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F900R: ASA ratings and gamma settings


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#1 Demian Barba

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Posted 01 October 2008 - 10:35 AM

hi,

I am shooting a feature with the F900R, which has a supposed ASA rating of 300 according to the manual. I have the step gamma at 0.45, the gamma at Hyper Gamma 1 and the gain at -3, detail off, matrix off, black gamma off, master ped between -3 and -7 (depending on the scene) and saturation anywhere btw -15 and -21.

I have came up with a method to use my light meter (because I don't like relying solely on the monitor and waveform) in which I set up the lighting for my master shot judging exposure solely with the monitors. Once I am content I measure my key light and set the ASA on my light meter according to the T-stop on the lens (digi primes) and proceed to measure all the other lights and take notes of the contrast ratios so that then I can light the next shots like I would do with film: whit my light meter, only going to the monitors sparselyand staying next to the camera.

My problem is this, I have found out that I am rating the camera anywhere between 50 and 100 ASA... to damn slow. I am aware that this is not a scientific method and that sometimes I over or underexposed my key and therefore I rate the camera at different ASAs, but in best case scenarios I get 100. I need more! I listed my settings to see if anyone can help me to get more speed out of the camera without pumping the gain past 0. In some cases I had to remove the shutter to get an extra stop, but I can only get away with that when there is not much motion and most of the film is hand held. If this camera is supposed to be 300 ASA, where are my one and a half stops gone? Am tired of lighting with 5ks and up and I have some pretty big set ups coming up.

Thanks in advance,

demian barba
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#2 Jonathan Bowerbank

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Posted 01 October 2008 - 12:48 PM

As far as getting exposure, your settings seem fine. You could try different gamme curves, perhaps loading Sony LOG would help.

But 50-100 ASA seems really extreme, might wanna make sure the ND dial is turned to "Clear"? he he
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#3 Demian Barba

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Posted 01 October 2008 - 05:14 PM

As far as getting exposure, your settings seem fine. You could try different gamme curves, perhaps loading Sony LOG would help.

But 50-100 ASA seems really extreme, might wanna make sure the ND dial is turned to "Clear"? he he



but that is the thing, the NDs are off. that is why am surprised am getting such a low ratting.
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#4 Andre Labous

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Posted 01 October 2008 - 06:23 PM

Are you setting the T-stop on the lens with a grey scale measuring white at 100IRE by using a waveform or zebras set at 100?
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#5 Demian Barba

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Posted 03 October 2008 - 02:45 AM

Are you setting the T-stop on the lens with a grey scale measuring white at 100IRE by using a waveform or zebras set at 100?




what?


i do not understand this method. would it be more useful to get 50 IRE (medium grey)?


and my main question is: how I get more speed out of the camera with the gamma settings? no gain, no shutter.


thanks
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#6 David Mullen ASC

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Posted 03 October 2008 - 04:20 AM

Unless something is wrong with the camera in terms of the menu set-up, you must be misexposing it because the F900 should be at least 320 ASA at 0 db, 24P, 1/48th shutter.

You can set the zebras to appear at 100 IRE or 99 IRE and point it at a white field, or you can set them to appear at 70 IRE, which is not middle grey, but close to Caucasian skintone brightness (Zone 6 instead of Zone 5, i.e. about one-stop lighter than 18% grey) - generally you get some zebras to appear in the hotter spots of the skin on a Caucasian face.

If you need more exposure, basically your choices are:

1 - increase the light level
2 - increase the gain
3 - use a longer shutter speed time
4 - use a faster lens

Switching from 1/48th to 1/32nd at 24P gives you a half-stop exposure increase with only a moderate increase in motion blur (compared to turning off the shutter, i.e. 1/24th at 24P) and using a 3db gain is another half-stop increase with only a moderate amount of noise, so both tricks together (at 24P, 1/32nd shutter + 3db gain boost) gets you a full stop's worth of extra exposure.
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#7 Walter Graff

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Posted 03 October 2008 - 07:02 AM

I have came up with a method to use my light meter (because I don't like relying solely on the monitor...


Sort of like saying I don't like to look out the windshield when I drive so I put a camera on the bumper and watch a monitor instead.

While light meters are fun to use with video and make the experience feel like it's a film shoot they are not always accurate, especially when you start to vary exposure a few stops. Overall video cameras MTF is very different than film as the s curve is far flatter at the ends of the slope and hence why EI is not really a viable method for calculating exposure across the range of exposure.

Manufactures struggle to try to use these standards (EI,ASA, etc) but the engineers do not allow it as it's a misnomer in video and hence why they use terms in the specs of sensitivity in the literature is always stated as something like "f10 at 2000 lux". Lately manufactures marketing departments are erroneously using such terms as ASA but it is misleading for them to do so.

That you are needing 5ks to make enough light for your exposure tells me something is wrong with how you have the camera set. Make sure you have no ND dialed in. Where are your peds set? Other than that, unless you have a more scientific baseline for an EI at a particular exposure, you're really spinning your wheels.

Aim a camera at a 14 step chip chart. Light it evenly so that your iris makes the mid grey chip (the center of the "x" fall on 55 units on a waveform). Now look at the lens stop. Take a reading with your light meter which matches the same 24/48 setting as the camera frame rate/shutter. Adjust your light meter sensitivity so it matches that f-stop on your lens. Your meter now shows relatively proper exposure ONLY AT THAT camera f-stop at that light level. Change the f-stop on your lens a couple stops either way and that calibration for the meter now changes too.

Alternatively: You can also aim your camera at that chart and hit auto iris. Now compare the meter to the lens exposure the same way as above. Same result.
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#8 Demian Barba

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Posted 03 October 2008 - 07:47 AM

Unless something is wrong with the camera in terms of the menu set-up, you must be misexposing it because the F900 should be at least 320 ASA at 0 db, 24P, 1/48th shutter.


first of all: thanks for the replies.


i am not miss exposing, I do know how to read a waveform. I am new to the F900 so the chances that something I set-up in the menu is working against me are very, very high. what could be wrong in terms of menu settings that is making it so slow?

let me repeat my settings (and please let me know if I am forgetting to name something important, I am only naming what I consider the important ones and I can easily double check in the camera):

- 25 PsF (This is for PAL TV)
- step gamma at 0.45
- gamma at Hyper Gamma 1
- gain at -3 or 0
- detail off
- matrix off
- black gamma off
- master ped between -3 and -5 (depending on the scene)
- saturation anywhere btw -15 and -21.
- shutter at 1/50


Thanks,


P.S: please stop asking if I have the NDs off. I stated before that I did. Am new to the F900, but not new to ENG looking cameras.
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#9 Demian Barba

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Posted 03 October 2008 - 08:08 AM

Sort of like saying I don't like to look out the windshield when I drive so I put a camera on the bumper and watch a monitor instead.

While light meters are fun to use with video and make the experience feel like it's a film shoot they are not always accurate, especially when you start to vary exposure a few stops. Overall video cameras MTF is very different than film as the s curve is far flatter at the ends of the slope and hence why EI is not really a viable method for calculating exposure across the range of exposure.


I see... and that makes so much sense and explains why I set different ASAs in my light meter under different lighting conditions.

As for my method to use my light meter: As i said before, Its not like I come up with an ASA and use my light meter all day long without checking my monitors, nor I am trying to get a scientific ASA rating (I could care less for that). And the my method might not be pullet proof, but judging from the dailies my exposure has been pretty consistent.
Let me explain again: I set up my master shot with my monitor and waveform (deciding my exposure solely on those two), then I measure the key light and set up the ASA on my light meter according to the stop on my lens. Then proceed to measure all the other lights and keep notes of the contrast ratios so that when we move on to the next shots I light using my light meter and not my monitors, which I only use to double check my exposure. Then, when we are done with the scene and start a new one I start all over again.
I don't see why this is like saying "I don't look out the windshield when I drive so I put a camera on the bumper and watch a monitor instead". If you think about it, I think I am being even more careful, methodical and accurate by using both light meter and monitor than just one of them. First of all (I don't know about you guys) but I have never radically increased the light levels while shooting one scene (unless the scene starts indoors and finishes outdoors or something unusual like that, or we shoot part of it on location and finish in on a set). Second of all, I came up with this method because if I am shooting a long scene that will take an entire day or two, I will trust my light meter readings and notes more than my eyes and memory to keep a constant contrast ratio and exposure.

tks
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#10 David Mullen ASC

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Posted 03 October 2008 - 12:17 PM

I'd take the camera back to the rental house because either it is broken or it is set-up wrong, or you like overexposed video and/or your monitor is set-up wrong. The F900 is NOT a 100 ASA camera by any stretch of the imagination so something is wrong somewhere.

Obviously at -3 db, you've lost a half-stop, so I'm talking about 0 db. I'm also talking about the filter wheel being in the clear (3200K) setting since the higher color temp settings rotate a warm filter behind the lens. You'd lose nearly a stop by using the daylight (5600K) filter setting.

Take a Fotokem gray scale - it has I think six grey stripes (including a black one and a white one), an 18% grey field to one side and a one-stop lighter grey field below that is close to Causasian skin tone luminence.

If you set the camera for zebras to appear at 100 IRE and 70 IRE simultaneously, you should see the zebras appear on both the white stripe and the one Zone lighter than 18% grey stripe & field simultaneously.
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#11 Stephen Williams

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Posted 03 October 2008 - 01:39 PM

P.S: please stop asking if I have the NDs off. I stated before that I did. Am new to the F900, but not new to ENG looking cameras.


Hi,

Are you sure the ND filter wheel knob is correct, I.E. the clear is indeed clear?

Stephen
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#12 Demian Barba

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Posted 03 October 2008 - 01:44 PM

I'd take the camera back to the rental house because either it is broken or it is set-up wrong, or you like overexposed video and/or your monitor is set-up wrong. The F900 is NOT a 100 ASA camera by any stretch of the imagination so something is wrong somewhere.

Obviously at -3 db, you've lost a half-stop, so I'm talking about 0 db. I'm also talking about the filter wheel being in the clear (3200K) setting since the higher color temp settings rotate a warm filter behind the lens. You'd lose nearly a stop by using the daylight (5600K) filter setting.




aha! the filter wheel! I feel so dumb, I knew it saw something stupid... :$
If am loosing almost a stop there plus am close to 200 and if I add the -3db and some gamma functions I get the extra half 2/3 of a stop to get the camera to 300.


taking to the rental house its out of the question since I am in southeast turkey and the closest rental house is 300 miles away...


thanks david.
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#13 Stephen Williams

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Posted 03 October 2008 - 02:14 PM

taking to the rental house its out of the question since I am in southeast turkey and the closest rental house is 300 miles away...
thanks david.


Hi,

You could always use Skype if you don't have a phone.

Stephen
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#14 James Mehr

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Posted 03 October 2008 - 10:20 PM

This might be non-sequitur and even stupid, but are you shooting anything for Nuri Bilge Ceylan? I love his films, and am eagerly waiting for "3 Monkeys" to come to NYC. Yes, I'm aware it's a popular camera, but it doesn't hurt to ask... :)
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#15 Walter Graff

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Posted 03 October 2008 - 10:21 PM

Does the lens have an extender? Is it flipped in? If so you'll loose two stops.
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#16 Demian Barba

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Posted 06 October 2008 - 12:13 PM

Does the lens have an extender? Is it flipped in? If so you'll loose two stops.



nope, no extender, but problem solved.

at day, am shooting at -3d with the CC wheel at 5600K and at hyper gamma 1 with the master gamma at -10 which gives me an ASA of around 64 (once again, not scientifically and I do like to overexpose a bit since am in the dessert and it feels right). At night I am shooting again at -3db with the CC wheel at 3200K and hyper gamma at 3 with the master gamma at 0 which gives me an ASA of around 250 and am very happy with it.

Thanks everybody for their responses.


I'll be posting my experiences in the "on production" section, not because I believe I have wealths of knowledge to share but because this shoot is rather "unique" to say the least and because I will have more questions and I hope you guys will have more answers.


Thanks again
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