Issues with 70d video. Video Brightness changing during shoot, camera not in auto

[MarkStache]

This is a tough one to explain. I shoot cooking videos and I let the camera run throughout the shoot. I keep the 70d in manual mode. My settings never change as I am in my own studio. I shoot 1080p30 All I ISO 400 f5 60. I shoot 2 videos a week. My lighting doesnt change everything is stationary. 
The last 2 months when I import the footage half of the footage is fine but almost always on the 10th or 11th clip the rest of the clips look like they were shot 1 - 2 stops brighter, but the camera settigns dont change. I have been fixing this in post because this is my full time job and I don't have time for gear repairs, but it is driving me crazy! I used to do IT support for a media school so I did all the basic trouble shooting.  Checked all settings to make sure nothing is on auto, checked the batteries, tried different batteries, tried different SD cards, reset all settigns on the camera? Anyone have and ideas? 

[Waddizzle]

Try testing it at a different frame rate.  That would rule out flicker.  The fact that it only happens on a complete clip is very suspicious.  What is different about the “bad” clips compared to the “good” clips?

Again, if you are as dependent upon your camera as you say, buy a backup.  I suggest the 80D in the Canon Refurbished Store.  They are having a big sale this weekend.

https://shop.usa.canon.com/shop/en/catalog/refurbished-eos-80d-ef-s-18-55-ef-s-55-250-is-stm-bundle

A two lens kit for less than the cost of a body alone!

[BurnUnit]

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@Waddizzle wrote:

Try testing it at a different frame rate.  That would rule out flicker.  The fact that it only happens on a complete clip is very suspicious.  What is different about the “bad” clips compared to the “good” clips?

https://shop.usa.canon.com/shop/en/catalog/refurbished-eos-80d-ef-s-18-55-ef-s-55-250-is-stm-bundle

A two lens kit for less than the cost of a body alone!

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That's where I was going with this but Waddizzle beat me to it. I think it caught his eye as well as mine when we saw 30fps and 60hz AC power. Try shooting 24 or 25fps and see if there's any improvement. I don't think you want the fps and hz to be the same or an even multiple where they can sychronize. If the shutter opening synchs with when the LEDs light output is the brightest it may slightly over expose the shot. If the shutter opening occurs when the light output is less it's going to slightly underexpose the frame.

LED lighting can be a source of color shifts and other strange behavior even for still photography. And even though they don't flicker as noticeably as flourescent lamps, the effect is still there. This link to B+H Photo should help to explain the effect you might be seeing.

https://www.bhphotovideo.com/explora/video/tips-and-solutions/flicker-free-lights-and-why-they-are-i...

And that's a pretty sweet deal for that 80D refurb kit. That would be hard to pass up if my 60D wasn't still plugging away like new.

[BurnUnit]

Is your main lighting incandescent, fluorescent, LED, or possibly a mixture?

[MarkStache]

LED 

[JaredNel]

Hi Mark, did you ever solve this issue?

I'm facing the same randomly over-exposed video clips when using full manual settings and preset, consistent lighting. No apparent reason for the change. It's so frustrating!

[BurnUnit]

Have you checked to make sure that you don't have Auto ISO turned on? Are you using any sort of lens filter? Does your continuous lighting happen to be flourescent or LED?

[JaredNel]

Thanks for your message. 😉

So I'm using a Canon 70D with EFS 18-55mm lens. I have camera switch to video, dial on Manual, ISO set to 400, FR set to 50, and Arp on 4.

I have 2 LED lights above me and 2 LED lightboxes in front of me. I have two power sources, (a) the national grid, (b) a solar-inverter system. Random issue occurs on both power sources.

I am wondering though, even with manual settings, Arp does seem to change depending on how zoomed in the lens is... I wonder if zooming the lense slightly is bumping the Arp from 4 to 4.5 and therefore increasing brightness?

I'm going to experiment.... 🙂

[BurnUnit]

I don't shoot a lot of video with my DSLR and I'm not familiar with the term, so explain what "Arp on 4" means. I probably knew at one time but have forgotten the details.

If you aren't already aware of it, LED lamps do have a flicker to them like fluorescent lamps do, though it's less obvious to the human eye. I think the problem may exist mainly with AC powered LEDs. They can cause some exposure and color problems with still photography as well under certain circumstances.

For your videos try a different frame rate and/or shutter speed. I don't know if changes in ISO would have much of an effect.

Do you see the same exposure problems when shooting in daylight or with incandescent lighting?

[kvbarkley]

I think he is referring to the Aperture on a non-constant Aperture zoom.

[JaredNel]

Thanks BurnUnit,

Yeah, the 70D is a great camera for video - I love it - other than this recent issue.

Kvbarkley is correct. By Arp I mean Aperture. And he's correct that the Aperture changes when the lens zoom is adjusted.

Doing another test today, it doesn't seem that the zoom amount I used should have been enough to change the Aperture. But I put it back to 4, did a couple of tests and it worked okay again so far.

I'll do more tests tomorrow and see if it still behaves. Usually, it takes several shots before it acts weird.

Quick correction: my FR (Frame Rate) is actually 30. It's my SS (shutterspeed) that is set at 50 to match my power phase.

Yeah, I get definite flicker from my ceiling lights if the shutterspeed is set to something other than 50. I also get flicker on some Frame Rates though I can't remember exactly which ones.

When shooting outdoors I've only ever used the camera in Auto mode so never noticed an issue.

I'll do some more shooting tomorrow - hoping to actually record a video for my channel - and will see how it goes. I'm also streaming to my laptop via HDMI so that might catch any changes in picture.

Thanks so much again for your time and input guys, it's much appreciated! 🙂