A f2.8 Lens or a f4~5.6 Lense Which is a better Choice?

For many photographers, there is a debate about whether to invest in a f2.8 fixed aperature lense or a variable f4~5.6 lense.

Recently, I had to chose between a fixed f2.8 zoom (70mm-200mm), a fixed f4 zoom (with slightly shorter reach... max 105mm), or a variable aperture f4-5.6 zoom (with greater reach ... max 300mm).  For me the choice became very clear at a recent shoot.

My client wanted me to take pictures of him doing an afternoon workshop. Of course I brought my light stands, electronic flashes and diffusers. But a snag developed.
My client asked me to be low profile, so as not to disturb the audience. Flash lighting was out. In order to be low profile, I also had to position myself behind the audience.

I approached the shoot with my Canon EF 70~200mm f2.8 L II IS USM lense. I used this lense on a Canon 7D body. Since the 7D has an APS-C sensor, the 70-200mm lense became a 112-320mm f2.8 lense. The 112~320mm zoom range gave me the potential to get both full figure photos and close up facial photos of my client. The fixed f2.8 aperture gave me enough light to capture the event without flash. The client was very happy with the results.

His initial comments after the shoot were: "you were very professional ... you were invisible."
When he saw the pictures, he commented, "You really have a gift ... you captured me, my emotional energy ... everyone who saw the pictures became excited because you really 'got me."

I was happy to have a pleased client. I was also happy that I chose the Canon 70-200 f2.8 lense for my tool. Initially I was also considering a Canon 70-200 f4 or a Canon 70-300 f4-5.6 lense. Both the f4 and the f4-5.6 lenses are L lenses; both are considerably cheaper than the f2.8 lense; both are well rated.

Although all the lenses considered were Canon L lenses which therefore marks them as Canon's best lenses, the f2.8 offers a big advantage. The f2.8 lense allows twice as much light to pass to the Camera's sensor as the f4. This allows the photographer to use a higher shutter speed and to hand hold the lense in lower light that the f4. The larger aperature is also a plus even in flash photography. The second advantage of the lens I chose was that it is a II generation lense. In other words, it's optics, image stabilization and auto focuse mechanisms are all updated and improved over the previous version which already had a good reputation.

Although the Canon 70-300mm L f4-5.6 lense was also tempting because of the extended range (112mm-480mm with an APS-C sensor) I felt it would not be a good choice for people or event photography. The variable aperture starts at f4 which means half the light of a f2.8 lense is admitted to the Camera's sensor.  But the f4 only remains f4 up to 103mm then gradually moves to a f5.6 by the time it reaches 229mm and remains at f5.6 to 300mm. This means that at f5.6 only 1/4 of the available light is reaching the camera's sensor. Although the 70-300mm is rated as a quality lense, which is good for bright light, it is not the best choice when you don't have full control over the light and have to take people or event photos in whatever light is available.

The Canon EF-S 70-200 f2.8 L II IS USM is an expensive lens but is an excellent lense when you need to shoot in all kinds of lighting situations. In short it has high quality optics, mechanically sound and is bright.

I highly recommend the Canon EF-S 70-200 f2.8 L II IS USM over a variable aperture lense.