean by your statement.. It's the size of
the circles of confusion in the negative and in the print that gives rise to
the whole concept of depth of field. I'm sure you know that only one plane
in a photograph can be in focus. Everything in that plane is represented by
a point. Everything in front of or behind that plane is out of focus and is
therefore is represented by circles in the negative and in the print. But if
the circles are small enough our eyes can't distinguish between them and
points so we say those areas are "in focus" or more accurately "appear to be
in focus" in the print even though they aren't. The size of the circles of
confusion in the negative is the starting point for this process and is
therefore critical in determining depth of field in the print..

"Severi Salminen" wrote in message
...
Vladamir30 wrote:

One of the reasons it's unclear I think is that things get confusing
when
print size or degree of enlargement is thrown into a discussion of depth
of
field. Degree of enlargement relates to "acceptable sharpness" in the
print,
not to depth of field as such. Depth of field (i.e. the size of the
circles
of confusion on either side of the plane of focus) in the negative is
affected by only three things, lens focal length, distance from the
subject,
and aperture. "Acceptable sharpness" in the print is affected by those
things and also by others such as viewing distance from the print,
degree of
enlargement, and personal standards of what is "acceptably" sharp and
what
isn't. Since those things vary from person to person and print to print
it
gets very confusing to throw them into discussions of depth of field and
the
factors affecting it.

It still think it is dangerously misleading to speak about "DOF in the
negative" and "acceptable sharpness" as being two different things.
There is no DOF in the negative, as the whole point in defining DOF
(either mathematically or just visually) is to define the region of
acceptable sharpness. The point is not to calculate the sizes of CoCs on
the negative but in the viewer's field of view, no matter what he is
looking at. Acceptable sharpness is _allways_ affected by viewing
distance and print size. And if one does not print, then we can think
viewing distance and negative size - there is no difference.

If I look at a 35mm slide from 10 meters, it will be 100% in DOF no
matter how hard I try to look: everything seems to be very sharp. If I
look a 8x10" negative from 1 feet the DOF is possibly clearly shallower.
Many people have a very hard time to comprehend this issue. Many people
would say that the DOF of the negative is allways constant regardless of
viewing distance. And that is obviously false statement if we understand
the meaning and purpose of DOF and how it is defined.

And the above is one thing why DOF scales on lenses can never be
accurate and suitable for everyone.

Regards,
Severi Salminen