Choosing between Canon 70-200mm and 100-400mm telephoto lenses on a 5D Mark III
Asked 6/19/2017
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I shoot with a Canon 5D Mark III and currently own a 17-40mm f/4, 50mm f/1.8, 100mm f/2.8 Macro, and an older 70-300mm IS USM (non-L). I want to replace the 70-300 with a higher-quality telephoto that will last for years.
I’m considering the Canon 70-200mm f/2.8L IS II and the 100-400mm f/4.5-5.6L IS II, and I’m also thinking about using a 2x III extender. I mainly shoot in daylight and usually use a tripod at night, so I’m unsure how much f/2.8 really matters versus f/4-f/5.6 in real use. I’m also wondering whether depth of field differences at longer focal lengths are significant enough to matter.
My current 70-300 images often look grainy, and autofocus seems slower than it used to be. Should I prioritize aperture, focal length, image stabilization, or teleconverter compatibility when choosing between these options?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
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I also plan to get a 2xIII extender
For most Canon bodies, a 2X teleconverter will only be practical with f/2.8 lenses. It's how aperture works.
f-number = focal_length/aperture_diameter
therefore:
aperture_diameter = focal_length/f-number
Which is why we write an aperture setting as f/f-number: e.g., f/2.8.
When you use a 2X teleconverter, you're doubling the focal length, but the maximum aperture diameter remains the same. So you're adding two stops to the maximum aperture of the lens.
An f/2.8 lens becomes an f/5.6 lens. An f/5.6 lens becomes an f/11 lens.
Most Canon dSLR bodies stop autofocusing when the maximum aperture of a lens hits f/8. Some stop when the maximum aperture hits f/11. If you plan on using this new telephoto lens with autofocus, and you don't have a 1-series or dual pixel sensor in the body, then you can only use a Canon 2X extender with an f/2.8 (or faster) lens.
You could use a non-reporting 3rd-party extender, but the optical quality is likely to be less than that of the Canon MkIII extenders. And the AF performance will take a hit. I use a non-reporting Tamron 1.4x extender on the EF 400mm f/5.6L USM prime. It considerably reduces AF accuracy and causes a bit of "chatter" in the lens as it hunts for AF lock on my 50D.
Originally by user27440. Source · Licensed CC BY-SA 4.0
user27440
9y ago
0
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The main decision is focal length, not just aperture. A 70-200mm and a 100-400mm serve quite different needs, so first decide whether you actually need reach beyond 200mm.
If you don’t specifically need f/2.8, a 70-200mm f/4 is also worth considering; it’s lighter and less expensive than the f/2.8 version.
A 2x teleconverter costs you 2 stops of light. So:
- 70-200mm f/2.8 becomes 140-400mm f/5.6
- 100-400mm f/4.5-5.6 becomes roughly 200-800mm f/9-11
That matters because autofocus on many Canon DSLRs becomes limited or impractical once the effective maximum aperture gets smaller than about f/8. So if you want reliable AF with a 2x extender, an f/2.8 lens is the more practical pairing.
Your current “grainy” images are more likely caused by high ISO or low-light shooting than by the lens being old. Slow AF can also be due to low light or using small effective apertures.
So: choose the 100-400 if reach is your priority, and the 70-200 f/2.8 if you want speed and better compatibility with a 2x extender.
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