Opacity of undeveloped vs developed film?

Scheimpflug · Aug 11, 2011

Hello.

Off hand, does anyone have any knowledge of wether fully-exposed and developed negative film is more or less opaque than undeveloped film? I would be interested to know for both C-41 color and B&W film, if they happen to be different.

At a glance, the developed film which is solid black (instead of the undeveloped orange/brown/grey) *looks* like it would block more light, but I suspect this is just an illusion based on the color. Unfortunately I don't have the right equipment to test it to know for sure.

Also, am I correct in my thinking that developed but un-fixed film would be more opaque than the same film after fixing?

Thanks.

Photo Engineer · Aug 11, 2011

Fully processed color and B&W films have less turbidity than unprocessed film due to the emulsions themselves. Fully opaque films use a rem jet backing to prevent antihalation, but other films are just cloudy until processed. Opacity is also caused by the presence of dyes which sharpen films by reducing internal reflections caused by the emulsion grains acting as tiny mirrors.

This is much more complex than the average person thinks, but basically, all of the materials that cause this effect are removed at the end of the process.

PE

Scheimpflug · Aug 12, 2011

Thanks, Photo Engineer.

I'm not sure that I fully understand your explanation, so let me double check some things.

Are you saying that only rem jet backed films can be *fully* opaque, and that other films (developed or not) will always be slightly transparent?

Also, does higher turbidity equate to higher opacity?

frobozz · Aug 12, 2011

Amongst the many freaky characteristics of Kodak's 5360 Direct MP film (or 2360, the Estar-based variant I've been playing with) is the fact that the unexposed film looks like a translucent red filter. You can see right through the stuff! I haven't measured it with a densitometer but it sure looks like the developed film is denser. While the black areas aren't quite as densely black as a normal negative film (some of which might just be from the clear base), they certainly look denser than the unexposed film. The red is just a dye that washes out.

Duncan

Photo Engineer · Aug 12, 2011

Scheimpflug said:
Thanks, Photo Engineer.

I'm not sure that I fully understand your explanation, so let me double check some things.

Are you saying that only rem jet backed films can be *fully* opaque, and that other films (developed or not) will always be slightly transparent?

Also, does higher turbidity equate to higher opacity?

Only rem jet backed films are totally opaque. Light does not pass through.

Other films are translucent or near opaque. They vary from a color such as the post by Duncan to varying degrees of being "frosted" in appearance to "passes light but no apparent image". You can see shadows through these films at the minimum.

PE

Erik Petersson · Aug 12, 2011

I always wanted to ask what the colour of unexposed film is, just because the question seems to be logically impossible. (Colour implies that light is hitting the film, and it would not remain unexposed.)

Photo Engineer · Aug 12, 2011

Pure unexposed panchromatic film emulsion is gray and is about the consistency of heavy cream when melted. Other addenda change the colors. Pure orthochromatic emulsion is red and about like cream. Pure blue sensitive emulsion is white and looks just like cream.

When cold, the emulsion is like cream mixed with jello. You can break it with your fingers or a knife.

When coated, the addenda such as acutance dyes and trimmer dyes alter the color to what you see when you look at the exposed leader of 35mm film.

PE

Erik Petersson · Aug 12, 2011

You make me hungry, Engineer!
And thanks for the answer to this tricky question!

Scheimpflug · Aug 12, 2011

Hmm, ok. So how then do the "Daylight Spools" work for the films that don't have rem jet? Is it just assumed that the combination of several wraps of film are going to block "enough" of the light so as to not fog the whole roll when being loaded?

frobozz said:
Amongst the many freaky characteristics of Kodak's 5360 Direct MP film (or 2360, the Estar-based variant I've been playing with) is the fact that the unexposed film looks like a translucent red filter. You can see right through the stuff! I haven't measured it with a densitometer but it sure looks like the developed film is denser. While the black areas aren't quite as densely black as a normal negative film (some of which might just be from the clear base), they certainly look denser than the unexposed film. The red is just a dye that washes out.

Interesting! Perhaps Photo Engineer would know if it is possible that the film really is more dense after the developing? You might be in the same situation I am in... Where the subjective perception of the color makes it hard to judge by eye what is actually happening with the amount of light transmission through the film.

Photo Engineer · Aug 12, 2011

With unprocessed film, the density goes up as it is wrapped onto a spool, such that about 2 or 3 layers block all light, but loading instructions do specify "dim light" or "away from direct sunlight", and the loading assumes that the edges are completely protected. See a spool of 8mm film for an example.

After development, film has the density that results from the effects of: exposure + sliver halide quantity coated + development + the form the developed silver takes when developed. The maximum density is usually about 3.0 but is rarely used.

PE

frobozz · Aug 14, 2011

OK, just to add some pictures so you see what I see. (This is SO-291 which is apparently what Kodak called 2360 while it was in its experimental phase. I just happened to be unspooling some of that yesterday...)

Here is what the raw film looks like:

And here is what it looks like after just washing out the red dye (i.e. its "natural state" though you'd normally never see it this way because after washing the dye out, you proceed to process it!)

And here is what they look like front lit instead of backlit, just so you get a better idea of the colors:

Duncan

Newt_on_Swings · Aug 14, 2011

That film has been the coolest thing Ive seen today. Thanks for the pics!

frobozz · Aug 14, 2011

Well, then there's always SO-379 Fine Grain Release Positive (which I believe is the same thing as the production version, 5302). Despite the name it's a negative film (it's for making release positive prints from camera negatives) and it's nearly as translucent as the reversal film above. It passes about as much light, but there's enough frostiness to the emulsion that you can't really see stuff through it distinctly unless it's laying right on top of something. That's a fairly yellow color before processing, but then turns into a very normal looking negative with a greyish base once processed. See below.

Duncan

Wade D · Aug 14, 2011

A very interesting thread. Thanks to all of you for posting your knowledge and findings.

Opacity of undeveloped vs developed film?

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