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#1 renata gutierrez

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Posted 01 May 2009 - 12:17 AM

Hello! Does anyone know if you should over or sub expose when you want a 50% silver retain process in the film.... trying just to have a good quality of the image with contrast, etc... in this case: ISO 500T vission 3?


Thank´s!
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#2 Satsuki Murashige

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Posted 01 May 2009 - 01:44 AM

Hello! Does anyone know if you should over or sub expose when you want a 50% silver retain process in the film....

Are you doing silver retention to the negative or the print? Silver retention to the negative will add density (making the image brighter) so you should be underexposing a little to compensate. Doing it to the print will make the final image darker so you should overexpose slightly to compensate. David Mullen is the resident expert here on silver retention processes so I would do a topic search using his name - you'll probably find at least 20 posts that will give you more specific information on what to do.
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#3 David Mullen ASC

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Posted 01 May 2009 - 10:49 AM

If you are doing the silver process to the print, you don't have to change how you are exposing the negative. You may want to use more fill light though.

If you are doing it to the negative, you can end up with a lot of extra density, as if you had overexposed. The question is if you want to leave the image that way, with blown-out highlights, or print it "down" to normal. In which case you may want to underexpose to compensate. I found that with a full skip bleach to the neg, my picture was printing in high 40's, which is tricky because some colors would print near 50, the limit. So underexposing to compensate gives you more printing flexibility.

How much to underexpose should be based on tests. Now I haven't ever done a 50% skip-bleach to a negative -- most labs have trouble doing a partial skip bleach without streaking problems. For a full skip bleach, underexposing one-stop is a good starting point (you get about 1.5-stops or more extra density with a skip bleach).

I suggest reading Mark Wood's article on these special processes:
http://www.cameragui...ting_limits.htm
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#4 Saul Rodgar

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Posted 01 May 2009 - 10:45 PM

You may also want to consider exposing normally and pulling the negative 1 stop in processing to get the highlights to behave and reduce the grain, which is usually accentuated by the silver retention process. This may cost more (in addition to the bleach bypass lab fee?), but could be a better path if one is using a faster (read grainier) stock.

This sort of technique yields best results when proper testing is done in pre-prod to avoid nasty surprises.

Also, some talented colorists are very good at recreating the silver retention look in post, should you have a DI or finish to video in your future. That way you can have absolute control over the look of the movie without incurring in special photochemical processing costs and potentially damaging your camera neg. ;)
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#5 K Borowski

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Posted 02 May 2009 - 06:43 AM

That way you can have absolute control over the look of the movie without incurring in special photochemical processing costs and potentially damaging your camera neg. ;)


There's no extra potential to damage film using this technique. Bleach bypasses essentially just dilute or remove the bleach.

Where there (might) be an issue is the silver still left in the film not really being properly fixed, as the ECN-2 fixer isn't exactly designed for this.

And, the wash isn't necessarily long enough in ECN-2 for a silver either.

But, in general, silver images are more permanent than dye-based images.
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#6 Phil Rhodes

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Posted 02 May 2009 - 08:31 AM

As I understand it you can have problems, as Mr. Mullen mentioned, with streakiness or blotching on the film if you do a partial skip bleach. I'm told, though I've never had to do it, that in this case it is possible to re-bleach the film, effectively running it through solely the bleach part of the process, to get it to the state it would have been in if you'd processed it normally. Of course, if you'd made significantly different exposure decisions based on your anticipation of special processing, that may still leave you with problems.

P
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#7 Saul Rodgar

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Posted 02 May 2009 - 11:27 AM

I personally have never had problems running full bleach bypass, but have heard horror stories with partial BB processing, some of the streaks referred to above. I do know that some movie production insurance companies balk at insuring productions who are to employ BB processing, as it is considered risky.
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#8 Dominic Case

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Posted 04 May 2009 - 04:44 AM

but have heard horror stories with partial BB processing,

The bleach process reduces the silver image to silver bromide, which will be removed in the fixer, leaving just a colour image. It is designed to be carried out to completion - in theory the three minutes in that solution is more than enough, so it doesn't matter if the reaction occurs a little unevenly due to low turbulation in the solution.

But the downside of this is that partial bleaching is likely to be uneven in effect, leaving more uncoverted silver in some areas than others - and also it is likely to give a slightly different result from day to day. This is because the temperature control in the bleach tank is usually +/-1C, which is enough to vary the amount of bleaching that has happened in one minute, although the bleach is always complete in less than three minutes.

(by comparision there is much more turbulation (pressure jets) in the developer solution, and the temperature is +/-0.1C).

So, beware of a lab offering partial bleach bypass. You might be lucky and get the result you want - but the result on the day might differ from the test run, and you might get the streakiness that others have reported.

Also note that if you ask for pull processing, the machine will be run about 20% faster, so any partial bleach time will be reduced even more, probably counter-acting any contrast or density change you get from the pull. As well, the lab surcharges will probably add half as much again to your processing bill.

Bottom line - if you are using a digital finish, process your neg normally and get the effect you want from a professional and competent colorist.
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#9 K Borowski

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Posted 04 May 2009 - 05:23 AM

Bottom line - if you are using a digital finish, process your neg normally and get the effect you want from a professional and competent colorist.


Well, I would say, yes, never do a partial BB or a pull, especially since the latter also will reduce your *wash* times by 20% (unless you use one of the labs that has machinery that can add another wash rack to offset the shortened time through the solutions), because either of these processes is chemically risky.

But a full BB still makes sense to do (and may be cheaper) than a comparable amount of special digital timing [grading].

Ultimately it comes down to what is cheapest. Likewise, with push and pull (pushes aren't usually harmful chemically), sometimes when labs are slow, you can get them to push for free (or at least only be out a case of beer ;-) ).
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