JOBO tank on roller base?greenspun.com : LUSENET : Large format photography : One Thread
Hello, I've a JOBO 2500 multitank with 2 4X5 reels. I'm going to use it for B&W film on a motorized base. I'm wondering how much time I should subtract from the normal development time for this continuous aggitation/rotation. Or even if I should water down the developer and maintain the same time for that matter? Thanks for any info, David
-- david clark (email@example.com), November 07, 2000
I usually subtract 10% off the intermittent agitation development time to come up with a time for constant rotary agitation for "standard" and Ilford Delta films; that 10% has been close enough that no further adjustment has been needed.
For TMX I subtract 5%.
If you're going to use a presoak as recommended by Jobo, use your standard intermittent-agitation development times as the starting point.
-- John Hicks (firstname.lastname@example.org), November 07, 2000.
My preference is to water down the developer. When I used HC110 at 1:7 with rotary processing, it yielded a characteristic curve which had low contrast in the shadows and high contrast in the highlights, sort of like a long toe film. Watering down the developer to 1:10 yielded better contrast in the shadows. Good luck. Cheers, DJ.
-- N Dhananjay (email@example.com), November 08, 2000.
I use the same tank you mention on a Uniroller motorized base. Initially I ran EI/Development tests using the principles/techniques discussed in any number of texts-Adams, Picker, atc. What I found was that I could take the mfg suggested time and reduce it by 15% and be real close to the time I generated in my testing. I used D-76, 1:1 at 70 degrees, and TMax RS 1:9 from concentrate, mixed as suggested by John Sexton. While the tests were needed to corrorborate these time and importantly to determine the working EI ( TMax 100 = 80 at N; Tri-x- 250 at N) at least the mfg. time x 85% gave me a good ball park start. All times include a 5 minute prewet in the tank with water at same temperature as developer with motor running. A while back at a workshop I used the same EI and times for some images made there. The instructor commented that the negs were "perfect." There we used a JOBO CPP2. Made me happy to get nags without paying for that unit! Bob Bob
-- Bob Moulton (firstname.lastname@example.org), November 08, 2000.