focusing - Help needed

hey everyone,

i was trying to take a picture the other day of a bunch of trees lined up in a row and i kept the focus on infinity so that everything would be

in focus, but the trees that were closest to me were still out of focus while everything behind it wasnt. i dont know if it has to do with my

lens or what, im shooting on film with a canon rebel g, and my lens size is 55. its 28-80mm 1:3.5-5.6 II and its a sigma zoom lens. any

help would be much appreciated.

If you focus your lens on infinity, only those objects at infinity, and those covered by the depth of field, will be in focus.

See:

http://www.photo.net/learn/making-photographs/exposure

And scroll down to the part on depth of field.

The main problem you had is probably that the camera chose a fairly wide aperture, which would limit the depth of field. For landscape work, I think that focussing at infinity (or the furthest subject in the image) is often preferable to hyperfocal focus technique. Harold Merklinger exlpains why here:

http://www.trenholm.org/hmmerk/DOFR.html

However, you still need to use a narrow aperture. I'd try f/16, or maybe even f/22 (set the camera to Av mode). You may find that you end up with a slow shutter speed in anything but good sunshine - so you might also need to use a tripod, or at least brace the camera against a tree/fence post for added stability, using the 10 second timer to help minimise camera shake.

>> Harold Merklinger exlpains why here:

Harold does a terrible job explaining this concept. I can't follow what he means. He states:

Set the focus at the distance of the most distant object. Then set the lens opening to the size of the smallest object to be resolved in the foreground. No calculations needed!

But how is one to determine the size of the smallest object? In his example, he says the canon is 11mm. Obviously, the canon is bigger, so I can't follow what he means.

Be careful when reading Merklinger. What it is saying is ""All objects in size of 1.4 mm and larger will be resolved (show up)". They may be soft and out of focus, but they will be there. His techniques aren't so much about good focus but just getting objects to be on the film, blurry or not. There is a bit of discussion on this old thread:

http://www.photo.net/casual-conversations-forum/00QOd9

Be careful when reading James Dainis too! Let's say your trees are beautiful autumnal beeches with roundish

leaves an inch or so across. If you use hyperfocal technique, you might focus at 2 metres with the lens at 28mm

using an aperture of f/16. Consider a tree 30m (~100ft) back in the avenue. At that distance an individual leaf

if perfectly sharp would cover roughly 1/1000th inch on film. However, the degree of blur of each point in the

leaf would be the same size - so leaves would appear as a blur (and further away in the avenue as a mush of

colour). Focus instead at the far tree at say 300m (in practice not significantly different from infinity focus)

and the blur of each point in a leaf at 30m is about 20 times smaller, allowing the leaf to appear. In practice,

you might be limited by the resolving capacity of your film, especially for the most distant trees.

Now consider the nearest tree - say 3m away. Each leaf is 1/100th inch on film, because it is 10 times nearer.

With hyperfocal technique the leaves will be about twice as sharp as with focus at 300m. But all leaves will be

visible, and you'll be able to pick out the central vein. If instead of f/16 you took the shots at f/4, then the

near tree would be 4 times as blurry in either case. Only the furthest tree would appear sharp at the long

focus distance; it would be quite blurred to the point where you wouldn't be able to distinguish medium size

branches using hyperfocal technique.

The key message is that it is most important to ensure that you use a narrow aperture to maximise depth of field

(the choice of f/16 or f/22 is a rule of thumb that applies to 35mm film and is related to avoiding loss of

sharpness to diffraction effects). You may wish to experiment with the alternatives of hyperfocal and infinity

focus and decide which you prefer.

If you want to understand how landscape photographers manage to do even better, then you will need to master

using tilt on a tilt/shift lens, or using a large format camera that offers equivalent movements (and more).

http://www.cambridgeincolour.com/tutorials/tilt-shift-lenses2.htm

>>Now consider the nearest tree - say 3m away. Each leaf is 1/100th inch on film,

So in order to use Merklinger's technique, you have to calculate how large each object will be on film?

The Rebel G is a 35mm film camera, so comments about using film are appropriate. If you want to compare the consequences of using hyperfocal technique and Merklinger's method, you need to do some calculations. I use the comprehensive calculators here:

http://www.vanwalree.com/optics/vwdof.html

and here:

http://www.eosdoc.com/manuals/?q=jlcalc

To use Merklinger's method is actually far simpler with today's lenses and autofocus systems than attempting hyperfocal settings: you simply set the aperture (chosen to avoid diffraction softening, but otherwise maximise depth of field) and focus on the furthest element in the scene, regardless of lens focal length.

With hyperfocal settings, you need to refer to a table of hyperfocal distances appropriate to the focal length and aperture and sharpness criterion you use and ensure that you select a combination that covers your closest subject: then you need to find a target at the hyperfocal distance to focus on (perhaps you need to carry a tape measure). Alternatively you could calculate the hyperfocal distance from the formula (f^2)/NC +f. All this elaborate procedure is because modern lenses have very imprecise distance scales (if they have one at all) and lack aperture marks to show the depth of field range.

It's worth noting that hyperfocal distances are rather sensitive to the sharpness criterion - and that the sharper your criterion, the further is the hyperfocal distance. Moreover, since the closest subject that meets the sharpness criterion is at half the hyperfocal distance, you need to close down the aperture further to achieve a higher sharpness criterion: however, if you close the aperture too far you will lose sharpness to diffraction at all subject distances.