Shedding Light on Black and White


A comparison between the way film-based cameras and digital cameras capture spectral information and transpose that information into black and white images.
 
Photography is all about Light. The more we understand about the way light behaves, the better we will understand how to capture it, edit it, and render it in both display and printed form.
 
If you shoot with a digital camera and love black and white photography, this series will give you some insider information that should help you understand why digital black and white images don’t have the same “feel” as film-based black and white prints. And I’ll present some suggestions about how to bridge the gap and regain the feel.
 
There are three issues that I’d like to address in this mini-series that will shed some light on the whole black and white issue. The first session will examine how film emulsion and silver halide grains capture and interpret the spectral qualities of light. The second session will look at how digital camera sensors deal with that same spectral information. The third session will present some insights and settings you can employ in both camera capture and post editing that can help you get that film feel back in your black and white photography.
 
Session One: The Silver Connection
First, a little background (and to some folks, a review) about the element of silver and the part it plays in black and white photography. This amazing art form is based on the light-sensitive nature of silver halide. The primary element in the light capture process in photography is the silver halide crystal. 
 
The photographic term “silver halide” refers to the cultured crystals that are formed when silver and bromoiodide atoms are joined and “cultured” on a molecular level. These silver halide crystals are then spread evenly within a gelatin layer and coated (in total darkness) on to a plastic film base. 
 
Black and white (or monochrome) films are produced and marketed by several film manufacturers. Each of these films is engineered to produce a unique visual characteristic. Photographers all have their own preferred “signature” look that is produced by one of these different film brands. These films produce specific results to satisfy the discerning eye of the photographer. Different lots of films also display unique characteristics causing serious photographers to buy a quantity of films from the same lot, storing them in very controlled coolers until they can be used. This produces great consistency in the work of discerning photographers.
 
Depending on how fine the grain is (how small the crystals are), the higher the count of these photo-sensitive light receptors will be in the film window of the camera. Note that smaller (or finer) silver halide grains are less sensitive to light than larger grains. 
 
This is why Kodak’s Tri-X film has a higher ASA rating than Plus-X, and a much higher rating than Panatomic-X film. The larger the grain size, the more sensitive it is to light, and thus the “faster” the film. Larger, more light-sensitive film grain produces much higher levels of contrast. Thus Kodak Tri-X produces images from lower levels of light and appears “sharper” because of the more pronounced definition properties of the silver halide grains.
 
Each of these silver halide grains reacts molecularly to the light hitting it. When exposed to light, each crystal forms a small, stable “latent image.” This latent is invisible to the eye because it has not yet been chemically affected by a development solution. This latent image remains “exposed” as long as the film is kept in total darkness.
 
FILM DEVELOPMENT
When it time to develop the exposed images on the film, the film is removed from the film canister (in total darkness), and wound carefully onto a stainless steel reel; a process that takes significant practice to accomplish without crimping (and thus permanently damaging) the film. This reel is then placed inside a light-tight stainless steel tank. 
 
Development of the latent images on the film takes place when the film comes in contact with an alkaline development solution. There a number of specific development solutions that affect the latent images, each with its own characteristics. Serious photographers carefully choose these development solutions for specific results. 
 
The silver grains darken during the carefully-timed and gently-agitated contact with the developer. Each grain darkens in accordance to its individual exposure to light. This development solution chemically chars the exposed silver grains. Grains that have been subjected to greater light turn darker than grains that have been exposed to lesser light. 
 
The different development solutions produce different internal contrast levels. The timing of the development is critical and lighting conditions during the exposure process can be compensated by “pushing” or overdeveloping the films.
When the development cycle is complete, the spent development solution is drained from the canister and an acid based solution called “stop bath” is poured in. This stop bath solution arrests the development process.
 
The canister is again drained and a hypo-clearing agent (or fixer) is poured into the canister which removes the unexposed silver particles from the emulsion layer and clears away any residual light-blocking properties. 
 
The canister can be safely exposed to normal room light and film is then thoroughly rinsed in flowing water to remove the fixing solution. The film is then submerged in a whetting agent solution to remove any calcium deposits from the water, squeegeed of excess fluid, and is hung in a drying cabinet under very low heat until dry. Until the film’s emulsion is totally dry, it is particularly vulnerable to scratching. Great care is taken to preserve the integrity of the developed image all the way through the development process.
 
So what is the cause of the visual romance with black and white photography? Sensitivity to light, or photographic speed, is one of the most important attributes of the emulsion. Here’s something you might not know…light sensitivity is typically enhanced during manufacture by a heat treatment in the presence of tiny amounts of sulfur and gold compounds (chemical sensitization). Organic dyes, usually cyanine dyes, are then applied to the crystal surface to extend the basic UV and blue sensitivity to other colors in the visible spectrum (spectral sensitization). Different film brands contain emulsions that have been dyed to respond selectively to blue, green, and red light, thus giving b/w photography a visual personality. Simply desaturating digital color images cannot possibly deliver this same tonal character. Converting color images to full-bodied monochromatic images requires a bit of understanding about the behavior and personality of light. A topic near and dear Tom my heart, as you probably realize by now.
 
I’ll get into this issue more in the third session.
 
Factoid: A single ounce of silver can produce enough silver halides to take 5000 photographs.
 
When you are finished, you have a negative image of the original scene. It is a negative in the sense that it is darkest (has the highest density of opaque silver atoms) in the area that received the most light exposure. In places that received no light, the negative has no silver atoms and is clear. In order to make it a positive image that looks normal to the human eye, it must be printed onto another light-sensitive material (usually photographic paper), which reverses the negative image into a positive one. Actually, you could say that the whole film- based photographic experience is a very negative one! (Sorry about that, it was just too easy to pass up.)

Anyway, that’s the way I sees it. 

Join me next time when we look into the way digital cameras deal with black and white images. In the mean time, please take five (actually more like six) minutes to watch a shameless plug about my new video series at http://gottaknowvideos.com/keyfactor.html This is stuff you just gotta know in order to shoot like a pro.

See you next time. Herb

hpaynter@imageprep.net

 

About Herb Paynter

I'm an author, photographer, lithographer, color consultant, and speaker living in Sarasota, Fl. I've been in the color game for more years than I care to admit. In that time I have picked up a lot of insights and experience that I like to share.
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2 Responses to Shedding Light on Black and White

  1. Kent Miles says:

    Just a small correction: Hypo Clearing agent is not the same as fixer (Hypo). Hypo clearing agent facilitates washing of residual hypothiosulfates (fixer) out of the negative or print.

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