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Picture darkens on zoom - how to fix?

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Jen Musselman
Picture darkens on zoom - how to fix?
on Mar 20, 2018 at 1:12:39 pm

Hello,

I regularly film concerts for a school choir - in fact, last fall, some folks on this forum were invaluable in helping me improve my tripod game! I'm hoping that someone can give me a tip on how to fix another problem.

I'm very happy with my camcorder (Canon G40). At wide shots, it takes beautiful, bright shots of the choir on the stage. However, I've noticed a phenomenon that sometimes happens during my closer zooms and pans. Basically, after I've zoomed in and start panning across the group, the picture becomes much darker and the colors shift. When zoom back out, the picture returns to its well-contrasted, colorful self. It doesn't happen all the time which is why it's so frustrating.

From what I understand, this has to do with exposure, but I am at a complete loss as to how to fix it.

Has anyone experienced something similar? What can I do to improve this issue?

Thanks so much for any assistance!

- Jen



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Mark Suszko
Re: Picture darkens on zoom - how to fix?
on Mar 20, 2018 at 2:07:14 pm

I never heard back on how you did with the tripod....

It sounds like you have automatic iris control and automatic white balance engaged on the camera. Such features are best used once at the beginning to get the camera settings where you like them, then they should be switched to manual, because they will continue to adjust, usually at inconvenient times. Some cameras have the option to stay in manual iris, with a momentary button-push to let auto-iris fix your issue rapidly... then you let go the button and you are back to manual control. This is ideal.

Consult your camera owners' manual for how to engage and dis-engage auto white balance and auto iris.


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Jen Musselman
Re: Picture darkens on zoom - how to fix?
on Mar 20, 2018 at 4:12:29 pm

Hi Mark,

The advice on the tripod made SUCH a difference! The external zoom controller was a game-changer. I can't believe how much easier that makes everything. I am still struggling with working the rubberband-pan apparatus (it's harder in tight situations), but when it works, it works much, much more smoothly than just using a hand. Then there was the tilt/balance issue. Apparently my tripod head model actually has a real issue with balance, so the problems I was having were normal (I found a review by a pro that described it). That said, I was able to better balance the camera so that it holds tilts and pans without me having to engage/disengage the locks all the time. Seriously, I have improved so much with the advice here!

Back to the current problem. The manual calls iris "aperture adjustment." I have it set now so that the camcorder automatically adjusts aperture and shutter speed to obtain optimal exposure. You can also set the shutter speed manually (and the camcorder automatically sets aperture) or set the aperture manually (and shutter is set automatically). There is also a manual exposure option where you can adjust both manually as well as the gain. (I will now admit that this is the part of the camcorder that I least understand!) The manual lists available aperture value settings from F1.8 to F8.0.

I guess what I don't understand is - would I need to manually adjust the aperture value every time I zoom in or out? Is that how it works? (Yikes - I can barely manage the zooming and panning themselves!)

I understand the concept of white balance and how to set it - the problem is, I don't know how to set it for my current situation. Even if I set it manually before the concert, once the lights go down, the lighting will be completely different. So how can you set white balance manually in that situation?

The camcorder does have assignable buttons. A button can be set to jump to the White Balance panel, where you can switch between auto, a number of presets, or manually set the temperature. Another button can be set to Exposure, which I believe jumps to the panel where aperture/shutter/gain are all set manually. Are these the type of buttons you are talking about?

Thank you so much for helping me!

- Jen



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Mark Suszko
Re: Picture darkens on zoom - how to fix?
on Mar 20, 2018 at 5:04:19 pm

Ideally, you set aperture (iris) and white balance during rehearsal, and leave them that way for the performance. If you don't have the opportunity to set them in advance that way, you should set the white balance to a default preset for "indoor" (about 3200 degrees Kelvin) and then you'll have to adjust colors in post production as needed.

Something that will help you in post is to shoot full frame of a white card, just before the show, and use that as a point of comparison when adjusting colors later. Ideally, you'd shoot a color bar chart on location; or what we call a "Macbeth chart" of color chips - that's a bit more advanced, but really helpful in post for getting colors right. Color bars that are electronically generated in the camera don't do you any good here: you need to see the colors as they have come thru the lens, under the existing lighting conditions, onto the sensor.

Here's the thing about shooting theatrical material with a "prosumer" camera. Stage lighting is not "normal" everyday lighting. It's done not just to light things to be seen, but also for dramatic effects, so if they throw up a lot of red or blue in a scene, that's intended... but an auto-white, auto-iris camera doesn't understand that. It's going to try to un-do the lighting director's work and "correct" it to make it look like everyday daylight or tungsten. And auto-iris is going to obsess on the brightness level of one , small bright white item in your frame and clamp aperture to that, making everything else around it too dark. Or it will concentrate on a large dark area and over-expose, blowing-out people's faces. Then what you get looks like junk.

So in these kinds of settings I recommend all-manual settings, and yes, that may mean manually "riding" the iris controls up and down to keep a reasonable level of exposure as you zoom in or out. If your camera has "zebra bars" as a display option in the viewfinder, turn those on and learn how to read them. They will show you where you are in danger of over-exposing.

The most important thing to capture on stage is a clean, well-exposed FACE. Everything else takes second priority to that, because nobody can or will watch blown-out faces. You can bring up the mids and blacks in post, but you can't restore blown-out detail, so make all your exposure and color decisions while shooting based on making the FACES readable and clear.

This is also another reason why shooting with two or more cameras is so useful: the wide shot and closeup shots can stay fixed at the proper settings for each, without constantly having to ride their iris.


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Jen Musselman
Re: Picture darkens on zoom - how to fix?
on Mar 21, 2018 at 1:23:44 pm

I have figured out how to set the white balance to 3200 Kelvin. None of the presets are for "shooting from a dark audience into stage lights" so I'll go with that for now. The picture seems very cool here in my studio but maybe it will work for the auditorium.

As far as the exposure: the camcorder has a feature called "exposure compensation." Basically, if the automatic exposure isn't right for a certain shot, you open the exposure panel and can touch a subject on the screen to force the automatic exposure to readjust. Alternately, you can also adjust the exposure manually at that point too, with values, which can be locked. And automatic exposure can also be re-engaged from this panel.

What I'm wondering: if the auto exposure is good at the wider shot, shouldn't I just open the exposure panel and lock the exposure at that value, and then it will hold for the zoomed shots? I actually read similar advice on another forum. Is there a downside to doing this?

I forgot to mention: while I still am only using one camera, I am adding a separate digital audio recorder for this concert, which I believe you or another poster recommended. It will be set up on a tripod right in front of the choir. I'll still use my shotgun mic but hopefully the recorder will capture clearer sound that bypasses most of the audience noise and echo. This is the test run though and I'm a little nervous about it!



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Mark Suszko
Re: Picture darkens on zoom - how to fix?
on Mar 21, 2018 at 1:54:22 pm
Last Edited By Mark Suszko on Mar 21, 2018 at 1:58:40 pm

" if the auto exposure is good at the wider shot, shouldn't I just open the exposure panel and lock the exposure at that value, and then it will hold for the zoomed shots?"

Maybe.... It will hold... but will it be *right*? The trouble started when your auto-iris kept changing depending on wide or tight shots. I guess you'll find out at the next performance.

Expose so faces are clear, and not blown-out: everything else will have to fall where it may. And you can bring up mids and darks in post.

That audio recorder could be planted center stage or at the foot of the stage...or on a low mic stand in front somewhere... or, with an appropriate matching cable, you can connect it to the audio control board, if you're using mics and a mixer. To make things simpler in post, once the audio recorder is started, start the camera and then let it free-run without stopping until the very end of the performance. That will make synching the external audio much easier. Any pauses in the program can be edited out after you synch the tracks.

It sounds like you are progressing well in your pursuit of a better image. Good luck, and let us know how the next one looks (and SOUNDS!)


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Jen Musselman
Re: Picture darkens on zoom - how to fix?
on Mar 23, 2018 at 3:55:06 pm

I am back with my results!

Well, exposure was kind of a disaster. I did set a custom white balance, but unlike previous concerts, the house lights were kept on so there was not as much of a contrast between the house and the stage - and that kind of threw me off. I have been trying to learn how to set Final Cut Pro's color corrector this morning in an attempt to better expose the image. It's still not great, but I think I did improve the image. I'm thinking I should have just left the WB on auto, since I had the exposure on auto - wondering if that made everything worse.

And then there is the audio recorder. Also unlike every previous concert, the choir did not do an on-stage warmup before the concert, so I was not able to get an accurate level. The accompanist did help me get an idea by playing the piano for me ahead of time, but I was terrified of distortion and set a very conservative level. Well, the audio is audible but too soft. (But it DOES sound great! Such an improvement in clarity over the echo and audience noise captured by the shotgun mic.)

So now I'm trying to figure out if I should (or can) boost the audio levels of the recorder track (and not use the shotgun audio) or combine the recorder and shotgun mic tracks. The shotgun would boost the volume, but the clarity of the recorder is so much better - I hate to ruin it. What do you think?



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Mark Suszko
Re: Picture darkens on zoom - how to fix?
on Mar 23, 2018 at 4:56:53 pm

To fix the exposure, highlight the entire video track, then select the color correction tab. Pick the version of the tab that handles "exposure", and move the middle and left slider-puck thingies while watching the results and watching the waveform monitor scope, so your levels stay under 100 IRE units.


Well, too-low audio is better than clipped, over-loud audio. Final Cut has some good plug-ins like "normalize", and "loudness" which will bring it up, but may also introduce some hiss and noise, and reduce some of the "dynamics". Then you may have to add some equalization.

One technique people sometimes do with too-low audio is to layer multiple identical tracks of the low audio, like three or more.

You can also bring the low audio track into Logic, or, a free audio editing tool called "audacity", and play with enhancing it there. Then re-import it into the timeline and synch it back up.

You can mix in the shotgun, I suppose, but there will be a little bit of phasing or echo happening if the distance between the two mics was great. It may require bumping one of the audio sources a frame or so to synch them up.

Auto iris is not your friend on this kind of gig: you need to ride it manually.

The audio recorder has an automatic gain control, I suggest you enable that on the next try. You're getting better with each effort - keep it up!


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Jen Musselman
Re: Picture darkens on zoom - how to fix?
on Mar 23, 2018 at 6:15:44 pm

Can I ask you two more questions? First, if I layer the audio recorder tracks, what db level should I shoot for with the loudest material? I've never attempted that before so I'm just curious as to how loud it should be (so I know how many dupe tracks are needed).

And as far as the exposure - I found good directions online for using the FCP 3-way color corrector. The picture is underexposed and it's the whites that need boosting. However, if I follow the directions online that advise boosting the whites to reach near the 100 level (which improves the picture a lot), I get an excess luma warning. I have to dial the white way back down, almost to the point of pointlessness, before the luma warning goes away. So my question is: how worried do I need to be about the luma warning?

Thanks so much for your help with this. I am learning!



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Mark Suszko
Re: Picture darkens on zoom - how to fix?
on Mar 23, 2018 at 6:31:32 pm

If you're making DVD's or a file for broadcast, you have to honor the 100 IRE limit. If it's for YouTube only, maybe you can get away with going higher, but I'd still advise against it. Blowing out the whites kills detail and ruins the contrast.


Do you understand how to use the waveform monitor or a histogram display in FCPX? Blacks (unless you are in Japan, where black level is zero), are to be at 7.3 IRE units. Brightest white is no more than 100. Everything else rests somewhere in the middle. If you raise the blacks or mids, it bring the whites up too, so you'll have to bring them down again after the mids and blacks have been set.

As to audio levels, on my system I make everything peak at minus 12 DB. Other people do it differently.


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Jen Musselman
Re: Picture darkens on zoom - how to fix?
on Mar 23, 2018 at 7:23:14 pm

OK, thanks. My original blacks are hitting near 0, so I will try raising them a little.

This is just for YouTube and Facebook video. I guess it might be used elsewhere someday, but right now web distribution/sharing is all we're doing.

Yes, the guide I found has a pretty good description of using the histogram to adjust the blacks and whites. No expert, but I think I get the basic concept.

-12 db is in the guide for my audio recorder too - I just didn't know if that was a guideline for live capture or for a finished product. But sounds like that's good to go with.

Thanks again for your help.



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Mark Suszko
Re: Picture darkens on zoom - how to fix?
on Mar 23, 2018 at 7:51:47 pm

I expect nothing but a progress report on this one and the next one:-)


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