EX1 Depth of field issues

[Bob Hayes]

When I shoot wide and close focused on my EX1 at a wide stop I noticed the deep back ground was a little soft. I checked the Depth of Focus meter and I found that as the lens zoomed out it kept the focus point in the center of the field. I think most lenses pull deeper as you zoom out. The result was if I was focused at 5' infinity never got sharp but everything from 5' closer was sharp. If I put the lens on Auto I noticed that initially this was the focus setting for the lens then after analyzing the image it slid the focus much deeper to 15' which still held lens to 5' in focus but now carried Infinity. I am inclined to shift focus deeper on wider lenses. Anyone notice this issue?

[Dana Kupper]

Look into "hyperfocal distance". It is a mathematical calculation of where to focus your lens so that half of that distance and all the way to infinity is in focus. For example, if your hyperfocal distance is 15', you would put that distance on the lens, and everything from 7 1/2' to infinity will be in focus.
Understanding Your Camera's Hyperfocal Distance
Of course, to do this you will need to figure out what 'circle of confusion' number to use for the EX1. Hmm.... Barry Green suggests 0.0062

[Les Wilson]

And for a video explanation of the circle of confusion:

Depth of Field Explained (by snodart.com) on Vimeo

[Serena Steuart]

Originally Posted by Bob Hayes

I think most lenses pull deeper as you zoom out. The result was if I was focused at 5' infinity never got sharp but everything from 5' closer was sharp.

What you have is a lens that stays focussed on 5' as you zoom, which is highly desirable. Generally varifocal lenses (at least of the inexpensive type) do not hold focus on a point as focal length is changed; known as "breathing". As others have explained, if you want 5' to infinity to be in focus you must set DOF appropriately. Alternatively pull focus during the shot to bring infinity within the DoF, noting that the DoF changes with focal length.

[Doug Jensen]

Originally Posted by Serena Steuart

Generally varifocal lenses (at least of the inexpensive type) do not hold focus on a point as focal length is changed; known as "breathing".

Serena,

You have explained the concept of "breathing" backwards.

Breathing occurs as an unwanted side effect when you rack focus, not when you change focal length. The focal length appearing to change when you change the focus IS the breathing effect. Not the other way around.

Here's a better explanation:
Breathing (lens) - Wikipedia, the free encyclopedia

[Serena Steuart]

Thanks for pointing that out. I did query, while writing that statement, why I would assign a term "breathing" to the characteristic I was describing. Happy to be corrected.

[David Morgan]

I typically do stage shows where my camera is anywhere from 40 to 60 feet from the stage. The stage is usually about 20 feet deep. Where is the best spot to focus the EX-1r in this case?

thx

[Dave Morrison]

The usual "rule of thumb" on this was that the focus will hold properly both 1/3rd in front of the subject and 2/3rds behind, so on a 20 foot deep stage, you'd probably be safe focusing about 6 or 7 feet into the stage area.

[David Morgan]

seems like a plan. I'll give it a shot :-)