kitcar Loc: Liverpool.Merseyside. UK

I hope I am explaining my self properly. Question - Cannon 400D DSLR. If I focus on a point with spot focus, would the light readings be captured as with the focus point if the shutter button is half held down ?

rpavich Loc: West Virginia

Not sure you are making yourself clear.
There are two things; focus and exposure.

They are different things.

When you hold the shutter half way down, your focus and metering settings are set then...not matter what they are set to.

kitcar Loc: Liverpool.Merseyside. UK

I presume that is my question answered, i/e correct light exposure of near subject (darker subject) then moving camera, thus recomposing frame without being influenced by say a bright sky, then fully taking shot.

kitcar Loc: Liverpool.Merseyside. UK

I presume that is my question answered, i/e correct light exposure of near subject (darker subject) then moving camera, thus recomposing frame without being influenced by say a bright sky, when fully taking shot.

rpavich Loc: West Virginia

Not sure, but I believe you are correct (I shoot manual so I don't know if the exposure is locked or not)

potmead Loc: 191miles North of London, England

Half press on the shutter will lock the exposure AND the focus on whatever you have in the centre of the frame, This may be ok for the exposure when you re-frame but depending on where you re-frame too, the image may now not be in focus.
Beter to use exposure lock or Manual

jerryc41 Loc: Catskill Mts of NY

A similar question came up a while back. There is always confusion about focusing points vs exposure points. After a lengthy discussion, I think the final conclusion was that the focusing point you select will affect the exposure.

I believe MT Shooter gave the final explanation. Maybe he'll jump in here.

BermBuster Loc: Hi Desert S.Cal

I recommend setting your camera up for 'Back-Button Focus'. I set up my 40d like this a few years ago, and wonder why they don't come this way :)
You can focus, release back button(Which locks it in), recompose and shoot.
Also great for 'manual' focus, no need of reaching around and turning off auto focus on lens, just manually focus and shoot.
Metering; will depend on how you set it up and use it; In 'Manual' mode-metering never changes (From the exposure triangle you have set).
For the 'Auto' modes, here are a couple choices in your camera;
Your C.Fn“Shutter/AE lock button”, choices;
(Taken from... http://www.learn.usa.canon.com/resources/articles/2011/backbutton_af_article.shtml)

A: Metering start / Meter + AF start
Back-button AF activation. Shutter button no longer activates AF, but of course fires the shutter. Metering is continuously updated — if you shoot a sequence of pictures, the camera takes a fresh meter reading for each one. There’s no locking of exposure, unless you separately press the AE Lock button (this last item is not possible on some EOS models).

B: AE Lock / Metering + AF start
Back-button AF activation. Difference between this setting and option 2 directly above is that when you press the shutter button half-way, your exposure is locked and won’t change until you pull your finger off the button entirely. Thus, if you shoot a sequence of pictures in any auto exposure mode, the exposure setting used for the first shot is used for each subsequent shot. Can be useful if you were using back-button AF to easily lock focus and shoot a series of portraits, where you wouldn’t expect lighting to change.

Just another option you might not have considered, Good luck !

emmons267 Loc: Arizona, Valley of the Sun

I've included a link to the 400d manual, which explains auto-exposure lock. This allows you to expose and then recompose without changing the exposure settings. This will not work in manuall mode.

http://gdlp01.c-wss.com/gds/7/0900000357/01/EOSDRXTi400DIM-EN.pdf

GrahamS Loc: Hertfordshire, U.K

This is not correct. Half press of the shutter button will lock the focus only - the exposure will not lock unless you press the AE-L button. If you don't press the AE-L button, the exposure is set the instant the shutter fires.

jerryc41 Loc: Catskill Mts of NY

From a Nikon D5000 manual, concerning Spot focus.

"Camera meters current focus point; use to meter off-center subjects (if Auto-area is selected for AF-area mode as described on page 56, camera will meter center focus point). Ensures that subject will be correctly exposed, even when background is much brighter or darker."

GrahamS Loc: Hertfordshire, U.K

I think you are confusing "Spot focus ???" with "Spot metering".

jeep_daddy Loc: Prescott AZ

There are two settings that will effect what you are concerned with.

Spot or singe point focus only affects the point in which the camera focuses.

The exposure is affected by a metering setting.

Most cameras have center spot metering which differs from spot focus. Metering settings affect only metering and focus affects focusing.

jerryc41 Loc: Catskill Mts of NY

You mean Nikon is confusing those two: "Camera meters current focus point;" You select the focus point, and that is what gets metered.

Like DX vs FX cropping, this topic will never die.

birdpix Loc: South East Pennsylvania

Kitcar, are you confused now? Interpreting your posts, I think I understand what you are trying to do. If you half press the shutter button while focusing on a dark subject with a bright background then recompose the photo will the exposure be locked? The answer is no. On your camera, the * button will lock the exposure. Assuming you are in "One Shot" mode for autofocus and "Spot Metering" for exposure, you half press the shutter button with the dark subject under the center focus point. Press the * button while still maintaining the half press of the shutter button, recompose, then shoot.

GrahamS actually has it right. Is that what you are tring to understand?