For most amateur users, film necessarily refer to negative films. More advanced users may have tried slide films. What are negative films and slide films ? What are the differences ? Why do some photographers prefer one over the other ? Here's a basic comparison of the two types of films:
 

 Negative and slide films - What are they ?

Almost all photographers started out with negative films. Negative films are the films which gives you the orange-looking negatives and prints when processed. The Kodak Gold, Konica SR films are all examples of negative films. All the neighborhood labs are able to process this film, some offering a quick-turnaround time with the one-hour service.

Slide film is also known as positive, chrome or reversal film. They all refer to the same thing. Slide films look like negative films physically, but they go through a different chemical process and gives you slides instead of negatives. Slides are like pieces of negatives, but instead of the usual orange hue you get bright colours. When you attend a slide show, the projector actually projects the image from the slide itself.
 

Film structure and processes

The film structure of both negative and slide films are very much alike. They both contain layers of colour sensitive materials coated over a gelatin base. However, they differ in the processing stage. Colour negatives are processed in C-41 chemicals. This turns the black piece of film in the canister into your orange-looking negatives. The orange hue comes from a layer of orange mask which is applied to negative films to ensure accurate colours when printing. Slides go through the E-6 process, and the end result is the brightly coloured pieces of slides, also called chromes or positives. Slide films do not have the orange mask, since they are not designed for printing on normal colour paper (more on this later).
 

Latitude

What is latitude ? Latitude is a type of Latin attitude. Just kidding.

Latitude is the degree which you can overexpose or underexpose the film and yet can get back acceptable results. For example, if the film has wide latitude, you can grossly overexpose the film and yet your photos may still turn out just fine. It is like the tolerance level of some parents. For some of you, your parents may use the cane on you for returning home after 11 p.m. That is what I call narrow latitude. For others, you can elope with your boyfriend for months and then return home with only a slight scolding. Now that is wide latitude !!!

Negative films have a much wider latitude than slide films. The typical negative film has latitude for 3 stops overexposure and 1 stop underexposure. Slide films usually has latitude for 1 stop on both ends. So if you are not very proficient with your metering, it is best to stick to negative films.
 

Contrast

Slide films are higher in contrast than print films. Contrast is the subjective impression of the difference in intensity between two adjacent colours. A high contrast image will have very different hues or tones in between colours. A low contrast image will have muted colours fading gradually into each other without sharp boundaries.

Photographers prefer negative films over slides for portraiture because of the lower contrast. It allows a more pleasing pastel tones in the portrait. On the other hand, architecture and still-life photographers may prefer slides because the higher contrast gives the picture more punch.
 

Correction during printing

When you send your negative film to the colour lab for printing, you are actually at the mercy of the printer. The printer will assess your negative and decide how the final print will look like. So if you send your negatives for reprinting at another shop, you will get prints which looks different from the first copy. This is because the colour printers can easily tweak the colours to their own preference. If you used a colour filter in your pictures, the prints may not show it, because the printer may have corrected it away if they thought that it was a mistake or weird colour cast.

Slide film is another story altogether. Slide films are the final product of your image. The slide is returned to you as the original copy. If you want a print from the slide, you simply send it to the professional colour labs. Paper for printing from colour slides is called R-type, and it is different from normal colour paper for negatives. There is little that the lab technician can do to change the outlook of the slide prints. And because you can see the exact brightness and colours of the original slide, the prints can be compared to the original to check for deviation. So if you like to use colour filters, slide film may be more suitable for you, since you can see the full effects of the filter.
 

Colours are punchier in slides

If you ever attended a good slide show, you will realize the power of slides. Slides are extremely saturated in colour and pack a punch in contrast. They are exceptionally brilliant and eye-catching when projected. This is because they are transparent and the image is formed when light shines through. Compare this to a colour print. A colour print is viewed by the eye when light falls on the paper. The image is on the paper, and the light is actually reflected off the paper backing to your eye. Thus, the reflected light image seems less brilliant compared to the slide viewed with direct light. However, this is also a weak point of slides. Most slides lose their brilliance when you make R-type prints from them, because they end up with reflected light.
 

Professional scanning

However, slides are unparalleled when it comes to photomechanical printing. This refers to the commercial printers doing calendars, magazines and books. Commercial printers have high-tech equipment for scanning images to reproduce on printed images. Most of them are geared towards slides scanning. So if your purpose is shooting for the printed page, slide film gives slightly better results than negative films.
 

Which is more costly ?

Most people tend to think that slide films are more expensive to use than print films. This is only partly true. Take a look at the following table comparing the two types:
 

Surprise! Slide film costs less to use, even with mounting. Mounting is when you request your slides to be returned in the white plastic mounts, ready for projecting. If you request that the slides be returned unmounted, the cost is even less at $4.20.

However, if you want do prints, then slides may turn out to be more costly. It will cost you only $5 for a 8R print from a negative. On the other hand, you have to pay $8 for a 8R print from slides. A 3R print from slide will costs you $1 each. So if you plan to do many prints, forget about slides unless you have a big Swiss bank account. Same thing applies if you're shooting group photographs. Use negative films unless your group is willing to pay so much more for the prints. You'll get killed, trust me.
 

Conclusion - Which should you use ?

Each type has it's own pros and cons. You should try both types so that you have a wider choice in future, but do keep in mind the various factors affecting the choice of film. The table below will give you a rough guide in choosing the film for the situation:
 
 

Last but not least, go out and try it out for yourself ! Happy shooting !!!