focal length

[jrockroll]

so like canon 35mm 1.2, the minimum focal length to take a picture is 35mm?
and for 50mm 1.2, the minimum focal length to take a picture is 50mm?

If you try to take a photo of your subject that is closer than those minimum focal length, the shutter button wouldn't let you take a picture right?

I have a 5d ii with 35L and was wondering why is it that when I try to take some pictures, the focus sometimes becomes very slow. goes backward forward, trying to focus a subject. know what the problem is?

 

[Bitter Jeweler]

Look up focal distances for those lenses.

Focal length, and focal distance are two different things?
For instance, the Canon 100mm 2.8L lenses minimum focusing distance is 12 inches.

 

[jrockroll]

yes focal distance. sorry about that.
how would you determine the focal distance?

 

[Bitter Jeweler]

Google: (your lens) + minimum focusing distance

 

[480sparky]

Try looking in the back of the manual.

Or the manufacturer's website.

 

[KmH]

Most DSLR's use phase-detection auto focus. Phase-detection AF uses edge contrast to determine if focus has been achieved.

There are several shooting situations that are problematic for AF.

• little or no contrast between subject and background
• objects at different distances at the point of focus
• regular geometric patterns at the point of focus
• sharply contrasting brightness at the point of focus
• background objects that are larger than the subject at the point of focus
• many fine details at the point of focus.

auto focus is not a be all to end all, and the photographer often still has to manually focus.

Autofocus - Wikipedia, the free encyclopedia
Understanding Camera Autofocus