I'm new to the world of DSLR shooting. I just got a Canon t5i with a 18-135 IS STM lens.

I've gone into manual mode and played around with the lens on manual focus, and the AF to single shot.

I find it helpful to use the red dot in the viewfinder to tell me when I have achieved focus, but I must half-press the shutter for the focus indicator to work.

My question is, is that an ok thing to do? Will it hurt the camera or lens in any way? And is there a better way to judge focus when manually focusing?


1 Answer 1


Yes, STM lenses do allow manual focusing override after auto-focus has locked (indicated by camera beep, which can be turned off in camera options). STM lenses focus should not be adjusted manually when in AI-Servo focusing mode (i.e. when the lens is constantly seeking for focus), nor before engaging AF when the lens is switched to AF mode. An USM lens would allow manual focusing also during AI-Servo auto-focusing.

The viewfinder on the Canon T5i is not optimized for manual focusing; a good alternative is to use magnification in Live View.

  • \$\begingroup\$ So if I'm in manual focus mode, then I half press the shutter button, then focus on my subject, everything will be fine? No harm done to the camera or lense? \$\endgroup\$
    – Rowley
    Dec 31, 2013 at 6:42
  • \$\begingroup\$ Yes. The focusing ring on STM lenses works "fly-by-wire", so you can't cause any mechanical damage by turning it. \$\endgroup\$
    – Imre
    Dec 31, 2013 at 7:09
  • \$\begingroup\$ I will add that this cant be done on Nikon AF lenses (the ones driven from the camera's internal AF motor (Im aware this was a Canon specific question) \$\endgroup\$ Dec 31, 2013 at 10:32
  • \$\begingroup\$ I don't think it is worth posting another answer, but it is worth adding that not all USM lenses support full time manual focus. The 70-300 f/4-5.6 USM for example is a non-full time manual focus USM lens. \$\endgroup\$
    – AJ Henderson
    Dec 31, 2013 at 14:31
  • 1
    \$\begingroup\$ @Rowley - you don't have to be in manual focus mode. In manual focus mode, any lens will be able to be manually adjustable. A full time manual focus lens (such as the STM lens you have or most USM lenses) will allow you to manually focus after the AF motor has stopped operating (even if AF mode). The only caveat is that you need to use One-Shot focusing or the AF will constantly make adjustments to correct for any adjustments you make, which, while it shouldn't cause direct damage, would cause excessive wear and tear. \$\endgroup\$
    – AJ Henderson
    Dec 31, 2013 at 14:32

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