Rebel T5i Goes out of focus in video

[FrontRanger]

My EOS Rebel T5i when in video recording, goes out of focus about every 5 seconds, and following that cycle leaves the lens significantly out of focus.

I am using a Canon Zoom Lens EF 100-400 1:4.5 - 5.6 L IS II USM with the camera. I am in autofocus mode on the lens, and image stabilized, stabilizer Mode 1, 3m ->infinity.

Coming from still mode, I switch the camera to video mode and it is focused. When I start to record, after a few seconds it goes WAAY out of focus, then seeks something close to focused and jerks slightly out of focus again and pauses for about 5 seconds and does it all over again. And over, and over every 5 seconds or so.

Do I have some setting incorrect to cause this behavior? I have the camera on a tripod so I am not waving it around, and it does this even when 90% of the scene is still.

Thanks for any advice.

[shadowsports]

Greetings,

If you are using a tripod, IS should be turned off. From a setting standpoint, this is the first thing to try.

What distance are you focusing at? The lens has a minimum focus distance. **3.2 ft. / 0.98m

Has this lens been tested elsewhere; do you know if it works properly on another body? Please report your results.

[FrontRanger]

Thanks for the reply, yes, I had IS ON, so maybe that is a problem - I was using a tripod, so maybe I did not need IS, but when heavy vehicles passed, it did seem to shake the tripod/camera a little. I do not have another body (maybe an excuse for me to upgrade?). I was focused at almost infinity (a couple hundred yards). I hope the setting is the cause of the problem, I will try again soon with IS off.... I have used the lens almost exclusively for stills and AF seems to work very well in still photos.

I also saw this behavior on closer shots (10 yards) on a moving creek. But I have done so little video I don't know how it behaves "normally".

[stevet1]

FrontRanger,

Do you have Movie Servo enabled?

Steve Thomas

[shadowsports]

If you'd like to review what Steve mentions, see page 196 of your user guide. Not sure it has anything to do with focus acquisition though. It looks like it's to minimize noise during focus in video mode.

eos-rebelt5i-700d-im7-en.pdf (c-wss.com)

Lens Manual here:

ef100-400f45-56lisiiusm-im-e.pdf (c-wss.com)

Also verify the setting of your focus distance range switch

[FrontRanger]

Thanks all for the ideas. I have tried IS=OFF, and I usually run focus 3m-infinity to avoid close focus delays, I can try the Full setting next trip out. One solution may be to turn OFF Autofocus, but the camera should be able to adjust focus as video scene changes - Canon even makes video ads highlighting this feature.

But now I am wondering if the scene itself is part of the cause - maybe a pathological behavior of the focus algorithm? The scene that most troubled me was a train approaching from a great distance at 400 mm setting to start. The headlights (Headlight and 2 ditch-lights) form a triangle of the brightest things in the scene. Is it possible that the focus tried to make these bright spots converge (they will NOT) and thus roamed all over the focus range to no avail? Anybody seen a behavior like this before?

Canon engineers - is this a possible side effect of the bright spots in the scene?

Thanks to all for ideas!

Chris

[Waddizzle]

“…but the camera should be able to adjust focus as video scene changes - Canon even makes video ads highlighting this feature.…”.

Except, the camera does not do it.

It does not have a Dual Pixel AF sensor, which would imply that it does not feature Movie Servo AF. When you are in Video Mode, is there an option to enable or disable Movie Servo AF?

[FrontRanger]

Wadizzle: Thanks for the reply and ideas. The camera does have Movie Servo AF, and it was enabled. The lens has USM (Ultrasonic Motor, above human hearing) so I was not concerned with audible lens operation. I have alternatives of both camera-mounted microphone and remote wireless microphones, so I have a couple options around lens noise. 

I appreciate the remark about Dual Pixel AF Sensor, Since this camera does not have that, I will have to investigate further (i.e. it is not in my manual, I was unaware of this feature in other cameras). I am continually surprised at the complexity of the camera! I started with a manual SLR years ago, and when I graduated to a DSLR so much has changed. Lots of features to cope with so many shooting conditions, which not only yields simple operation, but also complex learning experience. Imagine a manual with almost 400 pages... Then add the Speedlight capabilities and manual, etc.

Again, Thanks.

[FrontRanger]

I have found in the manual page 165 "Shooting conditions that make focusing difficult" item 7, "Night scenes or points of light" -- well, this may be the source of the problem... I have tried all sorts of combinations of Tripod with/without stabilization, autofocus long (3m/infinity vs full range), and all sorts of scenes of stationary and moving objects. But the worst problem was looking at a locomotive head-on with three headlights in a triangular configuration. The lights were very small and bright and to my eye, noticeable when they went out of focus over and over. At this point I must assume that it is a firmware defect in the camera or the long lens and will have to avoid autofocus in these types of scenes in video mode due to the bright point-source lights. Disappointing, because it would be great to allow the train to approach without manually adjusting the focus, but I worked on embedded firmware for decades and understand problems can arise in corner cases. 

Since I have seen several threads with other autofocus problems, in other models of EOS cameras, I guess this is fairly pervasive, but since I actually use video fairly rarely, I can live with the fix - do it yourself focus...