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I have nikon d3300. it have 24.2 mega pixel sensor but some where i read that kit lens have only 12 mega pixel effective but the actual resolution of image is 24MP.
My question:
1.what is blocking the camera sensor to take up to 12MP photo only?
2.what lens should i use to take full advantage of 24.2 mega pixels?
Clearly you need a better lens. The 18-55mm is extremely soft which shows even more with 24 MP sensors. Instead, if you are looking around the same focal-range, the AF-S DX 17-55mm F/2.8G is immensely better. You will get much higher resolution with it but know that optically resolution rarely is uniform. Even with a sharp lens you will have to stop down a little to get maximum performance which will minimize softness near corners.
Know that the 12 MP figure though is misleading. As I mentioned already , sharpness is not uniform. Most lenses are reasonably sharp in the center and get softer towards edges. When the aperture is stopped-down from wide-open, sharpness increases up to a point, until the diffraction limit is hit. An 18-55mm kit lens only gets sharp around F/8 to F/11 with the diffraction limit being around F/13 which does not leave much room and is very dim which increases chances of shake which adds softness.
To answer the first part of your question, it is simply the lens which is blocking sharpness. Light blurs as it enters the lens and therefore the sensor cannot record an image which has sufficient definition. You will set get a 24 MP image out but it will have details comparable to a 12 MP image according to the figure you quote. Again, this is not entirely accurate as the center could look like one taken from a 16 MP image and the corners from an 8 MP one.
I think you must be referring to the DxO lens tests, who does it that way. I would take that with a large grain of salt. They have their own ways, whatever it is.
For example, the Nikon 18-55mm lens there...
http://www.dxomark.com/Lenses/Nikon/AF-S-DX-Nikkor-18-55mm-f-3.5-5.6G-VR-mounted-on-Nikon-D5300__919
The lens tests DxO 15 on a 24 mp D5300, sharpness 9 megapixels
and same lens tests DxO 9 on a 12 mp D300, and sharpness 6 megapixels
Whatever that means. It is not comparable to anything else.
I'd suggest a better lens test site, with conventional tests, like http://www.photozone.de/nikon--nikkor-aps-c-lens-tests
This is very much the sort of megapixel-folly that beginners think about. Rather like believing a faster car is a better car. Let's try get you out of that mindset.
I have nikon d3300. it have 24.2 mega pixel sensor but some where i read that kit lens have only 12 mega pixel effective but the actual resolution of image is 24MP.
The modern kit lens is capable of as practically the same resolution of detail as the best lenses, and any differences are small, generally too small to be noticeable when viewing the image in any sensible way ( i.e. not zooming in at a ludicrous magnification of the image ).
A very common beginner belief is that you can buy better lenses, camera or whatever to make your images better. Not really.
If your composition, use of light, framing and technique are not producing great images with a kit lens and a basic DSLR, then the problem is not the equipment.
The number of pixels is a not a measure of quality. People used to use 6Mp DSLRs for the front pages of major magazines, and the quality of those images far exceeded what most people shoot with 24Mp ( or the even more ludicrous 50Mp models that have appeared ).
Don't worry about pixels.
I have never, ever had or heard of anyone looking at a print or image and saying not enough pixels. I've heard them like or dislike or not care about an image, based on it's emotional content, style, colour, composition and even the frame it was in, but not based on it's pixel count.
what is blocking the camera sensor to take up to 12MP photo only?
The biggest "block" to stopping you getting the most out of your lenses and camera is almost certainly not the lens. It's you.
Want dazzling images that wow people ? Learn composition, lighting, exposure principles, framing. Learn to concentrate on the image as a whole not the pixels. Great pixels never made a great image.
what lens should i use to take full advantage of 24.2 mega pixels?
The one on your camera.
Never worry about the lens. Worry about your technique.
Better technique, better images.
Better pixels ? Practically useless.
But if you really, really, really can't get over pixels then guess what gets you the best resolution from your camera ?
Better technique ?
Technique, technique, technique.
Learn it. The more you learn, the better everything gets.
And maybe, just maybe, you'll forget about pixels.
