Changing light when in front of the lens with video with a projector behind me

[Steve Crow]

I think you are not filming in full manual mode so that the camera is making some auto corrections to the exposure as the overall light conditions change. Set your exposure manually and then leave it alone and I think the problem will go away – let us know if that works for you.

Steve Crow

[Tom Nash]

Thanks Steve. I was trying that last night but couldn’t get the exposure right since my test setup has the audience a bit under lit and was worried if I opened it up, people in the third row would be out of focus. Gave up when it got late last night but I’ll try again.

BTW, any chance you know why when shooting video, if you’re in Av, you can’t control aperture where it sets it at f/4 (widest for this lens). Seems like Av and Tv are the same in video.

[Steve Crow]

Not sure I 100 percent got your question but let me take a shot at it, and forgive me if I blow it.

For your filming situation I would set my aperture way more towards the “closed” end because that way you will have a deep depth of field and most everyone in your audience is going to be in focus. F8 or even higher.

I think at first I misunderstood your question and I wanted to point out to you that your exposure and your focus are two separate things. I thought perhaps what you meant was that you were afraid that the some of the audience members would be overexposed or blown out but now I think you were actually talking about Depth of Field issues.

Anywho….unless you set up a professional lighting grid to ensure even lighting throughout the audience area, yes there are going to be different levels of exposure.

What I’m saying is go into manual mode and then pick an exposure that works out the best OVERALL even if some areas are SLIGHTLY over or under exposed. For an F8 aperture, I would expect to have to use a fairly high ISO because 95% of the time I keep my shutter speed at 1/50th or twice my 24fps frame rate.

AV and TV modes are not DOING the same thing in video. In AV mode you are selecting the aperture and the camera is selecting the shutter speed and ISO while in TV (t for “time”) you are selecting the shutter speed and the camera is selecting the aperture and ISO for you. Now, in both cases, the camera will try and work out a combination of settings that gets you an acceptable exposure, somewhere right in the middle between not too dark or too bright, and the resulting shot may very well look exactly the same in terms of overall exposure in both AV and TV modes. The only difference is HOW the camera is achieving that exposure.

But of course, yes, different apertures, shutter speeds and ISO can make a HUGE difference in the overall look of the video – the depth of field, the “smoothness” of the movement and exposure. That’s why I only really shoot in manual mode for my projects, because I want to control all 3. If I were doing fast moving action type stuff yes then I might choose AV or TV mode (most probably AV) but in your case, I’d go manual all the way since it doesn’t sound like the lighting conditions are going to change.

Steve Crow

[Tom Nash]

Hey Steve

Thanks for that. I understand Av vs Tv and needing to pump up ISO if I close it a bit to like f8 but for some reason when in video mode, I can’t get it to do anything but f/4 which is odd. Though maybe it’s something that I couldn’t do in Av when in video mode but then what’s the sense of Av if I can’t set the aperture. Weird. Will play around with that again.

I also didn’t take into account FPS. Wasn’t sure if that mattered in terms of the exposure. I’m set at 1920 with 30fps the highest in the camera. Since I was projecting back live I thought the highest FPS might be best but maybe not.

Thanks

[Steve Crow]

So you’re saying while in aperture priority mode the only aperture you can set is a 4.0 and it won’t let you set it to anything else? What happens when you try and select another aperture like 8.0?

Is this a fixed aperture lens by any chance? What lens do you have?

When taking still photographs can you use other apertures besides 4.0?

Steve Crow

[Tom Nash]

It’s the 24-105. Normally I can set it like you would expect but won’t budge in movie mode in Av. I’ll keep playing with it and let you know if I figure it out.

[Steve Crow]

Dude, that lens is fixed aperture at 4.0 meaning that’s the only aperture it has!! 🙂

Steve Crow

[Tom Nash]

Ahh, right Variable vs Fixed. So how does this work with a fixed aperture but with an aperture range of f4-f22 (according to BH). In Av, while taking pictures, I can scroll through F4-F22. Not sure I understand how that works then.

Tom

[Blaise Douros]

The answer is to not use any of the program modes when shooting. You need to expose this scene manually if you want it to work. Av and Tv modes are not as smart as you are when it comes to what in the scene needs to be exposed correctly. Additionally, they will make automatic adjustments to the brightness of the scene, which is undesirable.

If you can’t change your aperture in Av mode, there may be a problem with your camera. I have the same camera and lens, and have no problem doing exactly what you describe. Make sure you’re not making a bonehead mistake like trying to use the wrong dial for the aperture. Or, make sure you’re not trying to adjust it using the exposure compensation setting.

In the case of the 24-105 f4L, the fixed aperture means that your lens can shoot at a maximum of f4 at any focal length; other lenses will automatically change their maximum f-stop (almost always to a higher number) as you zoom in. It does NOT mean that you can’t change the lens from f4. You can dial the lens to f8 if you want, or f22, whatever, at any focal length. But it doesn’t mean that f4 is its only aperture.

In this case, here’s what you need to do: go into manual mode. Set your shutter speed to double your framerate (1/60 for 30 fps, 1/50 for 24 fps). Set your aperture to a midrange number like f8, to get you some depth of field. I would suggest zooming out, and placing your camera slightly closer to your audience; a wider angle on the lens means a deeper DOF, so you won’t have to stop up quite so much to get more DOF. Now, set your ISO. Find a balance of ISO and f-stop that works to get you enough DOF, without having to set the ISO too high. In my experience, the 6D’s ISO can go pretty damn high without too much noise; 2000 or 2500, even 3200 can be perfectly acceptable.

Consider adding additional light on the audience. This will help you better control your exposure.

[Steve Crow]

Wow Blaise, I’ve just been schooled! 🙂

I always thought that a fixed aperture lens meant it had ONLY that one aperture to select from throughout its entire focal range (24-105mm in this case) but what I guess you are saying that F4 is the most open aperture available on that lens that works throughout the entire focal range but that at the same time you can still shoot at 5.6, 8,11,16 and 22. Is that right?

Would those other apertures beyond 4.0 also be available then throughout the entire range or only part of it or….?

Steve Crow