dumb question

[evilenglishman]

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[PeterS45]

When it's in manual mode there will be no change in aperture and exposure time. Zooming in will narrow the view, thus decreasing the amount of light reaching the chip and therefore you will need to adjust the setting of aperture or exposure. Compare what happens to the settings when you use one of the automatic or creative settings and you'll see what the problem is.

[topeju]

When it's in manual mode there will be no change in aperture and exposure time. Zooming in will narrow the view, thus decreasing the amount of light reaching the chip and therefore you will need to adjust the setting of aperture or exposure. Compare what happens to the settings when you use one of the automatic or creative settings and you'll see what the problem is.

Umm, not quite. In manual mode (well, in any mode really), you set the aperture ratio, i.e. the ratio between the focal length and the aperture. Zooming while keeping the same aperture setting (=ratio) and the same exposure time should get you the same results exposurewise. The actual size of the aperture changes, but not the aperture ratio.

However, in this case, not knowing which lens is in question so this is purely a guess, it is most likely that evilenglishman used a fairly wide-open aperture in the short end, and the lens in question doesn't have a "fixed" maximum aperture throughout its focal length range.

For example, the 28-135 IS USM has a maximum aperture of f/3.5 in the short end. At approximately 35 mm the maximum aperture is f/4.0, at 50 mm it is f/4.5, and from around 85 mm the maximum aperture is f/5.6. So, if evilenglishman selected an aperture of f/4.5 at the short end, that would be valid all the way up to ~85 mm, above which an aperture of f/5.6 would be used as that is the largest aperture possible.

The fact that the aperture ratio is not the same should be apparent in the EXIF data for the images.

[chris.bailey]

Are you sure the head and shoulders is actually properly exposed in full length mode. On a full length pose it is normal to have to open up a stop to prevent darker clothes looking black. If you zoom right in on the head and shoulders portion of the full length shot you may find the face a little too bright but overall it works.

On a head and shoulders shot flesh tones dominate and you tend to expose more for the highlights, whilst trying to avoid blowing them out.

To confirm this take a full length shot and look at the histo. Then crop it to the head and shoulders you want and histo again.

The background does not really have an effect, it will just darken a little for the head and shoulders shot if the lighting stays the same. Remember that by lighting a white background more than two stops below the mid-point it will look black in any event

[evilenglishman]

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[chris.bailey]

Very hard to get portraits right without a flash meter as it is useful to measure the lightfall on each side of the face, the background etc. you want enough contrast to create depth and speration but not so much as to cause blowouts or level black. Doing this with a flash meter is a bit trial and error, without it is even more so.

[CyberDyneSystems]

Lens is the 28-135 IS buy the way

So this is the problem most likely as topeju says,. as you zoom closer the aperture ratio of the 28-135mm closes down.... so even if you are set to a manual exposure that works with a given aperture at the wider end, as you zoom in the lens can't actually keep that aperture..

The metering in the viewfinder should be telling you that the exposure is off however,.. and that the aperture you have set is no longer available,. it does this by flashing the aperture number if I remeber correctly...

[evilenglishman]

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[billfranklin]

evilenflishman,
You might want to read Will Crocket's discussion on how to get the correct exposure using the facemask histogram. It will be difficult without a handheld exposure meter, but it can be done by trial and error. Good luck. http://www.shootsmarter.com/infocenter/wc001.html

Bill F

[topeju]

http://www.shootsmarter.com/infocenter/wc001.html


That looks like an excellent article. I use a somewhat similar method in Capture One, where I first select a crop area covering most of the face, then adjust the exposure with the histogram (a caucasian person's skin colour should generally be about 1 stop above the middle?), and then adjust the crop to what I really want. It's not perfect, I tend to slightly overexpose pictures this way, but that's just me most likely.

[evilenglishman]

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[evilenglishman]

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