Variable aperture on Canon XC15

[Distoviolin1]

Can you turn off the variable aperture on the Canon XC15? I’m using it for a series of group interviews and need to be able to zoom in on each speaker quickly without the aperture changing. If not is there a workaround? Thanks. 

[Hazel_T]

Hi Distoviolin1,

The variable aperture on the XC15 is a limitation of the lens itself. The variable aperture has to do with how the lens is constructed, so unfortunately there isn't a way to disable the variable aperture for that camera and lens. 

[Distoviolin1]

Thanks for the reply. Would locking the exposure be a solution for this? I don’t understand why anyone would want the aperture to change while zooming and have no control over it.

[AtticusLake]

It's not a case of what people want; it's a case of physics. The entrance pupil is the focal length divided by the F-number; so if you want the lens to keep an F/2.8 aperture at the 89mm maximum focal length, the entrance pupil would be 31mm, which I bet is a lot wider than the glass elements in your lens. A lens which can do that would therefore be a lot bigger, heavier, and a LOT more expensive.

You can see this in all lenses. For example, the Canon RF 24-105mm drops to an aperture of f/7.1 at the long end of its zoom range; that lens costs £450 and weighs 395 grams. If you're not happy with the changing aperture, you can get the RF 24-70mm f/2.8. That lens keeps its F/2.8 aperture all the way to the end of the zoom range. It costs £2,400 and weighs 900 grams -- despite having a significantly shorter zoom range. Or you could go for the 28-70mm f/2.0 lens, at £3,300 and 1.4 kilograms.

The XC15 has a 10x superzoom -- that's an extreme lens.  You won't find a fast (i.e. wide) lens like that, which can work for a large-sensor camera, and deliver excellent image quality.  The compromise which makes it work for the XC15 is allowing the maximum aperture to drop to f/5.6 when zoomed in.

If you're going to be zooming in on your camera, then you need to accept that your aperture is going to drop to f/5.6, because that's how your camera is constructed.  That's simply how wide the internals of your lens physically are.  You're perfectly right to want the aperture to be constant during filming; so my advice is to set f/5.6 as your manual aperture, then set the ISO to compensate. Or invest in more lights.

[Distoviolin1]

But can the issue be solved by locking the exposure?

[AtticusLake]

Aperture is part of the exposure, and I'm suggesting that you lock the aperture, specifically, so that it won't change unexpectedly.

For serious video shooting, where you're concerned about those kinds of changes -- and it seems you are -- you should generally shoot in manual exposure mode.  Page 55 of your camera's manual explains that, including how to set aperture.

You may well be able to achieve the same thing with exposure lock.  Basically that gets your camera to set the base exposure, then lets you lock it and fine-tune it manually.  That could work.  But manual mode gives you full control, and keeps you with the settings you choose throughout your shooting session.  The camera still gives you an exposure meter in manual mode, so you can still get the exposure set correctly (page 58).

One thing about M is that you can pick the shutter speed you want and leave it there.  Generally in video you don't want to change shutter speed -- it affects the feel of your video -- which is why I suggested to compensate with ISO.  For shutter speed, 180° (half the frame interval) is a widely-used starting point.

If you're not comfortable with how aperture, shutter speed and ISO work together to control exposure in photography, then you should really read up on that.  It seems like you're keen to produce quality results -- and of course that's awesome -- but a little study on your part will help a lot.  And it really is just a little.