hyperfocal distance

Tony Spadaro wrote:

But nobody is talking about a P&S with a
10mm normal lens - they are usued for 4x6
prints at the largest and quite frankly no one
cares how sharp the picture is -- it's uncle
Harry and aunt Matilda at the Grand Canyon.

I think I just wasted some bandwidth in answering
seriously your other post. In that one, your response
was "don't get bogged down in formulas." In this one,
it's "no one cares." I guess I see the pattern here.
You're not serious, and your initial post, "There is
no difference," can be ignored.

Other posters have supplied ample rigorous
discussions to prove that the crop factor must
be included in determining the hyperfocal distance
for a lens when it is switched to a camera with
a different sensor or film form factor.

Sorry, not to be difficult, but "who cares" and
"forget the formulas" are not arguments to be
taken seriously.

Big Bill wrote:

Question:
Using that formula, does it work for *any* sensor size, or the one the
image size on the focal plane was designed for (in the case of the
lenses in question, 35mm)?
Or, to put it a different way, if you take a 35mm film image at
hyperfocal distance, does cropping that image alter the hyperfocal
distance, or was the HD set when the pic was taken?

I'm wondering, if the CoC formula includes 1525d (and I'm assuming it
does), does d refer to the sensor, or the image on the focal plane,
and the sensor size that image is designed for?
I mean, in a DSLR, the lens uses a smaller part of the image on the
focal plane than 35mm film does. In effect, it crops that image. As I
ask above, does this really change the hyperfocal distance of that
lens?

I think you've asked the relevant question here.
All the formulae I've seen use focal length, focal ratio
and CoC to calculate HD, with a resolution factor
in the CoC that presumes capture area and a diagonal
measure for the other two.

Can you really say a lens is "designed for" 35mm,
or that the image is "cropped" by a DSLR? Wouldn't
it be just as appropriate to say that a cone of clarity
is projected, and that any plane intersecting that
cone is appropriate, whether 35 mm length or shorter?

The question is, does the change in that diagonal
measure of the capture surface slide the HD calculations
the way Tony Spadaro implies?

Has anyone worked this out, or can they show
how this works?

I'm thinking for the HD to change with crop factor,
there must be a constant that pins the calculations
to the focal length regardless of diagonal measure
of the capture area. Is that an oxymoron?

"M Barnes" writes:

Well, give yourself a gold star, then. Anyway, isn't the
circle of confusion a characteristic of the lens, not the
sensor?

The circle of confusion size *on the print* can be regarded as fixed.
But different film format sizes and digital sensor sizes require
different degrees of magnification to produce the same-size print. So
the CoC size scales down directly in proportion to the sensor size.

Dave

Dave Martindale wrote:

The circle of confusion size *on the print* can be
regarded as fixed. But different film format sizes
and digital sensor sizes require different degrees
of magnification to produce the same-size print.
So the CoC size scales down directly in proportion
to the sensor size.

OK, but in a lens lab, don't engineers use a standard
line chart to determine the CoC. In other words, no
print is generated. Rather, the techs use the chart to
determine CoC by focusing the image on the capture
area, whether a 35x24 for film or a 66% sensor area
for digital. The question being, will this scaling, if a
print is not used, cause the HD to scale as well?

"M Barnes" writes:

OK, but in a lens lab, don't engineers use a standard
line chart to determine the CoC. In other words, no
print is generated. Rather, the techs use the chart to
determine CoC by focusing the image on the capture
area, whether a 35x24 for film or a 66% sensor area
for digital. The question being, will this scaling, if a
print is not used, cause the HD to scale as well?

You're thinking of something else. "Circle of Confusion" is a
theoretical concept, not a measured value. Perhaps you are thinking of
resolution tests for a lens? The minimum blur spot size for a lens is
normally quite a lot smaller than the CoC used in depth of field
calculations.

The way you calculate depth of field is (more or less) this:

Pick a print size and viewing distance. Pick an angular resolution that
will look "sharp enough" for your eye. This gives you the Circle of
Confusion size on the print. A standard value is 1/1740 of the diagonal
of the print, but there are other possible choices depending on how
critical you are about sharpness.

Now scale the CoC diameter down by the reciprocal of the printing
magnification. This tells you the CoC size on the sensor that gives you
the desired CoC size on the print. If you picked diagonal/1740 as the
print CoC size, then this will be sensor_diagonal/1740.

From here, we use pure geometric optics. This assumes that lenses are
aberration-free, that there is no such thing as diffraction, and thus
that a point in the scene is focused to a point on the sensor when focus
is perfect, or to a round disc on the sensor when focus is not perfect.
Using these assumptions, and a starting focus setting, you can figure
out the depth of field. The process goes something like this:

- Assume a particular value for lens focal length and f/number
- Assume we adjust the lens so that the plane of best focus is
at some distance (e.g. 10 m) from the lens front principal plane,
so a point in that plane becomes a point on the sensor
- Points closer than 10 m focus to a point *behind* the sensor, so
the cone of converging light is still a disc when it hits the sensor.
Calculate how far behind the sensor the apex of the cone must be in
order for the disc size to equal the chosen CoC size. (This obviously
depends on the steepness of convergence, which depends on FL and
f/number)
- Using standard lens formulae, calculate the distance from the lens
of an object that would focus at this plane behind the sensor.

This is the near limit of the depth of field, because points located
that distance from the camera are imaged as a disc the size of the CoC.
Calculation of the far limit of the DOF is done similarly, except that
the best focus occurs some distance in front of the sensor, and the
light then spreads out in a second cone that reaches the CoC diameter in
the plane of the sensor.

Finally, to determine the hyperfocal distance, just calculate the lens
focus setting that places the far limit of the DOF exactly at infinity.

(There's one lie in the above. Real DOF tables usually give distance
from the film plane, not distance from the lens front principal plane.
This makes the exact calculations messier, but there's little practical
difference between the two methods for non-macro photography).

Dave

Big Bill writes:

But, that begs a question:
Using DSLRs, which sensor size do you use? The one that's actually
there, or the one that everything else was designed for (35mm)?

The one that's actually there, because the actual sensor size determines
the magnification needed to produce a same-size print, and CoC depends
on printing magnification.

Dave

Ok -- let me put it this way, Ace.
If you wish to find out exactly what size you can enlarge you P&S stuff
to --- get it enlarged and LOOK at it.
Formulas don't tell you anything.
If you think that is not serious enough for your scientifical
mind go talk to other anal retentives and leave the real world to people who
are not obsessive compulsive.

--
http://www.chapelhillnoir.com
home of The Camera-ist's Manifesto
The Improved Links Pages are at
http://www.chapelhillnoir.com/links/mlinks00.html
A sample chapter from my novel "Haight-Ashbury" is at
http://www.chapelhillnoir.com/writ/hait/hatitl.html
"M Barnes" wrote in message
...
Tony Spadaro wrote:

But nobody is talking about a P&S with a
10mm normal lens - they are usued for 4x6
prints at the largest and quite frankly no one
cares how sharp the picture is -- it's uncle
Harry and aunt Matilda at the Grand Canyon.

I think I just wasted some bandwidth in answering
seriously your other post. In that one, your response
was "don't get bogged down in formulas." In this one,
it's "no one cares." I guess I see the pattern here.
You're not serious, and your initial post, "There is
no difference," can be ignored.

Other posters have supplied ample rigorous
discussions to prove that the crop factor must
be included in determining the hyperfocal distance
for a lens when it is switched to a camera with
a different sensor or film form factor.

Sorry, not to be difficult, but "who cares" and
"forget the formulas" are not arguments to be
taken seriously.

HEY ACE --- Viewing distance cancels out enlargement!!!!

I've pointed out that once you take into account enlargement you also have
to take into account viewing distance.

GET IT? Viewing distance cancels out enlargement!!!!

Think Rover think:

Viewing distance cancels out enlargement!!!!

Sing it with me

Viewing distance cancels out enlargement!!!!

If this concept is too difficult for you - forget it. This won't be on the
test and you won't be penalized.

--
http://www.chapelhillnoir.com
home of The Camera-ist's Manifesto
The Improved Links Pages are at
http://www.chapelhillnoir.com/links/mlinks00.html
A sample chapter from my novel "Haight-Ashbury" is at
http://www.chapelhillnoir.com/writ/hait/hatitl.html
"M Barnes" wrote in message
...
Tony Spadaro wrote:

Don't get all bogged down in formulas ....

Well, frankly, when a technical question
is asked -- "Is the hyperfocal distance
affected by sensor size?" -- then I expect
that the technical, formulaic if you will,
answer is the correct one.

Engineering education consists not only
in learning boring stuff -- formulae -- but
also in overcoming intuition, which is often
incorrect.

If you can't show logically how your answer --
that hyperfocal distance is not affected by
sensor size -- fits the published engineering
formulae and data, then I must assume that
it is incorrect since it has been contradicted
by other posters who can do so.

Take an 8x10 print and hold it where you
can see the entire print at one time -- this
is proper viewing distance for an 6x10.
Now take an 11x14 and do the same ....

But this is not relevant to the discussion at
hand. The viewing distance factor is considered
in the CoC formula, and applies to a family
of hyperfocal calculations. Can you show
with logical, formulaic methods how the
viewing distance of a print has an effect on
hyperfocal distance calculated for a sensor
of a given size?

I'm willing to listen to your arguments, but
I'm not willing to forego the use of formulae
in making technical calculations.

If you are saying that adjusting sensor size
causes the calculations to slide up and down
commensurately -- through the focal length
and focal ratio calculations, or perhaps the
CoC calculation -- and thus cancel out any
hyperfocal distance changes, I would need
to see this cranked through the accepted
formulae published all over the world and
accepted by everybody in the business.

I don't see how comparing print sizes has
anything to do with this discussion.

Tony Spadaro wrote:

Ok -- let me put it this way, Ace.

Ooh, touched a nerve, have we?

If you wish to find out exactly what size
you can enlarge you (sic) P&S stuff to ---
get it enlarged and LOOK at it.

Well, evidently you haven't been paying
attention. I don't use a point-and-shoot.
And I'm not looking for enlargement
resolution. I'm looking to use hyperfocal
focusing to keep foregrounds sharp while
focusing to infinity. That way, I can stretch
the hyperfocal boundary with a semi-wide
prime on my D100 and get those stunning
closeups of bugs sitting on smoky quartz while
the Costa Mesa range is still in focus. Ace.

Formulas don't tell you anything.

Well, let's put it this way. Evidently they don't
tell _you_ anything. They've told me a lot
through the years. If you knew how to use
them, they'd tell you things to. Evidently you're
too busy busting spammers and making threats
to learn a little basic math. And basic math is
what we're talking here. It's not calculus.
It's not even analytical geometry. It's just a tad
of elementary school albegra.

If you think that is not serious enough for your
scientifical mind go talk to other anal retentives
and leave the real world to people who are
not obsessive compulsive.

Right. Like the anal retentives at JPL who
computed the VVJ swings to Saturn, using formulae,
by the way. Last time I looked, they exist. They're
real.

And the wackos who computed range tables that
allowed Grandpa to factor in the Coreolis force
to correct his artillery shells firing north-by-northwest
in France, so as not to take out B Company coming
in from Omaha. They were real. At least my Grandpa
was. Can't testify to yours. Ace. Maybe he left
you inside a fairy ring. Stranger things have happened.

Oh, let's not forget the dim bulbs at Canon and Nikon
who use formulae to design those lenses you try to
use from time to time. Or did you think they sketched
them out on napkins with #2 Ticonderogas, as you
seem fond of doing. Ace. They're real. At least my
D100 is, and the lenses I use are.

I guess in your limited reference frame, there are
10 kinds of people (binarily speaking, of course):
those who shoot from the hip and speak from the
cuff (I'm being polite -- another extremity came to
mind, and I don't mean your hat), and those who
retain their feces, love it, plate it with bronze, save
it in little file drawers for posterity.

Something tells me that the anger you express at
having your first glib answer challenged and a mild
request for explication put forth tells more about
which side of the fence you're on than it does about,
say, the effect of sensor size on computing hyperfocal
distance.

And by the way, Ace, blowing up my prints isn't the
point. It's where to set the manual focus ring when I
have a 17mm prime loaded with a 2/3 frame sensor,
and I'm trying to edge off on a subject at 1.5 meters
stopped down to 22. I'm accustomed to doing this
with an N2020 body, and just entered the discussion
to see if anyone had definitive info about any changes
I might need to make, and why.

But since you don't seem to even comprehend the
question, I can safely disregard your "real world"
snerk responses, since they're informed not by
"scientifical" reasoning but voices from, it would
seem, your bunghole, a place where your head
seems to have been residing while most of the rest
of us were learning how to use simple formulas
to resolve technical matters. And Ace, it resides
there still.

Tony Spadaro wrote:

HEY ACE --- Viewing distance cancels out enlargement!!!!

I've pointed out that once you take into account enlargement you also have
to take into account viewing distance.

GET IT? Viewing distance cancels out enlargement!!!!

Think Rover think:

Viewing distance cancels out enlargement!!!!

Sing it with me

Viewing distance cancels out enlargement!!!!

If this concept is too difficult for you - forget it.
This won't be on the test and you won't be penalized.

Mm, hmm. And what does enlargement have
to do with hyperfocal focusing? That was the
intent of my question. Do you know what
hyperfocal focusing is? Something tells
me you don't, and you're shouting out the
answers to the wrong question, naked in front
of the church choir, thinking your robes are
peachy keen.

I'm beginning to think maybe you don't
even know what "hyperfocal" means.

Look here, for example:
http://www.outsight.com/hyperfocal.html#hyper

The DOF calculator for hyperfocal focusing
assumes an 8x10 print (notice -- no enlargement,
Ace). It also stipulates focal length, not 35mm
equivalent. See the purpose of this? It's to
focus from a known point to infinity.

I could be impolite, as you, and state my
response in big caps, call you a dogbrain
and all that, but it's easier to simply point out
that I'm not looking to enlarge, but to focus,
using standard hyperfocal techniques you seem
to be unaware of, and which has been under
discussion here for a while as you were ...
shouting in the corner to yourself?