Prt. 6 Lenses Continued

LONG LENSES

Long lenses tend to be large and bulky. Many people tend to leave the longer lenses at home when they go out for a day trip. Nobody wants to lug around a big, heavy lens all day.

A TYPICAL 400mm LENS



The very good long lenses also tend to be quite pricey.

The longer the focal length of your lens the more steady the camera must be to avoid blurring the image.

A general rule in photography: Only hand- hold a lens when your shutter speed is equal to or faster than your lens focal length.

Example: A 200mm lens should not be hand held at speeds under 1/200th of a second. Any speed equal to or greater than the focal length should be fine.

As you can see most telephoto lenses will need to be mounted on a tripod for maximum performance. Now you not only have a large lens to lug around but also a heavy tripod.

One last point, no matter how good your lens is, when taking photos from a great distance your image is at the mercy of atmospheric conditions. Dust, haze and other elements can hamper your efforts of obtaining a sharp image.

TELE-CONVERTER / DOUBLERS

There are ways of getting around using telephoto lens.

A doubler or tele-converter magnifies the image; you attach the doubler to your lens. You then mount the lens to your camera body.

Example: 135mm lens with an added doubler becomes a 270mm lens.

There are different size converter such 3x tele-converters or smaller.

Tele-converter will degrade your image. You may be able to find a good converter with multiple elements, but any added glass to your lens will always degrade the image in some manor.

A 2X tele-converter M42 mount.



If you do decide to use a tele converter be aware that the converter will cause a loss of light. If your using a through the lens meter, such as the type found on most new SLR’s and DSLR’s you wont have to compensate for the loss of light. If your using a hand held meter then you have to make corrections for the light loss.

Example:

2X converter - open up 2 stops

3X converter - open up 3 stops


THE CAT LENS / MIRROR LENS

The Cat lens is a catadioptric lens. A catadioptric lens is a telephoto lens that uses a curved mirror to increase the size of an image.

The design of the Cat lens enables a very long focal length to be obtained in a short barrel. A 500mm Cat lens can be as short as 4 inches long. Compared to a normal 500mm lens, which can be as long 12 inches or more, this is quite an advantage.

A Cat lens does have a drawback. The best catadioptric lens does not produce as sharp of an image as the equivalent telephoto lens. Although with today’s technology some very good catadioptric lenses have been manufactured.

Catadioptric lenses do not have variable diaphragms. The aperture is fixed usually at f/8 or f/11 and cannot be adjusted.

An inconvenience? When I discuss depth of field the inconvenience will become apparent.

ZOOM LENS

Zoom lenses are quite convenient. A zoom lens will allow you to change focal length without changing lenses. A 35mm – 105mm zoom lens can be adjusted by simply turning the barrel in most cases; some lenses have a push – pull type adjustment.

Nikkor 35mm-105mm MF zoom lens.



Zoom lenses have a complex optic design causing most zoom lenses to be heavy and a bit bulky. Also, most zoom lenses are not as sharp at any given focal length as their fixed length equivalent.

There have been many changes in the design of newer zoom lenses. With the new computer designed lenses the optics and bulk have improved dramatically.. You can find some very sharp zoom lenses, but most of these come with a hefty price tag.

Some zoom lenses are designed with two separate control rings. One ring controls focus while the other focal length. Once you have set the focus you cannot accidentally change the focus while adjusting your focal length.

The push – pull zoom lens is a one-control ring function design. You twist the ring to focus and push or pull the ring to adjust focal length. It is very easy to lose your sharp focus while adjusting your focal length, so careful use is required for razor sharp images.

THE MACRO LENS

A macro lens is a close focusing lens. Some macro lenses will allow you to focus close enough to obtain an image that is about the same size as in real life.

Fujinon EBC 55mm macro 1:3.5 M42 mount



The relationship to the size of the image on film or digital sensor to the size of the actual object is called the reproduction ratio. A ratio of 1:1 (one to one) means that a life size image is produced on film/digital sensor. A 1:2 ratio means the image produced is one half the size of the actual object, and 1:3 is a one third the size of actual object.

Common terminology:

Macro lens – reproduction ratio of about 1:1

Macro- Focusing lens – reproduction ratio between 1:1.2 and 1:2

Close- Focusing lens – reproduction ratio between 1:2 and 1:4

A macro lens can be a lens of any focal length, although they tend to be of medium focal length. Common macro lenses may be a 55mm, 100mm, and 70-180mm macro zoom. This simply means that in addition to its focal length it can be used to focus closer than a standard lens to create life size images.

PORTRAIT LENS

A good portrait lens produces an image free of perspective distortion. We want the nose of the model to be proportionate to the models face. We also don’t want to flatten out the models face.

A good portrait lens will produce an image that flatters the model.

85mm to 135mm lenses should produce the most flattering images for portrait work.

A GOOD 35mm FILM PORTRAIT LENS



A GOOD PORTRAIT LENS FOR A CROP DIGITAL



Keep in mind that on a crop digital camera you have to multiply the focal length by the crop factor. So, a 58mm lens will function as a 87mm lens when multiplied by 1.5. This would make a good portrait lens on a digital crop camera.

Prt. 5 Normal, Wide, and Telephoto

If we were to see the world through a 20mm lens we would be able to see a wide scene, a vast area of coverage, a very scenic view. A 20mm lens is considered a wide-angle lens. Now, if we switched our perspective and seen the world through a 300mm lens we would cut down our angle of view and only see a small portion of the entire scene. A 300mm lens is conceded a telephoto lens.

A 50mm lens is not very wide nor is it really telescopic. For this reason it’s known as a normal lens. Why do we call it “normal”? It’s called a normal lens because it takes in an angle of view that is about the normal field of view we see the world around us.

A NORMAL LENS FOR 35mm FILM CAMERAS.




Lenses that cover wider fields of view are called wide-angle lenses while those that cover a narrower filed are called telephoto lenses.

50mm lenses are not normal lenses for all cameras. The larger the negative, the longer the focal length needed to create an image covering the normal field of view. This applies to digital cameras also. Some digital cameras will have a crop factor such as 1.5. Multiply the crop factor by your lens size to determine the proper focal length. Other digital cameras are full frame so the general film rule applies.

With a 35mm film camera a 50mm lens is considered normal.

Other normal lenses for different film sizes follow,

FILM CAMERAS

35mm = 50mm (normal)

21/4 x 21/4 = 75mm (normal)

4 x 5 = 150 (normal)

8 x 10 = 300mm (normal)

DIGITAL CROP FACTOR

1.5 crop = 35mm (normal) this equals 52.5mm equivalent to film.

1.4 crop = 35mm (normal) 49mm equivalent to film.

And so forth.

This is all approximation. Any lens between 40mm and 60mm could be considered a normal lens for a 35mm film camera. Same is said for the larger film sizes.

We can look at this from a different perspective. Lets try measuring the diagonal dimensions of a picture frame. The diagonal measurement of a 35mm frame is about 50mm long. There for the normal lens size for this film is about 50mm or there about. Same is to be said for other film sizes.

Remember that regardless of film size, the shorter the focal length, the wider it’s field of view. The longer the focal length the narrower it’s field of view.

TELEPHOTO

Previously I discussed the focal length as being the distance from the center of the lens to the film plane when focused at infinity. This would imply that the length of the lens barrel would have to be approximately the same length as the focal length. So, a 100mm lens would have to be 100mm long. But when measuring your lenses you will find that many are considerably shorter than their focal lengths.

Why? There are special lens elements that magnify the image. This enables a telephoto lens to be constructed in a shorter barrel, a lens that is as long as its focal length is generally called a long focus lens. Since most long lenses are of telephoto design, the term telephoto is applied (and sometimes misapplied).

A typical telephoto lens.



ANGLE OF COVERAGE

The angle of coverage depends on the lens focal length; the longer the lens focal length the narrower the angle of coverage.

Here are a few samples:

8mm = 180 degree angle of coverage.

28mm = 75 degree angle of coverage.

35mm = 63 degree angle of coverage.

50mm = 43 degree angle of coverage.

85mm = 29 degree angle of coverage.

135mm = 18 degree angle of coverage.

250mm = 10 degree angle of coverage.

350mm = 7 ½ degree angle of coverage.

500mm = 5 degree angle of coverage.

Prt. 4 Focal Length / F-stops

When talking about the speed of a lens it becomes necessary to examine the focal lengths of lenses. The focal length of a lens is the distance from the center of the lens to the image it forms on the film plane or sensor.

The focal length you chose will determine how large the image forms on your film or digital sensor.

Example: Shooting with a 135mm lens 10 feet away from your subject will form a larger image on your film plane or sensor than shooting with a 35mm lens from the same distance.

Another way to look at the focal length: A 200mm lens will produce an image twice as high and twice as wide as a 100mm lens. A 100mm will produce an image twice as high and twice as wide as a 50mm lens. And so forth.

How do we measure the focal length of any given lens? The answer is simple. There are three ways to measure the focal length of a lens, inches (in.), centimeters (cm), and millimeters (mm). Millimeters are the most common measurement for 35mm lenses.

There are about 25mm to an inch so a 55mm lens would be the equivalent of a 2.2 inch lens, or there about,a 50mm lens about 2 inches as pictured below.



LENS APERTURES

I have discussed the aperture (iris) opening in a previous post. I covered how a large opening admits the most light and the larger the opening the faster the lens.

Samples of aperture openings.






Lets take a closer look at the aperture and how it relates to the focal length of a lens.

In photography we are not just interested in how much light enters the camera. Our concern is how much light reaches the film or digital sensor. This is determined on how far the lens is from the film or digital sensor.

The closer the lens is to the film or sensor the more potent the light source will be. The farther the lens the less potent the light source becomes.

Example: Take two lenses with the same size aperture. Both lenses will let the same amount of light in. If both lenses are the same distance from the film or digital sensor they will each let the same amount of light reach the film or sensor. What happens if one lens is closer than the other?

Lenses with short focal lengths are shorter in length than those with larger focal lengths. Being that a short focal length lens is shorter in length also means that is sits closer to the film or digital sensor. If its closer to the film or sensor it will allow more light to reach the film or sensor than the longer focal length lens.By using various focal lengths we can control the amount of light, which reaches our film or digital sensor. Is this practical? Do we have other options? The answer is “yes”.

We could simply vary the size of our aperture.

We don’t have to calculate our exposure by relating the two variables. (Focal length and aperture). A system has been designed that combines both variables into one number; the f-number system.

An aperture of f/5.6 lets a specific amount of light reach your film or digital sensor. Any lens set at f/5.6 will admit the same amount of light to your film or sensor. Let your exposure meter tell you what f/stop to use then set your lens to the appropriate number. This will apply to all focal lengths.

The f/stop system allows you to calculate proper exposure regardless of the camera or lens you are using. The f/stop is an important tool, a tool you will use extensively in photography.

Part.3 F-stops (How they work)

F-stops

F-stops control the diameter of your diaphragm (aperture). The f-stops are clearly marked on the lower ring of your lens. (Some new lenses designed for digital cameras will not have this ring.

For now on we will refer to the iris opening as the aperture. The f-stops control the aperture.




Opening up one full f-stop doubles the amount of light entering the camera. Closing down one full f-stop cuts the light in half.

f/2.8 lets in twice the amount of light as f/4, f/4 lets in twice the amount of light as f/5.6, f/5.6 lets in twice the amount of light as f/8, and so forth.

A typical f-stop sequence wil look like this:

f/1.4 - f/2.8 - f/4 - f/5.6 - f/8 - f/11 - f/16 - f/22

The full range of f-stop number :

f/1 - f/1.4 - f/2 - f/2.8 - f/4 - f/5.6 - f/8 - f11 - f/16 - f/22 - f/32 - f44 - f64

Becoming familiar with your f-stops is very important. Knowing the full sequence of f-stops will be a valuable tool in the future.

A helful tip is to remember that with minor varitations, each whole f-stop is twice the f-stop that is two stops back.

Take a look at the sequence above.

f/1 will let in the greatest amount of light while f/64 will let in the least light.

Knowing this we will now move on to lens speed. Lens speed simply refers to the greates amount of light your lens will let in.

A fast lens is a lens that allows in greater portions of light and a slow lens refers to lenses that let in small anounts of light.

A typical fast lens would be f/1.2 - f/1.4 - f/1.8

These apertures allow for much more light to enter the camera.

Slower lenses such as f/2 - f/2.8 - f/3.5, let in smaller portions of light.

When more light enters your camera the less time is needed to expose the film or activate your digital sensor to record an image. Slower lenses need more time to record the image.

A typical fast f/1.4 Fujinon lens.



I hope you can see why we call f/1.2 and f1.4 fast lenses.

Prt. 2 The Camera and Lens

Paris, 1839, Daguerre introduces the world to photography. America’s George Eastman brings photography to the masses in 1890. The Germans jump onboard and bring the highest quality of engineering and optical performance to mass-market production; by 1920 Leica and Rolleiflex are introduced and remain on the market for many years to come. The Japanese are not to be left out, by the1950’s using computer technology they design lenses and optics of very high quality. They then took micro circuitry concepts and computer chips to a new level developing the metering systems, automatic exposure systems, and auto focus systems that we take for granted today.

And now the digital age!

Photography has come along way.

What is a camera?

1. A camera is a lightproof box. That’s all there is to it. The body keeps unwanted light out.

2. A lens is glass that gathers light rays and focuses them to form an image on film or your digital sensor. Most lenses contain multiple lens elements. (More than one piece of optical glass.)



3. Film/Digital Sensor – film is a light sensitive material (silver halide) that records your images when treated with chemicals. A digital sensor reacts to the light and stores information onto your memory card.

4. Your viewfinder shows you the image that will be recorded. Some viewfinders are just little glass window (rangefinder cameras) while other viewfinders allow you to view directly through the lens, such as an SLR /DSLR camera.

5. The shutter is a mechanical or electronic device that controls the length of time that light is allowed to enter your camera.

6. The shutter release simply activates the shutter.

7. The diaphragm is the lens opening, which varies in size. The opening controls the amount of light that enters the camera at any given time. The “iris” (diaphragm) is a series of metal leafs that overlap leaving a circular opening in the center. This opening can be made large or small by rotating a ring on your lens. Some camera lenses are auto focus and will automatically change via a microchip.

8. Film advance is a lever on manual cameras used to advance film to the next frame. Auto focus cameras will advance automatically, digital cameras the same.


This is the basic camera design. Digital cameras of course have much more circuitry but the light tight box and amount of light let in to capture an image are of the same principal. This may seem old hat to many who read this, but to those who just picked up a camera this is information well worth reading.

Prt. 1 With Eye's Wide Open...

Photography is more than a passion, for me it’s a way of life and enables me to view the world from a different perspective.

I started taking simple snapshots as a young boy with an old Polaroid B&W instamatic camera. This takes me back to 1974 – 1975 or there about. I fell in love with photography after watching my first polaroid print develop before my eyes. From that very moment I knew photography would become part of my life in some way, shape, or form.

Moving into the new era of photography has been very exciting. There have been many discussions on film verse digital. I use both medias and I enjoy both medias. I feel photographers should use whatever media makes them happy and concentrate on the important aspects of making a good image. It’s not how we got there; it’s getting there that counts.

The eye of the photographer is the foundation on which all good images emerge. We need a theme and more importantly we need to focus attention on the theme. Keeping a photograph simple (eliminate everything that might distract) helps to meet these goals.

I completely understand that art is subjective; you cant please everyone with every image you take. Focusing on a theme and keeping your image simple will move you in the right direction.

Until next time…