Smooth out exposure changes from a kit lens while zooming

Canon t5i with kit lens 18-55mm.

I'm working on a dolly zoom where I start at max zoom out and dolly away to max zoom in over about 3 feet of dolly travel.

As I reach max zoom the exposure changes. I realize this is due to the kit lens not having fixed aperture and that my focal length is changing.

I'm wondering if there is a plugin in Hitfilm pro 2017 that will automatically compensate and keep the exposure changes even throughout the shot.

I do have a variable ND filter but I already need 2 operators on the camera, one for dolly/zoom  the other for focus pulling.  And I have little confidence having another hand on the end of the lens twisting the ND filter will work out, but I haven't tried it yet.

Any other ideas?  I was thinking to perhaps have another person dim or move lighting to at least compensate to some degree.

Here's an example video:
https://www.youtube.com/watch?v=vxhUgIwwYF8&feature=youtu.be

Thanks

Comments

  • Not automagically but you should be able to use the Exposure plugin and keyframe the values to compensate.

  • Can you shoot using manual settings?  This way the exposure will be the same through out the zoom.   And as @Aladdin4d says you can keyframe the exposure when you do the color correction/grading.

  • Triem23Triem23 Moderator

    Um. There is an auto level and auto contrast filter. Might do the trick. 

    Otherwise there are a lot of filters you can use to manually adjust. Aladdin suggested Exposure. Brightness/contrast is another. I could rattle off another five or six, but those are easiest. 

    BobDiMarzio gives good advice with shooting manual. AV mode is another good one. Lock the Aperture at the lower value and that should help. Manual offers most control, AV is a good compromise. 

  • @Triem23 I know you can't see it, but I didn't mention auto levels and auto contrast because they tend to shift if the clip is shifting like the sample clip and you end up keyframing anyway.

  • So far I'm always shooting in manual mode for video.

    But interesting, I didn't think to try any of the non-manual camera modes because the problem is due to the focal length changing during zoom, not the video settings at any particular zoom level.  Higher end lenses allow you to lock the aperture during zoom.  Kit lenses don't.  I believe it's referred to as variable vs fixed aperture lenses. Here's one youtube link about it:
    https://www.youtube.com/watch?v=f4y-03LhVnk

    The clip i need to do is short so at least I can count on manual keyframing the exposure.  I really was hoping for that automagical plugin though 

  • edited November 19

    Disclosure: 1)  My stills experience far exceeds my video experience, although I have read extensively, watched a ton of  Youtube videos and Lynda Tutorials.  2) I shoot a Nikon 7100 not a Canon.    That being said I decided to test the fluctuating exposure.   I tested a Kit lens (18-70)3.5/4.5 and a old 28-105 also 3.5/4.5.    My findings were rather interesting.  and not unexpected.   I chose well lit scenes that allowed a base Shutter/Aperture/ISO that equaled   1/60 F11  ISO 100.     I noticed on mixed lighting (bright shadow) that there would be a difference of 1/3 stop to 1 full stop as a zoomed though the range.    I was able to change that by changing the metering mode.     Spot mode had almost no variation,  Center weighted and 3D matrix metering  had the most variation witch I assuming is related to the fact that wider focal length allows more of the "lighted" portion.  

    Finally I focused on a evenly lit external wall.  Since there was no variation in lighting,  there was no change in exposure throughout the complete zoom range regardless of the metering mode. 

    To validate the kit lens variable, I repeated the test using a 17-35 2.8 and an 80-200 2.8 lens.  Regardless of the lighting and metering  changes, the exposure change was almost 0  ( less than 1/3 of a stop with mixed lighting) in most of the instances it was rock solid. 

    Finally I remounted my cheapest Kit lens and repeated the tests using the auto ISO mode.  With auto ISO there was no variation in exposure during the full range of zoom.    remember I was using aperture between F8-F16 depending on the lighting and traditional video shutter speed of 1/60.

    So in a nut shell, If was going to reproduce the scene provided by @Hitfilmer172101 I would  add lighting and  use Auto ISO since the fluctuation  was (For me)  about 1 stop.  From a noise or quality perspective, the difference between  ISO 100 and ISO 200 should not be noticeable.

     

    Just my 2 cents.

    Bob

     

     

  • Hey Bob, thanks a ton for all of that info and effort.  I really appreciate it :)

    I've done more tests and have concluded that the kit lens aperture is simply too slow to keep up with the zoom.

    To start with, I'd say I have the scene decently lit.
    I have 2 lights on the background and a single spot on the subject.

    In full manual mode, I have to use ISO 400 (my camera only goes from 100/400/800 etc) and it is about a 1/2 step over-exposed.

    In full auto camera mode, the ISO ranges from 200 - 800 (closest zoom to furthest).

    Here's some pics of the setup in a video:
    https://www.youtube.com/watch?v=UaDkkMl105M&feature=youtu.be

    According to my camera manual, if I choose any dial setting other than M, it treats it as P.  Which takes over exposure and shutter speed.  When I do a test with those settings iso goes from 200-800 and shutter speed goes from 80-30 or something like that.

    This test is me simply fast zooming in full manual mode.  Nothing on the camera is set to auto so to me, this makes me think it is the lens itself that is having the issue with the exposure keeping up with the zoom.  
    https://www.youtube.com/watch?v=iwGLUBt50T8&feature=youtu.be

    And here's another go at me trying to keep consistent framing on the subject.  Since the shot is very short, I think I'll just assume I'll have to fix this in post.
    https://www.youtube.com/watch?v=iC0mOGYfqjM&feature=youtu.be

    Thanks again for the assistance.

  • @rotterjones

    In the two newest tests, there  appears to an exposure  parameter changing.  Make sure you do not have auto ISO selected.  If it was purely manual it would not  get darker and then lighter at the end.  The fact that it goes dark to light either indicates that one of the 3 exposure controls (shutter,aperture or ISO) is changing.  or it could be that the dolly or or an operator was blocking light and they moved out of the way at the end.  If you are varying one of the exposure controls, the background you have chosen may make it difficult for the camera as it  cycles from  wide to narrow.  The drum cases are flat black, the bins are a little more reflective and to the right of the bins is something very reflective.  Also, it looks like you are using the two side lights and a light in upper back of the room.  Make sure the dolly rig or operators are not blocking any of the lights. 

    Just my 2cents.  I hope it helps.

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