Sensor 14.2 vs 16.2 MP.
- D7000 better but who cares about MP like so many said
Auto focus 11 AF vs 39 AF; 0 cross type, 9 cross type; multi cam 1000 auto focus module vs multi cam 4800DX focus module
- Mumbo jumbo to the amateur. Extra AF pts and latest technology are great, but perhaps not worth upgrade. I wanted the 51pts on D300s, but settled on 11pts of D90, I still use the joystick to select my focus pt most of the time. Yes 51 (or 39) would be better, but it's not the be all end all. 11pts work fine if that's your hangup.
no custom exposure modes
- Not sure how these will work on D7000, but I always find myself at -0.3 or -0.7 on the D90 and if the custom settings remain that way after a 2-button reset in other modes, this could prove more useful than one might think.
metering 420 pixel vs 2016 pixel
- Improved technology...Would I buy a D2x over a D90? Technically a pro camera for a high consumer model? Well the technological advancements could very well make the D90 more attractive. I wish I knew what this particular advancement means, but we'll know soon enough after hands-on reviews. As above, I find the D90 meters bright and some have complained that D300s metering is different/better. Not sure if D3100 vs D7000 vs D300s is the same deal.
no AE Bracketing
- If you plan on doing HDR or you are not sure about your lighting and metering in modes other than automatic, this can prove useful. On my old D40, I learned to do HDR using more than 3 exposures easily. D90 with only 3 max (same as D7000), HDR stills works but you might want to use the manual technique anyway to get more shots. That's it for HDR. As for regular family photography or a tricky sky, etc. 3-shot bracketing can be nice to have shooting in burst mode where you take the 3 shots (or 2) to get the one you want...drawback being you have tons of huge files later and pull your hair out selecting them OR the good shot is on the dark/light setting. Doing same on a camera with no bracketing is not easy. Conclusion: It does not sound like you want bracketing, but neither did I and I personally like having it despite it pissing me off as often as it helps. D3100 does not have bracketing apparently...you might not miss it. Again, long story that depends on what you plan on doing or how much you already undersand.
iso to 3200 vs to 6400
- Again technology. D90 better than D40. D7000 professes much better than D90 (rivaling the D700 so they claim). Not sure on D3100, but again depends on what you shoot.
penta mirror type viewfinder
- Yeah whatever...we're amateurs, it'll do
only 230,000 pixel display vs 921,000
- D90 screen rocks, but still get blurrier pictures than you tought you had looking at screen. Nothing jumps out at me that these screens (D3100 or D7000) are superbly better. I'd love to see first hand, so take my comments loosely.
more wireless flash modes
- You can buy either a sync cable to get flash off camera or you can buy Chinese wireless triggers...you need to manually set your flashes in the latter case. I tried briefly the Nikon CLS with my D90 and I find it a bit cumbersome, but I'm still learning. Realistically, I would not drool so much over this feature, but like everything it's there when you need it if you have it.
continuous shooting 3 fps vs 6 fps
- Aside from a zillion files on your PC, how can one not be happy with more frame rates. 3 is fine, but 6 is better. Kids do move quickly even for a DSLR. Another technical advancement for a relatively still-amateur camera (D7000).
smaller and lighter
- I like the big camera, but the bag gets heavy with lenses and stuff.
The one thing mentioned previously and I'll say again is the buttons. I have not studied the D3100 in great depth, but the D40 had one programmable button. I chose ISO (push the button while turning the thumb wheel and your ISO changes). Otherwise on the D40 (and D5000, so I will assume D3100) you need to push the INFO button, then move the joystick to your desired change on the rear screen and use different ways of changing the setting. The D90/7000 line has a few more buttons where you can change the settings almost on the fly looking only at the top LCD. You get the following on the D90 for example:
- QUAL: Push and hold while turning rear thumbwheel to set picture quality
- ISO: Same thing to change ISO
- WB: Same to change white balance, plus if you turn the front thumbwheel you can add warmth/coolness to the white balance tone. First advantage of two wheels.
- BKT: Turn on bracketing, choose number of frames and direction of exposure using rear wheel and the EV stops using front wheel.
- FLASH: The wheels can adjust the flash modes/strength. This may be also the case on D3100 (rear wheel at least)
- Shooting mode: When held, wheel will change between shooting modes. D7000 has the same method as D300s so even better than D90.
- Metering: Wheels permits switching from matrix (99%), center weighted (0%) and spot (1%)...jokingly you change this less often so not a huge advantage.
- Front custom button: I set this to the focus mode (too complicated to type here)
- FOCUS: Permits changing between stationary or continuous focus modes
Above said, those are a lot of functions to screw around with on the rear screen after pressing INFO button on the lower end camera. Maybe D3100 fixes some of this. REMEMBER that if you plan on shooting in Auto mode, all above is moot since you cannot change much in that mode anyway.
Apologies if above sounds too technical, but it's your money that you plan to spend wisely. Again, if you are serious think hard, if you are casual the D3100 is great and you will not regret. The above poster said he had D40x for 4 years. I had D40 for 2 yrs. I am not buying D7000 to replace my D90.
Product lines exist for a reason...each camera is designed for different users. ALL of them can take the same picture given the same lens (with slight metering exceptions).
Definitley buy the SB-600 as your flash...others are either too limited (SB-400) or expensive (SB-700/800/900).
I know I wrote a lot and some may say I'm full of crap, but I was in your boat a while back so I speak as a fellow amateur that has gotten very serious when the possibilities of what I could create were known.