10 out of 10 points and recommendedIdeal focal length range for full frame Superb sharpness Constant aperture Internal focusing Tripod mount Build qualityNot weather sealed Discontinued by Sigma Not stabilized
While I am a big fan of the "classic" 70-200mm focal length range, I often find 200mm is too short for outdoor sports and wildlife. Getting to 300mm brings action on the opposite side of a soccer or football field into better view. When shooting baseball from behind home plate it gets second base and outfield action close enough to isolate subject from background more effectively compared to 200mm. I often here people say "just shoot 200 and crop it". This is just not an effective strategy. Shooting at 200mm where the subject only takes up 20% of the frame limits the usefulness of your AF and the chances of getting AF lock on the background or another player is very high during fast action. By zooming in to 300mm you are able to fill 30% of your frame with the same subject and utilize more of the AF points.reviewed December 22nd, 2016 (purchased for $600)
I find 300mm is a real sweet spot for many situations, especially on a full frame camera. There are no shortage of "kit" zooms that get to 300mm but do it by reducing aperture to f/5.6 or slower. This is nearly useless for sports or wildlife. I can hardly think of a time when I wanted increased DOF at a long focal length. f/2.8 lenses are amazing but incredibly expensive and heavy. f/4 is again that sweet spot of being fast enough to capture high speed shutter action without using super high and noisy ISO. It provides a narrow DOF to isolate subjects from the back ground while still providing a little margin for error. Even with an f/2.8 lens I often shoot it at f/3.5 to improve sharpness and provide a little greater DOF.
The relation of max aperture to AF function is an important yet rarely mentioned consideration in lens reviews. Auto focus (and manual focus) both work more effectively with a brighter wide aperture lens. More light equals faster AF. Also, many cameras limit the number of AF points available as the max aperture is reduced. So by using an f/5.6 lens you only have access to a small subset of the AF points in the camera.
The Sigma 100-300mm is internal focusing. This is a huge advantage over other similar lenses in this range. Internal focusing (IF) is a feature I did not pay much attention to until I had trouble with a non-IF lens. The extending barrel can be a real pain when shooting up against a fence (baseball) or glass (hockey). The constant movement of the front of a lens barrel and changing of length means you cannot simply set the end of the lens against the glass and shoot. You have to leave room of allow yourself to move back and forth as the lens extends and shrinks. That is a pain and can lead to missed shots near fences when you accidentally move out of a gap in the chainlink fence and end up with the fence in your shot. With an "IF" lens I can physically set the lens barrel end against my hand or the fence with it properly lined up and shoot without moving the lens around.
Why Sigma discontinued this lens is a mystery to me. It remains much sought after and is worth acquiring if you can find a good copy.