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exposure metering – shifting exposure settings

September 26, 2010

exposure metering – shifting your exposure settings

When shooting in consistent light, and I have a specific exposure setting that is correct – then changing settings to a an equivalent exposure  is as easy as counting the clicks. These clicks on your digital camera – whether aperture, or shutter speed or ISO – change the exposure by 1/3rd of a stop. You can then simply count these up and down to get to an equivalent exposure with a different combination of settings.

Most (if not all) digital cameras change settings by 1/3rd stop.  Older lenses changed by 1/2 stop settings, but all (most?) modern cameras with electronic controls between the camera and lens, will change the aperture settings by 1/3 stop values. Older cameras changed shutter speeds by full stop settings.  But with D-SLRs and as far as I know, any modern camera that has electronic controls, have 1/3rd stop settings.

Back to the photographs here: The second image was shot first, and the settings were 1/200 @ f5.6 @ 400 ISO … a good combination.  The aperture gives a crisp image on the zoom, and 400 ISO isn’t a high ISO, and 1/200 is certainly hand-holdable on a stabilized lens.  I liked the background, but thought it was too apparent in the frame due to the f5.6 aperture.  I needed shallower depth of field than the f4 zoom I was using, would allow me.

I then changed to an 85mm f1.8 lens to get to a wide aperture to throw the background completely out of focus for a tighter portrait of Anelisa. The resulting image, shown at the top, was shot at 1/400 @ f2.0 @ 100 ISO with the 85mm lens.

Getting to 1/400 @ f2.0 @ 100 ISO, from the previous 1/200 @ f5.6 @ 400 ISO … was then just a simple matter of counting the clicks. A certain number of clicks on the aperture, shutter speed and ISO, had to balance out.  This would give me the same exposure, without me having to meter again for my subject. The number of clicks have to balance out. A few clicks up on the shutter speed; a few clicks wider on the aperture, and a few clicks down on the ISO … and there we are.

Still keeping with the basics:  going wider on the aperture means more light is allowed in. To counter this, we have to raise the shutter speed .. or drop the ISO setting.  Or a combination of raising the shutter speed and dropping the ISO. Counting the clicks is easier to do than calculating the exact same exposure by counting by the third stop values for shutter speed, ISO and aperture.

If your camera offers the choice between 1/2 stop indents and 1/3rd stop indents, then I strongly suggest staying with 1/3rd stop values.  It allows a finer control of exposure.

Equipment used:
The image at the top was taken with the Canon EF 85mm f1.8 USM, and the second image was taken with the Canon EF 24-105mm f4 IS USM zoom.  The camera was the classic 5D.  Only available light.

I do believe that the lack of the aperture scale on modern lenses are the cause that newer photographers aren’t familiar with the sequence of numbers, and hence what they mean.

The values for full apertures settings: _ f22 _ f16 _ f11 _ f8 _ f5.6 _ f4 _ f2.8 _ f2

That is something that every serious photographer needs to know. I would even say it is an absolute. You *have* to memorize those values, and understand that they are one full exposure stop difference in brightness. Also, that each value indicated a doubling (or halving) of the amount of light that will hit the film / sensor. (If any of this isn’t doesn’t make sense, then it is time to do some further homework.)

And while I think it is necessary to know the full stop values, it also makes sense to know the in between third-stop numbers.  It helps in counting exposure values up and down, and getting to equivalent exposure settings quickly.

Now if only Nikon and Canon would implement something like Pentax’s ingenious Hyper-Manual mode where the shutter speed and aperture settings are changed in tandem.

 

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