What is the purpose of the distance scale?

I have just purchaed a AF-S 18-200mm f/3.5-5.6G IF-ED to be used with my D40.

How do I use the distance scale?

If you need to know the distance for whatever reason, just read it.

for example, it can be used to set up manually the hyperfocal distance in some cases.In AF pointing to something works better.

The distance scale helps you verify the focus of your subject.

 

In fact in cinematography (because focus is ALWAYS DONE MANUALLY), we use the

distance scale to place the chosen subject in focus versus focusing by eye. The camera

assistant has a tape measure right by his side AT ALL TIMES and measures the focal plane

to the part of the subject that we would want to maintain in critical focus - i.e. the eye, lip,

etc.

 

DSLR cameras have focal plane markings on their body as well which appears as a "O" and

a horizontal line "-" thru it. You measure from there and to wherever you chose.

 

With the readout of your tape measure, you dial in the distance on the lens.

 

The problem with DSLR lenses, aside from the fact that the markings are too close to each

other, is that I can't compare the accuracy of the distance markings versus

cinematography quality lenses that cost at least ten times as much.

 

If you've done manual focusing, I'm sure you've come across thinking you've focused

properly by eye but upon taking the photo what you thought you wanted to be in focus is

actually blurry. So the distance scale aids in determining that the subject distance to focal

plane is in tune with the distance marking on the lens.

Also the scales permit hyperfocal focusing.

[sort of off topic but.... i have a nikon zoom, that at a certain focal length focuses on infinty at infinity. at another focal length, it focuses infinity much closer, according to the distance scale.. i never managed to understand the phenomenon, but for me it did reduce the value of the scale in question somewhat...]

The focus puller (cinematography) uses many tools, including the viewfinder. He generally makes pencil marks on the focus knob for that particular scene.

 

In general photography, the focus scale is used for DOF and manual flash settings. Street photographers often preset the distance by eye, so they can raise the camera and shoot VERY quickly before being noticed.

 

Zoom lenses are traditionally "parfocal" - the focus plane remains relatively constant as the focal length is changed. This issue is much less important for autofocus lenses, hence tends to be relaxed considerably. Lens design is always a compromise between features and performance. If parfocus is not critical, performance can be improved in other areas.

 

Zoom lenses tend to have many elements and groups. The refractive index (and possibly the zoom mechanism) changes with temperature. Special glass (ED) or fluorite elements are highly temperature sensitive. Consequently, the infinity mark on many AF zoom lenses goes past infinity. As a minor point, servo mechanisms work much faster if they can overshoot slightly.

Back in the old days (when all lenses had aperture scales), the distance scale could also be

used to approximate the depth of field at selected apertures (normally at f16 & 22).

 

Have a look at an older lens and you will see what I mean, you read off between the two

marks of the same colour which then gives you the minimum and maximum distances

from the camera which are in focus for the given f-stop.

 

Not sure if this really helps (especially nowadays)

 

Cheers

Mike

In addition to the other fine answers, I'll add that most if not all of Nikon's accessory flashes have a readout of the acceptable flash range for the current camera / flash settings (e.g. 0.6 - 2.8m).

 

Knowing your approximate subject distance helps you understand if you're over-reaching with your flash. All other things being equal, I often strive to be 'well within' my max flash range (say, no more than half the max) as this gives faster recycling.

Since i don't make macro photography i don't really know about this, but i think the scale may become useful for fine tunned focusing.

The scale can also be used to convert between feet and meters, in case you forget your pocket calculator. This is especially helpful for international travel.

The Hasselblad SWC has no focusing EXCEPT the distance scale. You guess the distance or measure it. I used to measure it with the distance scale on my Leica while using the Leica to get a light reading, then get the picture with the Has whenever possible.

It is historic and has no function if you use automatic focusing or viewfinder assisted manual focusing. But sometimes (in a dark club) you may be much more accurate when measuring a critical distance of 2,40 m and setting it on the lens barrel by hand, say, than what the focus assists can provide.

 

What good is a speedometer in a car when you have a radar detector and go with the flow if it beeps for a bear?

 

Good question! Why do cameras have model numbers? Or manufacterers' names? Apples do not have them and we still eat them ..