focus point question

[santer36]

hello, i just purchased ann 11-16mm tokina 2.8 of course its not out yet and i

will be waiting for it. i have a question i just asked myself. this is

basically a question for any lens really. i am looking to do indoor wedding

pictures and use this lens spec. for indoor pics during the ceremony of the

entire church. its get that the lens is fast but what about depth of field for

this type of shot. if i stop at 2.8 and i get 3 different focus points to lite

up (from the rear of the church) am i going to have in focus and out of focus

areas in my photo?

also, what does the term focus to infinity mean? i guess i know what it means

but how do you achieve this? thank you in advance.

joe

[ronald_moravec1]

Focus 1/3 of the way from the nearest required focus point to the farthest required focus point. At some point near the center will be the real focus point and the others will appear to be sharp based on the the tolerence of the print ( circle of confusion) and the F stop in use.

 

If your lens has a debth of field scale, pick the F stop marks near and far on the scale , then find the distance to required near and far points, and focus so the near and far points fall within the marks on the scale.

 

If the lens has no scale due to cost reductions, then then you need to consult a table.

 

A fast lens may be of no benefit, but a tripod might , so you can use a small enough stop to get all close to focus.

[santer36]

sounds good ronald. thank you. i will be using a tripod for that type of photo. ty

[paul_sokal___dallas__tx]

With a focal length that short, DOF is not going to be much of an issue except for things very close to you, assuming you're focusing on the ceremony.

[William Michael]

As an example of it not being much of an issue . .

 

If you have the lens at the most telephoto end (i.e.16mm) and set it wide open at F2.8 and focus at around 15 ft, everything will be in acceptable focus from about 8ft to infinity.

 

Decreasing the aperture, and / or widening the FL will increase that DoF.

 

Other issues you might consider is that the lens will most likely have a Light Fall Off vignette at the wide end when wide open or close to it.

 

Also the IQ is likely to be at its (relative) worst wide open and perhaps at the widest FL wide open.

 

To address both these issues you might consider, using F4 if you want to take advantage of the 11mm FL.

 

WW