I'm new to digital SLRs and debating between D40 & D80. I've used Nikon N70 few years ago and then have been using Canon Powershot S45 for past 4 yrs or so.
Here are my key requirements:
1). Faster operation: Instant startup (less than a second), focuses and takes photo quickly 2). Capture fast moving action + continuous shooting (aka rapid fire shooting or burst shooting) 3). Fully automatic + complete manual control in case I need to exploit 4). Good resolution: at least 6-8 MP, more is ok 5). Reuse the zoom lens (Sigma 100-300mm F4.5-6.7 UC) and filters bought for Nikon N70
With D80 double the price of D40, which of D40 & D80 will serve my needs better ?
The Sigma lens you have will not autofocus on the D40, but it will work properly on the D80. Also, the D80's more sophisticated AF system would be better suited for the fast action shots that you mention.
Arun the D80 has the cam 1000 AF system this system is the same as in the D200. With the D80 you have eleven AF spots this makes it easier to focus on off center subjects without moving the camera, the D40 has only 3. Next the cam 1000 is more sensative in low light making it easier to focus in darker enviorments.
Last the D80 has an internal focus motor that turns a screw in the lens to focus. The D40 can only use lens that have thier own motor built in this is called AF-S for Nikon and HSM for Sigma at current Sigma is the only after market lens maker that supports HSM/AF-S lens, Tamron and Tokina do not have AF-S lens so they will not auto focus on the D40.
Hope this helps Jim
PS the viewfinder is much larger in the D80 than the D40 this is a huge help for me since I wear glasses.