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How to detect bad processing


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#1 Tony Brown

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Posted 14 July 2009 - 02:22 PM

If I suspect that a particular lab is not producing results that are quite what they should be, is there a test that can be done on unexposed processed neg (in other words completely clean) that I can request and the results be compared to known specs on line?

I use two labs in Mumbai and Istanbul that seem to produce consistantly 'muddy' looking negs compared to labs in other locations.

Any advice, particulary from Kodak would be appreciated
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#2 Robert Houllahan

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Posted 14 July 2009 - 03:28 PM

Any advice, particulary from Kodak would be appreciated



Talk to your Kodak rep and have them send you a sensiometric test strip and then send it to the lab to have it run. After you get it back send it to Kodak and have them run an evaluation on it which will tell you how far off it is.

We run a Sensiometric test and check it with a densitometer before running any processor i.e. every day and sometimes more often (usually with B+W to make target gamma) in order to check the whole process. Any good lab will do the same.

-Rob-
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#3 Tony Brown

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Posted 14 July 2009 - 11:08 PM

Talk to your Kodak rep and have them send you a sensiometric test strip and then send it to the lab to have it run. After you get it back send it to Kodak and have them run an evaluation on it which will tell you how far off it is.

We run a Sensiometric test and check it with a densitometer before running any processor i.e. every day and sometimes more often (usually with B+W to make target gamma) in order to check the whole process. Any good lab will do the same.

-Rob-


Thanks Robert.

The 'local' reps in Mumbai and Istanbul are not as helpful as they might be, this has been an ongoing issue for some time.

When you say "have them send you a sensiometric test strip"....wouldn't that just involve sending them 30' of MY unprocessed stock? Thats what I've done in the past....

And could you / anyone please explain 'target gamma'

Thanks
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#4 Robert Houllahan

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Posted 15 July 2009 - 01:09 AM

A sensiometric strip has nothing to do with your film, they are "control" films produced to a exact specification by Kodak which are designed to be processed and then tested (by densitometer in the lab or by kodak after processing) which show problems with chemistry or other factors with the processor. A lab will generally run a test strip through the processor before running any "real" film to detect problems.

Target Gamma is how sensiometric measurement is done in B+W processing and can apply to each roll of film in exacting circumstance i.e. YCM seperation work.

-Rob-
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#5 K Borowski

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Posted 15 July 2009 - 06:55 AM

Target Gamma is how sensiometric measurement is done in B+W processing and can apply to each roll of film in exacting circumstance i.e. YCM seperation work.

-Rob-


Gamma (the greek letter "G") was shorthand for the name given to the slope of the sensitometric curve. It is basically a measurement of contrast, more important with B&W than with color, although you do want proper contrast with color, but that isn't a normal processing problem with modern automated color machinery.

Basically, labs run several control strips with sensitometric data (ECN-2 is probably D-min (base density/fog), middle grey, D-max and "Y-max) to test for retained silver) printed on them. It's a piece of film exposed by Kodak under exacting circumstances to give you a precise, verifiable standard with which to compare actual production work.

THen Kodak has references processed under as-ideal-as-possible processing conditions that you compare the control strip to to measure deviation from "ideal". What always makes this confusing for me, personally, is that even the "reference" strip Kodak processes itself deviates from this golden standard of perfection, which is apparantly impossible to achieve, lol.


So, I never knew this, but apparently Kodak gives filmmakers individual control strips so they can "audit" a lab, so to speak, correct Rob?

If you are experiencing "muddy" results, Tony, I would interpret that as physical dirtiness, high base fog (either over-development or retained silver halides), or underreplenishment.

A test strip will tell you for certain which of these it is. IIRC, retained silver causes a funny reading in the Y-max, underdevelopment or exhausted developer causes a low D-max, and physical dirtiness will show up as physical dirt or splotches on your strip.

There are also a whole host of other problems that show up as varying densities of the Red Green and Blue channel readings; you can drive yourself crazy trying to keep track of all of them.

But results aren't perfect at any lab, hell, not even at Kodak's ideal test strip processing facility. The acceptable variances are, if I recall correctly +/-1/4 stop before corrective action must be taken.

Problems aren't always easy to verify or identify either, as different causes can take similar forms on a control strip.
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#6 Tony Brown

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Posted 15 July 2009 - 01:46 PM

Thank you gentlemen - good info

I'm familiar with sending in strips in the old days to check for different emulsion batches being usuable ....anyone else remember doing that? Or to check for x ray damage, but never knew that Kodak supplied strips for checking the processing side

Excellent - thanks again
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#7 Stephen Williams

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Posted 15 July 2009 - 02:35 PM

Thank you gentlemen - good info

I'm familiar with sending in strips in the old days to check for different emulsion batches being usuable ....anyone else remember doing that?


Hi Tony,

When doing optical effects in the late 70's early 80's I did the same. We always specified the printer lights, Kodak would hold 18 months of stock for us from 1 batch, only invoicing when we took delivery! IIRC Humphries was the most comsistant followed by SFL followed by Rank Denham. Used SLF the most as they would allow tests prosessed in their 'test' bath so we could have film processed 4 times a day.

Stephen

PS The worst processing by a long way was BBC News for 7240!
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#8 Tony Brown

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Posted 15 July 2009 - 03:19 PM

Thats very funny Stephen.... my era also

I was often instructed to rip off 30' of 5254 or 5247 beacuase the emulsion number was different to the existing batch and could NEVER load it until the tests had come back. Just what i needed at the end of an 18 hour day.....strip tests.....

I think Humphries folded, Studio Film Labs became Soho Images (there was a brothel in that (meard?) street and the girls once chased me down the road - I was terrified)....

But they seemed only to do commercials in the main, mostly I dealt with technicolor and ranks.... wish I could remember the contact names....Les....?
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#9 Stephen Williams

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Posted 15 July 2009 - 03:54 PM

I think Humphries folded, Studio Film Labs became Soho Images (there was a brothel in that (meard?) street and the girls once chased me down the road - I was terrified)....

But they seemed only to do commercials in the main, mostly I dealt with technicolor and ranks.... wish I could remember the contact names....Les....?


Hi Tony,

Humphries folded around 1983. Ted Gerald had a rostrum camera in a room above the 'Golden Girls Club', mainly transvestites IIRC!

Les Holland & Jim Timmes at SFL.

Stephen
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#10 Tony Brown

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Posted 15 July 2009 - 04:08 PM

Soho is so sterile these days....

;)
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#11 Dominic Case

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Posted 16 July 2009 - 04:52 AM

THen Kodak has references processed under as-ideal-as-possible processing conditions that you compare the control strip to to measure deviation from "ideal". What always makes this confusing for me, personally, is that even the "reference" strip Kodak processes itself deviates from this golden standard of perfection, which is apparantly impossible to achieve, lol.

Kodak usually spends several days getting its test strip processor up to exact standards before processing the reference samples - and usually gets pretty close to "ideal". Though what makes "ideal" is hard to say: emulsions do vary very slightly over time, so even if a result is different from the same batch processed three months ago, it might not be a processing variation.

However, it's easy to be accurate and consistent within a quarter of a stop or even a sixth of a stop (which is a negative density variation of about 0.03 in the mid-scale).

An increasing number of labs are taking on the Kodak Imagecare system, which requires a very high level of quality control, regular testing and record-keeping, routine maintenance, etc. The labs are inspected by Kodak every six months, and their sensitometric records for the entire period since the last visit are examined. There are labs all around the world with Imagecare certification (including, in reference to another thread, Indai and Mexico, though not many in the US).
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#12 Brian Pritchard

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Posted 16 July 2009 - 05:10 AM

Thats very funny Stephen.... my era also

I was often instructed to rip off 30' of 5254 or 5247 beacuase the emulsion number was different to the existing batch and could NEVER load it until the tests had come back. Just what i needed at the end of an 18 hour day.....strip tests.....

I think Humphries folded, Studio Film Labs became Soho Images (there was a brothel in that (meard?) street and the girls once chased me down the road - I was terrified)....

But they seemed only to do commercials in the main, mostly I dealt with technicolor and ranks.... wish I could remember the contact names....Les....?

Did you mean Les Ostinelli; he also worked at Humphries for a while? He died a couple of years ago.

Brian
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#13 K Borowski

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Posted 16 July 2009 - 07:38 PM

There are labs all around the world with Imagecare certification (including, in reference to another thread, Indai and Mexico, though not many in the US).


Yeah yeah yeah, but maybe in said thread that person was referring to Kodak's test strip processing facility as the best lab in the world :-p
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#14 K Borowski

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Posted 16 July 2009 - 07:50 PM

Though what makes "ideal" is hard to say: emulsions do vary very slightly over time, so even if a result is different from the same batch processed three months ago, it might not be a processing variation.

However, it's easy to be accurate and consistent within a quarter of a stop or even a sixth of a stop (which is a negative density variation of about 0.03 in the mid-scale).


This is part of what drives me nuts thinking about it. . .

How can you tell, say, what the proper D-Min is going to be and the contrast, when one stock, say '45 or whatever it is, I forget that they print ECN-2 test strips on, is replaced by another stock like '01 with different characteristics?

And, each emulsion batch has its own unique characteristics. If one wants to be really picky, you can have variances in the same batch between the beginning of the roll and the end. They are very small, but they're there.

As for being accurate to within a sixth of a stop, are you talking about for Kodak or for an individual lab? Even with huge amounts of volume (not a small E-6 lab or a B&W lab, for certain) isn't the aim point more than 1/6 stop?

I guess I am not saying it very concisely, but this is more like baking a cake than plugging numbers into formulae. It is very difficult if not impossible, especially considering that different films eat up different amounts of developer activity, and that there are different average densities with different customer films, to be able to precisely keep a process in control.

Or, to put it another way, the corrective action that you are supposed to take for a given process problem, say a certain number of milliliters per linear foot of 35mm, will *never* match up with the actual amount it takes to correct the problem. This is my experience at least.

Machine replenisher pumps tend to behave differently from one day, one cycle even to the next. Ambient temperature, humidity, condensation, rust, and bad water filtration are just a few more of the variables I've seen.

And some equipment I've seen Kodak mention and recommend in its literature, like hydrometers for measuring specific gravity, I have never seen in a single photographic processing lab I've been in.
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#15 Dominic Case

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Posted 16 July 2009 - 08:44 PM

Machine replenisher pumps tend to behave differently from one day, one cycle even to the next. Ambient temperature, humidity, condensation, rust, and bad water filtration are just a few more of the variables I've seen.

And some equipment I've seen Kodak mention and recommend in its literature, like hydrometers for measuring specific gravity, I have never seen in a single photographic processing lab I've been in.

Well no-one ever said it was eay running a lab well.

Every lab I've worked in has had a chemical analysis department, which takes samples and analyses the solutions on a daily basis. Specific Gravity (yes with a hydrometer) and pH are among the first and easiest tests: others involve quite complex procedures with pipettes, burettes, separating flasks and the like.

Replenisher flows are calibrated regularly (that is the sort of thing that Kodak Imagecare requires), and the temeperature controllers in thge machine are cross-calibrated against a standard thermometer.

And, each emulsion batch has its own unique characteristics.

Correct, although they are much more uniform than they used to be. But that's not an issue anyway. Labs run regular sensitometric strips on a standardised emulsion, not on the batch or emulsion type(s) that they are processing on the day. The process is maintained as a standard against a standard emulsion with known aim points: if a different batch produces different results that is entirely a matter for the manufacturer, not the lab. You don't vary a process to chase after emulsion differences.

If things are done carefully and consistently and accurately, there isn't often any need for a replenisher correction, or temperture or anything. If a correction is needed, it's a bit like steering a car (or more like a boat really) - you apply a correction, and see how it goes: if it brings you back on course that's good - if you need a little more, you apply a little more - and so on. It's a skill to get it right.
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#16 michelle arakelian

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Posted 24 July 2009 - 11:58 AM

In our lab every day before starting to develop we do all bath tests and PH test, we use kodak sensitometric pre exposed
control strips for Kodak films and the Fuji pre-exposed control stips for Fuji films, to check our solutions, then if every
thing is ok we do a test with the negative we have to develop, we cut a 10cm piece from the roll and we do a
sensitometric test with Kodak sensitometer we have and we develop it, we have a ref for every tipe of negative
(kodak, Fuji, ORWO,...) and we can check if the neg is ok or not, if it's ok we develop it
if not we contact the client before developping. as the program of Image care of Kodak every lab has to do these tests.

Michelle
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#17 John Hoffler

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Posted 24 July 2009 - 01:07 PM

good info.

also, tony... your avatar ant got me... i tried to smush it on the screen...lol :P
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