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#1
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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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