Full Frame versus Crop Sensor

Since my primary camera body became a full frame camera (Nikon D800), I have always had a crop sensor body as my backup (D300S). I am looking at replacing the D300S and was looking at the D7100, again with a crop sensor. My son, who is a professional photographer, posed the question as to why I would want a crop sensor instead of buying another full frame camera. Obviously cost is one factor but is there any other reason that we like to use crop sensor bodies in this hobby. I know that this gives you the apparent extra 50% zoom capability but it is not a real zoom and is there any difference between using a 200 mm lense on a crop sensor that makes the image appear full frame, or using it on a full frame body and cropping the image to make it full frame?

Trevor

Some of the key differences between crop sensor and full frame include depth of field (increased on crop), high ISO/low light performance (generally far better on full frame), apparent field of view, cost (as you've noted). As far as the apparent field of view goes, on a Nikon system, the 200mm focal length on a DX format camera will show you the equivalent crop of a 300mm lens on an FX camera.

I am pretty sure the D800 you're shooting with now has a DX crop mode, which will give you the same effect as using a crop sensor body, using only the center of the frame (with something like 15.4 megapixels). A D7100 would provide you with 24 megapixels (6000 x 4000 px) for the same image area, though due to the higher pixel density it's not necessarily going to beat the D800 for resolving power. There is a lot of complex optical science that explains this much better than I have here, though I don't have a good enough grasp of it to explain it in simple terms.

For what it's worth I've been shooting a D7100 as my primary camera for over a year now and absolutely reccommend it. Compared to your D300s you're vastly improving the resolution and high ISO performance. Those improvements come with the trade-off of being a bit less ruggedly built and a different button layout (primarily lacking the AF-ON button on the rear of the camera). While the AE-L/AF-L button on the D7100 can be re-configured for AF-ON functioning, the lack of a dedicated button may be a turn off to some.

It wouldn't surprise me if Manny or one of the others with a better way of explaining this steps in to help set it straight.

I have this article bookmarked, it's an excellent explanation and a great FX vs DX read(it's just centered on wildlife shooting but, close enough to what we do to be able to transfer the knowledge): http://photographylife.com/dx-or-fx-...fe-photography

Personally, I own a D700 and D300s and they are two different machines as far as I'm concerned. If I had a D800, the DX mode would render my D300s obsolete except for the FPS