focusing x number of feet ahead of you.

[sbakewell1101]

hi, i am reading bryan petersons understand the exposure triangle and there is one thing that i dont understand... my lenses dont have distance meters on them at least i dont think that they do if they do i dont know how to use them hence my post (i have nikon: 18-105, 50 1.8 ,105 macro , 55-200, 70-300, anyways how do you set your focus point for a certain # of feet ahead of you'?

[zona5101]

without distance marking on the lens (and most lenses now days do not have the markings) your only option is to estimate
or I suppose go get a tape line and measure it...
or a laser range finder...

[inkista]

Get an old manual focus lens that has a distance scale?



Nikkor 55mm S f/1.2 (pre-AI).

[JFSanders]

My 18-200mm vrII has a distance scale on it. But for those lenses that don't you just estimate about 1/3 into the scene depending upon how much DOF you need at what f/stop you have set. Google DOF calculator and there a bunch that will diagram it for you so that you can get a visual feel for what will be in focus more or less and what your near focus distance will be.

Jim

[sbakewell1101]

ok i understand that but how do you physically do that in your camera? point the camera at the ground use single point focus and select a few feet or whatever then recompose?

[zona5101]

Originally Posted by sbakewell1101

ok i understand that but how do you physically do that in your camera? point the camera at the ground use single point focus and select a few feet or whatever then recompose?

most len/cameras will let you manually focus the lens. If you have a lens that doesn't have a focus ring, then I suppose you could do as you suggest...but the problem is unless you can assign the focus to a button other than the shutter button, you'll override your pre-focus when you press the shutter for the image.

[autofocus]

Originally Posted by sbakewell1101

ok i understand that but how do you physically do that in your camera? point the camera at the ground use single point focus and select a few feet or whatever then recompose?

...basically, yes. With your lens switched to manual focus, and off from auto-focus, manually focus on the point in question, don't switch the lens back to auto-focus, compose and take your shot. Remember, any movement on your part after you've established that point of focus will compromise the clarity of that point. I'd also recommend use of a smaller aperture such as f/8 for greater DOF and clarity.

[sbakewell1101]

thanks for the help.. my camera allows me to choose 1 of 11 focus points so i would be able to use autofocus... i need to get better at manual focus... its one of those things i am working on thanks guys!!

[autofocus]

Either I'm confused by your post,. or you're confused in what you are asking. If you're looking to prefocus on a given point, it really doesn't matter how many focus points you have. Example... Let's say you want to catch some action at a ball game at first base by pre-focusing manually on the bag, and wait for the action to arrive in order to capture the shot. Is this the type of thing you're looking to do?