Dynamic Range, Mid Tones, Metering and ETTR

I recently uploaded a video to my YouTube channel showing you an easy way to find the ‘usable dynamic range’ of you dSLR:

 

The other day I was out with Paul Atkins for a landscape session in the awesome Dinorwic Quarry in Llanberis, Snowdonia.  Highly dynamic clouds and moody light made the place look more like Mordor!

Here are the 6 unedited shots that make this finished panoramic view:

As you can see, the images are are shot in a vertical aspect ratio.  Shooting at 200mm on the D800E this yields an assembled pano that is 16,000 x 7000 pixels; the advantages for both digital sales and print should be obvious to you!

As you can see, the bright parts of the sky are a lot brighter in the captures than they are in the finished image, but they are not ‘blown’.  Also the shadows in the foreground are not choked or blocked.

In other words the captures are shot ETTR.

Meter – in camera or external.

Any light meter basically looks at a scene (or part thereof) and AVERAGES the tones that it sees.  This average value value is then classed by the meter is MID GREY and the exposure is calculated in terms of the 3 variables you set – Time, Intensity and Applied Gain, or shutter, aperture and ISO.

But this leads to all sorts of problems.

All meters are calibrated to an ANSI Standard of 12% grey (though this gets a bit ambiguous between manufactures and testers).  But you can get a good idea of what ‘light meter mid grey/mid tone” looks like by mentally assigning an RGB value of 118,118,118 to it.

However, we – humans – find 18% grey a more acceptable ‘mid tone grey’ both in print and on our modern monitors.

NOTE: 18% grey refers to the level of REFLECTANCE – it reflects 18% of the light falling on it.  It can also be reproduced in Photoshop using a grey with 128,128.128 RGB values.

So problem number 1 is that of mid tone perception and the difference between what you ‘see’ and what the camera sees and then does in terms of exposure (if you let the camera make a decision for you).

Click on the pano image from Dinorwic to view it bigger, then try to FIND a mid grey that you could point your camera meter at – you can’t.

Remember, the grey you try to measure MUST be exactly mid-grey – try it, it’ll drive you nuts trying to find it!

This leads us to problem number 2.

Take your camera outside, find a white wall.  Fill your frame with it and take a shot using ZERO exposure compensation – the wall will look GREY in the resulting shot not WHITE.

Next, find something matte black or near to it.  Fill your frame with it and take another shot – the black will look grey in the shot not black(ish).

Problem number 3 is this – and it’s a bit of a two-headed serpent.  An exposure meter of any kind is COLOUR BLIND but YOU can SEE colours but are tonally blinded to them to some degree or other:

Simple primary red, green and blue translate to vastly different grey tones which comes as a big surprise to a lot of folk, especially how tonally light green is.

Scene or Subject Brightness Range

Any scene in front of you and your camera has a range of tones from brightest to darkest, and this tonal range is the subject brightness range or SBR for short.  Some folk even refer to it as the scene dynamic range.

If you put your camera meter into spot mode you can meter around your chosen scene and make note of the different exposure values for the brightest and darkest areas of your potential shot.

You camera spot meter isn’t the most accurate of spot meters because its ‘spot’ is just too big, typically between 4mm and 5mm, but it will serve to give you a pretty good idea of your potential SBR.

A 1 degree spot meter will, with correct usage, yield a somewhat more accurate picture (pun intended) of the precise SBR of the scene in front of you.

Right about now some of you will be thinking I’m hair-splitting and talking about unnecessary things in todays modern world of post-processing shadow and highlight recovery.

Photography today is full of folk who are prepared to forego the CRAFT of the expert photographer in favour of getting it half-right in camera and then using the crutch of software recovery to correct their mistakes.

Here’s the news – recovery of popped highlights is IMPOSSIBLE and recovery of shadows to anymore than a small degree results in pixel artifacting.  Get this, two WRONGS do NOT make a RIGHT!

If the Mercedes F1 team went racing with the same attitude as the majority of camera users take pictures with, then F1 would be banned because drivers would die at an alarming rate and no car would ever make the finish line!

So, one way or another we can quantify our potential scene SBR.

“But Andy I don’t need to do that because my camera meter does that for me…….”

Oh no it does NOT, it just averages it to what IT THINKS is a correct mid tone grey – which it invariably isn’t!

This whole mid tone/mid grey ‘thing’ is a complete waste of time because:

• It’s near impossible to find a true mid tone in your scene to take a reading off.
• What you want as a mid tone will be at odds with your camera meter by at least 1/2stop.
• If you are shooting wildlife or landscapes you can’t introduce a ‘grey card’.
• Because of the above, your shot WILL BE UNDER EXPOSED.

“Yeah, but I can always bracket my shots and do an exposure blend Andy so you’re still talking crap….”

Two answers to that one:

1. You can’t bracket shots and blend if your MAIN subject is moving – de-ghosting is only effective on small parts of a scene with minimal movement between frames.
2. The popular “shoot and bracket two each end” makes you look like total dickhead and illustrates that you know less than zero about exposure.  Try doing that on a paying job in front of the client and see how long you last in a commercial environment.

By far the BEST way of calculating exposure is the ETTR method.

ETTR, Expose to the Right.

If you meter for a highlight, your camera will treat that as a mid tone because your camera ASSUMES it’s a mid tone.

Your camera meter is a robot programmed to react to anything it sees in EXACTLY the same way.  It doesn’t matter if your subject is a black cat in the coal house or a snow man in a snow storm, the result will be the same 118,118,118 grey sludge.

Mid tones are as we’ve already ascertained, difficult to pin down and full of ambiguity but highlights are not.  So let’s meter the brightest area of the image and expose it hard over to the right of the histogram.

The simplest way to achieve this is to use your live view histogram with the camera in full manual mode.

Unlike the post-shot review histogram, the live-view histogram is not subject to jpeg compression, and can be thought of as something of a direct readout of scene tonality/brightness.

Using your exposure controls (usually shutter speed for landscape photography) you can increase your exposure to push the highlight peak of the histogram to the right as far as you can go before ‘hitting the wall’ on the right hand side of the histogram axis – in other words the camera sensor highlight clipping point.

Of course, this has the added benefit of shifting ALL the other tones ( mids and shadows) to the right as well,resulting in far less clipping potential in your shadow areas.

So back to Dinorwic again and here’s a shot that has been exposed ETTR on the live view histogram using spot metering over what I deemed to be the brightest area of the sky:

I was a naughty boy not recording this on video for you but I forgot to pack the HDMI lead for the video recorder – I’ll do one shortly!

The problem with using the Live View Histogram is that it can be a bit of a struggle to see it.  your live view screen itself can be hard to see in certain light conditions outside, and the live view histogram itself is usually a bit on the small side – no where near as big as the image review histogram you can see here.

But looking at the review histogram above you can see that there’s a ‘little bit more juice’ to be had in terms of exposure of the highlights because of that tiny gap between the right end of the histogram and the ‘wall’ at the end of the axis.

Going back to the video the maximum ETTR ‘tipping point’ was centered around these three shots:

The review histogram puts the Dinorwic shot highlights firmly in the same exposure bracket as ‘Safe, but -2/3rd stop below Clipped, and tells us there is another 1/3rd stop ‘more juice’ to be had!

So lengthening the exposure by 1/3rd stop and changing from 160th sec to 1/50th sec gives us this:

That’s what it’s all about baby – MORE JUICE!

And you will not be in a position to confidently acquire more juice unless you find the USABLE DYNAMIC RANGE of your camera sensor.

The whole purpose of finding that usable DR is to discover where your highlight and shadow clipping points are – and they are very different between camera models.

For instance, the highlight clipping point value of the Nikon D850 is different from that of the Nikon D800E, but the shadow clipping point is pretty similar.

There is an awful lot more use to discovering your cameras usable dynamic range than a lot of folk imagine.

And if you do it the precise way then you can acquire a separate meter that will accept camera profiling:

You can create a dynamic range profile for your camera (and lens combo*) and then load it into the meter:

and then have your cameras usable dynamic range as part of the metering scale – so then you have NO EXCUSE for producing a less than optimum exposure.

(*)Note: yes, the lens does have an effect on dynamic range due to micro-contrast and light transmission variables – if you want to be super-picky!

AND THEY SAY HANDHELD METERS ARE DEAD, OLD TECH and of NO USE!!!

Anyone who says or even thinks that is a total KNOB.

Your camera dynamic range, the truthful one – FIND IT, KNOW IT, USE IT.

And don’t listen to the idiots and know-nothings, just listen and heed the advice of those of us who actually know what we’re doing.

NOTE:  The value of grey (gray) cards and how to use them for accurate measurement is a subject in its own right and provides the curious with some really interesting reading.  Believe me it’s far more expansive than the info I’ve given here.  But adopting an ETTR approach when exposing to sensor that you KNOW the physical behavior of (dynamic response to light/dynamic range) can alleviate you of all critical mid-tone concerns.

This article has taken me over 8 hours to produce in total, and is yours to view for FREE.  If you feel I deserve some support for doing this then please consider joining my membership site over on Patreon by using the link below.

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