Focus with a zoom

[Thespudster]

Hi, newb to this forum!

I have a question that has bothered me for a few years, but I have not seen it answered anywhere.

When I use a zoom, say my Canon EF-S 18 - 135 mm, and am using it at a wider angle, I often want the distant objects as in-focus as possible, such as landscapes. I will often zoom out, focus on my subject, and then zoom back. If I focus while at a wider angle, then I zoom in, what looked in focus is often actually not in focus, and this is shown when I enlarge the photos.

So my question is, when I zoom in, focus and zoom out, will this change my focal point from what it was at the tighter angle? Since the lenses are moving within the zoom, I imagine it is. But I cannot come up with a better way to get a distant object into better focus with a zoom lens when shooting a wider angle.

 

[2WheelPhoto]

youtube search "aperture tutorial" and" landscape photography tutorial" and you'll find a plethora of good info

 

[joealcantar]

I would leave the zooming in and out stuff alone. If you zoom in or out to you focal point you want to use "LEAVE IT THERE" and focus at that focal point. Here is a link that covers Depth of Field etc. to give you an idea of how it works.
Online Depth of Field Calculator
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Shoot well, Joe

 

[scifitographer]

theres two types of zoom lenses, parfocal and varifocal. parfocal lenses maintain the focus when you zoom, varifocal lenses don't maintain the focus as you zoom the lens in and out. it sounds like you have a varifocal lens.

 

[Overread]

Most zooms are varifocal, its rarer to get parafocal ones even in the L range of zoom lenses simply because its a far more complicated optical formula and, up until the release of video into DSLRs there was never a great demand for retaining the focus as you shift through the zoom range, esp in the days of AF when you just refocus.

The key is thus to set the focus at the focal length you want to work with, make use of the outer AF points when you can and also use manual focus if needed (though admittedly this is harder with modern DSLRs which lack AF aids in the viewfinder, if you've a newer DSLR with liveview you can often use the magnify function to zoom in on a select bit of the terrain and manually focus very accurately to that point (tripod, beanbag or similar support is thus needed for this to be of use). It's one reason liveview is very popular with landscape photographers for allowing them accurate focusing at distance.