Understanding how to use exposure

massahwahl

massahwahl

VIP Member
Still being very new to the world of semi-professonal photography, time and time again I reach the point where I 'just dont know' what to do to capture a really fantastic shot. Im confident in my ability to scope out a good scene, but when it comes to getting the exposure 'just right' I simply dont get it....yet.

I want to make myself a 'cheat sheet' to carry with me with what settings are best with different situations or at least to ballpark those settings so I can make finetuned adjustments once Im in the situation.

(I dont have the 'Understanding Exposure' book yet but Ive heard its very good.)

Ive been doing research and reading a few books that talk about the subject but expect the reader to have a certain predefined understanding of concepts that I must not yet possess. So im looking for some experienced individuals to give me a helping hand in putting all of these things im learning into a understanding.

First off, mechanics. Here is what I understand, correct me or elaborate if i am missing the point. I know all of these things working together make up the good shot, but im not sure HOW and WHEN these things come into play. If you could, try and provide some examples of settings you have used in different situations, or what settings SHOULD produce good pictures.

f/stop- I dont know what the hell this means, but apparently a low one is good on lenses?

Shutter speed- How quickly the shutter opens and closes. Determines how much light will expose the image. The more light=shorter shutter speed. Less light= longer shutter speed.

Aperture- The focal length of the image as in, how the foreground focuses with the background. A smaller aperture puts the subject in focus and the background out of focus, wider aperture puts both the background and foreground in a more equal focus. Aperture interacts with shutter speed, a wider aperture requires a longer shutter speed. Smaller requires shorter shutter speed.

ISO- The cameras sensitivity to light. Im really lost on this one. I know a higher ISO=more noise but I dont really understand how to use the other ISO settings and WHEN to use them.

Metering Mode- Again, lost on this one. I use evaluative mode but dont know what the other settings are best used for.

WB- I know white balance, but I shoot RAW so its not as important.

For whatever reason, I usually lean towards shooting in the Tv mode (shutter priority right?) because the one element I understand the best is that fast moving subjects require a quick shutter speed to capture them in the moment. Even in this mode I get some very blurry pictures or very dark pictures and im not entirely sure what I did wrong afterwards.

Any help you can give would be greatly appreciated.
 
Hey there Ninja,
lets give you a quick crash course.

The main three things that your going to be working on are: shutter speed, aperture (which is the f number) and iso.
I'll just give you a quick run down of what each does, and when to use it.

-Shutter Speed- As you already stated this controls how long the shutter is open for. You camera probably ranges from a 30 second to 1/4000th of a second exposer. You would use a shutter speed of 1/500th and above for action photography. While on the other hand, you'd use a 15 or 30 second exposer for night photography (just one example).

-Aperture- Mainly this controls the DOF (depth of feild).
DOF controls how much of the shot is or isn't in focus. Using a higher F# such as 18 (smaller opening), will result in the majority of the photo being in focus, however less light is being let into the camera, so you have to compensate for that with either the shutter speed or iso. If you only want the subject to be in focus then your going to be using a lower F# 2.8 or so(larger opening). Your most likely not going to have a F# of 2.8 or less until you start spending some serious money on glass. The reason lower F#'s are wanted (and expensive) is because it allows you to shoot in lower light conditions, or allows you to gain a faster shutter speed when needed. However it's not always beneficial to shoot wide open. The lenses sweet spot is probably around F# 8.

-ISO- If you were familiar with film, you would then refer to this as ASA or the film speed. I tell people to think of it as "Fake Light", since that is effectively what it is. Since your using a Rebel XT (if I'm not mistaken) then I would recommend staying with in the range or 100-800. If you try to boost it higher then that, you'll most likely start to get very noisy shots. Granted some times it's needed. If your shotting outdoors in good light then keep your ISO as low as you can get away with, but if your shooting in less then adequate light or need the extra light for a faster shutter speed then your going to need to bump the ISO. However, resort to ISO above 800 for a last effort. First make sure your using your lowest F# and that the shutter speed isn't way above what it needs to be. Also, if you have a good flash unit, do let it go to waste.

Hope this helped.
If you need anymore help just ask.

Bob

Heres a quick example for a longer shutter:
IMGP8546.jpg

(Photobucket killed the quality so don't mind that)

This shot was taken using:
Shutter Speed- 30 seconds
Aperture (F#)- 9.5
ISO- 200

I wanted to keep the noise down so I used a iso setting of 200, so in order to properly expose the shot I then needed a long SS, in this case 30 seconds. Now I could have lowered the F# to say 3.5, however the sweet spot for my lens is around 9.5, so I decided to keep it there.

I hope that settled some confusion.
 
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that all sounds good to me nice job vroom

just one small note
is that you would probably do better not to use a hand held exposure(not on a tripod or camera support) of less than 1/125 maybe 1/60 if you really have to, because you will start to see camera shake in your images if you go any lower than that with out the tripod

Edit: i find that F8 to F11 to be the so called "sweet spot" too :P
 
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wonderful tutorial vroom! Ive been tons of research on all of this and am taking some of the best photos of my life now thta im shooting in manual mode. I also picked up the 'understanding exposure' book and that cleared up A LOT of the questions i had.
 
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