Exposure help

On 03/31/2011 07:58 PM, goldtech wrote:
Hi,

This is probably basic exposure how-to...but I was trying to take a
series of pics w/Digital SLR and stitch them together w/software. I
noted a problem w/exposure which I'll try to explain. I have it set to
aperture priority/sunlight. In every pic there's some beige sidewalk
at the bottom but each pic 's center is different - some have sky vs.
some trees. Looking at pics - some have dark sidewalk vs. others have
OK exposed sidewalk. Maybe camera is exposing per different center
areas so sidewalk is not taken into account re the exposure(?)

Likely. For photo stitching you must lock the exposure (the simplest way
is to use manual exposure). You also don't want the focus to change, so
manual focus is often a good idea, too.

This brings up related exposure problem I'm having as I get more into
digital photography, with auto exposure settings. Took pic of white
cat in center and pic was underexposed. Took flash pic of black cat w/
white wall in immediate background - cat looks OK - maybe a bit
underexposed - but wall was is too white/washed out.

What are strategies? How do you deal with stuff like this?

It all depends on the picture. The camera usually has several metering
modes, from "spot" where only a tiny part at the center is taken in
account to some general mode (often called matrix) where the camera
attempts to have a somewhat correct exposure everywhere, often at the
cost of not being perfect anywhere. It's your choice, as a photograph,
to decide which parts of the picture are important and should have a
correct exposure. In a scenery about everything is equally important,
unlike a ladybug on a leaf.

It's also your photographic experience that will tell you to avoid
certain lights or shooting angles. Otherwise a DSLR also has some form
of exposure correction so you can ask it to over- or under-expose.

Please explain grey card - how to use. Would it help?

Its main use is to give you a reference to remove any color bias later
(shoot it as a reference and keep it together with the other photos from
the shooting session), or to use it on the spot to set the white balance
of your camera (but this is often a bad idea).

My camera can change meter areas w/in a frame? Bracket with over and
under shots?

How else? Thanks.

One thing I do find is that even if histogram is skewed to the
underexposed left I can adjust with software and get good results.

--
Bertrand

Likely. For photo stitching you must lock the exposure (the simplest way
is to use manual exposure). You also don't want the focus to change, so
manual focus is often a good idea, too.
[]
--
Bertrand

What I do for a quick 3-picture or 5-picture hand-help pano, is to note
carefully the centre of the image (and use exposure compensation if
necessary) and expose for that, take the central picture, half press for
exposure, pan left, take, return to centre, half-press, pan right, take,
and repeat until the pano is complete, each time coming back to the
central framing for exposure (and focus). A lot easier to do than to
write about! The same principle of using manual, of course.

Cheers,
David