AE Lock & Difficult Shooting.

There's often times when you encounter a situation where no matter what you do you just don't seem to be able to get a well balanced shot. Either the sky overexposes or the foreground gets too dark and it doesn't seem to matter which setting you use nothing really works.
Sound familiar?
Thats where AE Lock comes into its own. The AE Lock button is the one directly below the red video button on the back of the HS20.
You find the settings in the setup menu and there are two that you need to set. The first is how you want the button to work. It can be set to toggle which means as soon as you release the button it reverts to the settings the camera chooses or you can select it to be used in an On/Off function. Just remember to switch it off when you have finished the current shot(s)
I prefer the On/Off method as it means I can recompose my image and refocus without the settings for exposure changing.

The following images show the scene in question. The camera was set in EXR Dr Mode, Auto ISO800 and Auto DR 800. The time was 8:35am, approx 35 minutes after sunrise. Conditions were frosty and the light comes from left to right. As can be seen the light at this time of the day is very low and angular and quite intense, creating heavy shadows and contrast.
The first image was taken using spot metering with -0.33 EV and centered on the middle shed roof.

The same was repeated in the second shot but average metering was selected. Why the change in metering?
While the first exposure looks good, it isn't right. The sky has suffered some burnout and the distant mountain has lost contrast and detail. The foreground shadows were a lot darker than the image suggests, in fact so dark that the black and white cows further into the shaded areas were all but invisible.

The switch to average metering didn't help either but made things a lot darker.The blue in the sky is now correct as is the color/contrast/detail of the small mountain in the background, although this too is a little darker than in reality. So we need to marry these to images together to get something a lot closer to how the scene actually looked. At this point you could try Matrix (multi) metering but all you would get is a combination of both these images without alleviating the problems.
With a little experimenting I settled on a area just by the yellow bus sign as the point for getting a good exposure, you can see the scene change in the LCD as you search for an area to use as the source of metering. Once you have a good balanced look in the LCD, adjusting the Ev as necessary, simply press the AE-l button and you will see the EL indicator come up at the bottom of the LCD showing the set exposure. Its then just a matter of recomposing and refocusing on the image and take the shot.
Note: Once AE-L is pressed you cant use any exposure control and this includes the Ev setting.

After resetting Exposure
& Setting AE-L

In the third image even after setting the AE-L there is still a little less light in the foreground. 

Final Edited Version

To offset this I adjusted the foreground fill light in Post Processing to balance out the shadows closer to me. The finished image is now very much how the scene looked at the time I took this shot. 
The only problem I encountered doing this was my fingers going numb from the cold. It was -3C at the time and I had taken my gloves off to better select the buttons on the camera. Gloves aren't your friend on this sort of occasion.