Any new DSLR should be capable of producing a good sharp A4 print. The quality of the lens will have more to do with how sharp it is than the DSLR camera (particularly at the edges of the shot)..
The difference in price of different DSLRS has more to do with features than IQ but there are IQ differences. I would expect better IQ from the 40D (but have seen no reviews)..
My general advice is..
Camera body - spend as little as you need.
Lenses - spend as much as you can afford.
The kit 18-55 lens which may come with the 40D is very poor indeed. You would need a better lens to get the best out of the camera..
You are not really comparing like with like. The 400D is more in the same league as the 510. The Olympus has a smaller sensor which has some impact on IQ.
You really must go and try them out using the controls before you decide and remember also that you are buying into a system. Check out what else there is i.e upgrade path..
*Nikon* D Eighty + Fifty - Other equipment in Profile.
Thank you, those were good points..
There is actually one review outthere: blocked URL..
I try again... Look in camera lab for a review of Canon 40D..
I agree in comparing the E-510 to the 400D rather than the 40D..
If you are familiar with DIWA testing, you will find that the 400D and the Oly E-500 receive the same rating (82%). DIWA hasn't tested the 510 yet..
And keep in mind, the E-500 does not have IS and Live view..
I'm still selling stock images made with Olympus C-750UZ PS camera. Thought in DSLR world for almost 3 years now....
Olympus kits have good lens range from 14mm ultra wide to 150mm telephoto. (same as 17-200 on APS cameras like Canon 40D, 400XT; Nikon D300,D80; Sony A700;A100, Pentax K10D, K100).
On the other side Olymus cameras have smaller sensor size. (more noise).
With Canon, Nikon, Sony(Minolta Maxxum), Pentax kits you will get same great out of box focal lengh coverage for little more $$ , but later will be easy to add new lenses from super fast portrait f/1.4 , super wide from 12-24mm, to telephoto up to 600mm. Most of these lenses were build for full frame film camera bodies (will work on next generation DSLR bodies).http://www.stan-pustylnik.smugmug.com..