How to test negative film developer?

Hey Everyone,

My local Costco (which has been great with digital prints, really!) is able to process C-41 120 format roll film. I want to try a 'test' roll first.

I recall reading years ago, to test a C-41 machine processor, you use an 'unexposed' roll of film or is it a 'exposed' roll of film shot with the lens cap on. And then look at the film base for consistency, machine marks, dirt, etc.

Am I remembering correctly? Does this make sense???

I want to test their processing before I use them..

THANKS...

Unless you have access to sensitometry equipment - Why not just run a regular exposed roll through and see how it turns out? Take pictures of your kitty cat or back yard. Or that fabulous moonrise over Hernandez? Who knows, you might get lucky...

Hey Robert,

(That would be too easy...)

If I recall correctly, the unexposed film would be easier to examine for roller marks, consistency, dirt, etc.

Quote:

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Originally Posted by Michael Nelson

Hey Robert,

(That would be too easy...)

If I recall correctly, the unexposed film would be easier to examine for roller marks, consistency, dirt, etc.

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Definitely unexposed if that's what you're looking for.

Ian

One thing you may see is light leaks from them unrolling / loosening the film prior to developing it. For that, you may as well send them an fully unexposed roll.

By the way, exposed and unexposed 120 are wound differently (the tape is on the inside once it is exposed). I might be inclined to roll it through a camera or wind it on a different spool in a dark room / dark bag. One minute might save some consternation at the lab.

A blank roll of film will show any dirt and roller marks, light leaks, etc.,but the chemistry; Developer, Bleach, Fixer and Stabilizer activity level needs to checked on a daily basis.
You may want to ask the lab if C-41 control strips are run and plotted on a daily basis. This is a pre-exposed piece of film with areas exposed for D-Min LD ND and D Max. The strip should be processed daily, before any customer work is run. It also has an area to check for proper bleaching and silver retention. To maintain a proper chemical activity level these strips should be run and then read on a densitometer and the results plotted. This is the only way to know for certain the chemistry will process a roll of film to it's optimum. This should be standard operating procedure for any lab.

Jim

One frame unexposed to check for rollermarks, and one frame exposed to medium density of a textureless tone (like an out-of-focus cloudless sky with a long lens) to check evenness of development and grain structure, (well, as close as C-41 gets to grain!). Depending on the machine type, you might want to do each of these at the beginning of the roll, and again at the end. And one frame of a color scale, if it's color C-41, for trueness. And some shots "typical" of your lighting and subject matter, just to see what it looks like. Maybe under-expose and over-expose one just to see the difference.

And check the whole thing for waterspots.