-OIS intermittently stops working.
I can only go by my FZ18 but OIS mode 2 will do this, because as far as i know, OIS in mode 2 only comes in when you press the shutter button.
-Diopter adjustment wheel very loose, have to adjust it every few hours.
This could well be a manufacturing fault, and you may have to take the cam back to the shop. I'd least get them to look at it
-Images not as sharp as Canon XS with 250 IS lens
You're trying to compare the wrong cameras. A dedicated DSLR with a prime lens against a point & shoot is not a comparison.
-In bright daylight the EVF is like looking at a silouette
Maybe you had the light behind the subject ?
-Quite often at long end of zoom if you take your finger off the shutter button the lens retracts slightly causing you to refocus and more often than not to search for the subject again.
Mine does this , so i dont take my finger off. Sorted
-Low light performance not very good, images tend to be poor.
Not many cameras are brilliant in low light, but remember, its still a point and shoot. Maybe you're expecting this camera to perform miracles. It wont
-Took me almost 5 minutes to get the camera to focus on a duck at about 50 yards. Camera would beep and display the infinity symbol constantly.
Perhaps there wasnt enough contrast around your subject. I've had this problem with a £700 Sigma. If the contrast is poor, this is what happens.
My wifes Canon XS outperforms the FZ100 in focus and image quality.
It should.
Attached are pictures of a hawk taken at about 30 feet, the Canon XS photo has been darkened a little and the FZ100 lightened a little. Both cameras in A mode. Although the FZ100 produced a larger photo the Canon photo is quite a bit sharper.
Also attached are pictures of a tree the blurry photo is taken in Manual mode, the clearer picture is in A mode. IS was turned on in both of these photo's and is supposed to work in manual mode. This has happened several times in the different modes I have used.
What aperture did you set on the FZ 100 ? What ISO ? Which OIS mode ? Did you use Tele Macro AF ? Was the lens at full tele ? Did you hand hold the shots ?