Finally after so many months managed to get an Olympus OM lens adapter for my E-300 so that I can use my old school manual lenses from my OM-4, including that cheap and cheerful centon 500mm mirror lens.
Tried emailing olympus in september about the adapter after finding it out on the net that they did supply the adapter for free but they replied me saying that the offer ended in August :-( And they directed me to a germean reseller selling the adapter for £80!
Had a look in the town center last weekend, there is a little second hand camera shop just off Market sq. here in cambridge called Kampkin Cameras and they had the the adapter for £40! Well, slightly pricey but more reasonable so I did get it.
Now just tried with my Centon 500mm, it is slightly easier to focus on the E-300 than on the OM-4 as the focusing screen is less grainy. The focusing mirros on the OM-4 did not work at all with this lens, they blacked out. The speed is not so bad, get 1/30 on a dark cloudy day with snow and 1/250 on a sunny shot.
Still it is hard to get pixel perfect focus and there some ammount of vigneting.
Also it is hard to keep it steady, even with a light weght tripod, as 500mm lens on the E-300 gives 20x maginification!
You can find the results in the Gallery.