1D the 4 mp camera

Hows this camera compared to the 40d? would it be worht getting it to use along with my 40d? to replace my canon 400d

No

Its a good camera, but a 40d will outperform it in every way except build and fps

ok thank you very much

I don't know if I'm alone on this, BUT the 1D (original, Mk 1) produced some amazing images!

1. It used a nice CCD sensor which worked wonders in good light
2. It had a very weak AA filter that produced amazingly sharp images
3. Electronic shutter allowing 1/500 flash sync

The CONS I felt were:

1. "Only" 4MP, but enough for 10x8" photos or even double page spreads; taught me to crop with the lens!
2. Not very good in low-light
3. Suffers from purple corners at long exposures (a few seconds to 30s or so); forget astrophotography
4. Battery sucker... I had to modify the battery packs with larger mAh batteries.

I had all 3 cameras you mentioned... 400D, 40D, and 1D. I'd say 40D and 1D are on par with each other in terms of bang for the buck... depends what you need it for! I prefer the 1D. They both are better than the 400D except in portability.

I'd pick a 1D up if it were in good condition though I would doubt Canon would have parts for it today!