Distance settings

[Brill]

Bryan Peterson's "Understanding Exposure" is a real good book, but he's not real specific in explaining some things.
He talks about Distance Settings in the DOF sections and I can't get it. He says to preset your focus by the numbers at the end of the lens--????
He says, choose your aperture f22 and then align the distance above your distance settind mark on the lens. Your focal length will determine which distance you choose.???????
Can anyone explain this for me?

[Dave B]

Hi Brill,

Not exactly sure what he means by "preset your focus by the numbers at the end of the lens" unless he's talking about Depth of Field Scales. Some lenses do not have these scales, those that do sometimes have them etched on to the lens barrel and some have them positioned under a clear viewing window.

If this is what he means then this link explains it better than my cumbersome typing

Dave B

[rpcrowe]

Some lenses have a distance scale on which you can set your focus manually and without any assistance from the focusing capability (either manual focusing or auto focusing) of your camera.



Using the distance scale on the above lens, you can pre-focus the lens to any distance you might need. This was a very vital capability in the days of manual focus cameras when focusing might be somewhat slower than todays auto focus. Say if you were shooting an image of an athlete running, you might decide on a spot a certain distance from the camera, prefocus the lens by aligning the estimated distance of your shot with the yellow marker and shoot the picture as the athlete crosses the imaginary line.

Of course, in really early cameras, there were no rangefinders built in. All focusing was done with the distance scale on the lens.

The lens in this image has two distance scales, one for meters and one for feet. The photographer would just choose the way he/she was used to judging distances with.

You will also notice that the lens has two sets of f/stop indicators, One on each side of the yellow focus point. This indicates the distances in focus for the f/stop you are using. As an example if you were shooting with this lens using f/16, you would be in focus from a bit over 2-feet to 10-feet where the f/16 indicators match up with the distance scale.

You will also be able to choose the hyperfocal distance for any f/stop by aligning the f/stop (to image right of the yellow focus point) with the infinity mark on the distance scale. The infinity mark looks like the number 8 on laying on its side. You will then be in focus from infinity to wherever the corresponding f/stop to image left of the focus point corresponds to the distance scale.

Another use for the distance scale was in determining exposure for manual exposure flash units by dividing the shooting distance into the guide number to determine the correct f/stop. A photographer might just look at the distance scale of the lens to determine the camera to subject distance.

BTW, the red dot image right of the yellow focus point is the infrared focus point. Shooting with infrared film you would focus the camera normally and then move the red dot to where the yellow line had been. If you were focusing using the distance scale, you would use the red dot as the focus point when shooting infrared film. That way, since the focus point of infrared light is different from that of visible light, you would have correct focus.

Although they are still handy things; with today's autofocus lenses, distance scales are often dispensed with. As an example, as a cost cutting measure; Canon did not include a distance scale on the 50mm f/1.8 mk.II (nifty fifty) lens. The original Mk.I model had a distance scale.

It is a lot easier to use today's cameras with autofocus and auto exposure. However, in the "Dark Ages" when focus and exposure were done manually, the photographer would actually be forced to gain a better concept of what the camera was doing...

[PRSearls]

There are apps that can give you DOF and hyperfocal distance information for any combination of focal length and f/stop. I use "Field Tools" on my iPhone.

Paul S

[Dave B]

I use "Field Tools" on my iPhone.

Hey Paul ...... TVM for the suggestion. I will give this one a bash

Dave B.

[William W]

Nice answer,

A Rokkor Lens, Richard?

WW

[rambler4466]

Most of the new lenses do not have the focus rings on them any more. The apps work great. But, you still have to estimate the distances. Hmm...is that subject 60 feet away or 80. Ever tried a rangefinder that golfers use to find distances to the pin? They work if there is clear sky in the background, but if you are focusing on a rock in the woods, the rangefinders might not recognize your target. Any hunters with scopes? Maybe they are better, but maybe save the money for a new lens! Good luck figuring out the dial system:
http://www.expoimaging.com/product-d...of-Field_Guide

I just focus on two or three objects at various distances and hope one will be correct.

BTW If you use filters there is an app called ND Timer that will help you set the correct shutter speed. For example if you are shooting at 1/125 and using a ND 2 filter the app will tell you the shutter speed. No need for math in your head (eg. correct exposure shutter speed is 1/125, you have an ND 2 one stop filter, you shutter speed can be set to 1/60) (10 stop filter at 1/125 should be set to 8 seconds) Right? Can you do the math?

[dubaiphil]

Distance scales are one of the things which can make a manual focus lens faster to operate than an autofocus lens - particularly in low light when autofocus might hunt to lock. You can pre focus and not worry about attaining a focus lock as long as you subject is within the acceptable range marked on the scale for focus.

Sometimes with autofocus lenses I do the same sort of thing - pre focus on a point in a scene where I think something interesting is going to happen (using the AF-On button) and then take the camera away from my eye, bringing it back up to my eye at the last possible instance to shoot, as my shutter release does not affect my focusing. This way you can shoot on the street a lot more subtly.

Also, a lot of the older lenses with distance scales have a hard stop at infinity - very useful when shooting in the dark and shooting cityscapes/landscapes/nightscapes