Which of the following statements is true about the development step in film processing

   Film is not equally sensitive to all wavelengths (colors) of light. The spectral sensitivity is a characteristic of film that must be taken into account in selecting film for use with specific intensifying screens and cameras. In general, the film should be most sensitive to the color of the light that is emitted by the intensifying screens, intensifier tubes, cathode ray tubes (CRTs), or lasers.

Blue Sensitivity

   A basic silver bromide emulsion has its maximum sensitivity in the ultraviolet and blue regions of the light spectrum. For many years most intensifying screens contained calcium tungstate, which emits a blue light and is a good match for blue sensitive film. Although calcium tungstate is no longer widely used as a screen material, several contemporary screen materials emit blue light.

Green Sensitivity

   Several image light sources, including image intensifier tubes, CRTs, and some intensifying screens, emit most of their light in the green portion of the spectrum. Film used with these devices must, therefore, be sensitive to green light.

   Silver bromide can be made sensitive to green light by adding sensitizing dyes to the emulsion. Users must be careful not to use the wrong type of film with intensifying screens. If a blue-sensitive film is used with a green-emitting intensifying screen, the combination will have a drastically reduced sensitivity.

Red Sensitivity

   Many lasers produce red light. Devices that transfer images to film by means of a laser beam must, therefore, be supplied with a film that is sensitive to red light. 

Safelighting

   Darkrooms in which film is loaded into cassettes and transferred to processors are usually illuminated with a safelight. A safelight emits a color of light the eye can see but that will not expose film. Although film has a relatively low sensitivity to the light emitted by safelights, film fog can be produced with safelight illumination under certain conditions. The safelight should provide sufficient illumination for darkroom operations but not produce significant exposure to the film being handled. This can usually be accomplished if certain factors are controlled. These include safelight color, brightness, location, and duration of film exposure.

   The color of the safelight is controlled by the filter. The filter must be selected in relationship to the spectral sensitivity of the film being used. An amber-brown safelight provides a relatively high level of working illumination and adequate protection for blue-sensitive film; type 6B filters are used for this application. However, this type of safelight produces some light that falls within the sensitive range of green-sensitive film.

   A red safelight is required when working with green-sensitive films. Type GBX filters are used for this purpose.

   Selecting the appropriate safelight filter does not absolutely protect film because film has some sensitivity to the light emitted by most safelights. Therefore, the brightness of the safelight (bulb size) and the distance between the light and film work surfaces must be selected so as to minimize film exposure.

   Since exposure is an accumulative effect, handling the film as short a time as possible minimizes exposure. The potential for safelight exposure can be evaluated in a darkroom by placing a piece of film on the work surface, covering most of its area with an opaque object, and then moving the object in successive steps to expose more of the film surface. The time intervals should be selected to produce exposures ranging from a few seconds to several minutes. After the film is processed, the effect of the safelight exposure can be observed. Film is most sensitive to safelight fogging after the latent image is produced but before it is processed.

Let's look at some examples of statements and non-statements to define the kind of sentences that form statements.

To talk about statements, we’ll start with some examples of statements and non-statements.

Statements

So what makes something a statement?

• Definition: Statements are the kind of sentences that are either true or false.

As such, a statement is an assertion that something is or is not the case. A statement is true if what it asserts is the case, and it is false if what it asserts is not the case.

For instance, the statement “The trains are always late” is only true if what it describes is the case, i.e., if it is actually the case that the trains are always late. This is false in Auckland. Sometimes trains are on time, and sometimes they are early. Someone may impatiently complain that the trains are always late to express their exasperation with the train system, but strictly speaking what they say is false.

It is true that bananas have no bones, and I do like bananas, but I like bananas because they are tasty and healthy, not because they have no bones. I would thus say something false if I said “I like bananas because they have no bones.” That’s why “I like bananas because they have no bones” is a statement. It is the kind of sentence that is either true or false – in this case false.

Non-statements

However, it doesn’t make sense to say that the sentence “Welcome to the University of Auckland!” is either true or false. Wouldn’t you be puzzled if someone answered “true” in response to the greetings? It wouldn’t be an appropriate answer. “How can I stop tailgating?” is a question; the sentence doesn’t express something that is either true or false.

Finally, “When the car ahead reaches an object, make sure you can count to four crocodiles before you reach the same object.” is an advice. It advises you to make sure you can count up to four crocodiles (one crocodile, two crocodiles,…,four crocodiles) before you reach the same object as the car preceding you. Try it! You’ll be a much safer driver (that’s a true statement!).

More about Statements

So sentences that can be true or false are statements. Quite simple. But things can get more complicated. Let’s see how.

Something can be a statement even if we don’t know whether it’s true or false. All that matters about statements is that they are the kind of things that can be true or false, not that we know whether they are true or false. For instance:

• Ivan Slotvsky, the famous Irish builder of Madrid, is eating ham steaks and chutney at this very moment.

True or false? I don’t know. But it is the kind of thing that could be true or false.

Here’s another one:

• Sometime in the next 39 years, I will have a creepy next door neighbour.

So far, so good. I’ve been lucky and I haven’t had a creepy next door neighbour. But the statement is true if it will be the case some day that I have a creepy next door neighbour in the next 39 years. Otherwise, the statement is false. But I don’t know whether the statement is true or false. Regardless, what matters is that this sentence is the kind of thing that is true or false.

Another example:

• Vero is part of Promina

I have no idea what Vero or Promina are. But the sentence expresses something that is either true or false.

The same statement can be true on some occasions and false in others. That is, statements are not always true or always false.

Here’s an example:

• I’m a Kiwi.

This statement is true of Tim, and it’s false of Patrick. Or the statement

• Patrick is a happily married man.

was false before Patrick got married, it is true now (while I’m typing this), and it may become false in the future.

Ambiguous Statements

One difficulty with statements is that they may sometimes express two different things. We call those ambiguous statements. Here’s an example:

• John greeted everybody with a smile.

What are the two states of affairs that this statement may be describing? Try and answer this for yourself before proceeding.

Answer:

1. John was smiling and then he greeted everybody. In this case, it’s true that he greeted everybody with a smile – his smile.
2. Maybe there were smiling people and non-smiling people, and John only greeted the ones that were smiling.

The sentence “John greeted everybody with a smile” can thus be used to describe two different things. That’s what makes it ambiguous.

You need to be careful about this. If you use ambiguous statements, you run the risk of having others misunderstand what you are saying. In some cases, what others think you are saying may be very different from what you were trying to express. For example, Tim is an early bird. He gets up early every morning, and always before his wife. Now, suppose he tried to express this by saying:

• I beat my wife up everyday.

That would most certainly be taken the wrong way. Try and make sure you don’t use ambiguous sentences!

Questions and Commands

In the second list of non-statements, we had questions and commands, and those are typically not statements.

• If humans evolved from monkeys, how come we still have monkeys?

This question does not express something that can be true or false. It makes no sense to respond “true” or “false” when you hear it. It’s not a statement. Notice that a part of the sentence is a statement, namely “humans evolved from monkeys”. This is a false statement. Humans did not evolve from monkeys. Humans, monkeys, and apes in general, have a common ancestor that is no longer around. Even though the question contains as a part a false statement, it doesn’t make the question itself something that is true or false.

Sometimes, however, in a special context, the same question could be used to express a statement. Can you imagine a context in which someone might use this question to express something that is true or false? If so, then presumably the person would be using the question to express that it is false that humans evolved from monkeys, since there are still monkeys. We call questions that are used to express statements rhetorical questions. When you see a rhetorical question, you should always rephrase it as a statement. In our case, the statement would be something like this:

• Humans did not evolve from monkeys, because we still have monkeys.

Summary

In summary, statements are the kind of sentences that are either true or false. Sentences are ambiguous when they can be used to express several statements. When you have an ambiguous sentence, you need to decide which statement it is being used to express. Questions, commands and advice are typically not statements, because they do not express something that is either true or false. But sometimes people use them rhetorically to express statements. We saw an example of a question which by itself is not a statement, but can be used to express a statement. When you see rhetorical questions, always rephrase them as statements.

© Patrick Girard, University of Auckland

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