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Canon Rebel T1I Autofocus?


Hi there,

I recently purchased this camera and I looked everywhere online but I was unable to find an answer to whether or not this camera is capable of automatically focusing during video capture. When I mean auto I mean without pressing the buttons since I like to record from above my desk.





I am almost positive the answer is no. 

John Hoffman
Conway, NH

1D X Mark III, M200, Many lenses, Pixma PRO-100, Pixma TR8620a, Lr Classic

Likely no but a shutter release cable could be used to work the camera. There are lots of in expensive aftermarket versions out there. 

"A skill is developed through constant practice with a passion to improve, not bought."

@jrhoffman75 wrote:

I am almost positive the answer is no. 

I'm pretty positive that John is correct.  Most videographers want complete control over the focus, and prefer to manually focus their lenses.  Professionals only use lenses that can only be focused manually.

"The right mouse button is your friend."

I'm trying to make a video of myself so it's hard to manually focus while I'm trying to record.

A video is here:

I have to hold the cards close since the camera is focused to that extent. Should I just continue to film like this or do you guys have any other comments on how I could improve it.

OTHER THAN GETTING A BETTER LIGHT SOURCE (Which I will do in the future)


You really need a newer Rebel.  The newest ones have very much updated video featuers and software.

EOS 1DX and 1D Mk IV and less lenses then before!

Ah okay maybe I will sell this one and try to pick up something newer


There's really two different tings...


There's "auto-focus", and then there's "continuous auto-focus".


On the back of your T1i there is a button (near the upper right corner) with an asterisk (*).  If you press that button while shooting video it will force the camera to re-focus... but it will only re-focus when you press the button.  


The T1i does not support "continuous auto-focus" while shooting video.  The first camera that supported that feature was the EOS 70D.  


This is for a very good reason.  


When you are shooting normal still images and using the view-finder (looking through the camera instead of using the LCD screen), there's a mirror in the camera which bounces some light up to the viewfinder (so you can see to compose) and some light is bounced down into special "phase detect" auto-focus sensor on the floor of a camera.  This system is able to tell (based on analysis of two phases of light after passing it through a prism which works as a beam-splitter) if the image is focused at that point and if not focused it knows instantly how far it needs to adjust focus (and in which direction) to nail the focus.  This is why DSLR cameras focus so much faster than point & shoot cameras.


But when you shoot video, that mirror has to swing up and clear of the light so it can reach the imaging sensor.  So there's no way to do "phase detect" auto-focus using those sensors in the floor of the camera.  Instead of the camera does something called "contrast detection" focus.


Imaging taking a photo of a barcode.  The background is white.  The striipes on the barcode are black.  In theory, if your image is focused, every pixel should be either a "white" pixel (background) or a "black" pixel (a stripe on the barcode) with no other tones.  If your image is not focused, then you'll have some black pixels and white pixels, but the images near the edges of each stripe will be shades of gray (due to the blur.)    You'd have a black pixels, next to a very dark gray pixel, next to a middle gray pixels, next to a light gray pixel, next to a white pixel (a slow contrast change from black to white).  But if focused sharply you'd just have a black pixel next to a white pixel with no shades of gray.


This is basically how "contrast detection" works.  The camera looks for "edges" in your image and inspects how rapidly constrast changes between adjacent pixels.  It experiements with focus and compares the differences in how rapidly contrast changes and it keeps hunting until it finds a point where it's maximized contrast in the spot you asked it to focus on.


But the downside of the contrast system is that when not in focus, it doesn't actually know how far it needs to adjust focus.  It doesn't even know if the focus is too far or too near.  The camera has to "hunt" for optimal focus.  When the camera does this WHILE you are recording video, you'll see the camera make several "guesses" before it finally refines focus and this is VERY distracting.  (In pro-video they manually focus and will even pre-establish the focus points for a scene they are about to shoot before they start recording that scene so that during the video recording they smoothly adjust from subject to subject.  This can be as simple as wrapping a piece of masking tape around the focus ring and marking the tape with the focus points before recording the video.)


Canon has somewhat recently (within the past couple of years) developed a special way of designing a sensor with special focus point built into the sensor surface itself so that it can effectively do the equivalent of phase-detect auto-focus WHILE shooting live video.  No more focus hunt!  


This feature is found in the newer cameras such as the 70D, the T6i & T6s.  The T1i, T2i, and T3i don't have it.  The T4i, and T5i had an earlier version of it (not nearly as good as the 70D).  The 70D is probably the first camera where it worked extremely well.  The T6i and T6s came out after the 70D and they have it too, but in comparisons it still looks like the implementation on the 70D is the smoothest and most accurate.




Tim Campbell
5D III, 5D IV, 60Da
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