Any reason not to use light reversal in E6?
I've been quite busy getting my small-volume motion picture lab up and running. I've been running some customer ECN-2 films as free "test runs" with good success and am now testing E6 processing.
I've done E6 a lot in spiral tanks, of course, and always used chemical reversal bath. AFAIK, there is no reason why it couldn't be substituted with light reversal. In spiral tanks and dip&dunk processors, I understand pretty well that a chemical reversal is a lot easier to handle than a light that would need to come near to all areas in all film being processed.
However, thinking about a roller transport film processor (such as mine), it would make much more sense to use a bright white LED or any light source near the film path. I'm thinking about cost savings, less risk of cross-contamination, less chemical waste, and no risk of low-volume reversal bath "sudden death" syndrome.
Is there any real reason why roller transport labs still use chemical reversal? Is there ANY difference in the image quality between the reversal method, something I miss? Can there be too much light?
I think reversal is better if you are replenishing. Reversal bath is cheap though? And also cheap to make your own too if need be.
Originally Posted by Athiril
when you say "reversal is better if you are replenishing" are you referring to re-exposure using a light source is better in that case?
I mean reversal bath. The process is designed to account for carryover into colour developer.
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Nice machine you built there!
I’m doing a light reversal too, never found a problem in home development neither. But for commercial processing I do have 3-4 proposals why this is maybe not desired…
Perhaps a question of keeping the standards, in official E6 simply no light reversal step is destined. So a reversal process using light as reversal agent should be named different, something like E6-xy
As far as I know E6 was designed to have less ecological impact / use less wash steps as possible, to keep the (waste) water bill low. With optical reversal (in opposite to an slightly acidic reversal bath) you have to wash your Films better and use preferably a stop bath too, to exclude the possibility of unwanted silver development during reexposure.
A chemical reexposure is maybe easier to maintain, or can be controlled the very same way as all other steps. The higher densities in the final slide may reach uniformity better/easier this way in commercial processing.
In terms of designing developing machines, it may be more complicated to exclude light leaks, especially for the dip and dunk machines, during a light reversal step.
Last edited by stefan4u; 04-02-2013 at 08:42 AM. Click to view previous post history.
Thanks for answers.
For my purpose, the light reversal would be indeed easier because this style of lab has separate dark and light side; the film comes out of the dark side through the light-trap opening in the wall. So in fact the light reversal happens to some extent anyway from the room light, proper light reversal is just about increasing the amount of the light near the film.
But the point about the "stopping" effect of chemical reversal is a good one, I didn't think about that. It also acts as an extra "wash" step. I realize that I need to have a very good wash stage before light reversal, whereas the chemical reversal would prevent a minute amount of carry-in First Developer from working.
Currently I have an air knife only after final rinse, but I guess after I add air knives after the First Developer and all three subsequent wash stages, I can minimize FD carryover to practically zero, and have a go with light reversal.
Using a stop bath is much safer than a wash step alone, if you do a light reversal.
But because the wash step after FD is more or less part of the process, in meaning of gradually tapering off the FD activity, I would recommend 2 min wash first, than 2 min stop and then the reversal exposure. After this one may have think about a wash step again, to get rid of the acid / acid carryover in the CD…
The alternative would be your prolonged/extended wash, something about 4-5 min. including your “air knife” after FD. In terms of needed tank capacity it would be quite the same…
My procedure is 2 min wash, 2 min stop, again 2 min wash, than 4min light reversal. Because I do only drum processing in a Jobo, after the light reversal follows again a short wash/prewarm step prior CD, to maintain desired temperature in the drum… And again, this light reversal works pretty perfect and as you stated already, there is one chemical bath less to take care about.
Because of homebrewing this is my main argument for this processing variant…
Last edited by stefan4u; 04-06-2013 at 08:44 AM. Click to view previous post history.
+1 for stop bath. Just from personal experience, stop baths are reliable; washes are not for eliminating the first developer.