I plan to develop 2 rolls of RPX 25 today. Inside the house it must be around 25 degrees C. What is the procedure for developing times when temperature is above 68 degrees F?
No - the times get shorter with higher temperatures. You need to be careful if the increase in temperature results in times less than 5 minutes.Adding time as it gets hotter? I would think heat would reduce times, wouldn't it?
The Dataguide dial would recommend 4:45 - so close to the same.My rule is to shorten developing time for increased temperature; 4% per degree F (which comes to 7% per degree C). Apply this as a power -- if you have a time for 20 C and can't get your solutions below 25 C, you'd divide your original time (say, 7 minutes) by 1.07 ^ 5 = 1.4m giving 4.9 minutes or 4:55 in this example starting time.
The Dataguide dial would recommend 4:45 - so close to the same.
Can you explain this in more detail, Donald. I think I can get to the 4.9 minutes except that I get 4.99 minutes but couldn't see where the 4.55 comes from. ThanksMy rule is to shorten developing time for increased temperature; 4% per degree F (which comes to 7% per degree C). Apply this as a power -- if you have a time for 20 C and can't get your solutions below 25 C, you'd divide your original time (say, 7 minutes) by 1.07 ^ 5 = 1.4m giving 4.9 minutes or 4:55 in this example starting time.
My rule is to shorten developing time for increased temperature; 4% per degree F (which comes to 7% per degree C). Apply this as a power -- if you have a time for 20 C and can't get your solutions below 25 C, you'd divide your original time (say, 7 minutes) by 1.07 ^ 5 = 1.4m giving 4.9 minutes or 4:55 in this example starting time.
It's easy - for a 5 C difference, just raise 1.07 to the fifth power in your head and then divide the original development time by the resultCan you explain this in more detail, Donald. Thanks
pentaxuser
Can you explain this in more detail, Donald. I think I can get to the 4.9 minutes except that I get 4.99 minutes but couldn't see where the 4.55 comes from. Thanks
Thanks Donald. It may be that what I did was with a calculator so resulted in a difference of a few seconds. I couldn't do 1.07 to the power of 5 in my head to save my life. This was what I presume was 7% decrease in time per one degree centigrade over the 5 degrees Braxus mentioned. So this becomes 1.07 to the power of 5 which is 1.402551731 which as we are looking for a decrease from 7 minutes @ 20C means dividing the 7 by 1.402551731 which is 4.99 mins so as near as damn it 5 mins.I got 4.9 minutes by mentally multiplying 0.7 (reciprocal of 1.4, approximately, which I happened to recognize from square root of two in geometry) by 7 -- and 0.9 minutes is 54 seconds, which become 4 min 55 (after rounding) seconds, notated in h:m:s form as 4:55.
And @MattKing I can do that (1.07 ^ 5) in my head, but I'd rather use a calculator if there's one handy (got one on every computer I use and one in my phone, should be set); if it were a number like 1.24 instead of 1.07, I'd probably stoop to writing it down without a calculator handy.
This is what you get for living in paradise where you rarely need AC (or are too cheap to turn it on)Well my temperature for the developer was 27 degrees C. With that in Xtol 1:1 (normal time is 8 minutes), I got a little over 4 minutes with the temp. Rolls are done now and rinsing in the sink. I'll view them to see if the time looked correct.
The Massive Development Chart app has a time/temperature feature.You know what would be super cool. A iPad program that looks just like the Kodak dial. Thoroughly researched and developed by the MIT physics department, paid for by pandemic rescue money.
I have the same film computer as Matt, the only current films listed are Tri-X and TXP. Developer choice is D-76. If you want to process Ektapan, Super XX, Royal Pan, or Panatomic X in Microdol-X or Polydol you'll be all set.
XTOL charts from Kodak, and Agfa's times for Rodinal get me through
Just use the dial to reverse engineer a development number for current films by locating the manufacturer's recommended 20C/68F developing time.I have the same film computer as Matt, the only current films listed are Tri-X and TXP. Developer choice is D-76. If you want to process Ektapan, Super XX, Royal Pan, or Panatomic X in Microdol-X or Polydol you'll be all set.
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