Saturday, August 21, 2010

Rule of -2/3rds

It's possible you've heard of the Rule of Thirds. It's a guideline for composing photographs so that your focus *isn't* the dead center of the picture. This, however, is not what this post is about.

Instead it's a personal rule of mine to override the camera's Exposure Compensation.

Now when you take a picture the camera decides, based on some other settings I won't go into yet, how bright to make the picture. It adjusts (depending on what mode you're in) the ISO (sensitivity to light) and/or shutter speed and/or amount in focus.

More often than not, I find it's a bit brighter than I'd like. Colours are often washed out, and natural things don't look that real.

Normal Exposure

- 2/3rds Exposure

Now it's a little difficult to tell after the fact what the exposure compensation is, since it doesn't show up in most programs - even the ones that normally show the ISO, shutter speed and all that other fun stuff. It is recorded as 'Exposure Bias' in the EXIF information - check the >Properties of the picture in question (Details tab if you have to click farther).

Normal Exposure

- 1/3rd Exposure

- 2/3rds Exposure (/w Auto Contrast in Picasa)

-1 Exposure (/w Auto Contrast in Picasa)

While this is a personal preference, there is a technical benefit as well. When dealing with digital cameras, it's better to err on the side of too dark. Shorter exposure time means less chance for a blurring. If you're happy with the shutter speed, a negative exposure compensation will allow more of your picture to be in focus. When both of those are fine, it will allow for a lower ISO setting, which means less rainbow speckles in the picture and richer colours overall.

Often if something is dark and you'd like it to remain that way in the picture a lot of negative Exposure Compensation is needed.

-5/3 Exposure

Another benefit is making details of white things visible - and not clipped out beyond the upper range of the camera.

Normal Exposure (above) - 4/3rds Exposure (below)

 As with most camera rules, there's times when they should be broken. If you're outside on a bright day, but your subject is under some small shadow it would be worth going to positive exposure compensation. Similarly if your subject is backlit and not showing up properly, this is a quick fix.

Most cameras do have Exposure Compensation. However, you will have to go into the letter modes of the settings (previously linked). Some cameras will show it as a fraction, in steps of 1/3 or 1/2 while others will show a decimal value. Check your manual.


Shadowsdream said...

Hmm, one thing that is very important when adjusting exposure is to adjust contrast with it. If you don't, the images tend to get a gray tint to them and look, off for lack of a better word. Now, I totally agree that most cameras will over expose to a certain extent, but this cannot be digitally corrected by adjusting the exposure (often termed brightness) alone, contrast must be increased as brightness/exposure is decreased.

You have some perfect examples of this, your final picture has had the brightness decreased which corrected the colors, but it also gave it a slightly grayish tint which a slight bump to the contrast should help. You can clearly see the benefit to this in the pictures of the red flower (the last one is best imo) where contrast was automatically adjusted with the exposure/brightness adjustments.

James said...

That I find depends very much on the camera in question - as well as the subject.

The top two shots and last two shots are with a Rebel XSi. -2/3 with that is hardly noticeable 'greyness'. Both tree shots are uncorrected.

The red flower was photographed with an old 5MP Kodak - which made the pictures noticeably darker (black not grey even) hence the correction with Picasa.

Most cameras have an adjustment for contrast and saturation - but here I'd recommend post processing. The in-camera option is an absolute value while the software often includes a reasonably 'intelligent' auto correction.

Shadowsdream said...

Well, if you really want to get good in-camera exposure, you should set your cameras white value with a grey card in the scene and lighting you are in.

James said...

Which is fine. Unless you're moving. Or the light is changing. Or the subject is moving ;)

"To use one you stage your picture, focus on the card, and meter it, remove the grey card -- and shoot."

Fine for product photography and and portrait shoots, not so handy for out and about.

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