question regarding focusing technique

wheresdavid

in his book "understanding exposure", the author writes, a perplexing question where the heck do you focus [concerning how to get DOF from foregound to bachground] ... The solution to this common dilemma is simple: you don't focus the lens at all, but rather preset the focus via the distance settings."

question, how do you preset the focus via the distance settings"":scratch :dunno

thanks

Dave

HiSPL

By using this window on top of most lenses. This little window will do two things for you that are very useful.

1) You can calculate the distance to your subject and focus the lens without looking through the viewfinder. If you know how far away something is, you can always get it in focus.

2) You can use the auto focus and get a lock on something in the distance, then look at the distance window and see how far away that item is from you. This is especially useful if you need to calculate a flash exposure for something that is an unknown distance away.

BTW this is the only way to focus a rangefinder camera. Hence the name!:D

Nikolai

wheresdavid wrote:

in his book "understanding exposure", the author writes, a perplexing question where the heck do you focus [concerning how to get DOF from foreground to background] ... The solution to this common dilemma is simple: you don't focus the lens at all, but rather preset the focus via the distance settings."

question, how do you preset the focus via the distance settings""

thanks

Dave

David,

In the days of yore, when SLRs were not even in existence, focus by distance was the only way the things were done. Given, there were no zoom lenses either.

An avid traveler like yourself most likely use zooms. And unless you work with expensive one that feature same aperture throughout the focal range (EF-S 17-55 f/2.8, EF 70-200 f/2.8, EF 24-105 f/4, etc.), the focal distance WILL change while zooming.

Also, due to the 1/X nature of the infinity focusing, any such scale/gauge becomes quite useless at the distances longer than 30ft (and often longer than 10 ft), while at the same time DOF may remain quite shallow.

When I have to use "focusing by distance" I tend to use hyperfocal distance (www.dofmaster.com) myself, since it's more reliable.

HTH

Stu Engelman

Hi Dave,

Per the previous responders, in the days of film cameras, lenses had a DOF scale on the lens. This let you determine the range of clear focus for any focal distance (the "from/to" points of the range in your scene disclosed by a range finder). Since the scale needs to change with lens length, and zoom lenses are all the rage today, this strategy has fallen into
disuse (i.e., lense manfacturers no longer provide DOF scales on their products).

You could of course employ the above general strategy by carrying around the lens manfacturer's DOF charts. This, in combination with a VERY expensive range finder, would permit accurate focusing for landscape shots (closer pics could be accomodated by a much less expensive range finder). While this process would "work," it is very inconvienient to carry the
DOF charts around and refer to them.

A better solution is to learn to use your DOF preview, which takes some practive. Your camera's DOF preview shows you what your pic will look like in your viewfinder before taking the shot, taking into account the aperture setting. The DOF preview will get darker as you stop the aperture down, and not be reflective of your pic's exposure level. The main thing it does
reflect is the effective range of clear focus.

While, as stated, using the DOF preview will take some practice (mainly, learning to see where focus falls off, even in dark previews involving high F stops), try the following "recipe" and see if it helps (the recipe is best done with a tripod):

(1) Set your camera to manual exposure mode
(2) Set your white balance
(3) Set your ISO to 100
(4) Compose your shot
(5) Set your focus on a point about 1/3 into the range between the closest and farthest points you want in clear focus (i.e., closer to the front point)
(6) Use your DOF preview to find the widest aperture that renders the desired range in clear focus
(7) Meter the shot to determine the shutter speed
(8) If the shutter speed is slow enough to cause potential chromatic noise (say above 1/30 second, depending on camera), use a higher ISO and remeter. Try to keep ISO under 250 and shutter speed under 1/30 second (these are general guides, which of course you can fine tune based on your camera model)
(9) Take the shot!

Expect this process to be a little slow at first, with results improving over time. Don't expect perfection at first, as it takes some time to master using the DOF preview.

Stu