[IMPOSSIBLE] Expo lock in video

[ReinisK]

Hello!

Could it be possible to implement expo lock (if you can call it like that) in video? It could be useful for non-fixed aperture zoom lenses. For example Canon 18 - 200 lens.
When you are @18mm max aperture ir 3,5, but @200mm it's 5,6, so when you zoom in, it gets darker. It could be very useful to set the exposition, and when you zoom in, the camera automatically adjusts the ISO to compensate for the darker f-stop.
Of course, you can set the aperture to f5,6 already in the beginning, but everyone knows, that the aperture adjusts itself all the time, while zooming, and it creates some flickering during the zoom motion. It doesn't happen when zooming from f3,5 to f5,6. So, if it could be compensated by automatically changing the ISO, that would create a usable zooming motion.
Another plus is that you could use the lens at f3,5 in the wider end, instead of f5,6 (now you can't because of the exposure change).

[a1ex]

Enable gradual exposure at the slowest possible ramping speed, and try it. That's pretty much the best we can get.

I think you'll get better results with auto ISO.

[ReinisK]

Auto iso kind of works, but then I can't adjust the exposure myself.
Gradual exposure is one of my favourite things in ml, but it seems to make the zooming from f3,5 to f5,6 worse than it is without the gradual exposure (tried different settings, 1ev/32 frames looks like the best). From f5,6 (@18mm) to f5,6 (@200) it improves the filckering though doesn't void it completely.
Looks like I'll have to wait for a fixed aperture 18-200 zoom Though on sony vg10 their 18-200 lens works without flickering.

[Malcolm Debono]

Why not just set the exposure manually with an aperture of f/5.6? That way the exposure will remain constant at any focal length. I understand that this may not be optimal when shooting in low light, but if you're considering zooming then you'll obviously need to use the f/5.6 aperture.

[ReinisK]

Since it's not a constant aperture zoom, setting it to f5,6 already in the beginning results in flickering while zooming. If you don't care what your zooming looks like and you are going to cut it out anyway, it's fine. But zooming motion on a fixed aperture lens will never look like zooming on a non-fixed aperture lens no matter what you set your starting f-stop to. The only way I see is to gradually compensate with iso while zooming from 3,5 to 5,6.

[Malcolm Debono]

You're right. Didn't know about that so I just tried it out on an old 18-55 kit lens and even if you set the exposure manually, you can still hear the aperture clicks at certain focal lengths. If you really need to zoom and keep the same exposure, you might try unscrewing the lens a little bit. Tried it out myself and aperture won't change since the lens isn't making any contact 

[ReinisK]

Interesting idea. The aperture indeed doesn't jump around if I do so and the exposure change is smoother than with the lens properly attached. The exposure change still remains though.