Exposure Compensation
Exposure Compensation – that’s something else that cropped up once or twice for the chaps on my recent Norwegian Eagle workshop!
We had something like 420 or more dives from eagles during the trip, and very few if any were shot with flat metering, or 0Ev compensation.
What is Exposure Compensation, and why do we need to use it?
It all begins with this little button:
D3 Exposure Compensation button – Nikon, Canon and most others use the same symbol.
Pushing this button and rotating your main command dial will select a certain exposure compensation value.
Why do we need to use Exposure Compensation though?
Cameras, for all their complexity and “intelligent whotsits” are basically STUPID! They don’t know WHAT you are trying to photograph, or HOW you are trying to photograph it.
They make a lot of very basic assumptions about what you are trying to do – 99.99% of which are WRONG!
The camera does NOT know if you are trying to photograph:
- A white cat in a coal shed
- A black cat in a snow storm
- A white cat in a snow storm
- A black cat in a coal shed
All it sees is a frame full of various amounts of light and shade, and depending on your metering mode (which should always be Matrix/Evaluative – see post here) it gives you an “average mean exposure value”.
Take a general scene of fairly low contrast under flat overcast light:
A scene as WE see it.
The same scene as the camera METER sees it.
Lighter tones within the scene.
Some darker area tones within the scene.
The exposure is governed by the PREDOMINANT tone.
As discussed in the previous metering article mentioned earlier, only MATRIX/EVALUATIVE takes the entire frame area into account.
Okay, so that scene was fairly bland on the old tonal front, so let’s have a look at something a little more relevant:
Straight off the camera with no processing. 1/2000th @ f4 1600ISO +1.3Ev
As the camera metered the scene WITHOUT compensation.
Why would the image be so dark and under exposed?
Well here’s an approximation of the cameras average tone “thought process”:
The approximate average value of the scene.
But if we look at some averages WITHIN the overall image:
Random tonal averages within the image.
We can see that the tonal values for the subject are generally darker than the average scene value, therefore the camera records those values as “under exposed”.
This is further compounded by the cameras brain making the decision that the commonest tonal value MUST represent “mid grey” – which it DOESN’T; it’s lighter than that – and so under exposing the image even further!
Now I’m not going to get into the argument about “what is mid grey” and do Nikon et al calibrate to 12%, 18%, 20% or whatever – to be honest it’s “neither here nor there” from our standpoint.
What is CRITICAL though is that we understand the old adage:
“Light Subject Dark Background = Under, or negative exposure compensation. And that Dark Subject Light Background = Over, or positive exposure compensation”.
Okay, but what are we actually doing?
In any exposure mode other than Manual mode, we are allowing the camera to meter the scene AND make the decision over which shutter speed or aperture to use depending on whether we have the camera in Av or Tv mode – that’s Canon-speak for A or S on Nikon.
If we are in shutter priority/S/Tv mode then the camera sets the aperture to give us its metered exposure – that thing that’s usually WRONG! – at the shutter speed we’ve selected.
If, as in the case above, we ADD +1.3Ev – one and one third stops of POSITIVE exposure compensation, the camera uses the shutter speed we’ve selected but then opens up the aperture WIDER than it’s “brain” wants it to.
How wide? 1.3 stops wider, thus allowing 1.3 stops more light into the the sensor during the exposure time.
If we were in Av/A or aperture priority mode then it’s the shutter speed that would take up the slack and become 1.3 stops SLOWER than the cameras “brain” wanted it to be.
Here’s an example of negative exposure compensation:
1/3200th @ f4.5 1000ISO -1.3Ev exposure compensation.
In this particular shot we’re pointing towards the sun – a “dark subject, light background” positive exposure compensation scenario, or so you’d think.
But I want to “protect” those orange highlights in the water and the brightest tones in the eagle, so if I “peg those highlights” just over a stop below the top end of the cameras’ tonal response curve then there is no way on earth they are going to “blow” in the final RAW file.
Manual Exposure mode can still furnish us with exposure compensation based on metering if we engage AUTO-ISO. If we decide we want to shoot continuously with a high shutter speed and a set aperture at a fixed ISO then our exposures are going to be all over the place. But if we engage AUTO-ISO and let the camera choose the ISO speed via the meter reading, we can use the exposure compensation adjustments just the same as we do in Av or Tv modes.
This get’s us away from the problem of fixed ISO Tv mode running out of aperture in low light or when very high shutter speeds are needed; or conversely, stopping the aperture down too far when the sun comes out! – I’ll do a breakdown on this method of shooting later in the year – it’s not without it’s problems.
Next time you get the chance to stand by a large lake or other body of water, just take a moment to notice that the water is dark in some places and light in others. ambient light falling on a moving subject can easily be very uniform and so the subject basically has the same exposure value all the time. But it’s the changing brightness of the background as the subject moves across it that causes us to need exposure compensation.
People seem to think there’s some sort of “magic” at play when they come out with me and I’m throwing exposure compensation values at them. But there’s no magic here folks, just an ability to see beyond “the subject, framing etc” and to actually “see the light” and understand it.
After all, when we click our shutters we are imaging light – the subject is, for the most part, purely incidental!
And there’s only one way you can learn to see light and grasp its implications for camera exposure, and that’s to practice.
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well heres a question
i usually have to have -0.3 steps EV dialed in because my d3 tends to overexpose.
depending on the light it will overexpose between 0.3 to 1 EV
i had this tested with a friend’s d3x and compared the two shots.
i know that both cameras work differently, as the d3 is more focused on iso.
all settings i got at 1/3 steps, iso, fstops, shutter because i rly do like it that way.
1/3, 2/3 and 1 just gives me a tad more room to play with in night situations.
the diference is subtle but it makes sense. at least to me. so i do not have to edit too much on the computer which i rly do not like..
nikon said i should send it in..yeah, i get it.they want my money.
but heres the thing, i am not buying. haha
they only told me that the d3 and d3x use different meting systems based on high iso perfomrance or something.
the test shots with the d3 and d3x were done in bright daylight and the d3 was about 1 step off, overexposing.
from the top of your head, could you think of anything i could try and test.
thanks in advance
Hi Norbert
My D3 always over-meters by +1/3Ev at ISO 400 to 1000 ISO. Above that, it over meters by +1.0Ev, and at 200 ISO and lower it doesn’t over-meter at all. But, and here’s the important thing, is it actually harming your images? I always adopt the old colour tranny approach to exposure – Expose To The Right, or ETTR.
An over exposed (but not “blown”) RAW file is always a better file to work up in Lightroom etc than one which has any areas of relative under-exposure. Pulling the exposure down in post will always reduce the visual appearance of luminance noise – useful tip for shooting at higher ISOs’ – expose the highlights properly, as highlights and not upper midtones, and you’re good to go!
The D3 has a Dynamic Range of about 12 stops at 200 ISO, this drops to about 10.5 stops at 1600 ISO, so within that ISO range you’ve got between 5 and 6 stops of highlight headroom. Now if you shoot wildlife, such as a squirrel with a 500mm f4 or longer then it’s highly unlikely that your frame area will contain an image with any more than 6 or 7 stops of Subject Brightness Range in TOTAL -3.5Ev to +3.5Ev, so this will easily fit inside a -5 to +5 Ev Dynamic Range of the D3 at 1600 ISO.
But put a 14mm wide angle on the D3 and shoot landscapes then you might have a frame area containing 20 stops or more of Subject Brightness Range – so exposure bracketing is the order of the day, even at 200 ISO.
In effect the D3, by accident NOT design, meters in a slight ETTR manner – which isn’t a bad thing Norbert, I’ve never really worried about it all that much to be honest – better that than under-metering. Just make sure you have the camera set to uncompressed 14 bit RAW recording, and only use Matrix metering – you’ll be fine.
well..i am still not used to mac and just closed that browser with a shortcut i don’t recall..
here goes again:
first off i want to thank you for your quick reply!
right now, i feel a little silly..and here is why
last year in may i bought a nikon d3, almost mint for very little money as i had to buy something after trashing my 1d mk4, so i thought this is a good time to switch back to nikon (f5 and d1x, which i got for almost NO money in 2001 got stolen) i soon noticed that the metering system works a little bit different on the d3 and needed some time to get a hold on it.
for whatever reason i could not forget this incedent, when the different exposures happened compared to the d3x, which i was also having with me.
since then i shot over 180k frames and now certainly know how to correct stuff but i always have -0.3EV dialed in, even at iso 200 if the entire frame is bright (no shadows, or maybe just very small dark parts).
i use the 14 bit raw recording in adobe colourspace, do rly know my autofocus and so on. id say i can take up a nikon d3,s,x and operate it without even thinking now.
and now comes the funny part.
i use ettr
quite often
not always
but with landscapes, architecture and sometimes everything else too, if i can without bowing stuff: i do use ettr
now, that one incedent never rly got out of my head since then and sometimes was bothering me as i had to edit more as i am used to.
so i am sitting here and wonder why it did not come to my mind that the camera is metering in an ettr kind of way.
for whatever reason i was keeping it in mind as a bad thing that happened to me over a year ago and obviously the lack of coffee after a night of heavy drinking made me write this without thinking..
there are no stupid quiestions they said
glad i can pull one off though
sometimes the obvious isn’t obvious at all
and with something like this now i feel kinda silly..haha well
anyway
thank you very much for your help with this
your awnser is very details, thanks
much appreciated!
before i actually ask something stupid again, next time i will ..try… to actually think first 🙂
thank you!
best,
norbert
I didn’t think your question was stupid Norbert, it never entered my head matey! And if my reply has brought a little more clarity to your thinking then my work here is done!
One thing though Norbert – you ARE NOT shooting 14 bit RAW in the AdobeRGB1998 colour space………..
You might have the Adobe space set as default in your menu settings, but that only applies to pixel-based images produced “in camera”.
You are shooting RAW, a RAW file is basically a data field – and so is NOT a recognisable image ‘per se’. You cannot therefore tag it with a colour space; other than the colour space of the camera itself – and that is way bigger than AdobeRGB.