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C100 tech shooting question: ND filters & ISO

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Joseph Livesey
C100 tech shooting question: ND filters & ISO
on Feb 3, 2016 at 1:47:19 pm

I have a question, which is perhaps a bit stupid, but one I still don't get: I understand the following increase and reduce exposure in different directions--ND filters, ISO, opening/closing the aperture--however, do they all affect the image in the same way?

I recently shot a scene in a church building where there was very bright sunlight coming in through windows in an upper tier of the hall, but quite dark lighting in the lower tier where people were sitting. This was for a documentary so I needed to set up in a way that was pretty versatile, getting coverage of individuals as well as the whole space--lots of beautiful light coming through the stained windows, but for the most part focusing on the people in the main space.

I used a gray card and wave form monitor to judge exposure (shooting with a Canon C100 mkI, using EOS Standard custom picture setting). However, I made a decision to actually add 1 ND filter, keep my aperture as open as possible (in this case F4 with Canon's 24-105 L), and boost my ISO way up to 6200. I know, crazy right?

I did this because without the ND filter but with lower ISO the contrast in the image was too big, and the beautiful sunlit windows were much more washed out when I exposed correctly with the gray card and WMF. So I went with the unusual combination of adding a filter and having a high ISO in order to expose, using the wave form monitor. I am really happy with the images I got this way--yes some noise in the picture but it looks great IMHO and there were lots of approving comments in my class, and I know that this is all that really matters. But then when I shared the surprisingly high ISO that I used, which shocked everyone, my instructor at school said afterwards that what I had described about my setup and my rationale made absolutely zero sense, technically. We have not been taught to expose using WFMs in our class. So, I've been cobbling my shooting technique together through tutorials and forum posts online.

Having been forced to question what I did, I figured that a better workaround would be to load the EOS Standard gamma settings into a custom picture profile and then play with the settings to bring the highlights I wanted to capture down in the WFM. One thing I do not understand still is whether with the workflow I used in that shoot, was it the ND filter that reduced the contrast of my image, which the high ISO then boosted to correct exposure? Or was it the high ISO that made details in the highlights visible in the image?

Sorry for such a long question. I just wanted people to tell me what's what.
Thank you everyone!


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Todd Terry
Re: C100 tech shooting question: ND filters & ISO
on Feb 3, 2016 at 5:55:04 pm

[Joseph Livesey] "do they all affect the image in the same way?"

No, they all affect your image in different ways.

For example, stopping down your iris reduces exposure, but it also greatly increases depth of field. I.e., if you were to want a shallow depth of field, then using a higher f-stop is not the desired way to decrease exposure.

Riding your ISO up and down can compensate for exposure differences, but you don't want to do that too much... ideally all shots in a particular scene should be shot with the same ISO, or at least in the neighborhood. Riding it up too high will increase grain. Your camera has an "optimal" ISO which I'm guessing is 850 (I'm basing that on the fact that it's 850 for the C300, so it's likely the same for C100).

I agree that your combination doesn't make a whole lot of sense to me. If you are shooting wide open at 6200 you were likely in a very very dark environment if you got good exposures. It makes no sense to add ND and also jack up your ISO to such a high level. It'd be smarter to use no ND and a lower ISO, you'd have much less noise in your images. Neither the ND filter nor the ISO settings should have any effect on the contrast range in your images. In your case you were doing a combination of two less-than-desirable things (adding ND and jacking up the ISO) in order to achieve a look that would likely have been better without either of them... no ND and much lower ISO.

Toss your grey card and don't use it for exposures at all. Yes, look at the waveform monitor and use that as a guide to make sure you don't have any blown-out overexposed areas (unless they are areas that you are okay with blowing out, as is sometimes the case)... and keep in mind as a general rule the lower the ISO, the better.

You didn't mention the fourth way of controlling exposure, shutter speed. Unless you are doing it for a particular effect, it's best to stick with a "normal" shutter speed... which is "one over twice the frame rate." That is, if you are shooting 24fps, a "normal" shutter speed (one that emulates a 180° shutter in a film camera) would be 1/48th. Best not to play with that setting unless you are looking for the specific "narrow shutter look" like you see in action movies way too much, or you are doing a remake of Saving Private Ryan.

The bottom line, though, is that as long as you are perfectly happy with the images you got, then what you did is ok. It doesn't matter how you make the soup, the only thing that matters is what the soup tastes like.

T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com



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Joseph Livesey
Re: C100 tech shooting question: ND filters & ISO
on Feb 3, 2016 at 6:34:59 pm

Thanks so much for your reply!

Yes, that's right, the "optimal" ISO is also 850 for the C100, although I have seen plenty of people posting that they like to use higher ISOs (although nothing as high as 6000) because of the textured effect it can produce in certain situations.

I'm interested in more about your objection to using a gray card to judge "correct" exposure. I've found that technique quite beguiling as before I learnt it I was finding my footage with the C100 coming out of the camera unpredictable--sometimes looking great, but sometimes underexposed.

Still asserting that, using the gray card to expose with the wave form monitor, the high ISO with the ND filter brought detail in the highlights out that exposing in the same way but without the ND filter and the lower ISO did not.

And thanks for your pointers about shutter speed!

All best,
Joseph


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Todd Terry
Re: C100 tech shooting question: ND filters & ISO
on Feb 3, 2016 at 7:18:02 pm

Exposing with a gray card is ok... if you are shooting a movie about gray cards. But in real life the exposures, in various places and orientations and lighting situations, just aren't going to be the same as your card.

Also you said this was for a documentary... usually those are sort of loosy-goosy run-n-gun (or at least quick and unpredictable setups) situations. I really can't conceive of the practicality of, for every shot, taking your gray card and placing it exactly at your subject (say, right at the face of someone you are shooting that is in frame) and adjusting the exposure for that, and then getting your shot. That's the only way a gray card is both accurate and useful. Also, a card is by its very nature a flat plane. Most objects, say a person's face, are not. What reads as "perfect" exposure for the card might be completely wonky for a person's face... because of highlights, shadows, and the way the light paints on a person.

As for "I have seen plenty of people posting that they like to use higher ISOs (although nothing as high as 6000) because of the textured effect it can produce in certain situations"... well... these days, with the single exception of depth of field, there are virtually no effects that years ago were accomplished in camera that cannon now be achieved in post, with much greater finesse, accuracy, and changability. Say, if you want a particular effect that you can just as readily do in post as in camera, doing it in post is almost always a better choice. If you do it in camera, you're stuck with it... there is no dialing the effect up or down (or removing it) if in the editing phase it's not something you like. These days there is hardly ever a filter in my matte box anymore, if at all. Maybe occasionally ND (just for exposure), but that's it. Everything else is done in post. In-camera effects are, obviously, baked in and there's no opportunity for adjustment.

But again, if it looks good... do it.

T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com



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