Help with 1.4 aperture

TCUphoto · Mar 3, 2011

Hi friends, I just got a new 50mm 1.4 lens last night. I didn't have that much time to play with it, but in the short time I did, I realized I was having a hard time getting my subject in focus. When looking through the camera, how do I know if my subject will be in focus...without taking 5 pictures to get it in focus?

Thanks for any tips!!

Trever1t · Mar 3, 2011

Focus and Depth of Field are 2 different things. If you're shooting at f1.4 and are fairly close to your subject I'd imagine a small plane of focus. Open your aperture or distance yourself from the subject, or both.

Hardrock · Mar 3, 2011

Don't focus and recompose at large apertures. But we really need pics to tell.

PJL · Mar 3, 2011

The depth of field when you're shooting a 1.4 wide open is razor thin, especially if you're close to your subject. If you're shooting a portrait, in most cases you want the point of focus to be on the person's eyes. If your camera is having trouble, try manually selecting the center focus point rather than having the camera automatically select the focus point(s). On most newer DSLRs, the center focus point is specially designed to work with 2.8 or faster lenses. You can then use focus lock to keep that focus and recompose the picture to your liking. Also, make sure the diopter of your viewfinder is correctly set, so that you can accurately judge when things are in focus. You can also use live view (if your camera has that capability) and manual focus.

TCUphoto · Mar 3, 2011

Thank you Trever. I guess that is what I mean, when taking a picture how can you tell if your subject is in your small plane of focus? Or is it just a learned skill?

Thanks

Hardrock · Mar 3, 2011

Focus-calculator this should help. But in reality I just played around with it a headshot at f1.4 the eyes will be in focus but the nose and ears will be out.

Big Mike · Mar 3, 2011

Thank you Trever. I guess that is what I mean, when taking a picture how can you tell if your subject is in your small plane of focus? Or is it just a learned skill?

Your DOF will encompass that point (distance) that you focus on. So if you want to to have a part of your subject inside the DOF, then you should focus on that point. Using auto focus, you could choose an AF point/area that is over the part of the photo that you want to focus on. Or you could focus and recompose, but keep in mind that changing the composition might change the distance from subject to focal point, which might mess you up when using a very shallow DOF.

If you are using manual focus, then you just have to look very carefully while adjusting the focus ring on the lens. Turn it just until your subject comes into focus, not past.

Also keep in mind that when your DOF is very shallow...even a slight movement of the camera can affect where the focus point falls on your subject.

Scatterbrained · Mar 3, 2011

Do not use focus/recompose at f/1.4! The question is what are you trying to shoot wide open that you can't get it in focus? I use my 50 1.2 wide open all the time but I'm usually a good distance from the subject. Up close the DOF is too thin even for head and shoulder horizontal shots.

Derrel · Mar 3, 2011

Welcome to playing with fire. Welcome to juggling with knives. Welcome to wire-walking without a net. Welcome to free-form rock climbing. Welcome to f/1.4.

KmH · Mar 3, 2011

Trever1t said:
Focus and Depth of Field are 2 different things. If you're shooting at f1.4 and are fairly close to your subject I'd imagine a small plane of focus. Open your aperture or distance yourself from the subject, or both.

Actually, focus and depth-of-field (DOF) are the same thing.

DOF is a physical property of the camera/lens combo, and shot set up, that defines the near and far distance from the camera image sensor the range of acceptably sharp focus will be, based on the focal point used. The DOF is parallel to the image sensor plane, so if the parts of your subject you want to be sharply in focus aren't parallel to the image sensor plane, those portions in front of or behind the razor thin DOF area won't be in focus.

As mentioned the DOF is razor thin shallow when using an aperture as wide as f/1.4. So much so that if the photographer just leans a tad forward or backward, changing the distance to the focal point, focus can be missed. Even tilting the cama up or down slightly can have an adverse effect on focus when the DOF is shallow

Focus sharpness also tends to soften a bit when a lens is used wide open so a common recommendation is to stop the lens down a couple of full stops, and that makes the DOF slightly deeper but still pretty shallow.