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Z1P - Iris, Gain and Shutter speed for exposure control? Whats the difference


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#1 Kavanjit Singh

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Posted 24 October 2008 - 02:17 PM

Hi - I want to know the difference between IRIS, GAIN and SHUTTER speed on Z1P. All 3 can be used to control exposure. However, when to use which? What is the relationship between all these 3?

Q1 - If I have low light conditions, how these 3 should be used?
Q2 - If I have burnout issue, then what should be way to go?
Q3 - If my BG is burning out and FG is low lit, then how can i go about it?

I want to know how these 3 work...how does one affect the other?

Hope you got what I am tryin to say...

Thanks
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#2 John Brawley

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Posted 24 October 2008 - 02:55 PM

Hi - I want to know the difference between IRIS, GAIN and SHUTTER speed on Z1P. All 3 can be used to control exposure. However, when to use which? What is the relationship between all these 3?

Q1 - If I have low light conditions, how these 3 should be used?
Q2 - If I have burnout issue, then what should be way to go?
Q3 - If my BG is burning out and FG is low lit, then how can i go about it?

I want to know how these 3 work...how does one affect the other?

Hope you got what I am tryin to say...

Thanks


You left one out. The ND filter....

Iris is usually the first control you want to use with the range of controls you have on this camera. By default we shoot most moving pictures at 24, 25 or 30 FPS depending on the end use and country you're in. Historically these frame rates have a shutter speed associated with them of 1/48th, 1/50th or 1/60th of a second. Since you have a Z1P i would gather you're in a 25FPS environment. While you can change the shutter speed, it does have an effect of the perception of temporal motion. So we don't tend to mess with that unless we want a very specific effect. (i hardly ever do it.)

Iris will affect exposure and also affects how much of the image is in focus (which is also affected by your focus distance and zoom range neither of which affect exposure)

Gain is like amplification. When you turn up the volume you also turn up the noise. You'll get a noisier and *denatured* image. Useful sometimes for a certain look, but again, usually avoided.

Ok to your questions.

q1. So iris first. ONce you run out of iris start using gain to shoot in lower light. If really desperate you can lower you shutter speed but everything gets streaky as you do this.

q2. Use iris first and if you start getting towards the f16 end, then start using ND filters. Again use higher shutterspeeds as a very very last resort unless you want the effect.

q3. You have to make a choice. You can shoose the background OR the foreground. Or you can choose to do something about it since youre the cinematographer. INcrease the FG level with lighitng or decrease the BG level with solids, flags Nets, ND etc.

jb
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#3 Adrian Sierkowski

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Posted 24 October 2008 - 02:59 PM

Zoom on that camera does effect exposure. IT's only really wide "open," when you're zoomed out. As you zoom in you loose some stop through the lens (i think it's about 1 stop). This is a caveat to most prosumer cameras, on professional lenses, you'll have a T stop (true stop) as opposed to an F stop. I'm thinking back.. and the lens opens up to F1.9 on the wide end and as you zoom in it goes to about an F2.8 You'll see if if you look at the LCD and zoom in.
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#4 John Brawley

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Posted 24 October 2008 - 03:03 PM

Zoom on that camera does effect exposure. IT's only really wide "open," when you're zoomed out. As you zoom in you loose some stop through the lens (i think it's about 1 stop). This is a caveat to most prosumer cameras, on professional lenses, you'll have a T stop (true stop) as opposed to an F stop. I'm thinking back.. and the lens opens up to F1.9 on the wide end and as you zoom in it goes to about an F2.8 You'll see if if you look at the LCD and zoom in.



Of course I was trying to keep things simple for someone asking the question in the way it was but yes it should be noted that most zooms will ramp or loose some exposure as you zoom. even the ones that are constant iris ;-)
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#5 Adrian Sierkowski

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Posted 24 October 2008 - 03:15 PM

Yeah, I know; i was just pointing out something that bit me in the ass once that i "forgot" about ;)
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#6 Chris Durham

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Posted 24 October 2008 - 03:31 PM

I'd add that if the camera has an ND filter as you suggest that in certain situations you should go to that first.

All of these effect the exposure by limiting the amount of light your sensor is digitizing.

Iris - the size of the hole through which light comes.

Shutter - the amount of time you let light in (or the amount of time the sensor collects light)

ND Filter - evenly filters all colors of light to reduce the intensity at which it comes through the lens

Gain - An electronic increase or decrease to the light-sensitivity of your sensor

Iris and Shutter are your main tools for affecting exposure in any photography; however there are some standards that have evolved in the realm of cinematography. The standard shutter in film is 180 degrees, which, sparing the mechanics lesson, means that the camera lets light hit the film 50% of the time. If you're shooting at 24 frames per second that's 1 second divided by 24 frames = 1/24 second per frame; exposed 50% of the time means your shutter is open for 1/48 second per exposure. There are reasons to adjust this but this is the standard and a good place to start from. I recommend not changing it at the beginning. Iris, then, is a better choice; however it comes with sacrifices - most commonly Depth of Field (DoF). The range of what can be in focus is smaller the wider your iris. Most people agree that a shallow DoF looks better fo a lot of shots, and since DoF also depends on the size of the capture surface (your small sensor), you can only really get good, shallow DoF with you iris wide open. This is where a Neutral Denisty (ND) filter can be very handy, because if you open your iris all the way, especially outdoors, you may very well be overexposing your image. Using an ND filter will filter out some of that light while allowing you to shoot wide open and have more control over your focus. If this seems like a lot to fidget with that's fine. It grows on you. As a beginner, I'd recommend setting your frame rate at 24 (25 outside the states), shutter at 1/48 (1/50 outside the states), and just work with Iris until you're comfortable. As far as gain goes, leave it alone. Set it at 0 and forget it's there. Digital cameras have enough problems with noise in the image to begin with, and adjusting the gain to get more exposure in a dark image just introduces more noise that you'll spend hours screaming at your monitor over. If you thing a scene needs a gain adjustment you're wrong, it needs better lighting. Gain is there for those times when you're really between a rock and a hard place. Since you're just learning this stuff, I expect you won't be putting yourself there.

That's my rundown. Leave gain alone because it's detrimental to your image. Leave shutter alone until you understand the reasons you should be changing it. Adjust exposure with Iris, and use an ND filter if that's not satisfactory for some reason.
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Visual Products

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