A depth of field UNcalculator

It struck me as being an interesting project to have a web-based
calculator whereby you put in depth of field values and f-stop numbers
as a set and then it calculates focal length, CoC size and distance
focus for you. Maybe multiple results with "goodness of fit" values.
This is special cameras wheer you are unsure what distance they are
focussed to because they do not tell you and yet they publish DoF
values.

RolandRB wrote:

It struck me as being an interesting project to have a web-based
calculator whereby you put in depth of field values and f-stop numbers
as a set and then it calculates focal length, CoC size and distance
focus for you. Maybe multiple results with "goodness of fit" values.
This is special cameras wheer you are unsure what distance they are
focussed to because they do not tell you and yet they publish DoF
values.

It should also calculate the print magnification and viewing distance.

see DOF expert program by Michael Davis at
http://home.online.no/~gjon/mdofcal9.xls

see Michael Davis' comments and others on varying mfgers DOF/COC values
etc. at http://medfmt.8k.com/brondofp.html

One of the funnier threads on one of the 35mm brand mailing lists was the
"discovery" that certain lens brands provided you with "more DOF" than
those of the (pricey) brand name optics for the same cameras, at the same
focal lengths (i.e., the different mfgers were using different CoC values,
a fact unclear to the "discoverers" ;-)

grins bobm
--
************************************************** *********************
* Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 *
********************Standard Disclaimers Apply*************************

"Q.G. de Bakker" wrote in message ...
RolandRB wrote:

It struck me as being an interesting project to have a web-based
calculator whereby you put in depth of field values and f-stop numbers
as a set and then it calculates focal length, CoC size and distance
focus for you. Maybe multiple results with "goodness of fit" values.
This is special cameras wheer you are unsure what distance they are
focussed to because they do not tell you and yet they publish DoF
values.

It should also calculate the print magnification and viewing distance.

And perhaps name the person viewing it as well.

RolandRB wrote:

It should also calculate the print magnification and viewing distance.

And perhaps name the person viewing it as well.

Rather, it should come in individualized versions. Easy, if you let users
enter their very own personal CoC size preference.

And remember, size does not matter, it's what you do with it. That,
remarkably, is very true for this thing called DOF.
Hence the need to include print magnification and viewing size, i.e. the
"what you do with it" bit.

"Q.G. de Bakker" wrote in message li.nl...
RolandRB wrote:

It should also calculate the print magnification and viewing distance.

And perhaps name the person viewing it as well.

Rather, it should come in individualized versions. Easy, if you let users
enter their very own personal CoC size preference.

And remember, size does not matter, it's what you do with it. That,
remarkably, is very true for this thing called DOF.
Hence the need to include print magnification and viewing size, i.e. the
"what you do with it" bit.

If it is an "UNcalculator" then only a limited selection of CoC and
focal length will fit a set of published values for near focussing
distance. But I understand what you mean and appreciate your point of
view. There is still room for a more sophisticated calculator out
there with more choice. Also, quite often, people do not make the
connection between CoC and the resulting limit on resolution and it
would be useful to display this. The maths for uncalculating a set of
close focussing distances back into possible values for CoC and lens
focal length seems very difficult to me at present but I am sure it is
possible. I feel my brain is getting a bit soft on maths and I should
give it more exercise in that respect and this seems like a worthwhile
project.

"RolandRB" wrote in message
om...
"Q.G. de Bakker" wrote in message
li.nl...
RolandRB wrote:

It should also calculate the print magnification and viewing
distance.

And perhaps name the person viewing it as well.

Rather, it should come in individualized versions. Easy, if you let
users
enter their very own personal CoC size preference.

And remember, size does not matter, it's what you do with it. That,
remarkably, is very true for this thing called DOF.
Hence the need to include print magnification and viewing size, i.e. the
"what you do with it" bit.

If it is an "UNcalculator" then only a limited selection of CoC and
focal length will fit a set of published values for near focussing
distance. But I understand what you mean and appreciate your point of
view. There is still room for a more sophisticated calculator out
there with more choice.

http://www.nikonians.org/html/resour...perfocal2.html

David J. Littleboy
Tokyo, Japan

RolandRB wrote:

If it is an "UNcalculator" then only a limited selection of CoC and
focal length will fit a set of published values for near focussing
distance. [...]

Ah, yes. Of course.
Then you could still include the "what you do with it" bit by infering, from
the uncalculated data, what the maker of the DOF scale thought one would do
with the negatives produced.

"David J. Littleboy" wrote in message ...
"RolandRB" wrote in message
om...
"Q.G. de Bakker" wrote in message
li.nl...
RolandRB wrote:

It should also calculate the print magnification and viewing
distance.

And perhaps name the person viewing it as well.

Rather, it should come in individualized versions. Easy, if you let
users
enter their very own personal CoC size preference.

And remember, size does not matter, it's what you do with it. That,
remarkably, is very true for this thing called DOF.
Hence the need to include print magnification and viewing size, i.e. the
"what you do with it" bit.

If it is an "UNcalculator" then only a limited selection of CoC and
focal length will fit a set of published values for near focussing
distance. But I understand what you mean and appreciate your point of
view. There is still room for a more sophisticated calculator out
there with more choice.

http://www.nikonians.org/html/resour...perfocal2.html

I was hoping to see an UNcalculator at that URL but couldn't find it.
You'd be lucky to find the correct maths for a DoF calculator
anywhere, let alone what is required for it to be an UNcalculator.

well, the formulas for DOF calculators are readily available, viz.,
http://medfmt.8k.com/brondof.html has javascript on that page and so on;

if you have a hyperfocal distance, you can just use one formula, viz. see
http://medfmt.8k.com/mf/hyperfocal.html

for more on DOF math, see Michael Davis article on subject at
http://medfmt.8k.com/mf/dofmath.html and followup with Harold Merk.

if you are like me, you may prefer a graphical solution?
http://www.dof.pcraft.com/dof-frames.cgi

given you know the lens focal length and film format, you can simply
iterate CoC values in a flexible DOF calculator spreadsheet to determine
the mfger's COC values used in creating the table (or lens) values

An excellent example would be Michael Davis' not just another DOF
calculator ;-) at http://home.online.no/~gjon/mdofcal9.xls

After that, it is just a matter of iterating on COC until the table
matches the printed chart.

===== Liberal Lenses (w.r.t. DOF)

that said, I usually don't use DOF charts in the field, though they are
usually in the manuals which I do have with me, so I tend to rely on the
lens DOF markings but using generally a stop more conservative DOF points.

But as noted, not all lens makers use the same DOF COC values, so lenses
also tend to have more or less conservative DOF markings, depending on
which mfger or production run they represent (e.g., vivitars may vary
between makers even if still a 28mm f/2.8 basic lens ;-).

So in this case, it may be useful or important to note that a particular
lens provides a more liberal DOF range for a given f/stop and distance
setting. When this is the case, I mark in my own DOF markings as a warning
to me that the DOF markings on that lens is too liberal and I should
derate the indicated DOF by the amount shown by my added "tic" marks. This
is esp. important if you intend to do hyperfocal shots to be blown up very
large (beyond the point expected by most mfgers, e.g., 8x10" in many
cases?)...

hth bobm
--
************************************************** *********************
* Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 *
********************Standard Disclaimers Apply*************************