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Calculations in the dark room



 
 
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  #1  
Old March 31st 04, 05:25 AM
rgans
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Posts: n/a
Default Calculations in the dark room

Is there an electronic device, like the old HP Calculator, a palm pilot,
etc., and formulae which I can use in the dark room? For example, if I
determine that the exposure I want at 58cm is 12 sec at f/8, but then I
change the distance to 68 cm, how would I calculate the new exposure? (I
know that light intensity falls off as the square of the distance) And, if I
first decide to use Magenta=80 (on a Saunders LPL 45) but then go to
Magenta=120 Y=9, besides trial and error, are there formulae for
recalculating the exposure and is there a preferred device to make these
calculations on?

Thanks.

RON
__________________________________________________ _______________
B&W Landscape and Still Photography: http://www.ronaldgansphotography.com


  #2  
Old March 31st 04, 11:54 AM
moda
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Default Calculations in the dark room

I would recommend a PDA like Palm etc.

If you know someone who can program a bit they can make a program for you
that can do what you want it to.

moda

"rgans" skrev i en
meddelelse ...
Is there an electronic device, like the old HP Calculator, a palm pilot,
etc., and formulae which I can use in the dark room? For example, if I
determine that the exposure I want at 58cm is 12 sec at f/8, but then I
change the distance to 68 cm, how would I calculate the new exposure? (I
know that light intensity falls off as the square of the distance) And, if

I
first decide to use Magenta=80 (on a Saunders LPL 45) but then go to
Magenta=120 Y=9, besides trial and error, are there formulae for
recalculating the exposure and is there a preferred device to make these
calculations on?

Thanks.

RON
__________________________________________________ _______________
B&W Landscape and Still Photography: http://www.ronaldgansphotography.com




  #3  
Old March 31st 04, 01:09 PM
Nicholas O. Lindan
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Posts: n/a
Default Calculations in the dark room

"rgans" wrote

Is there an electronic device, like the old HP Calculator, a palm pilot,
etc., and formulae which I can use in the dark room? For example, if I
determine that the exposure I want at 58cm is 12 sec at f/8, but then I
change the distance to 68 cm, how would I calculate the new exposure?


Most folks will tell you "The inverse square law" - which is close, but
no cigar: it only holds for point sources.

Your best bet is to make test strips/use an exposure meter at 5-10 heights
and make a table or graph for your enlarger/light source/lens combination.
You can fit the data points to a polynomial for easy (for the calculator)
calculation.

I can email you a simple polynomial curve fit program or I am sure
you can find something on the web, or maybe even in your spreadsheet
program.

--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer: Electronics; Informatics; Photonics.
psst.. want to buy an f-stop timer? nolindan.com/da/fstop/

  #4  
Old March 31st 04, 02:13 PM
Chris Ellinger
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Default Calculations in the dark room

On Wed, 31 Mar 2004 04:25:13 GMT, "rgans"
wrote:

Is there an electronic device, like the old HP Calculator, a palm pilot,
etc., and formulae which I can use in the dark room?


I use a cheap programmable HP calculator (20S).

Chris Ellinger
Ann Arbor, MI

  #5  
Old March 31st 04, 02:17 PM
Phil Glaser
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Posts: n/a
Default Calculations in the dark room

I'll try to beat Claudio to it and provide a link to his software page
http://www.bonavolta.ch/hobby/en/photo/labsoft.htm. The only thing
that this software requires a PC.

Claudio, any plans for a Palm version? That would help me out as I
could never fit a PC in my darkroom (not even a laptop).

--Phil



"rgans" wrote in message . ..
Is there an electronic device, like the old HP Calculator, a palm pilot,
etc., and formulae which I can use in the dark room? For example, if I
determine that the exposure I want at 58cm is 12 sec at f/8, but then I
change the distance to 68 cm, how would I calculate the new exposure? (I
know that light intensity falls off as the square of the distance) And, if I
first decide to use Magenta=80 (on a Saunders LPL 45) but then go to
Magenta=120 Y=9, besides trial and error, are there formulae for
recalculating the exposure and is there a preferred device to make these
calculations on?

Thanks.

RON
__________________________________________________ _______________
B&W Landscape and Still Photography: http://www.ronaldgansphotography.com

  #6  
Old March 31st 04, 03:16 PM
John Walton
external usenet poster
 
Posts: n/a
Default Calculations in the dark room

Get yourself a Texas Instruments or HP programmable calculator -- you can
take a look at the formula on Claudio's page (simplicity in itself.)
"Phil Glaser" wrote in message
om...
I'll try to beat Claudio to it and provide a link to his software page
http://www.bonavolta.ch/hobby/en/photo/labsoft.htm. The only thing
that this software requires a PC.

Claudio, any plans for a Palm version? That would help me out as I
could never fit a PC in my darkroom (not even a laptop).

--Phil



"rgans" wrote in

message . ..
Is there an electronic device, like the old HP Calculator, a palm pilot,
etc., and formulae which I can use in the dark room? For example, if I
determine that the exposure I want at 58cm is 12 sec at f/8, but then I
change the distance to 68 cm, how would I calculate the new exposure?

(I
know that light intensity falls off as the square of the distance) And,

if I
first decide to use Magenta=80 (on a Saunders LPL 45) but then go to
Magenta=120 Y=9, besides trial and error, are there formulae for
recalculating the exposure and is there a preferred device to make these
calculations on?

Thanks.

RON
__________________________________________________ _______________
B&W Landscape and Still Photography:

http://www.ronaldgansphotography.com


  #7  
Old March 31st 04, 04:54 PM
Patrick Gainer
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Posts: n/a
Default Calculations in the dark room



John Walton wrote:

Get yourself a Texas Instruments or HP programmable calculator -- you can
take a look at the formula on Claudio's page (simplicity in itself.)
"Phil Glaser" wrote in message
om...
I'll try to beat Claudio to it and provide a link to his software page
http://www.bonavolta.ch/hobby/en/photo/labsoft.htm. The only thing
that this software requires a PC.

Claudio, any plans for a Palm version? That would help me out as I
could never fit a PC in my darkroom (not even a laptop).

--Phil



"rgans" wrote in

message . ..
Is there an electronic device, like the old HP Calculator, a palm pilot,
etc., and formulae which I can use in the dark room? For example, if I
determine that the exposure I want at 58cm is 12 sec at f/8, but then I
change the distance to 68 cm, how would I calculate the new exposure?

(I
know that light intensity falls off as the square of the distance) And,

if I
first decide to use Magenta=80 (on a Saunders LPL 45) but then go to
Magenta=120 Y=9, besides trial and error, are there formulae for
recalculating the exposure and is there a preferred device to make these
calculations on?

Thanks.

RON
__________________________________________________ _______________
B&W Landscape and Still Photography:

http://www.ronaldgansphotography.com

I still have a slide rule. Most of you may never have seen one. I don't
know where you might buy one, and I don't know who might teach you to
use one, but at least when I tell you I'm 76 years old, you'll believe
me.
  #8  
Old April 1st 04, 01:51 AM
John Stockdale
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Posts: n/a
Default Calculations in the dark room

"rgans" wrote in message news:
................
For example, if I
determine that the exposure I want at 58cm is 12 sec at f/8, but then I
change the distance to 68 cm, how would I calculate the new exposure? (I
know that light intensity falls off as the square of the distance)

................


Actually, the formula for calculating enlarger exposure when the
magnification is changed is actually a bit different to simply using
the inverse square law.

new_time = old_time x (new_Mag +1)^2 / (old_Mag +1)^2

where new_Mag and old_Mag are the magnifications from negative to
print. So if you wanted to enlarge a 35mm negative to 8inch x 12inch
full frame, (say near enough to 8x magnification) and you had a time
for 4inch x 6inch full frame, (say 4x magnification) the time
adjustment would be:

new_time = old_time x 9^2 / 5^2 = old_time x 3.24

The inverse square law would give x 4. For smaller changes, say 7x to
8x, the error is less. Also, the formula ignores considerations like
a bigger print needing more contrast and maybe more density in order
to look its best.

Note that if the test print were from a cropped part of the negative,
then the magnifications would be different.

For more detail, search in rec.photo.darkroom for

Michael Gudzinowicz enlargement/reduction exposure formula
  #9  
Old April 1st 04, 06:34 AM
rgans
external usenet poster
 
Posts: n/a
Default Calculations in the dark room

Thank you (actually, thank all of you who responded). This is very helpful
to me.
"John Stockdale" wrote in message
om...
"rgans" wrote in

message news:
...............
For example, if I
determine that the exposure I want at 58cm is 12 sec at f/8, but then I
change the distance to 68 cm, how would I calculate the new exposure?

(I
know that light intensity falls off as the square of the distance)

...............


Actually, the formula for calculating enlarger exposure when the
magnification is changed is actually a bit different to simply using
the inverse square law.

new_time = old_time x (new_Mag +1)^2 / (old_Mag +1)^2

where new_Mag and old_Mag are the magnifications from negative to
print. So if you wanted to enlarge a 35mm negative to 8inch x 12inch
full frame, (say near enough to 8x magnification) and you had a time
for 4inch x 6inch full frame, (say 4x magnification) the time
adjustment would be:

new_time = old_time x 9^2 / 5^2 = old_time x 3.24

The inverse square law would give x 4. For smaller changes, say 7x to
8x, the error is less. Also, the formula ignores considerations like
a bigger print needing more contrast and maybe more density in order
to look its best.

Note that if the test print were from a cropped part of the negative,
then the magnifications would be different.

For more detail, search in rec.photo.darkroom for

Michael Gudzinowicz enlargement/reduction exposure formula



  #10  
Old April 1st 04, 06:37 AM
rgans
external usenet poster
 
Posts: n/a
Default Calculations in the dark room

But this can get complicated if you are not enlarging negs full frame. If I
am enlarging just a portion of a neg, don't the measurements become
complicated? No?

RON
"John Stockdale" wrote in message
om...
"rgans" wrote in

message news:
...............
For example, if I
determine that the exposure I want at 58cm is 12 sec at f/8, but then I
change the distance to 68 cm, how would I calculate the new exposure?

(I
know that light intensity falls off as the square of the distance)

...............


Actually, the formula for calculating enlarger exposure when the
magnification is changed is actually a bit different to simply using
the inverse square law.

new_time = old_time x (new_Mag +1)^2 / (old_Mag +1)^2

where new_Mag and old_Mag are the magnifications from negative to
print. So if you wanted to enlarge a 35mm negative to 8inch x 12inch
full frame, (say near enough to 8x magnification) and you had a time
for 4inch x 6inch full frame, (say 4x magnification) the time
adjustment would be:

new_time = old_time x 9^2 / 5^2 = old_time x 3.24

The inverse square law would give x 4. For smaller changes, say 7x to
8x, the error is less. Also, the formula ignores considerations like
a bigger print needing more contrast and maybe more density in order
to look its best.

Note that if the test print were from a cropped part of the negative,
then the magnifications would be different.

For more detail, search in rec.photo.darkroom for

Michael Gudzinowicz enlargement/reduction exposure formula



 




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