Little help needed......Metering ???

doozie

doozie

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Hi All,

I work on a different site every week, this week I am working in Thirsk near the top of what I can only describe as a small mountain. On the way home yesterday there was an amaizing sunset so today I took my camera to work with me in the hope of it been repeated......and it was.

Anyway, below are two photo's taken within a couple of minutes of each other, the sky was very orange for all of my shots but half of them look like normal daylight and the other half look as I expected them to(with an orange sky)

My question is....How did this happen ?

Dont forget I'm a newbie, so dont get too technical but could this be something to do with Metering ? If so how do I make sure the camera meter's how i want it to ?

Here's the pics. I know Some cropping is needed(Later)

SunsetThirsk.jpg


BridgeThirsk.jpg
 
Can you post the exif info from the original files ?? :shrug:
 
Exif #1
[Image]
Make = PENTAX Corporation
Model = PENTAX K10D
Orientation = top/left
Software = Adobe Photoshop CS3 Windows
Date Time = 2007-12-11 23:01:14

[Camera]
Exposure Time = 1/60"
F Number = F5.6
Exposure Program = Normal program
ISO Speed Ratings = 100
Exif Version = Version 2.21
Date Time Original = 2007-12-11 21:37:07
Date Time Digitized = 2007-12-11 21:37:07
Shutter Speed Value = 5.91 TV
Aperture Value = 4.97 AV
Exposure Bias Value = ±0EV
Metering Mode = Spot
Flash = Flash did not fire, compulsory flash mode
Focal Length = 55mm
Color Space = Uncalibrated
Exif Image Width = 2592
Exif Image Height = 3872
Sensing Method = One-chip color area sensor
Custom Rendered = Normal process
Exposure Mode = Auto exposure
White Balance = Manual white balance
Focal Length In 35mm Film = 82mm
Scene Capture Type = Normal
Contrast = Normal
Saturation = Normal
Sharpness = Normal
Subject Distance Range = Distant view

exif #2
[Image]
Make = PENTAX Corporation
Model = PENTAX K10D
Orientation = top/left
Software = Adobe Photoshop CS3 Windows
Date Time = 2007-12-11 23:09:47

[Camera]
Exposure Time = 1/30"
F Number = F5.6
Exposure Program = Aperture priority
ISO Speed Ratings = 800
Exif Version = Version 2.21
Date Time Original = 2007-12-11 21:46:58
Date Time Digitized = 2007-12-11 21:46:58
Shutter Speed Value = 4.91 TV
Aperture Value = 4.97 AV
Exposure Bias Value = ±0EV
Metering Mode = Spot
Flash = Flash did not fire, compulsory flash mode
Focal Length = 21mm
Color Space = Uncalibrated
Exif Image Width = 3872
Exif Image Height = 2592
Sensing Method = One-chip color area sensor
Custom Rendered = Normal process
Exposure Mode = Auto exposure
White Balance = Auto white balance
Focal Length In 35mm Film = 31mm
Scene Capture Type = Normal
Contrast = Normal
Saturation = Normal
Sharpness = Normal
Subject Distance Range = Close view

If I did my sums right the 2nd shot has 4 stops more than the 1st shot. The 1st shot is ISO100, 1/60s @ f/5.6 and the 2nd is ISO800, 1/30s @ f/5.6.

That explains why the sky is so much brighter in the 2nd shot.
 
that was quick pixl8! beat me!
So it appears he changed the iso and left the camera on aperture priority, i cant imagine an auto iso feature would have made those settings?
 
Wow, where'd you get that lot from???

I can't actually remember changing any camera settings during taking the photos. I think I took the first one, looked at it on the LCD, it looked ok so i went on a shooting pree. I will have to take my time next time.
 
Mistakes, best way to learn - especially if you can make really good mistakes ;)
 
You'll learn lots then :thumbs:

Next time keep an eye on the settings, it's easy enough to knock a button or dial when the camera bumps against you as you move around. After a while when you get an idea of what settings are roughly right for a shot you'll soon notice if they seem very wrong.
 
I dont know the camera you used but on my good old d70 its not easy to change the iso by accident, and i dont think it could have been auto iso that chose them so perhaps human error.
 
doozie said:
Definately didn't change ISO myself.
Click to expand...

doozie if you have the ISO set to 'auto' the camera will automatically adjust the ISO to whatever it thinks is best within a specified range. The default specified range is 100-400 so if it managed to select ISO 800 automatically the range has been adjusted somewhere along the line. Have a look at page 140 of your manual.
 
Camera operation aside, lets make sure you know what this actually means...

- First pic is...1/60 sec, f5.6, ISO 100,
- Second pic is.....1/30 sec, f5.6, ISO 800.

Three parameters:
- time : time that light gets through the shutter
First shot is 1/6oth 2nd is 1/30th. That means twice the amount of light hitting the sensor in the 2nd shot

- aperture : size of the "hole" that the light gets through.. larger fXX smaller hole.
Both are f5.6 so the "hole" is the same size.

- ISO : film/sensorsensitivity to light
First shot ISO100, 2nd shot ISO800 this means that the sensor is 8 times more sensitive

Totting this lot up means that:

Shot 2 is 16 (2*1*8) times more over exposed than the 1st.

How you make sure you dont do it again ... RTM :rules: methinks
and the hardest bit (like I remember) :thinking: think before snapping away.
 
Paul, I think "16 times more overexposed" is a bit confusing. Much better to stick with the terms everyone knows (or should be learning) :thumbs:

Everything to do with exposure is measured in "stops" (the term comes from old lenses where you physically changed the aperture setting by clicking a ring from one stop to the next). For every stop difference you double or halve the amount of light reaching the sensor.

Immediately you can see how shutter speeds and stops work together.

changing from 1/60s to 1/30s is double the time and double the light - so it's one stop brighter. If you double the time again to 1/15 you'll be 2 stops brighter than 1/60s.

The aperture of "f" numbers are a little more confusing but the following sequence have one stop between them.

2, 2.8, 4, 5.6, 8, 11, 16, 22 (the lower the number the more light)

That's not the complete sequence as lenses do go higher and lower than those values but these are the most common ones.

So if you use f/5.6 for one shot and then change to f/4 you'll have doubled the light again, assuming everything else stayed the same.

Finally ISO speed, each time you double that you get another one stop increase in the light. 100, 200, 400, 800, 1600.

Now if you put it all together you can easily compare a pair of settings to work out the number of stops difference:

ISO100, 1/125s @ f/4
ISO100, 1/250s @ f/2.8

The shutter speed is twice as fast so that's one stop less light. The aperture is one stop lower so that's one stop more light. One stop less + one stop more = no change in the amount of light reaching the sensor.

ISO100, 1/125s @ f/4
ISO200, 1/125s @ f/2.8

The ISO has doubled so that's one stop more light. The aperture is also one stop lower so that's another stop more light, total 2 stops more light.

The ISO and shutter speed are easy to remember because when they double or half you have also moved one stop. The aperture values (f numbers) is the one to learn but a good trick is to think of it in terms of how many clicks your camera needs to change the aperture one stop. Most cameras offer 1/3 of a stop increments (check by changing from f/5.6 to f/8 and count them off) so you can simply count stops by the number of times you change the aperture value.

You can experiment with shifting the exposure in P mode on most cameras. The camera will pick a setting and then you can shift it by turning the main wheel. In one direction the shutter speed will increase and the aperture value will decrease, turn the wheel the other way and the opposite happens. Likewise if you change the ISO setting in P mode the shutter and aperture will be changed again.
 
doozie said:
Definately didn't change ISO myself.
Click to expand...

You changed the mode, the first one is AUTO (A) = fully automatic the camera chooses everything, the second one is Aperture Priority = you choose the aperture the camera chooses everything else based on the aperture you selected.
On a D70 the fully auto mode is in green, but its easy to choose "A" thinking its fully auto when infact its ap priority.
You could shoot this scene at the time it was taken in fully manual mode, after first shooting auto, take note of the values for aperture and shutter speed that run along the bottom of the viewfinder, if the shot is how you want it in preview, recreate those settings in manual mode, if not you can alter them, still all manual to get what you want.
The point is, with a bit of practice trial & error, you can get a feel for the relationship between aperture and shutter speed, and move on from all auto shooting.
 
Dont we think he just metered from the foreground and as its black it lightened the pic to look like daylight?

isnt that just what he is asking... how did it meter differently and produce a daylight type shot in the dark?
 
Thanks for all your replies guy's and thanks for taking the time to come up with some very detailed explanations, some very useful info in there. Its helped a great deal:thumbs:.

I do now get how up-ing the settings by any number of stops increases either the amount of light or the sensitivity to light but.....

The sky was orange. Does over-exposure always result in (I'll call it white) white light ? The majority of light entering the camera was orange so where did all the white light come from.(I'm starting to feel really dumb now:bonk:)
 
Yes, it will usually end up white. The image the camera records is made up of Red, Green & Blue values. With an 8bit image the maximum value for each is 255. Say the orange sky had an RGB of 190, 120, 40. If you keep increasing those values eventually they'll all end up as 255 because they can't go any higher.

White balance can also play a part but as the sky was pretty much a flat colour with no detail you can discount that as a reason.
 
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