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Exposure changes when zooming even in fully manual

Discussion in 'Videography' started by harrisdpi, Apr 21, 2017.

  1. harrisdpi

    harrisdpi New Member

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    Has anyone else noticed that the image exposure changes when zooming in or out while filming, even though ISO, aperture, shutter speed and white balance have been locked down?

    If so, is there a way around it?

    When I get a chance I will post an example.
     
  2. Gaston

    Gaston Premium Member

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    Normal if your lens doesn't have a fixed aperture... like the 18-55 or the 55-200 for example...
     
  3. Goldingd

    Goldingd Premium Member

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    First answer, well actually a question first, is what particular zoom lens? If is one with a variable aperture, then that is fully expected.

    Second answer, if it is a fixed aperture (aka constant aperture) zoom lens, then that depends upon the quality of the optic design.

    Note, I am not talking about depth of field.

    Incidentally, focus can change as well (depending on quality of optic design)
     
    Last edited: Apr 21, 2017
  4. SausalitoDog

    SausalitoDog Premium Member

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    Depends on the lens. Many of the fuji zooms change aperture as they zoom.
     
  5. Shadowside

    Shadowside Good Glass is Forever...

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    In addition to the valid points already mentioned...

    Even if the lens has a fixed aperture your metering method will be affected by a change in content, for example if using average or matrix as the content changes so will the average EV, if using spot this can also happen as you zoom in your meter is less influenced by surrounding luminance.

    If you want to test the variance for this with you meter you will need an even (large) light source and a large consistent surface (wall),. focus at infinity (manually) and be within a meter of the wall (or so). Do your test with a high enough ISO setting to allow for hand held speed (meters are less accurate at either extreme end of their range) and stop down one stop to reduce the effect of vignetting changing at different focal lengths.

    When you are all done this test, read an article on the ISO-Less sensor like those used in Fujis. :)

    ISOless Photography With the Fujifilm X-Series

    :)
     
  6. starlights

    starlights Premium Member

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    Is your observation based on reviewing actual footage or just what you noticed through EVF while filming? What mode is your EVF set to? Is it possible that its only the EVF compensating ? Try setting it to the non-studio mode (I am forgetting what is it called in the camera menu)...

    If, as stated, your aperture, SS and ISO is locked down, then the only reason your exposure will change while zooming "out" with a variable aperture zoom such as 18-55 or 55-200 is if your aperture is locked down at the widest and you were zoomed in to a focal length where the available aperture was smaller than the value locked down. In this case while zooming out the camera will try to set it to the widest aperture that is locked down and now becoming available as your zoom out. Lock your aperture value to one of the constantly available apertures and you should not see this phenomenon.
     
    Last edited: Apr 21, 2017
  7. starlights

    starlights Premium Member

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    The metering should not affect the exposure if the aperture, SS and ISO are all locked... should it? Otherwise what would be the point of using all manual while filming? Unless I misunderstood and you were referring to how EVF handles it, not the actual recording

     
  8. Shadowside

    Shadowside Good Glass is Forever...

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    Correct, it shouldn't affect the exposure if the camera is on all manual. However, if you are testing the meter of the camera (as I wrongly assumed was the OP's point here) there are many things that will affect the meter that are not as 'fixed' as we think they are. :)

    Sorry to distract, I will go back to hockey and my scotch lol...
     
  9. Gennadiy Snopkov

    Gennadiy Snopkov New Member

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    The same. All in manual mode. Aperture - 5,6. When I zooming, exposure jumps, at the end of zooming - fine.
     
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  10. harrisdpi

    harrisdpi New Member

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    Hi again, and truly many thanks for all of your thoughtful and interesting replies so far.
    To answer some of your earlier questions, I have been using the 16-55mm f2.8 mainly shooting at f/5.6. I did some tests earlier today (which I can upload if interested) where the shutter was at 1/60, aperture at f/5.6 and ISO at 1600. I custom set the white balance and did one test where the metering was set to matrix and the other set to spot (neither setting made any difference). filming was shot at 1080p at 60fps, the film simulation was set to pro neg standard, shadow and highlight tone set to -2 noise reduction set to -4 and colour set to -2.
    As I zoom in though the whole 16 to 55mm ratio, you get three distinct incremental exposure shifts that I would estimate jump one third of a stop each time (this also applies when zooming back out as well).
     
  11. harrisdpi

    harrisdpi New Member

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    And yesterday I had a completely different problem that is a complete disaster given that I was shooting for a paying client!

    Having set the focus lever at the front to M (manual) I locked focus on my subject at f/5.6 and started to record a head and shoulders interview that I was conducting. After briefly reviewing the beginning of each piece of footage I was satisfied that I got what I needed and left only to review the footage this morning.
    I have no explanation how this could have happened but as the interview progresses the focus ever so slowly shifts.
    At the beginning the subject is in perfect crystal clear focus, yet by the end of the 5 min segment the guy is completely out of focus but the background behind him (2 metres behind) is perfectly in focus!
    I have never seen this happen before so I tried to recreate the issue today and couldn't!
    The footage is totally unusable and unfortunately my interview subject has as of today left the country!
     
  12. harrisdpi

    harrisdpi New Member

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    P.S. I can also upload this example if anyone is interested to see it (or wants to have a laugh at my expense).
     
  13. starlights

    starlights Premium Member

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    That is indeed strange and very unfortunate. Can you salvage the interview by using the part that IS in focus and then using voice over cut scenes (B-Roll shots of whats being discussed) and then finally, a bit more of the subject (perhaps a smiling shot or something carefully sliced out of the footage that is in focus) towards the end to conclude?

    It would be such a waste to throw it away (I have been there before for sound related issues....)
     
    Last edited: Apr 29, 2017
  14. harrisdpi

    harrisdpi New Member

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    Hi Starlights, yes it is indeed unfortunate but as you say, I plan to still shoot b-roll footage and I did get the guy to record audio separately as well so think I might be able to fudge something together. I rang Fuji yesterday but they had no suggestions other than make sure I was using the latest firmware for both camera and lens (yes) and factory resetting the camera (which seems to be their answer for everything).
     
  15. Greg_E

    Greg_E Premium Member

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    When you say exposure changes, do you see this on the in camera meter, or do you see this in the recorded video?

    Do you have any adapted manual lenses you can try to see if it is a camera sensor issue. I'm guessing it is a lens design issue and there is no way of fixing it.

    Not sure about to focus issue, but sounds like something in the lens drifted, or the camera commanded it to change.
     
  16. harrisdpi

    harrisdpi New Member

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    Hi Greg. Thanks for your response.
    In reply to your three points, firstly regarding exposure changes, it is clearly seen when zooming in and out on the camera meter (as it jumps) but is also clearly visible when viewing the recorded footage both in camera and after downloading on a computer screen.

    Unfortunately I do not have any adapted manual lenses to try out but my gut feeling is the same as yours that it is a lens design issue. However, I am wondering if it could be addressed in a firmware update?

    Regarding your third point, to me it feels more likely that the lens itself drifted and was not something the camera itself commanded. Either way, the question I then ask is, why did this happen, and how could it have happened, and how can I stop this from happening again?
     
  17. harrisdpi

    harrisdpi New Member

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    Hi again, I filmed another set of interviews yesterday and once again have more examples of the issues I am encountering (excuse the quality of this clip but its just to illustrate the exposure jump in fully manual mode). Anyone have any further thoughts? As Fuji UK suggested, I reset the camera to factory defaults over the weekend but it did not solve the problem.

     
  18. harrisdpi

    harrisdpi New Member

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    And an example of the focus shift....

     
  19. Greg_E

    Greg_E Premium Member

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    That's strange! The exposure seems to be a commanded function, like the programming changes the iris depending on focal length to try and keep it constant but is failing during video use. The only thing I can think of with the focus is that maybe things are getting warm and shifting. Either way I think I'd be moving to manual lenses for money making work. What sucks is the lack of decent manual zooms with prices that can be afforded.

    Can you swing the new Fuji cinema zoom? I think it was going to be in the $4000-$5000usd range which is a lot unless you are busy enough to justify it.

    The other choice would be Canon "new" FD (or nFD) 20-35f3.5 and 35-105f3.5 zooms, these are parfocal (when adjusted and in good repair) and both can be adapted to non-electric EF. You can get some light back through the use of a speed booster (either FD or EF). The big deal for these zooms would be to get an adapter that actually has the correct flange length, or you will never get the focus to hold doing the zoom (parfocal).
     
  20. harrisdpi

    harrisdpi New Member

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    Many thanks for your reply Greg (and sorry for the delayed response).

    Not sure I will be able to go to the cinema zooms or any other lenses for the time being but I am happy to say I finally managed to finish filming the short doc using my existing Fuji lenses without any more exposure shifts (basically I didn't bother zooming in or out at all).

    If interested here is the vid (all shot on the X-T2).

     

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