>The D600 will give you an image that's about 15mp with a DX lens.
In DX Crop Mode the D600 gives you about 10.2MP, not 15MP.
>But what about IQ? Is it fare to say that the image IQ from a >D600 with a DX lens is Going to be better than the same shot >taken with a DX body?
In general, yes. That's mostly because it's newer technology than the current top-end DX cameras like the D300s and the D7000. If and when either of those models gets replaced, things may change somewhat.
Personally, I don't like the idea of buying an FX camera with the aim of using it only in DX Crop Mode. The viewfinder image will be rather small, for one thing, and you'd be paying over the odds for something you won't be using.
Generally you will be a lot better off cropping a FullFrame image than shooting in DX mode even if you use a DX lens. But cropping the best part out of an image taken with the best FX glass is much better yet.
The closest you can get in camera to 15MP is to shoot FX at Medium size for 13.6MP images. However, you can crop a 24MP image to 15 in post processing.
Tue 01-Jan-13 12:45 AM | edited Tue 01-Jan-13 12:50 AM by pixures
The 70-300 would be the cheapest way to cover your range. You may want to give thought to how often you will need to change between the 24-85 and 70-300.
I recently purchased a D600. At the time of purchase, I had a very nice stable of higher quality DX lenses with my D90. With the D600, I chose to adopt FX as my mode of shooting, knowing this would result in a major change over of my lenses and recently sold 4 of the DX lenses.
I already had a 70-300 and 70-200 F2.8, but decided to get a more general purpose primary lens than the 24-85 for the D600. I bought the D600 kit that included the 28-300. I also picked up a used 24-120 F4. I plan to use the 24-120 as my "go to" landscape and inside lens and the 28-300 as my walk around snap shot lens. The 70-200 F2.8 will be used for sports. I will probably add a 16-35 F4 to cover the range my old Tokina DX 12-24 provided.
I am guessing the 70-300 will be used seldomly, if at all.
I know I have a lot of overlap in lenses. But, I find reducing or even eliminating the need to swap lenses when on a shoot to be a real plus. Most of my shooting does not lend itself to carrying a second body. I am also hoping to use the lenses in their sweet spots and when possible, not use them at their extremes where distortion and edge fall off becomes more noticeable.
PS- over Christmas, I shot a family portrait with the 24-120 and the D600. This was my first and only serious session with the D600. I was very pleased with the result - a noticeable improvement over the D90.
As Brian said, the D600 only puts 10.2 Mp into a DX frame, whereas the D7000 lays 16 Mp on the same image area. In spite of the more "modern" D600 sensor I think the D7000 would give more detail in most normal shooting situations. The D600 would have an advantage in poor lighting conditions ; fewer pixels but much less noise and more dynamic range.
D800 has 36 Mp and it will put 15.5 Mp into a DX frame. I suspect D800 would give superior output to D7000 in any situation where a DX lens is used, but again, more so in poor light.