1

Besides setting the lense to Manual focus, can single point Auto focus be used to focus 'beyond' a foreground of tree branches to infinity? Living in the mountains makes long distance focusing a challenge. Thanks! Canon t7i w/ 55m kit and 50-250mm tele. (amateur)

Dave Dutton
  • 11
  • 2

2 Answers2

3

If we are talking about the phase-detection autofocus (the one you get through your viewfinder), then it is important to know that the actual AF-point is larger in area than the one you can see in your viewfinder. Therefore it would be best to look for a gap that is slightly bigger than your chosen AF-point.

With contrast-detetction autofocus (LiveView), a gap that is as wide as the AF-point should be enough.

Another possibility is to use lenses with a focus-limiter-switch - this feature is most often found on (higher-priced) tele-lenses, such as the 100mm f/2.8 L IS USM Macro, the 100-400mm f/4.5-5.6 L IS II USM, the 70-210mm f/4, etc.p.p.. Lenses with that feature have a dedicated switch that can limit the focus-range; e.g. from 1m-∞ to 5m-∞. That way, the AF will ignore objects in front. However, few of these limiters are designed to ignore mid-range obstacles; they are mainly intended to allow shooting through fences at short distance.

The picture below shows the AF-limiter settings on the 100mm f/2.8 L IS USM Macro - notice that it has three settings (Full, 0.5m-∞ & 0.3-0.5m) that are designed to differentiate between macro and non-macro distances. Some/most lenses just have two settings.

focus limiter switch of 100mm L IS USM Macro Image stolen from GearOpen's Canon 100mm f/2.8 L IS USM Macro review

flolilo
  • 6,468
  • 1
  • 30
  • 45
  • Does the autofocus software take the limiter into account as far as differentiating near and far contrast points in software or does it simply act as a mechanical stop, keeping the focus from getting too near - but still allowing a near object to potentially "trick" the autofocus? – OnBreak. Jan 23 '18 at 21:38
  • @Corey that's a good question! I don't have the knowledge to give a detailed insight into the technology, but my (somewhat limited) experience is that the omitted range will not be cycled through at all; it's like your lens has a new minimum focussing distance (MFD). So just as with the real MFD, if the AF-point is out of the focus-range, the camera will cycle through the whole (usable) focus range - or simply stop autofocussing, depending on your C.Fns. All I can find in the lenses' manuals is By setting a suitable focusing distance range, the actual autofocusing time will be shorter. – flolilo Jan 24 '18 at 00:13
0

Yes, as long as the point is small enough that you have a clear view to a high-contrast pattern in the distance.

mattdm
  • 143,140
  • 52
  • 417
  • 741