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PostPosted: Fri Sep 03, 2010 2:48 am 
Stops.. a stop is just a measurement of light really. A stop can be increased or decreased by a wide or closed aperture or a slow or fast shutter speed. So when I say camera sensors can capture around a 7 to 8 stop range, it's really zones I suppose. Imagine zones being broken into different levels of tone - black being zone 1, an average colour (a middle grey, or a brick wall or blue sky on an averagely sunny day) being zone 5 and white being zone 10.

So if your scene contained a completely solid black element and a completely solid white element, either your black element would have to go dark grey to capture the white element - because the sensor captures too much light from the scene to keep the black element black or the white element would have to go light grey to capture the black element because the camera can't capture enough of the light reflected off the white element to keep the white element bright white. You'd have to decide which is the most important.

So if you wanted to capture a black cat who is sat on a field of snow, to expose your cat properly, you'd have to accept the snow is going to have to go a little grey because the sensor doesn't capture enough of the light reflected from the snow to make it bright white.

Or in another example, a sunset - because the sky is really bright as the sun sets on the horizon and your foreground is going to be dark, you wouldn't be able to capture all the detail of the foreground as well as getting all the colours in the sky (you can with graduated filters but that's another topic) so you'll often see sunset images being silhouettes with nicely exposed skies.

For example (a random creative commons image from flickr)
Image

The dynamic range here is too wide to get detail of the surfer who in the available light is going to be really dark and would need the shutter being open for a long time or the aperture to be opened up wide, and the sky which still has really bright tones. You'd have to decide if you wanted to capture the detail of the surfer - and have a really, really bright sky - or capture the colours of the sky - and have the surfer being a silhouette as we see. Your camera won't get both.

Hope this explains it!

Oh as regards to spot metering, I believe (I could be wrong for canon cameras) the camera meters the spot your focus square is aimed at rather than the centre of the viewfinder. So if you use your directional pad to focus on something on the left of your viewfinder, the light meter in your camera will read off that spot. Certainly this is how it works on Nikon.


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PostPosted: Fri Sep 03, 2010 3:02 am 
that explains but I have to read it twice to fully get it thank you Welly, about the meter type what type would you use in general purpose like the image I posted?


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PostPosted: Fri Sep 03, 2010 3:28 am 
Definitely matrix metering (or whatever it's called on canon). You'd probably want to use matrix metering for about 97.725% of the time. Spot metering is very specific to certain circumstances and I wouldn't bother with centre-weighted/average metering at all. Spot or matrix but mostly matrix. As someone said above, if you find your camera is over exposing in a scene such as that, use exposure compensation to bring down your exposure a little bit and you can always tinker with the image in lightroom/photoshop later if needs be. Just be aware of the scene.. if there's loads of dark areas and shadows and loads of bright spots, recompose until you minimise the range of tones/brightnesses and you'll probably get a better image anyway.


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PostPosted: Fri Sep 03, 2010 6:02 am 
Your camera can record light on 255 levels. A histogram is a representation of those levels in your image. The blacks are on the left and the highlights on the right with the mid tones in the middle.


Most of the "levels" are squeezed onto the right 1/3rd of the graph, so its very important to make sure your histogram is as far to the right as possible with out having "blinking" or overexposed parts of the image.

Our Professor explained it to us that your sensor is like a base ball bat it too has a sweet spot of where it preforms best. That just happens to be on the right side. So when your shooting manual try to push your histogram all the way to the right with out having too much "blinking".

And as Welly said it can be impossible to not over expose some parts of the scene but just make sure your subject isn't blinking.


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PostPosted: Fri Sep 03, 2010 9:11 am 
Quote:
Our Professor explained it to us that your sensor is like a base ball bat it too has a sweet spot of where it preforms best. That just happens to be on the right side. So when your shooting manual try to push your histogram all the way to the right with out having too much "blinking".


what do you mean push the histogram all the way to the right? are able to change the light setting in the histogram of your camera? or your saying when post processing?


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PostPosted: Fri Sep 03, 2010 8:23 pm 
just an additional question but out of the original topic, when taking picture like indoor (under the tungsten light) will you put you WB into tungsten as well?


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PostPosted: Fri Sep 03, 2010 8:36 pm 
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Joined: Mon Jan 18, 2010 3:52 pm
Posts: 2175
Location: The Netherlands
If the AWB doesnt give you a correct WB...Yes.

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Ruben

Panasonic DMC-FZ18, Panasonic DMC-FZ28, Canon G5, Canon 350D, Canon 50D + BG-E2N
Tamron 17-50 2.8, Canon EF 70-200mm f/4L USM,
Canon 18-55 II plus lots of Minolta MD/M42 lenses and bodies


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PostPosted: Fri Sep 03, 2010 9:43 pm 
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Joined: Mon Aug 17, 2009 9:46 pm
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Location: Norway
Another thing on WB: If you shoot outdoor scenes with a lot of green, AWB will make the scene too warm. The green will get a yellowish tone. At least it's been that way on my Canons. So set WB to daylight in those situations

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PostPosted: Fri Sep 03, 2010 10:33 pm 
@Ruben
thank you for your reply it just confused me earlier because my WB was still set at daylight so i tried to put it on tungsten.

@janern
Thank you, yeah I always set my WB to daylight when shooting outdoors.

@Welly
Today I was using histogram to check the exposure levels and it is really helpful but I don't think that am getting the right exposure on some of the pictures.


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PostPosted: Sat Sep 04, 2010 7:03 am 
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Joined: Mon Jan 18, 2010 3:52 pm
Posts: 2175
Location: The Netherlands
You really have to play with the camera (and learn) how to use it and make a correct exposure. It isnt that simple!

If the exposure isnt good/as you wanted it to be, use the EV+-.

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Ruben

Panasonic DMC-FZ18, Panasonic DMC-FZ28, Canon G5, Canon 350D, Canon 50D + BG-E2N
Tamron 17-50 2.8, Canon EF 70-200mm f/4L USM,
Canon 18-55 II plus lots of Minolta MD/M42 lenses and bodies


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PostPosted: Sat Sep 04, 2010 8:58 am 
Original Photo:
Image


1st with black and white @55 Opacity
Image

2nd adjusted the black "0" to "13"
Image

here are some photos taken yday whilst playing with the exposure also using the histogram. i'd love to hear some comments/suggestions about the photos.


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PostPosted: Sat Sep 04, 2010 10:41 am 
When I say 'Push the histogram to the right' I mean expose your image so the histogram is as far to the right as possible without over exposing your image.

Like I said the reason for doing so is because most the levels of light your camera can record are in that range.

I made a few samples to demonstrate using your histogram.

Over Exposed: (ISO 100, 2.5 seconds @ f/2.8 )
Image



Correctly Exposed:(ISO 100, 1/4 second @ f/2.8 )
Image



Under Exposed:(ISO 100, 1/40 second @ f/2.8 )
Image


As you can see when your image is over exposed your histogram will be too far to the right and will spike out.

When your image is correctly exposed your histogram will be to the right but not clipping, in otherwords your camera was able to recored all the light with out any parts being blown out.

When your image is under exposed you'll see the histogram filling the left side. This is bad because you missed a lot of tones that you could have had.


It took me a long time to figure out that the "correct exposure" looks over exposed on the LCD. I kept getting it wrong and I had to reshoot every assignment I was given.


Thats a nice portrait you've posted. It looks underexposed, but not by much. I like the pose, you have a nice head tilt and its also good that you aren't straight on with the model either. The only suggestion I would have aside from shooting brighter would be to pull the model away from the background, this would make the bricks less defined and less distracting but I still think you did a great job making them blurry in the first place.


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PostPosted: Sun Sep 05, 2010 9:53 am 
aw thank you Tomis.

I started using histogram when Welly suggested to use it instead of just looking at the LCD im still struggling about my shoots as well because I can get the right thing but i will get there bits by bits hehe...

thank you for the suggestion about my post, hmm which one do you think is underexposed?


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 Post subject:
PostPosted: Tue Sep 07, 2010 6:04 am 
They are all the same photo right? Just different processing?


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 Post subject:
PostPosted: Tue Sep 07, 2010 6:02 pm 
Yes, Tomis they're all the same I'm still working on my processing ways hope sooner or later i'll get the proper image.


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