Focusing EOS1-v

[william_foulk]

I have a new EOS1-v and I don't understand the autofocusing system.

Will all focusing points focus regardless of the F stop I am using.

For instance, if I am using F1 (Yes, I have an F1 lens) will all parts

of an exposure be in focus even if they are in the foreground or

backgro

[mark_messerly1]

The depth of field depends one the aperture you or the auto algorithm have selected. The electronics that select a focus point work the same regardless of the lens/aperture. One exception being a lens or lens/tube/filter combination that makes the effective aperture f8 or higher. In this case, autofocus will have difficulty. Once the the focus is selected and the 'x' number of LEDs indicate the object, it will adjust the aperture to that which you have selected, or the auto algorithm has selected when you trip the shutter. If you have a wide aperture, expect a shallow DOF. For example: you point the camera toward a baseball player who is 10 feet away standing alone on the field. The background is a brick wall with ivy on it, 25 feet behind the player. Autofocus LEDs will roughly select the outline of the player. Whether the ivy is in focus depends solely on the film speed/aperture/shutter combination. I hope this addressed the question.

[cliff_lesergent]

"Will all focusing points focus regardless of the F stop I am using"?

 

Yes.

 

"will all parts of an exposure be in focus even if they are in the foreground or backgro"?

 

Not likely.

[mark_messerly1]

More info.... In the custom functions, you can select a specific focus point or points. See a manual page 38. Also, a very nice photo illustration of your question, similar to example in my earlier post, is on page 35 of the manual. Good luck!

[tom_musselman]

Hi William,

 

The autofocus system will pick a "subject" in your scene. It only focusses on a single element, the chosen subject, in the scene. It will not focus on the foreground and background at the same time. It can't. Only one focus point will actually be used to focus. The camera doesn't focus everything under all 45 points. It only uses one.

 

Besides the subject, some other parts of the scene will also be in focus. This is because of the nature of lenses in general, and has nothing to do with the autofocus system of the 1v. There will be some distance in front and behind the subject that will be in focus. The size of the area in focus is called the depth of field, "DOF". (The depth of the field of focus.) How big an area, or how much distance in front and behind the subject, is in focus depends on the lens aperture.

 

If you are taking a picture at f/1 the DOF is very narrow compared to the DOF of a picture taked at f/16.

 

Hope this helps.

[will_perlis]

In its default configuration, the AF will try to lock on to the closest object within the oval showing the 45 focussing points. You can often see that more than one point achieves that lock, but those points will all be at the same distance from the lens. This defines the plane of "perfect" focus (as the camera understands it), which has nothing to do with the depth of field.

 

You can use the 1v's DOF mode feature to adjust that plane of "perfect" focus by pressing the correct buttons and picking two objects at different distances to focus on. The 1v will then try to adjust the lens to a distance about 1/3 of the way between the near and far points.

 

However, that only gives you sharp pictures if there's enough DOF available for those objects to appear sharp in the first place. At f/1 you don't have much DOF for the system to work with.

 

In other words, the 1v's AF computer hasn't managed to repeal or evade any of the old laws of optics.

[bill_goldman]

The DEPTH mode uses the aperture value calculated for the exposure, not necessarily the maximum aperture of the lens (e.g., f/1.0) in use. So even if you are using an f/1.0 lens, there may be adequate DOF for a range of subjects.