Confused about metering & focus!

maggie1969

Hi Everybody,

Please, please forgive me if the following questions seem really dumb - they come from a dslr newbie!!

Ok my problem is with metering a scene, mostly landscapes, and then focusing.

So as far as I understand to meter a scene, I point my 300d (in AV priority) at a point, let's say in the sky, that I want to meter, wait until my camera beeps (I use AF mode on my lens), press the shutter halfway to lock the exposure, then recompose and take the shot.

So am I correct in saying that when my camera beeps it has found focus?
Or has it found a metering spot too?
Are these AF points for focusing and metering too?

Because when I meter/focus off the sky and look at the shot after on my pc, the foreground if usually out of focus.
Is this where my f stop comes in?
Does a high f stop ensure that my foreground will be in focus no matter where I meter/focus from?
But if I use a high f stop and meter/focus from the sky then the foreground is usually too dark!! And vice versa.


And one other question please!! How do you use the distance scale on a lens?
Do you use it in AF or MF mode on the lens?

So confused (as you are probably now after reading this!!!). If anybody can help me I'd be so grateful!

Glowing

Hi there, this is a bit rusty for me so I hope the following makes sense.

When you half press the shutter, all you're doing is focusing on the sky, hence why when you take the picture with that focus setting, the foreground is out of focus since you're already set up to focus on infinity.

When metering, assuming you're using the Av (you set the Aperature, the camera looks after the shutter speed and exposure) or other semi Manual setting, by just pointing your camera at the sky, it's automatically taking a light reading. What you need to do next is to adjust your exposure levels so it is correctly exposed for the light coming from the blue sky. Then when you've adjusted the light meter, you can then point at your subject and half press for focus. Since you'll be using a manual (or semi-manual) mode, the light meter won't readjust and you should have correct settings.

Regarding F stops (or aperature), increasing the f-number by one stop reduces the light by a factor of 2. Practically speaking, the lower the f number, the shorter your depth of field, so less of your scene will be in focus. If you use a larger F number such as 11 or 18, (you'd typically use this setting for scenery), then most of the scene will be focused. For close up work or portraits, then a lower F number will give you that sharp-foreground, fuzzy-background that can look so well.

Now I'm rusty but I hope all that is correct and will help you understand a little more ... you'll get the hang of it!!

Thirdfox

SLR photography can be daunting at times, don't worry we all got through it!

I would recommend you to get a book on photography from the library - it will teach you the basics of aperture, exposure, focus, shutter speed, ISO etc.

But to answer your questions (I use a Nikon but the 300D should operate similarly):

1. If you half-press your shutter button the camera will focus itself and lock focus - if you recompose then the focus will remain at the same distance unless you release the shutter release button.

There may be a button on your camera to lock the exposure (usually labelled as AE Lock - check your manual) Using this function you can meter off the sky, lock exposure, recompose and focus on what you want (whilst keeping the exposure value).

2. Metering has various modes: matrix, center-weighted and spot (the 300D may not have spot). Matrix will look at the whole scene and calculate exposure. Center-weighted will look at the whole scene but give more emphasis on the central area and spot usual is a small circle in the middle where the exposure is calculated from. Check your manual to see how to switch between modes.

So AF points, depending on what mode you're using, does not decide the point where exposure is calculated from.

3. F-stop: this is what aperture your camera lens is opened to - the larger it is numerically e.g. f22 the more there will be in focus. But if you meter (and focus) on the sky then focus will probably be set at infinity and very little of close foreground will be in focus no matter how large you set the aperture to. To confuse you even more we normally say "stopping down" to indicate a larger numerical aperture value

4. High f-stop resulting in dark pictures: shutter speed, f number and ISO are all linked - if you change one without balancing the others then the exposure will change. The larger the f number the slower the shutter speed to get the same exposure e.g. f8 1/500sec = f11 1/250sec So the problem you may be getting is that shutter speed has not slowed down sufficiently for you to get the same exposure on a high aperture value as on a lower one.

Also I would expect the exposure to be very dark if you meter off something very bright like clouds. Metering off the whole landscape may be the best thing to do - not to confuse you further but using an graduated ND (neutral density) filter may help in bringing the brightness of the sky down to around that of the landscape.

5. Distance scale: wow, I haven't seen those in a while (I've been using "cheap" consumer lens). You can use it either in MF or AF, normally it is used in conjunction with your depth of field scale to tell you how much of a particular scene will be in focus at any given f-stop. After you have focused on your subject look at your scale - the depth of field scale will give you the two points where the area of focus is in. My explanation is inadequate without some visual aids so may I direct you to this website http://www.dofmaster.com/hyperfocal.html where you'll also learn of a potentially very useful "hyperfocal distance" focusing (quite useful in landscape photography actually!)




Whew! That took a good 15 minutes to write - hope it was of benefit! If you need further clarification on certain points be sure to ask. We're here to help

Enjoy your new camera (even if I am from the "opposite" camp )

Muineach

maggie1969 wrote:

So as far as I understand to meter a scene, I point my 300d (in AV priority) at a point, let's say in the sky, that I want to meter, wait until my camera beeps (I use AF mode on my lens), press the shutter halfway to lock the exposure, then recompose and take the shot.

When you press the shutter halfway then recompose, make sure your not letting go of the shutter button while recomposing, otherwise it's going to meter/focus again when you press the button.
When the camera beeps, in the viewfinder it should flashe a little red light to show what it's focusing on.

I generally use AF for most of my shots (wildlife,parties etc) and only get to use MF for set up shots, macros or landscapes where I have time to work on a tripod and get to be really picky about it :rolleyes:

hmboards

Hi Maggie,

Much of what I will say is repeating what was said above, but I have a 300D too. They aren't dumb questions either...

maggie1969 wrote:

So am I correct in saying that when my camera beeps it has found focus?
Or has it found a metering spot too?
Are these AF points for focusing and metering too?

It beeps when it has found focus (if the lens is set to AF). It does meter at the same time, but there are no beeps associated with that. The metering area is usually bigger than the focus point. How much bigger is configurable on the camera (centre-weighted average etc.) I wouldn't worry too much about that just yet. The 300D doesn't have spot metering.

maggie1969 wrote:

Because when I meter/focus off the sky and look at the shot after on my pc, the foreground if usually out of focus.
Is this where my f stop comes in?
Does a high f stop ensure that my foreground will be in focus no matter where I meter/focus from?
But if I use a high f stop and meter/focus from the sky then the foreground is usually too dark!! And vice versa.

The reason the foreground is out of focus is you are setting the autofocus as well as the autoexposure when you press the shutter half way. If you want to set your exposure on something that is closer/further away than the subject, there's a few ways you can do this:

1. Use manual exposure instead of AV. Set your aperture to what suits the subject, and then adjust the shutter speed until your meter reads that your exposure is correct. Then point the camera at your subject and pressing the shutter release half way will just focus.

2. Use AV as you are already doing (assuming landscape shots rather than moving subjects), but when you are setting your exposure (off the sky for example), use the AE lock button instead of pressing the shutter release half way. The AE Lock has a * icon above it. Then point at the subject and pressing the shutter release half way will just focus.

3. Do everything the way you already were, except use manual focus.

(1) above would probably be the best option if you have the time to experiment. After you take the shot you can examine the histogram on the camera (press Info when looking at the photo) and adjust the shutter speed if necessary.

A high f-stop does mean than there will be a larger Depth of Field, so more will be in focus between foreground and background, but that doesn't seem to be your problem (how you are using AF is). High f-stops can be good for landscapes though.

If the sky is very bright then you will end up with everything else underexposed. Blue skies and be okay for metering against, as is green grass. If you have a really bright sky you would ideally use a graduated filter to darken the sky and end up with an overall well exposed image. There are ways of fixing the issue in photoshop or similar software too. Try and get hold of the Understanding Exposure book you will see mentioned on this forum quite a bit. It will help with some of your questions. The 300D user manual will help with the exposure lock settings, histogram etc.

maggie1969 wrote:

And one other question please!! How do you use the distance scale on a lens?
Do you use it in AF or MF mode on the lens?

If you know how far you are from the subject, you can use it to focus in MF mode.

maggie1969

Thank you so much guys for replying in such a detailed way - I really appreciate it!!

I think it's much clearer now. I will start experimenting again tomorrow and use all the great tips you've given me!!

Thanks so much again!!

Thirdfox

You're very welcome and hope to see your shots soon!

kensutz

I guess maggie asked the questions I was wondering about today when I tested out the 400D. Although it was a bit frustrating and the weather wasn't great I still managed to pull out a couple of decent pics but now I get the whole f-stop and metering stuff I'll test it out again in the morning.

Sorry to hijack the thread but can anyone recommend a good DSLR book to read up on, especially covering such items as maggie asked.

hmboards

kensutz wrote:

I guess maggie asked the questions I was wondering about today when I tested out the 400D. Although it was a bit frustrating and the weather wasn't great I still managed to pull out a couple of decent pics but now I get the whole f-stop and metering stuff I'll test it out again in the morning.

Sorry to hijack the thread but can anyone recommend a good DSLR book to read up on, especially covering such items as maggie asked.

Most of the books on "digital" photography I've seen concentrate on digital editing and effects rather than photography. There are some great books available on photography in general. You will see Understanding Exposure recommended often as quite a few here seem to have it. It includes information on ISO as well and how it affects exposure. Recent threads suggest it's not that easy to get hold of locally, but you could pick it up online or order it in through your local book shop or library...

nilhg

This might be of some help