How do you calculate the reach advantage? Sony A900 vs Nikon D3S
The images below are given in support of a thread that was started on 19 April 2010 on the Sony SLR Talk forum, which is on the web site of Digital Photography Review. Click here to see this thread. The images below are of a Sumatran Tiger at the Wellington Zoo, New Zealand.
Image 1 (Above): Image dimensions (approximately to scale) 6048 pixels x 4032 pixels (Full frame Sony A900 image dimensions).
Image taken with a 300mm lens that provides a field of view (FOV) of 300mm.
Image 2 (Above): Image Dimensions (approximately to scale) = 4256 pixels x 2832 pixels (Full frame Nikon D3S image dimensions).
Image taken with a 300mm lens that also provides a FOV of 300mm.
However, the image size of the A900 image is about 42% greater than that of the D3S image. This is because the pixel density (in pixels per linear centimetre) of the Sony A900 is approximately 42% greater than that of the Nikon D3S (1685 / 1182).
Image 3 (Above): Crop of Image 1 to 4256 pixels x 2832 pixels (from 6048 pixels x 4032 pixels)
This cropped image effectively changes the "field of view" of Image 1, by 42% from 300mm to 426mm.
(6048 pixels / 4256 pixels x 300mm = 426mm).
This is because the pixel density (in pixels per linear centimetre) of the Sony A900 is approximately 42% greater than that of the Nikon D3S (1685 / 1182). However, the image widths of Image 2 and Image 3 are now the same (4256 pixels).
Note: The above conclusions are based on linear measurements, and deal only with the arithmetical aspects of the 42% pixel density advantage of the Sony A900. Therefore, the assessment of the quality of cropped images and the quality of the cameras, are separate issues that are not dealt with above.
Click here to see an analysis of the "pixel density advantage" of the Sony A900 (or Sony A850) when compared with the Nikon D3S.
Click here to see an article about the advantages and disadvantages of cropping images to gain extra reach, and for details of the formulas used.