7d exposure changing during filming

sambloxxy · 15 Mar 2013

Hi all,

I'm very new to using my slr for film, and I have a problem with the exposure change during filming. I'm shooting in manual mode, usually 25fps, 1/50th, and with an fd lens (so aperture locked).

I first saw this problem under incandesent lights, but I also see the problem in daylight. Everything is set - including wb - any suggestions to the problem?

The exposure usually flicks down a stop for a fraction of a second, as if I was changing the aperture.

Frantic_Inc · 15 Mar 2013

Are you using auto ISO?

Bleo · 15 Mar 2013

Welcome to dslr... Even if you move slightly the light will move even in manual therefore you will have to reset the apeture again. In auto the apeture will change but will look stupid on the video. These are the pit falls of the dslr. Frame, focus set apeture work to middle of the Meter bar. Having said that even on a tripod and its cloudy and you have set up, if it goes sunny then apeture will change.. Camcorder is only option

sambloxxy · 16 Mar 2013

Bleo said:
Welcome to dslr... Even if you move slightly the light will move even in manual therefore you will have to reset the apeture again. In auto the apeture will change but will look stupid on the video. These are the pit falls of the dslr. Frame, focus set apeture work to middle of the Meter bar. Having said that even on a tripod and its cloudy and you have set up, if it goes sunny then apeture will change.. Camcorder is only option

Thanks for the replys guys! I have been setting ISO manually, to answer the first question.

With the aperture; it physically cannot change - as there is no electrical connect between the body and the lens. The lens is a 1974 55mm f1.2 FD lens, converted to for EOS bodies. The aperture is set physically on the lens, so surely the camera cannot change this? I am by no means having a pop at what you said, I'm just trying to understand this very odd problem!

I will try and get some evidence up soon!

Thanks again

sambloxxy · 16 Mar 2013

Bleo said:
Welcome to dslr... Even if you move slightly the light will move even in manual therefore you will have to reset the apeture again. In auto the apeture will change but will look stupid on the video. These are the pit falls of the dslr. Frame, focus set apeture work to middle of the Meter bar. Having said that even on a tripod and its cloudy and you have set up, if it goes sunny then apeture will change.. Camcorder is only option

Sorry I forgot to add, this problem is occuring with a set composition, so not when the camera is being moved.

acetone · 16 Mar 2013

You doing the correct thing by shooting in manual mode, as above check that NOTHING in the camera is set to auto.

Bleo · 17 Mar 2013

Ha ok if no movement it may be the lens is faulty

sambloxxy · 17 Mar 2013

Hi, thanks for the suggestions guys. The lens not the problem - its fully mechanical, so cannot effect the exposure once it is set.

sambloxxy · 23 Mar 2013

Any more suggestions guys, I'm still scratching my head with this one?

CSB · 23 Mar 2013

If your aperture is physically set on the lens and your shutter speed and gain/iso is fixed, then the only thing I can think of is that the camera is faulty. My 550D doesn't change exposure in manual mode.

Can you post an example video?

troutfisher · 23 Mar 2013

You say incandescent lights,do you mean the old fashioned tungsten filament or do you mean fluorescent lights?
If its the latter,mercury vapour or sodium vapour then the exposure will change as the lights pulse at the frequency of the mains current.

sambloxxy · 23 Mar 2013

troutfisher said:
You say incandescent lights,do you mean the old fashioned tungsten filament or do you mean fluorescent lights?
If its the latter,mercury vapour or sodium vapour then the exposure will change as the lights pulse at the frequency of the mains current.

Hi thanks for you reply. I mean whichever lights you normally have in a typical house, which are filament I think? Either way its not that lights, as this occurs in Daylight too.

sambloxxy · 23 Mar 2013

CSB said:
If your aperture is physically set on the lens and your shutter speed and gain/iso is fixed, then the only thing I can think of is that the camera is faulty. My 550D doesn't change exposure in manual mode.

Can you post an example video?

I will post a video tonight that hopefully illustrates the problem; I dont think I doing a very good job of describing it!

farrance · 27 Mar 2013

I don't think it's a physical problem, I think it might be a function within the camera!

on your live view functions, make sure exposure simulation (exp.sim) is turned off. You might have an option for either exp.sim or movie display. If you put it on movie display, that should theoretically fix the problem.

I am recalling all of this from memory however as I haven't used a 7D in ages!

sambloxxy · 27 Mar 2013

farrance said:
I don't think it's a physical problem, I think it might be a function within the camera!

on your live view functions, make sure exposure simulation (exp.sim) is turned off. You might have an option for either exp.sim or movie display. If you put it on movie display, that should theoretically fix the problem.

I am recalling all of this from memory however as I haven't used a 7D in ages!

Thanks for the info; that wasn't something I was aware of, and havent seen it mentioned inbthe manual either. I certainly give it a go!