Enter a seedy boxing arena: clamoring crowds, smoke thick to the ceiling, incandescent lights barely bright enough to reveal the ring. The crowd is excited for the latest prizefight between two great pugilists. Long the battle has been between these giants and this fight promises to be no different. The announcer garbed in a tux enters the ring. In the center, a microphone drops from the ceiling and shadows right to his hands. The crowd hushes waiting for his words. Ladies and Gentlemen. Welcome to todays heavyweight contest. The audience goes wild with the announcement. Tux-man raises his hand for quiet. In this corner, the small guy with grit and glory to be the #1 contender, weighing in at 8.25 pounds and 14.6 inches long, the Nikon 500mm f/4 AF-S. An explosion of cheers erupts from the crowd as the trainers back away, revealing the contender in their corner. Once again, tux-man raises his hand making the crowd silent. In the corner to my left, the large man, the monster from Tokyo, weighing in at 12.8 pounds and 17.5 inches long, the undisputed heavyweight champ of the world, the Nikon 600mm f/4 AF-S. The crowd goes wild again as the trainers in the left corner back up to show their man sitting heavy on the seat, acknowledging the adulation from the crowd&

It could happen, couldnt it?

While this fanciful scenario is far fetched, it is a stylized interpretation of the real challenge between the two lenses. One of the greatest debates in nature photography circles is which lens is better, 500mm or 600mm. While most of this issue seems particularly pedantic, the problem is when youre on a limited budget like most people, choosing between these two can be quite troubling. If you only can afford to buy oneand even then its a stretch to justify what may be your third most expensive purchase ever right behind your house and caryou want to make the right choice the first time.

Whats the big deal here? On the surface it looks like theres only a small difference between the two lenses. Theyre both long lenses and they both are super huge. What can be so troubling to cause such angst among photographers? Well, its in the details and the details differ between the lenses significantly.
Lets look at what we have.

Here are some of the Nikon 500mm f/4 AF-S specs:

Weight 8.25 pounds
Length 14.8 inches
Field of View 5.0 degrees
Close Focus Distance 16 feet, 3 inches

Here are some of the 600mm f/4 AF-S specs:

Weight 12.8 pounds
Length 17.5 inches
Field of View 4.1 degrees
Close Focus Distance 19 feet, 6 inches

What does all this mean? Not a lot except the 600mm weighs about 50% more than the 500mm. Other than that, both look the same. I dont want to say too much about the minimum focus distances, except noting at minimum range, both lenses provide about the same image magnification. So, what else is different?

The magnification of each lens is tremendous. Both will expand your subjects size by at least 100 times over a normal, 50mm lens. In practical terms, this means you can be 10 times as far from your subject and get the same perspective as a 50mm lens. Obviously, you can even be further away with the 600mm over the 500mm lens. How much further? Thats easy; its 600mm/500mm away. At 100 feet with a 500mm, you only have to be 120 feet away with a 600mm to get the same image.

In subject enlargement terms the difference between the lenses is a 100x factor over a normal lens with the 500mm compared to 144x factor with the 600mm. Thats surprising, a 44% difference between the two lenses, almost a 50% increase in subject size. For some photographers, this may not be the most important decision factor when choosing between the two lenses. However, if youre looking to get as close as possible to your subject and cant move your feet for one reason or another, magnification becomes everything. Add on 1.4x or 2.0x converters, and youve expanded either lens focal length by 1.4 and 2.0 times respectively. Now youre in the realm of super tight compositions looking into a world previously available only to animals of the same species. Details in bird feathers explode on screen. Texture of a sheeps fur becomes real enough to touch. With this magnification, youre now close enough to invade the personal safety envelope of your subjects without making them budge. Its exciting and intriguing imagery thats only available to those who make the huge investments in the longest, most capable lenses.