Cloud and light problems

[Webmonkeyuk]

Hi all im a newbie looking for some help with my photos, ive only had my 300d and few months and mainly use it for aircraft shots but ive been having a few problems with lighting. When its bright and not much cloud around the pictures are fine as shown here

http://img.photobucket.com/albums/v445/webmonkeyuk/General%20photos/Picture010.jpg

but when theres cloud around they seem to turn out like this, & some are darker still

http://img.photobucket.com/albums/v445/webmonkeyuk/General%20photos/Picture026.jpg

They were taken with P & TV settings and everything as standard
could anyone give me a few tips on how to get round this happening.

Thanx

[scottbergerphoto]

Your camera meter is doing exactly what it is supposed to do. It is set up to make whatever it sees 18% Grey. That is called a "Normal Exposure". You need to get to a "Correct Exposure" or what the image should actually look like. In the first picture with the blue sky, the sky is about 18% grey. The sky takes up alot of the viewfinder. There was no significant difference between the Normal and the Correct Exposure. In the second picture, the sky is cloudy and white. The camera meter is set up to give you 18% Grey as a Normal Exposure and that's exactly what you got. In a simplified Zone System, white is two stops from 18% Grey. To get a Correct Exposure for the white sky, you need to open up your aperture or slow your shutter speed by two stops. Each tone listed represents one stop.
The principle is that if one of the major tones in a subject is correctly exposed, the rest will all fall into line.

In a simplified Zone System, you use your camera on partial or spot metering to fill the partial/spot metering circle with a major tone(your reference tone) in the subject. Take a reading in Manual Mode. Then adjust your reading based on the difference between the reference tone you selected and 18% Grey

Black(4.5%)- Dark Grey(9%)- 18%Grey- Light Grey(36%)- White(72%)

From the above, select the tone your reference tone is closest to. Adjust your "Normal Exposure" based on where the reference tone you selected is in relation to 18% Grey. For Black, reduce the exposure by 2 stops, Dark Grey, reduce by 1 stop, etc.

Regards,
Scott

[aam1234]

Thanks Scott, that was very informative.

Webmonkeyuk, if you want more explanation of what Scott said, you can read this link, especially the "When to Override Automatic Exposure" section:

http://www.shortcourses.com/using/exposure/chapter3.htm

I read it few times before but always find it useful to go back and read it again.

Hope that helps