04-28-2014 03:42 PM
Lenses with "USM" focusing motors are the fastest (the actual speed depends on the specific lens model... some USM lenses are faster than others.) STM lenses are fairly fast... but not as fast as USM. If it's not USM or STM then it's slow. E.g. the Canon EF-S 18-55mm (non-STM versions) and the EF 50mm f/1.8 have slow focus motor speeds.
Alan and Mike offer good guidance however... the camera needs to be in "AI Servo" mode and you must keep the focus system active by holding the shutter button half-way (it will stop focusing if you release it completely.) You can also configure back-button focusing as an alternative (Canon allows you to configure one of the buttons on the back as a focus-button so that you can use your thumb to control when the focus system is active rather than the shutter button.)
When in "AI Servo" mode, the camera uses "release priority" -- meaning it WILL take a shot even if the camera didn't have time to lock focus. YOU have to keep the focus system active and decide when to take the shot. In "One shot" mode, the camera will not continuously update focus (it focuses once... then stops updating focus)... but that mode uses "focus priority" which means the shutter wont activate until it can confirm focus lock on at least one AF point.
And of course even if focus is perfect, you can get blur because of movement (either camera movement or subject movement) unless the shutter speed is fast enough. You'll usually need a minimum of 1/500th but depending on the speed of the action you may need even faster.
04-28-2014 07:32 PM
04-29-2014 09:04 AM - edited 04-29-2014 09:12 AM
This is kinda a reversal role for me as I am usually the one bashing the lowly “Niffy Fifty” EF 50mm f1.8.
Now I am the one recommending it!
But you hadn't stated you were using ...”Was using shutter speeds between 1/400 and 1/150 with ISO 400 and f5.6-8 ...”
That shows you had plenty of light but thinking low light was the problem was the thought behind the 50mm f1.8 idea.
Which will focus in way less light than the kit lens you have. Focus speed is not an issue if the lens won't focus at all.
Also, it likely will focus in less light than the f2.8 you are considering.
But light is not your problem. After what you have stated afterward, your technique is the problem.
Do try the suggestions above. Even the kit lens will probably work for you than.
05-06-2014 06:47 AM