50-200 versus 18-55

I am a new kid to DSLR. When I use my 50-200 in the AV mode on my K20, everything looks OK. However, when I switch to 18-55 and using the same mode - AV, the images seem to be under exposed. What am I doing wrong, please,anyone?

That's a strange one, karlh.

The first thing I'd do is take a picture with each lens set to the same exposure manually, both set to f8. Plainly they should be very similar, otherwise something is wrong. And try to frame the shots similarly so that the meter is taking its reading from similar areas.

Have you tried the lenses on shutter priority - does the same effect occur?

Both these lenses change effective aperture through their exposure range but the camera should take care of that.

This is a guess, but see if this describes what you're doing:

When you're shooting a scene outdoors with a wide lens then the chances are that a good amount of the scene is sky. Sky is very bright so the camera compensates by darkening the image (to avoid blowing out the highlights).

When you're shooting with a longer lens the subject tends to fill the frame. Without the sky to throw things out of whack the camera will produce a well exposed image.

Once you know how your camera reacts to such things you can start playing with the exposure compensation to make sure you get the image you want.

Was I close?

lemmy abd hefty1 thanks. will try lemmy's test. Hefty, the images were taken outdoors - all of them, with both lenses.
Will do the test tomorrow and let you know.

Just another thought, are you using lens hoods? Using without could cause stray light to throw out metering.

greynolds999: strangely used hood with the 18-55, not with the other..

hefty1: had another look at the images. You are right, those with most sky, were overexp. Exposure compensation? Do I follow the 'Adjusting the Exposure' in the manual by turning the front e-dial, whilst pressing the +/- button. Or is there another way?

Not Hefty but you need to do with me for now
It's correct what you said, you will see the point on the EV meter move if you do that.
In the custom menu you can also remap your E-dials for those modes.
I don't know the combinations out of my head but you can map "Exposure compensation" directly under a E-dial of your choice.

I don't know which camera you're actually using so the advice I gave was generic and will apply to any camera from a basic point+shoot upwards.

On my K10D, when I'm using Aperture Priority, I hold down the EV compensation button (a divided square with "+" and "-" symbols on it) and spin the front control wheel - you can see the amount of adjustment on the shoulder LCD and in the viewfinder in the form of a little sliding bar. To reset to zero I simply push the EV button and the Green button simultaneously. Depending on your camera (and the mode) then the method may vary but the effects will be the same.

All cameras will meter for an "average" amount of light, when your scene contains a large patch of either dark or bright areas it will be thrown (cameras are quite dumb really). This is where you need to take control in order to take the picture you want, rather than what the camera thinks is best.

A little practice and it'll all become second nature.

hefty1; I got K20D. A little practice is required here, I guess. I have managed to lighten some of the imaged in my gimp and increase the contrast. They are all for my gardens of London website. The rest, I will just have to retake. Fortunately, the garden is only a short distance from Notting Hill...

The time of day that you shoot will also make a difference if you're including a lot of sky in your photos. If you shoot towards the Sun then the sky will be very bright and your subject will be in the shade; try and time your visits so that you capture what you want with your back to the Sun - this way your subject is illuminated and the sky/ground brightness balance will be more even.

Photography is all about light so you need to work it to your advantage.

hefty1: I am aware of light and time of the day. Yesterday, I started at 7am. Not only to get the early light, but also to avoid the hordes of people, who come out of the woodwork at the slightest thought of being able to strip to their basics and plonk themselves on the lawns of Kensington Palace Gardens, where I was yesterday..

If you are using average metering you could try centre-weighted. Alternatively, meter excluding the sky and lock the reading.

Thanks gartmore. Will experiment with all the suggetion over the weekend...

How about just using the Exposure Bracket Mode, chaps? Would that not solve my problem?

No, you would just have the same effect at three different exposures. Two of them could match, of course, but it would be better to get it right rather than filling cards and drives with duplicate images.

I would add to my earlier post that I use centre-weighted metering 99% of the time and it will certainly sort out the erroneous readings caused by a bright sky.

Ken