Abstract: Light field is a representation of full four-dimensional radiance of rays in free space. Plenoptic camera is a kind of system which could obtain light field image. In typical plenoptic camera, the final spatial resolution of the image is limited by the numbers of the microlens of the array. The focused plenoptic camera could capture a light field with higher spatial resolution than the traditional approach, but the directional resolution will be decreased for trading. Two models were set up to emulate the 4D light field distribution in both the traditional plenoptic camera and the focused plenoptic camera respectively. The 4D light field images of the two kinds of plenoptic camera were simulated by the software ZEMAX. The differences of sampling methods of the two kinds of plenoptic camera were analyzed. A variable focal length microlens array was presumed to be used in plenoptic camera to implement both focused and unfocused light field imaging. Based on the recorded light field, the corresponding refocusing process was discussed then. The refocused images at different depth were calculated. A new method of enhancing the resolution of the refocused images by image fusion and super resolution theories was presented. A reconstructed all in-focus image with resolution of 3 times of traditional plenoptic camera and same depth of field was achieved finally.