Birding with a 500mm F4 or 600mm F4

Started Feb 1, 2014 | Discussions thread
whoosh1 Senior Member • Posts: 1,687
1.2x => 1.44x should cut both ways (600/500 or 1.2x crop)

Bitcoin - similar to Arthur Morris' analysis (between 600mm and 500mm lenses which you mentioned below), shouldn't the 1.2x crop also measure both dimensions for number of pixels?


  • FX format (36x24): 7360 x 4912 (L), 5520 x 3680 (M), 3680 x 2456 (S)
  • 1.2x (30x20): 6144 x 4080 (L), 4608 x 3056 (M), 3072 x 2040 (S)

For jpg large - FX format has roughly 36 megapixels while the 1.2x has 25 megapixels. 36 divided by 25 is 1.44 (same as Arthur's ratio).

Also for the sake of simplicity - let us assume the 1.2x has 24 megapixels and the subject is 12 megapixels (from a given location shooting with the D810 with a 500mm lens). For the full frame (FX) shot - the subject is 33% of the total image (in terms of total pixels). For the 1.2x shot - the subject is 50% of the total image. 50% of the total image is roughly 1.5x of 33% of the total image.

So while JP may not be completely right (in saying you don't lose anything going to 1.2x + 500mm vs FX + 600mm - you do go down from 36 megapixels down to 25 megapixels) - he is not completely off (if you accept the compromise of losing 11 megapixels in exchange for the lighter weight of the 500mm).

bitcoin wrote:

JP Scherrer wrote:

I don't have the 500 nor 600mm, but I tried them both, and I found the 600mm. Much heavier snd bulkier than the 500mm. !

Also, the gain of the 600 over the 500 is only 1.2x !!! With your D800 set to 1.2x, you will get an equal viewing size and as in most cases you will crop and/or resize the image, so you won't lose anything !

Just my 2 cents....


Photo Galeries at
Spherical Panoramas (360x180 degrees) at
Equipment list in profile

Actually the gain in not 20%, but 44%. Source from Arthur Morris

The size of the subject in the frame is a function of the square of the focal length. A subject that fills 25% (5X5) of the frame in an image created with a 500mm lens will fill 36% (6X6) of the frame if photographed with a 600mm lens from the same distance. The huge advantage here goes to the 600 II which will render the subject 44% larger in the frame than the 500 II.

 whoosh1's gear list:whoosh1's gear list
Nikon D800E Nikon D810 Fujifilm X-T20 Nikon AF-S Nikkor 16-35mm F4G ED VR Nikon AF-S Nikkor 14-24mm f/2.8G ED +16 more
Post (hide subjects) Posted by
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow