Part 4. : What is Focus Point ?

This is a picture taken where the subject approached the camera from "infinity" shooting distance, 1.5 m(approx. 5 ft.), and to 0.45 m(approx.1.5 ft.).
Notice how the length of the lens (extension) changes .

See the above illustration of "plane of sharpest focus and depth of field", and observe how the background is blurred.

Infinity

1.5 m ( 5 ft.)

0.45 m (1.5 ft.)

As been said earlier, the focus will be set by measuring the distance from the main subject and adjusting the lens's focus ring to the appropriate number (but it has to be accurate).
Then, what changes with the lens when the focus ring is adjusted ?
If you have a lens in front of you, try turning the focus ring. Do you see any changes ?

With most lenses, the length of the lens (or the lens barrel) simply changes.

The "basics" of basics is the same as seen with the experiment done in the 2nd. issue, regarding the magnifying glass.

In order to shoot the subject at infinity distance, it just needs to make distance between the lens (more precisely, the lens's principal point) and the film equal to the focal length.
As the subject moves closer, the entire lens needs to be extended in order to create a distance between the film and the lens.

There are different mechanisms regarding focusing, but in the end it comes down to simply changing the distance between the lens and the film.
By doing so, the position of the plane with sharp focus is altered.

Within some zoom lenses and telephoto lenses, however, the lens does not "appear" to be changing its length, even if the focus ring is rotated.
This is known as the "internal focusing" type (it is indicated as "IF" for all Nikkor lenses).
The front group of the lens stays fixed, but the smaller lens group at the rear part is adjusted to set the focus (it is sometimes called "internal focus", or "rear focus", depending on the manufacturer or the position of the lenses).

Compared to the conventional lens, which moves all lens elements to adjust the focus, the optical design of the "IF" lens is very difficult.
But since the length of the lens does not change, the weight balance does not shift so much, and the focus ring is well-positioned, so it requires few efforts to set the focus.
Because of this benefit, zoom lenses and telephoto lenses with bright aperture, mostly AF lenses, adapt this mechanism.

For AF SLR cameras, the focus is adjusted automatically to make the subject in the focus area, seen in the center of the viewfinder (focusing screen), appear sharp.

However, this function varies depending on the focus mode selected. Choose the appropriate mode depending on the shooting situation.

2.1.4. Other modes

With the Nikon F5 and F100, there are 5 focus areas : one in the center and the others around it.
The photographer can set the focus using the focus area selector and choosing either of the 5 focus areas (single-area AF mode).
Also, by analyzing and using the data achieved from the five(5) focus area, it can react to the sudden movement of the subject (Dynamic AF mode).

Photo 2.
Focus mode selector of
Nikon F100

Photo 3.
AF sensor position of F5
(Image picture)

Photo 3.a.
Focus area selector of Nikon F5

Photo 4.
AF-L button of Nikon F100

How to use Part 1 : In case AF does not work well When the subject is dark, or in a blank background, like the blue skies or white wall, the image is difficult to be analyzed, thus the AF might not function properly. In such case, either set the focus manually, or use a focus lock. How to use Part 2 : Using focus lock Usually with AF cameras, you set the subject within the focus area (most AF SLR cameras have it in the center of the viewfinder). If you want to set focus at the edge of the image, you should use a focus lock. [S] With Single Servo AF, press the shutter release button halfway. [C] With Continuous Servo AF, use AF-L (AF Lock) button.

Well, these are the basics.
Depending on the model, there are different functions, so use these modes efficiently depending on circumstances.

Generally, it is the same as the aforementioned AF SLR camera's manual focusing.
Look at the viewfinder image and adjust the focus ring so that the subject may appear sharp.
But this is difficult, and it requires a bit of experience, as well as patience.

Generally, a MF SLR camera is focused easily using split image and/or microprism in the center of the matte surface of the focusing screen.
This is the same as the focus area of an AF SLR, thus if you want to change the construction, you must first adjust the focus and then determine the construction.
Once you get used to it, you might be able to adjust focus using the matte surface, a frosted glass around the screen. It is difficult to focus, especially with wideangle lenses (the focal length is short, thus it has deep depth of field).

Photo 5.a
Viewfinder of Nikon FM2
(New FM2 in the Japan(Nippon))

Fig. 2.
Interchangeable focusing screens of FM2
Left: Split-micro type (Type K2: Standard model)
Center: Matte type (Type B2: Optional)
Right: Matte type with grid pattern (Type E2: Optional)

If you do not know the correct focus, then adjust the focus ring widely, look at the focusing screen to check the focus, then gradually narrow the adjustment range.

In simple term, this is a convex lens., which is like a camera lens's farsighted spectacle.
Normally with the genuine model made by the camera manufacturer, the image quality reduction is made to be minimized.
Choose the appropriate lens, depending on the focusing distance of the aggregate or the attachment size (other companies call it "filter size").
With Nikon's close-up lenses, the larger the number of the product, the closer you can shoot.

One advantage of this close-up attachment lens is that it can use auto exposure and autofocus functions.
It becomes efficient with long focal length, like the telephoto lenses.

Photo 11.
Close-up lens (No.1) + Ai AF 50mm f/1.8S

Even if you don't have a close-up attachment lens, a magnifying glass can become a handy tool.
Simply put the magnifying glass in front of the lens to take close-up pictures (in this case, use it in MF mode)

As indicated earlier, further the lenses are from the film, it is able to focus a near subject.
Thus, by placing a hollow ring (extension ring) between the lens and the camera body, the lens can be further extended for close-up shooting.

There are various lengths, and it can also be used by combining them.

Photo 12.
Auto Extension Ring PK-13 + Ai AF 50mm f/1.8S

The image becomes darker when approaching the subject closer (higher magnification), thus you have to be very careful with camera shake and focusing.

This is an elastic bellow-type attachment placed between the camera body and lens, and it can extend the length of the lens.
This allows flexible close-up shooting, as well as making duplicates of a positive film using a slide copy device (Nikon Slide Coping Adapter PS-6).

Photo 13.
Bellows Attachment PB-6 + Ai AF 50mm f/1.8S

With a combination of a Lens Reversing Ring BR-2A , which will be mentioned later, it allows enlarged shooting at high quality (see Photo 14.).
Although it is a bit troublesome, it is nothing really difficult.

By attaching a normal or wideangle lens onto an SLR camera reversibly, you can take remarkably close-up pictures.
Try holding a wideangle lens, bring it to the camera reversibly, and see it through the viewfinder.

Since these lenses are optically designed so that the principal point of the lens is at the back portion of the lens (retrofocus type), simply reversing the lens will make it seem like as if the length of the lens has expanded.

The macro adapter ring is an accessory which enables the lens to be mounted reversibly by using the lens's front attachment screw (used to attach filters, etc.).
In the Nikon product lineup, Lens Reversing Ring BR-2A is the accessory.

However, the camera cannot adjust the focus since the lens is reversibly attached. You have to adjust the camera position to focus.
Also, most automatic functions of the camera cannot be used.
Together with the previously mentioned bellows attachment, it becomes easier to focus and shoot enlarged pictures (See Photo 14.b.).

Photo 14.a.
Lens Reversing (Macro Adapter) Ring BR-2A + Ai AF 50mm f/1.8S

Photo 14.b.
Bellows Focusing Unit PB-6 + BR-2A + Ai AF 50mm f/1.8S

In this case, by setting the lens reversibly, the distance between the lens front and the subject (working distance) can be made longer, and it can take enlarged picture at high quality.

This issue will stop here. Many of you might think that it is the camera which does the focusing, but in the end, it is done by the photographer.
There are different methods and traits of focusing, especially when shooting close-ups. It is quite exciting simply taking enlarged pictures of a small subject. I want all of you to try it out.
In the end, I would also like to say that there is a unique character with unfocused pictures as well. Out-of-focus pictures are not worthless pictures. Shooting pictures are something to be enjoyed.