Focusing / Exposure on off center subject...

[Shades of Blue]

This could seriously be a big face palm for some, but I'm having difficulty figuring out how to focus on a subject (face or what have you) that isn't centered. Let's say my subject is on the far left hand of the screen. How do I meter, focus, and adjust exposure for the subject when it isn't in the center? Is it a matter of using AL and AE lock? How to you lock both and how to you do that on say a Nikon D5000?

 

[john.margetts]

With most SLR cameras, you place the important part of the picture (the eyes, in a portrait) under a focus point,, half press the shutter release and then recompose the picture with the shutter release still half pressed.

Sent from my A1-840 using Tapatalk

 

[Shades of Blue]

With most SLR cameras, you place the important part of the picture (the eyes, in a portrait) under a focus point,, half press the shutter release and then recompose the picture with the shutter release still half pressed.

Sent from my A1-840 using Tapatalk

Ok, so if that works for focus, does it also do the same simultaneously for locking the exposure? Reason I ask is that I'm trying to determine what to use the AF/AE-L button for.

 

[john.margetts]

With my Canon camera as set up by the factory, half pressing the shutter release doesbothfocus and exposure. I have set up my camera so the shutter button only does focus and the AE button sets the exposure. I don't know about Nikon cameras but they will not be a lot different. Perhaps it is manual time?

Sent from my A1-840 using Tapatalk

 

[KmH]

Ok, so if that works for focus, does it also do the same simultaneously for locking the exposure? Reason I ask is that I'm trying to determine what to use the AF/AE-L button for.

It depends on what brand of camera you use, and what metering/AF mode you use.

What camera do you have?

Nikon DSLR cameras set to Spot metering and single AF point AF mode, the camera keeps the spot metered with the selected AF point if the center AF point is not the selected AF point.

Using Center-weighted metering the metering is centered in the image frame regardless the AF mode used.
Using Matrix metering the metering of the entire frame is averaged regardless the AF mode used.

 

[NancyMoranG]

Welcome to the Forum.
Someone will be along shortly to ask.....did you read the manual yet?
I agree with John above..

 

[soufiej]

Ok, so if that works for focus, does it also do the same simultaneously for locking the exposure? Reason I ask is that I'm trying to determine what to use the AF/AE-L button for.

Shutter buttons typically pair exposure setting with focus lock. The norm is to half press the shutter release and then recompose the framing of the image. In other words, you allow the camera to focus on the subject by half pressing the shutter release button and, while holding the button at half press, you move the camera to recompose the scene.

You, of course, must first select the metering format you will require for the scene. Doing a half press/recompose with a spot metering format will provide a different result than doing the half press/recompose with a wider metering value.

Sounds like you need to read your owner's manual and sit at the kitchen table with your camera in your hands. You can also find on line tips and tutorials for your specific camera by using a search engine.

The buttons on the rear of the camera are for "back button focus". You can replace the shutter release function with a back of the camera button. Once again, check your owner's manual and on line resources. There are several threads which discuss this practice in the archives of the forum.

 

[weepete]

Just make sure you have enough DOF to focus recompose if using that method, or you may find that you've changed the plane of focus by moving the camera.

I tend to keep my subject on an AF point and shoot wider than I require and then crop down in post to sort the composition.

 

[Derrel]

As weepete mentioned...make sure you have enough DOF to "cover" any focus differences. I have JUST set up a quick test with a steel rule, and I set up exactly 90.0 inches from a wall; At the center of the frame, 90.0 inches; at the left and right sides, 95.5 inches; with many lenses, a 5.5 inch discrepancy will make the focus "off". At close ranges, the difference is substantial between center and edge distances, and can exceed the depth of field. At longer distances, the effect would be less noticeable most of the time.

If you're shooting at a wide aperture, like f/1.8 or f/2 or even f/2.8, a 5.5 inch discrepancy at 9 feet is a big deal.

 

[AKUK]

Just to add to the already great advice, if you want to maintain exposure on your subject, simply place them in the centre of the frame with your metering mode set to spot and take a photograph in aperture priority mode, at your desired aperture. Look at the EXIF data and make a note of the corresponding shutter speed that was used by the camera. Then put the camera into manual mode and dial in the same exposure triangle variables (shutter, aperture, iso).

Providing the light source is constant (a lamp as opposed to sunlight which changes throughout the day), and your subject doesn't move nearer or further to it (inverse square law), your exposure will remain the same regardless of your position/framing (well apart from maybe some lens vignetting). I tend to move the focus point onto my subjects eye if possible, rather than focusing and recomposing. As I tend to work at reasonably close distances and like to maintain a shallow DOF in many of my shots, focusing and recomposing can result in OOF shots.

Failing that, I tripod mount and use live view mode and focus with that, to ensure accurate results. Depending on what and how you're shooting, this isn't always possible, as it's a slightly more long winded process. If you do have the time though, it should ensure the sharp images and won't have you swearing at the monitor when you transfer the RAW files to the PC and discover how many are destined for the recycle bin because the focus is off.