# How do you calculate the reach advantage? Sony A900 vs Nikon D3S

Started Apr 19, 2010 | Discussions thread
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 How do you calculate the reach advantage? Sony A900 vs Nikon D3S Apr 19, 2010

I have written some notes about the advantages and disadvantages of cropping images to gain extra reach, that you can see here:

http://www.robsphotography.co.nz/focal-length.html

The other day, I was talking to some friends about the differences between the full frame 24.6 megapixel Sony A900, and the full frame 12.1 megapixel Nikon D3S.

It’s clear, of course that, when you are comparing two full frame cameras, if you put a 300mm lens on both, the reach of the A900 and the D3S is the same, that is, 300mm.

Or is it? Does this take into account that the pixel density of the A900 (in pixels per linear centimetre) is about 42% greater than that of the D3S (1685 vs 1182)?

So, after a while, we decided that, provided the images from both the A900 and the D3S were not cropped and kept the same 300mm field of view, the reach of both cameras is the same.

But, when both images have the SAME FIELD OF VIEW , because of the higher pixel density of the A900, the image width of an A900 image (6048 pixels) is about 42% greater than the comparable image width of an image from the D3S (4256 pixels).

But, what if an image from the A900 is cropped from its original width of 6048 pixels to the SAME IMAGE WIDTH as an image from the D3S, that is, 4256 pixels?

If you apply the principles in the article linked to above, do you agree that, when an image from the A900 is cropped to the same image width as the D3S (4256 pixels), this effectively increases the “reach” of an A900 image by 42% from 300mm to 426mm (6048 / 4256 x 300mm)?

So, how do you define the term “reach”? Do you agree with the conclusions we came to?

When comparing the reach of two cameras, do you prefer the “same field of view” approach, or do you prefer the “same image width” approach?

Thanks very much for your feedback.

Analysis of the pixel density advantage of the Sony A900 compared with the Nikon D3S

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