Exposure,gain, iris and the big picture

[boke]

I'd first like to say thanks to all here, I've learned an unreal amount for the last 6 months. But I recently just got my camera (Canon Xh-A1) and while I've got a general grasp of things, I've still got a ton of questions and if there are any kind souls out there to help I'd sure appreciate it

- I guess my only real question is how can I use exposure, shutter speed, iris , gain , ND filter, white balance, to make a good picture? Now before you stop reading , I have actually looked at hundreds of past threads and have a good idea of what they do (except for knee, what is that??) , I just don't really have a good idea of how to use them correctly.

I understand that a ND filter can help in bright light situations, and gain can help in low light situations (but it adds noise), opening the iris exposes more light so it will lighten your picture, also shutter speeds can help in low light situations as well but you have to be careful of going below 1/24 as it'll look like a strobe effect (and is very bad for lots of motion), use the zebras to control the exposure, sometimes its ok to have your highlights blown out if it means keeping detail in your subject, but be careful because once somethings blown out and can rarely be corrected in post but underexposed can often be fixed, this is some of the things that I've read, but I haven't really found anything on putting them all together.

I read that a shutter speed of 1/60 is considered "normal" and an F stop (thats the iris ,right?) at 3.7 looks good for the XH-A1 (of course subjective), for interviews maybe set the white balance with a blueish white cause it give a "warmer" look to the subject. But I really don't know. I understand that it depends on the situation but can anyone give me a basic idea of what I should be looking for in certain situations? For example a talking head interview? or a greenscreen shoot ?(I understand the basics concerning lighting evenly and seperating talent and screen as much as possible)

Sorry if this is an impossible question
And what is knee?

 

[Barry_Green]

Well, it sounds like you have a pretty good handle on it, actually, you just need to practice.

As a practical matter, don't change the shutter speed and don't use the gain. Most of us don't; we use the default shutter (1/60 for 60i/60p, 1/48 or 180 degrees for 24p) and we control exposure using the iris. If the image is too bright to get a decent exposure by just adjusting the iris, that's when you flip in the neutral density filter.

As far as what f-stop to use, the wider you make it, the shallower the depth of field; the more stopped-down (i.e., towards f/11) the deeper the depth of field (meaning, the more of the image is in focus). That's your primary concern, is controlling how much of the scene is in focus. There are other concerns however; you never want to go to f/16 or deeper, and you pretty much don't even want to go to f/11, because diffraction will cause the image to become softer/fuzzier. The range from f/1.6 to f/8 is a pretty standard operating range.

You only use gain when you're otherwise doomed, or you like the grainy look it provides.

The knee helps control how the brighter areas get exposed; setting the knee lower will cause the system to actively compress the highlights, making the whites grayer and trying to hold on to detail before it overexposes. A higher knee setting does less compression, a lower knee setting does more signal compression. Try shooting a gray bar chart and adjust the knee while watching what happens to the whitest bars (or, if you don't have access to such a chart, you can try it with a cloudy sky and watch how the lower knee settings help separate the clouds from the blue sky, whereas a higher knee will probably make the sky blow out to white sooner, causing it to merge with the clouds).

 

[j1clark@ucsd.edu]

- I guess my only real question is how can I use exposure, shutter speed, iris , gain , ND filter, white balance, to make a good picture?

I think it would be better to think about 'lighting', rather than specifics of what to set the camera first.

In the olden days, video was typically 'lit' flatter than film. This was due to the limited range that a video process could represent light values in the scene. Too bright, video was washed out, too dark, video murky.

I personally hate 'video'... the development in digital video cameras has been to extend the range that the sensor can capture light, and allow for more dramatic, that is less 'flat' light. But still one has to keep in mind the limitations of the digital video camera.

So, with that in mind, lighting the scene becomes a paramount effort. Of course... if you are out on a location, using the 'sun' or natural light, you will be forced to some form of compromise. But even then, think 'reflectors', 'screens', and the like to modify the light on your subject to be within range of the camera.

Iris + neutral density, can cut light, so sure, look at the zebra lines, use ND settings, but then recall that the shadows are now equally reduced... and so use reflectors to kick light in those areas.

One point on the business of the F-stop (aka iris...). There is a lot of talk about using various adaptor lenses to get a 'shallow' depth of field... this is in keeping with current flim styles more than anything else... Look at say 'Citizen Kane'(1941) (in fact almost any Orson Welles film I can think of...), and you will see what is known as 'deep focus'. One shot in 'Citizen Kane' there was a special lens made to get sharp near field focus, and sharp distant focus... something that almost comes for 'free' with current prosumer level cameras (ok, not quite, but close enough...).

The point of that is, I think it is a philosophical choice to use the digital video camera as it is, and learn to compose, light, and place subjects, without recourse to a lot of additional accessories.

On the topic of shutter speed... I've not really changed the shutter speed out of what is 'normal' for the frame rate... The only occasion I'd think of changing the shutter speed, is if I need to have less motion blur on action. But... one of the complaints about 'video' is the fact that the interlaced 'shutter speed' is 1/60'th and gives a 'chopper' motion look for those who are looking for it... (There is also the herringbone jaggies that the successively acquired fields in the interlace mode produces...)

Gain... gain is for survailience cameras and the absolute need to get a shot, no matter what... If you are recording for 'forensic' purposes... sure... or if you are doing 'wedding/event' filming... well, that's close to 'forensic'... and the dance floor is lit for that 'romantic intemacy' look... do what you have to... because hell hath no rage like a bride disappointed... It is much easier if you clue the bride in before hand that when the lights go down, and they don't want a flood mounted on your camera, that this is what will happen...

White balance is important, because as far as I know, the 'white balance' in the camera is done before any digital compression, that is it is done with the 'raw' sensor data. The compression process is lossy, and so, while one can correct later, or even apply a cast in the editing process, it is using an image that has been compressed, and original data thrown away... unless you are shooting wiht very expensive high end cameras... you will not have even close to a 'raw' image in your editor to work with.

There are some tricks that one can do with White Balance to give a 'cast' to the resulting digital image. There are companies which make a set of 'balance' targets, with various color casts to give these effects... One may choose to do this 'in camera', but then one will be stuck with the result and it may not be preceived as so good later on in the post-production process... ideas change... one watch word is to defer certain choices to as late as possible... such as 'color cast', and the like...

 

[DanHD]

Good point.


That's why in most cases it's important to create the 'look' you want in camera before you capture/transfer into an NLE.. because there is no turning back after lossy compression. You can't get that color data back, and you don't have the freedom to push and pull as you do with today's new stocks.

It's a different case with cameras like the Red that allow for manipulation of RAW content, so you can basically change the red/blue/green channels in post to create your own white balance, persay

 

[boke]

well, it sounds like you have a pretty good handle on it, actually, you just need to practice.

As a practical matter, don't change the shutter speed and don't use the gain. Most of us don't; we use the default shutter (1/60 for 60i/60p, 1/48 or 180 degrees for 24p) and we control exposure using the iris. If the image is too bright to get a decent exposure by just adjusting the iris, that's when you flip in the neutral density filter.

As far as what f-stop to use, the wider you make it, the shallower the depth of field; the more stopped-down (i.e., towards f/11) the deeper the depth of field (meaning, the more of the image is in focus). That's your primary concern, is controlling how much of the scene is in focus. There are other concerns however; you never want to go to f/16 or deeper, and you pretty much don't even want to go to f/11, because diffraction will cause the image to become softer/fuzzier. The range from f/1.6 to f/8 is a pretty standard operating range.

You only use gain when you're otherwise doomed, or you like the grainy look it provides.

The knee helps control how the brighter areas get exposed; setting the knee lower will cause the system to actively compress the highlights, making the whites grayer and trying to hold on to detail before it overexposes. A higher knee setting does less compression, a lower knee setting does more signal compression. Try shooting a gray bar chart and adjust the knee while watching what happens to the whitest bars (or, if you don't have access to such a chart, you can try it with a cloudy sky and watch how the lower knee settings help separate the clouds from the blue sky, whereas a higher knee will probably make the sky blow out to white sooner, causing it to merge with the clouds).

ありがとう、先生

そうします

 

[Jokerswild]

This is why I love this forum. People take the time to lend help..Bravo. I enjoyed reading it all and learned quite a bit. Thanks.