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Occasional Contributor
Posts: 5
Registered: ‎04-19-2017

Auto focus stopped working in the middle of video shoot

Hi.

I have a canon EOS Rebelt1i, I was using video to shoot a small video and also switching back and forth to photo as well. in the middle of work, AF stopped working. The manual focous has no problem. Camera stopped shooting pictures in AF mode completely. here is what I did based on advise on different canon forums:

- Updated firmware and it makes the camera to shoot in AF mode but with no focus. 

-cleared all settings

-tried to clean the connectors

-tried to twist the lesne hard(ish) to the far left and far right....

no change.

I am wondering if something happens to the lens when I continuesly switch to video and back to photo!!!

 

Note: the lens is the kit lens ( came with camera ) . don't have another lens to switch and test yet: so that has not been done. 

Your help is appreciated.

Respected Contributor
Posts: 1,119
Registered: ‎02-06-2013

Re: Auto focus stopped working in the middle of video shoot

Nina, I don't shoot video much so I don't really know but my impression is that most Canon cameras, including yours, do not auto-focus in video mode.

 

Has it ever autofocus in video before and now quit working?

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Diverhank's photos on Flickr
Esteemed Contributor
Posts: 3,816
Registered: ‎06-11-2013

Re: Auto focus stopped working in the middle of video shoot

The T1i doesn't have continuous auto-focus during video... it never did.  

 

The issue back when the T1i was a new body is that cameras have two major auto-focus systems.  When shooting still shots through the veiwfinder (not live-view) the camera has special phase-detect AF sensors on the floor of the camera.  The reflx mirror has a semi-trasparent area with a second smaller mirror hiding behind it. This bounces light down into the AF sensors.  These include a beam-spliter (like a prism) and light is projected onto the sensors.  

 

The slick thing about these phase-detect AF sensors is that when you focus, literally every AF sensor takes a measurement at the same time and ... when something isn't in focus it's split-beam light will not be "in phase" on the sensor.  But the really impressive part is that in just a single reading the camera can determine exactly how far out of focus a subject is and if it needs to focus closer or farther to attain shapr focus.    So the camera basically takes one sample and immediately knows precisely how much to change focus and in what direction.

 

The result is that the lens snaps right into perfect focus very quickly.

 

When doing "live view" the reflex mirror is flipped out of the way to use the camera's image sensor.  This means it's not possible to send light through that phase-detect focus system.  So the camera has a second focus system for this situation.  

 

This alternate focus system uses something called "contrast detect" AF.  The easiest was to explain it is to imagine taking a close-up photo of a bar-code.  A typically bar code is white with black stripes.  

 

If that bar code is in perfect focus then every pixel in the image should be either a "black" pixel or a "white" pixel.  You'd have nice sharp edges with black pixels (for each of the bars) immediately next to the "white" pixels representing the background.   That means it's a very high-contrast difference along the edge of those stripes.  But if the lens was out of focus then you'd get a blurry edge... in other words you have a "black" pixel next to a very dark gray pixel next to a medium gray pixel next to a light gray pixel and eventually a "white" pixel.  So the transition from black to white isn't instant... it's gradual.  That's a low contrast change from pixel to pixel.

 

The "contrast" system toys with focus while looking for "edges" of contrast in your image.  When it thinks it found "edges" of contrast, it adjusts focus to try to maximimize the contrast along those edges.  To do this it has to sample contrast and look for edges, adjust focus and then re-evaluate, adjust focus again and re-evaluate and it tries to work out which direction improves focus and eventually finds optimal focus.  But it DOES take many "guesses".  This is often called "focus hunt" and in your video you'd see the camera quickly focus in and out as it works and settles on optimum focus.

 

Years later Canon introduced models which have some ability to do focus using technology similar to phase-detect auto-focus... but be able to do this directly on the camera sensor.  The Canon EOS Rebel SL1 had a feature called "Hybrid CMOS AF".  

 

The big advanced came with the 70D which had Dual-Pixel CMOS AF... and that technology has gone through a few iterations/generations of improvement.  

 

All the Rebels after the SL1 kept getting versions of Hybrid CMOS AF through the T6i... but the new T7i finally now has Dual-Pixel CMOS AF (the better system) which is the same system found on mid-range (70D and above) and pro series cameras.

 

You can still force AF during video.  During video you have to press the button with the asterisk (*) on it and this will force the camera to perform a contrast-detect AF focus... but you will notice this in the video because it does require several iterations to work out best focus.

 

The Dual-Pixel CMOS AF system works much more like the phase-detect system (except it can do this on-sensor).  As a result it actually can continuously track focus in live-video while your subject moves around and it will keep focus on your subject.   It is very good, fast, accurate, and you don't see "focus hunt".  

 

If you're video work is planned (not ad-hoc video) -- e.g. if you're making a film -- then you can wrap a piece of masking tape around the focus ring of your camera.  Pre-focus (before shooting) on each focus position and mark that focus position on the tape.  As you film you rotate the focus ring from point to point so that the resulting video has focus that moves perfectly from one sujbect to another with smooth focus transition and no guessing.

 

If you think you'll be doing a lot of video and want continuous AF, then I'd suggest upgrading to the new T7i, 77D, or 80D cameras (the 80D is basically the ideal camera for video right now.)

Tim Campbell
5D III, 5D IV, 60Da
Esteemed Contributor
Posts: 3,469
Registered: ‎02-17-2016

Re: Auto focus stopped working in the middle of video shoot

"If you're video work is planned (not ad-hoc video) -- e.g. if you're making a film -- then you can wrap a piece of masking tape around the focus ring of your camera.  Pre-focus (before shooting) on each focus position and mark that focus position on the tape.  As you film you rotate the focus ring from point to point so that the resulting video has focus that moves perfectly from one sujbect to another with smooth focus transition and no guessing."

 

This might not work as well with focus by wire.

Occasional Contributor
Posts: 5
Registered: ‎04-19-2017

Re: Auto focus stopped working in the middle of video shoot

I need to make a correction. Sorry if I confused everyone.
I don't need to AF in video mode.
My AF stopped working AFTER I used video.
I'm trying to photo shoot and AF is not working.
Esteemed Contributor
Posts: 3,469
Registered: ‎02-17-2016

Re: Auto focus stopped working in the middle of video shoot

Do you use live view?

Which Lens?

Is the lens set to M?

Occasional Contributor
Posts: 5
Registered: ‎04-19-2017

Re: Auto focus stopped working in the middle of video shoot

[ Edited ]

My lens is the kit lens. And no it's not on M

Not using live view for photo. 

 

Esteemed Contributor
Posts: 3,469
Registered: ‎02-17-2016

Re: Auto focus stopped working in the middle of video shoot

Did you turn the focus ring when it was on autofocus? that can disengage something inside. I couldn't find it, but there is a thread here telling how to fix it.

Esteemed Contributor
Posts: 3,816
Registered: ‎06-11-2013

Re: Auto focus stopped working in the middle of video shoot

The best way to evaluate if this is a camera issue or a lens isssue is to test with a different lens.  Do you happen to have another auto-focusing lens you can use to test if the camera can auto-focus?

 

The T1i is rather old and it's possible that the auto-focus in your lens has failed.  If this was a kit lens, keep in mind that while the kit lens does have fairly decent optics, the lens was designed specifically to be "affordable".  It doesn't have Canon's best/fastest focusing motors.  

 

Although lense generally can be serviced, keep in mind that the lens has been updated with a newer generation AND that these lenses were designed to be "affordable".  So the newer technology replacement is also relatively inexpensive.  The cost of doing repair isn't so much the cost of the parts... it's the cost of labor (parts are cheap... human labor isn't cheap).  

 

Your camera would have come with a Canon EF-S 18-55mm f/3.5-5.6 IS II lens (that was the "kit" lens).  The "new" kit lens is the Canon EF-S 18-55mm f/3.5-5.6 IS STM lens.  The "STM" is Canon's "stepper motor" technology.  The STM is not Canon's fastest focusing motors... but it is faster and smoother than what you would have had on your original kit lens (the "USM" lenses still usually have the fastest focusing motors (although there are a few USM lenses noted for the fact that they are not fast-focusing lenses.... so this statement is "generally" true but not "always" true.   The Canon EF 85mm f/1.2L USM is known to be slower to focus than most other USM lenses.)

 

Another advantage of the newer kit lenses is that they were designed with video in mind... the newer lens not only has improved optics and an improved auto-focusing motor... it also has a considerably quieter focusing motor.  It is so quiet that it is exceptionally difficult to detect the sound of the auto-focus motor working while the camera is recording video.  

 

I'd suggest:

 

  1. If you have another lens, attach that to determine if the camera body can auto-focus with any other lens.
  2. If you determine the the auto-focus isn't working with just one particular lens, you can contact Canon regarding the repair but....
  3. Keep in mind that since "kit" lenses are priced to be very affordable, it may actually be more economical to just replace it with the newer technology lens.

 

 

 

 

Tim Campbell
5D III, 5D IV, 60Da
Occasional Contributor
Posts: 5
Registered: ‎04-19-2017

Re: Auto focus stopped working in the middle of video shoot

I did go to Best Buy and tried different lenses and as you mentioned it, it was the lens issue. I'm not sure if I should invest in another kit lens or another camera. Since my lens works in MF, I can use it for photo and for video which is what I need it for, right now, I bought a 50mm, 1.8 lens for 125.
I'm trying to step into videography field and still clueless about cameras. I have to do research to see if I am better off to stay in cannon family or go mirrorless with Sony ( which I hate the setting ).... I wanna see everything not go tru hundreds setting under menu to change setting - by then the moment is gone!!!!
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