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A proper exposure

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  #11  
Old 07-02-2012, 05:08 PM
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Tony W Tony W is online now
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Re: A proper exposure

Sorry but I missed the point in post #6 where you said you shoot with strobes in the studio or on location

You suggested that you used a spot meter 'I use spot meter on the forehead and then find the suggested exposure', could you go into a little more detail e.g. make and model of spotmeter and how you actually use it to measure exposure?
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  #12  
Old 07-02-2012, 09:02 PM
ir0nma1den ir0nma1den is offline
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Re: A proper exposure

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Originally Posted by Tony W View Post
Sorry but I missed the point in post #6 where you said you shoot with strobes in the studio or on location

You suggested that you used a spot meter 'I use spot meter on the forehead and then find the suggested exposure', could you go into a little more detail e.g. make and model of spotmeter and how you actually use it to measure exposure?
In my beauty dish scenario, I am using strobes (elinchrom) and reading the metering that my in camera meter (Nikon D300) is giving. When I say spot meter, I mean using the spot meter function, taking a reading from the meter, and adjusting my aperture and shutter speed to expose 1-2 stops above the suggested reading.
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  #13  
Old 07-02-2012, 09:04 PM
ir0nma1den ir0nma1den is offline
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Re: A proper exposure

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Originally Posted by kav View Post
You're shooting with strobes. You can get a meter that also takes incidental readings rather than relying solely on the one in camera (ugh). They still vary, but that is why you just test it against your camera. Make sure it's appropriate for flash too as opposed to something like a cine meter, and make sure it can fire off pocket wizard controlled strobes without an additional connection. This stuff just takes a little testing.
What do I do if all I have is the internal camera meter?
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  #14  
Old 07-02-2012, 09:09 PM
ir0nma1den ir0nma1den is offline
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Re: A proper exposure

I think I'm beginning to understand the internal camera meter. Since it is a reflective meter, some of the light directed towards the model is being absorbed, while the larger portion is being reflected back towards the camera. Since we are only measuring the reflected light, we are essentially "losing" light, which is why we increase our exposure.

It's either that, or since the camera attempts to meter for neutral gray, it treats any tone as gray and gives a proper exposure for neutral gray regardless of the actual tone. So if we are metering for highlights we want to increase exposure, and if we are metering for shadows (blacks) we decrease exposure.


While we are on this topic, another question came to me. I also shoot video with a hacked GH2 on the highest settings (1080p @24fps). I know this isn't technically RAW data, but would the same exposure trick work here too?

Last edited by ir0nma1den; 07-02-2012 at 09:15 PM.
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  #15  
Old 07-02-2012, 09:30 PM
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Re: A proper exposure

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Originally Posted by ir0nma1den View Post
I think I'm beginning to understand the internal camera meter. Since it is a reflective meter, some of the light directed towards the model is being absorbed, while the larger portion is being reflected back towards the camera. Since we are only measuring the reflected light, we are essentially "losing" light, which is why we increase our exposure.
Stop right there. You are describing the reflective behavior of skin. It's not so much absorbed anyway. The issue is more one of subcutaneous reflection and sometimes mild translucence with thin areas like the ears (note how they tend to glow with heavy backlighting. The problem described is that skintones vary in reflectivity and density as influenced by porous texture, oil on the surface, melanin, and a few other things. You should be balancing to the light falling on skin rather than try to guess its properties. Otherwise you're just trying to make everyone the same color or compensating by guessing. You're using a beauty dish so you should be balancing a primary point of focus then adjusting lighting to get the correct falloff without creating shadows so deep that they start to go noisy with the rest being pushed to post after that point. If you start making up fake physics and bad napkin math, you're just going to make the problem worse.

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Originally Posted by ir0nma1den View Post
What do I do if all I have is the internal camera meter?
You end up testing and guessing. This means that you test different skintones for how many stops you should compensate above or below for a good exposure. If you're using strobes on someone with reflective skin, you should probably be careful what part you use for metering. Big shiny skin reflections are going to influence it. It is important that you stop making up bad math though.
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  #16  
Old 07-02-2012, 11:06 PM
ir0nma1den ir0nma1den is offline
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Re: A proper exposure

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Originally Posted by kav View Post
You end up testing and guessing. This means that you test different skintones for how many stops you should compensate above or below for a good exposure. If you're using strobes on someone with reflective skin, you should probably be careful what part you use for metering. Big shiny skin reflections are going to influence it. It is important that you stop making up bad math though.
Okay, lets start from a blank slate so I don't have bad math in my head.

When you mean " test different skin tones", do you mean Caucasian, black, etc. or do you mean reflective, matte, etc. ?

Thinking about it a bit more, black skin will obviously require a bump in exposure compared to Caucasian skin. Hopefully this isn't bad math taking over again.

Is there a good book or article on this? How would you get the exposure correct with strobes back in the days of film where you have one shot?
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  #17  
Old 07-02-2012, 11:48 PM
kav kav is offline
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Re: A proper exposure

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Originally Posted by ir0nma1den View Post

When you mean " test different skin tones", do you mean Caucasian, black, etc. or do you mean reflective, matte, etc. ?

Thinking about it a bit more, black skin will obviously require a bump in exposure compared to Caucasian skin. Hopefully this isn't bad math taking over again.
That's also not entirely true. If you were metering dark skin and I mean truly dark as within a given race there's quite a range of skintones, if you're taking a spot reading from the in camera meter of a dark patch of skin, that exposure is likely to be too high, not too low. Reflective meters attempt to direct you toward the exposure necessary to reproduce a given area as a midtone. Given variations in color temperature and the reflective properties of different objects, I don't actually say neutral grey. Highly reflective surfaces and very light or dark objects do not tend to give accurate results. If you're talking about very light caucasian skin, your meter reading is likely to under-expose if followed precisely. Again metering the light that is actually there rather than what is reflected would not change. Doing it the way you're doing it just means lots of testing to try to determine the best possible results. Testing with a grey card works well. As a starting point I'd figure out the high, low, and mid points with the grey card assuming a neutral exposure setting in raw processing.

Quote:
Originally Posted by ir0nma1den View Post
Is there a good book or article on this? How would you get the exposure correct with strobes back in the days of film where you have one shot?
That is very simple. Incidental/flash meter + polaroid for final test. Like I said, an incidental meter measures how much light is falling there. I also mentioned that it can vary slightly due to inter instrument variations. I can't think of any specific articles even though they most likely exist.
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  #18  
Old 07-03-2012, 05:15 AM
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Re: A proper exposure

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Originally Posted by ir0nma1den View Post
In my beauty dish scenario, I am using strobes (elinchrom) and reading the metering that my in camera meter (Nikon D300) is giving. When I say spot meter, I mean using the spot meter function, taking a reading from the meter, and adjusting my aperture and shutter speed to expose 1-2 stops above the suggested reading.
Ahh, now it is clear. You cannot use your inbuilt Nikon meter to read anything other than the ambient light falling/reflecting off your subject.

The only way to have your camera metering system read the light falling on the sensor from a flash unit is to use the Nikon Creative Lighting System strobes using Nikon TTL or iTTL modes.

So far the discussion of spot exposure metering and compensation had assumed a continuous light source not flash, therefore is pretty much irrelevant in this case. If you use any of the camera metering modes to measure a highlight and adjust exposure to compensate for light or dark skin that exposure should be correct for the conditions you metered in only.

If you then use that exposure calculation with flash it will be wrong and in many cases the flash will overide the ambient light and lead to overexposure.

You will need to either invest in a dedicated flash meter or with some testing and using the Guide Numbers provided by the manufacturer arrive at the correct exposure based on the distance of the flash unit from your subject.

With respect it sounds like you need to go back to basics with both exposure metering for ambient light and similarly with flash. There are many books and videos on both techniques. Although I have not read them two books that may help are Understanding Exposure By Bryan Peterson and Understanding Flash Photography by the same author.

EDIT: Some good information on using Incident flash meters on the Sekonic site. Have a poke around in the articles and videos it may be of help http://www.sekonic.com/Whatisyourspe...sitioning.aspx

Last edited by Tony W; 07-03-2012 at 07:10 AM. Reason: Added information
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