Perceived sharpness with regard to contrast

 

The eye/brain combination perceives sharpness quite differently from the way we might measure resolution on a lens testing bench. Perception is an impossible thing to measure yet we, as cinematographers, need to get a grasp of how our audience will see our work and need to know if they will consider our pictures to be sharp. Increasing the contrast of a scene will, most likely, increase the perceived sharpness of the scene. That said, it might also reduce the artistic value of the scene or even take it away from the cinematographer’s initial concept of the scene as represented in the script. A cinematographer might wish to show a scene with a reasonably high resolution but having a gentle, low-key feel to it. To do this, the cinematographer needs lenses that have a very long tone range and a gentle contrast, but that still appear to be sharp.

 

Telephoto lenses

 

A telephoto lens is not the same as a prime long-focus lens. Telephoto means the lens has been optically telescoped and is therefore physically shorter than its stated focal length. This can make the lens very handy, but does put more glass between the subject and the film plane. A true long-focus lens usually has few elements and is thus optically very pure but has, by its very nature, to be physically at least as long as its prescribed focal length.

 

Wide-angle lenses

 

Wide-angle lenses have a problem. Imagine looking down the empty lens port of a 35mm camera and think of a point 18mm in front of the film plane. You will see that this space is occupied by the mirror shutter when it is in the closed position. How then do we regularly use a lens of 18mm focal length, let alone shorter? It is achieved by using a retrofocal design. Retrofocal means that the lens contains elements in addition to those forming the 18mm prime lens, whose sole job is to refocus the rays further away from the back element so that the lens will produce a sharp image at the film plane despite being perhaps, physically, 50mm or so away. This is one reason why the wide-angle lenses are often the most expensive of a set, as they contain a lot of very sophisticated glass. One of the problems in designing wide lenses is that they are very prone to distortion, usually barreling.

 

Zooms

 

Zoom lenses, by their very design, have far more elements within them than prime lenses and therefore come with all the same problems, plus a few more. Many zooms change the image size when the focus is changed. They may vignette at certain focal lengths. The problems are minimized by the designers keeping to sensible maximum apertures and not trying to offer too long a zoom range. Most high-quality 35mm zooms are around T3 and 16mm zooms around T2.5. While the 16mm Zeiss T2 10–100mm, when first introduced, seemed like a miracle, in fact it was, in my opinion, not as good as its predecessor the T3 10–100mm in some respects, especially with regard to image shift, vignetting and, at around 16mm, definition. Most of these problems were ironed out with the introduction of the Mark 2, but this necessitated the use of a much larger front element cluster, and subsequently having to use a different, larger and more expensive matte box.

 

Conclusions

 

You must be very careful and aware when you choose your lens set. Lenses that, on paper, seem to have a high specification may not per- form as well as some others given the way you are going to use them. The character of the lens, under the circumstances you are going to use it, often means more to the cinematographer than the technical specifications of the lens, such as the minimum aperture, which may never be used. Most importantly, remember that your audience has come to be entertained and will probably never know what lens you used, nor will they care – all they are interested in is that you stir their emotions.

 

 

Film Stock

What is film?

 

Rolls of film are always known as film stock. You will hear unexposed film referred to as raw stock. Once it is exposed, but not yet processed, it becomes known as the rushes. Once exposed and processed, it is the master negative. Confusingly, the print or tape sent back to production by the laboratory the morning after processing is also known as the rushes. In America, these rushes are known as the dailies, which removes the confusion.

 

Today’s colour film stocks are fairly complicated affairs, consisting of a support medium, known as the base, which is coated on one side with as many as nine layers of light-sensitive emulsions. In addition, there are several other layers such as the yellow filter layer. All of these layers are collectively known as the emulsion. The top layer of the emulsion is known as the supercoat, whose purpose is both to protect the film from mechanical damage and to lubricate it through the camera gate. On the reverse side of the base, there is a removable coating called the rem-jet backing. This is black and eliminates halation – haloes around bright points of light. It is anti-static and also lubricated.