Let's talk exposure

[extreme8]

Well, I have tested many things today (in retrospect!)
PS why was it last night when DD had earache the only word she knew was Daddy!!!

Rob

Mine only know mommy as well
consider yourself blessed!

Signed: one undervalued dad.

 

[DueyDooDah]

Hi All,

There seems to be a common theme in some messages I've seen lately: Exposure. I too have been struggling with overexposed shots recently. Specifically, when using the Tv mode.

My issues have arisen when shooting scenes with alot of white in them. This week, while driving over Steven's Pass in Washington, I came to a spillway that was very active. I wanted to set my shutter to about 1/5 of a second to get that wonderful flowing effect, so set Tv and 1/5. Each time, I ended up with an extremely overexposed shot.

I assume I am metering in the wrong spot. I tried metering off the white-water and off the green water, but neither case gave me what I wanted. I also tried setting exposure compensation, to no avail.

Let me also ask about my metering method. I normally point to a spot I want to meter off of. I press the button halfway down, recompose the scene then press the button the rest of the way down. Is this correct? My concern is that while using this technique, my lens seems to focus on the spot I meter on. It does not seem to refocus when I press the button the rest of the way down. At least I don't hear the mechanism change at that time. This metering, recomposing, focusing thing keeps nagging at me, so I ask the experts.

Does anyone have any tips to overcome these problems?

 

[Pea-n-Me]

Guess I need to join the discussion (or at least take notes.)

 

[tinksdad]

Hi All,

There seems to be a common theme in some messages I've seen lately: Exposure. I too have been struggling with overexposed shots recently. Specifically, when using the Tv mode.

My issues have arisen when shooting scenes with alot of white in them. This week, while driving over Steven's Pass in Washington, I came to a spillway that was very active. I wanted to set my shutter to about 1/5 of a second to get that wonderful flowing effect, so set Tv and 1/5. Each time, I ended up with an extremely overexposed shot.

It depends on what your camera is capable of. Most of the advanced PnS have at least spot and partial/evaluative metering. Spot metering will meter off the "spot" your focus bracket is on. Partial/Evaluative looks a a larger area and then balances for best compromise,effective when the background is much brighter than the subject due to backlighting. To shoot water falls or flow and capture the "flow with action" it's recommended that you use a slower shutter speed like you did. However, to balance the exposure you have to use a smaller aperture to limit the amount of light entering the sensor.

I assume I am metering in the wrong spot. I tried metering off the white-water and off the green water, but neither case gave me what I wanted. I also tried setting exposure compensation, to no avail.

Let me also ask about my metering method. I normally point to a spot I want to meter off of. I press the button halfway down, recompose the scene then press the button the rest of the way down. Is this correct? My concern is that while using this technique, my lens seems to focus on the spot I meter on. It does not seem to refocus when I press the button the rest of the way down. At least I don't hear the mechanism change at that time. This metering, recomposing, focusing thing keeps nagging at me, so I ask the experts.

Does anyone have any tips to overcome these problems?

What metering mode are/were you using? What camera is it?

Check out this site, it has some good information about exposure and lighting levels.

 

[DueyDooDah]

Oops, sorry. I am using a Canon 30D. I used spot metering.

 

[tinksdad]

Another issue that affects digital photography is the range of exposure possible. Many times the scene we see with our eyes has a greater dynamic range that is possible to capture with one exposure.

To overcome this you can bracket the shot with a mix of 3-7 shots with varying levels of EV, over and under the base exposure. Blending these can give a more even shot of the scene and is more like our eyes "see" the scene.

Link to Popular Photograhy HDR

Of course this can be taken over board and the scene starts to look surreal as well.

 

[tinksdad]

Oops, sorry. I am using a Canon 30D. I used spot metering.

If you use spot metering, then you should be able to set the metering bracket over the mid range exposure level (not the darkest, but not the brightest) and get a decent exposure based on the lighting level.

You might try using the full manual mode and then balancing the shutter and aperture for the best mix. Then adjusting your EV for fine control.


If you have a tripod set up the camera and meter for the midrange at the same scene. Set bracketing for a 2/3 or full stop differential with a five shot range and see what you come up with. It's pretty interesting!

What image processing software are you using?

 

[DueyDooDah]

What image processing software are you using?

Photoshop Elements 4.0.

 

[Anewman]

I normally point to a spot I want to meter off of. I press the button halfway down, recompose the scene then press the button the rest of the way down. Is this correct?

I dont own the 30D(own 20D), but the half pressing the shutter does not lock in meter readings and/or exposure settings arrived at.

I believe the way to lock in the metered settings is the star button on the back of the camera(upper right hand corner).

But I shoot full Manual 95% of the time so I have not tried this at home.

 

[handicap18]

Show us some example pictures of your issue with all the exif data available (ie: ISO shutter f/stop metering exposure compensation etc...)

Seeing the picture might help get some more info.

I don't see from your description what your doing wrong. Though one thing you can do differently is to take your meter reading on where you want, make note of the settings (shutter and f/stop) then switch to Manual and plug in those settings. Either that or hit the exposure lock button, they both do the same thing.

 

[boBQuincy]

I wanted to set my shutter to about 1/5 of a second to get that wonderful flowing effect, so set Tv and 1/5. Each time, I ended up with an extremely overexposed shot.

I assume I am metering in the wrong spot. I tried metering off the white-water and off the green water, but neither case gave me what I wanted. I also tried setting exposure compensation, to no avail.

1/5 second is likely out of the range for proper exposure. I was having trouble getting as slow as 1/15 at f/22, ISO 100, with a polarizer. To get a really slow shutter speed on a bright day you will need a neutral density filter, like a 8x or more.

Metering can be tricky. The Zone System is a great tool for determining exposure, especially for things like white water where you hope to avoid overexposing the water. Just meter the water (in Spot mode) and give three stops more to get the water in Zone 8.

 

[Groucho]

I would agree with Bob. I'd guess that you can't take an exposure that long as there's too much light.

To rephrase what Bob said - lower the ISO as far as possible. Try shooting in full manual. Set the shutter to 1/5th and go with a smallest aperture possible.

If you're at the sensor's lowest sensitivity and the lens's smallest aperture and you're still overexposed - you're either stuck or you need a filter.

(And I knew your line in the other thread about 100% of your 30D pics coming out perfect, including composition and subject matter, was baloney. )

 

[fuse04]

Mine only know mommy as well
consider yourself blessed!

Signed: one undervalued dad.

 

[DueyDooDah]

(And I knew your line in the other thread about 100% of your 30D pics coming out perfect, including composition and subject matter, was baloney. )

I was hoping you'd miss this thread, cause I knew you'd call me on it.

 

[jann1033]

Well, I have tested many things today (in retrospect!)

a) Firstly tested the efficiency of Canon and retailer customer service 10/10. The new body arrived less than 24 hrs after phoning Canon.....

Rob

i'm thinking of immigrating to the UK on this sentence alone since the US counterpart, well lets just say is less than stellar

 

[Groucho]

I was hoping you'd miss this thread, cause I knew you'd call me on it.

Nothing gets by me. I just love that both messages were posted in such close proximity.

Anyway, that's nothing. Check out some of the threads last year where we were hunting down DVC eBayers who were abusing the system, I did some real sleuthing there.

 

[tinksdad]

Nothing gets by me. I just love that both messages were posted in such close proximity.

Anyway, that's nothing. Check out some of the threads last year where we were hunting down DVC eBayers who were abusing the system, I did some real sleuthing there.

Dr. Holmes, I presume...........

 

[fuse04]

i'm thinking of immigrating to the UK on this sentence alone since the US counterpart, well lets just say is less than stellar

How about we swap then because I want to come live in the states!

I supose I just got lucky. Today I see Canon have launched some cash back deals in the UK which means if I had waited a couple of weeks I would have saved about $150 ! Have just written to Canon asking for a retrospective cash back

Rob

 

[MarkBarbieri]

Want to know the trick to getting the best possible exposure when taking a picture? The histogram is the key.

Your camera probably has lots of different exposure modes - spot, partial, center weighted, evaluative, matrix, etc. For this lesson, don't worry about which mode you use because it doesn't matter. The reason is that we are going to use the histogram as our meter.

Set up your composition and take a picture. Now check the histogram. If you have a line on the far right-hand side of the histogram, your exposure is too high and you need to reduce your exposure. You can do that by shooting in manual and just lowering the shutter speed or aperture, lowering the ISO, or using exposure compensation.

If you look at the histogram and you have room between the rightmost part of the graph and the rightmost edge of the histogram, you want to increase your exposure. The trick is to get the exposure as far to the right as possible without hitting the edge.

Hitting the edge is bad because those pixels are "blown out." They are just plain white. Sometimes you can't avoid it. If the sun is in your picture, it's going to blow out. Specular reflects also tend to blow out. If you can't or won't change your composition or lighting to make them go away, decide what parts you can ignore and let them blow out. Most of the time, however, you should strive to keep everything off of the right edge.

Why try to get close? Your camera records better information on the more exposed (but not over-exposed) pixels than it does on the darker pixels. This is primarily because the signal (the stuff you want) to noise (the grainy, extraneous stuff you don't want) is higher for the more exposed pixels.

Won't that mean that my picture will be too bright? Maybe right out of the camera it will, but you can adjust it back down using your photo editor. When you do so, the picture will be better than it would have been if you'd shot it dimmer in the first place.

What about the left edge? Ideally, you don't want pixels piled up against the left edge either. These represent parts of the picture that are just plain black with no detail. However, these don't hurt the look of a picture as bad as blown out parts do, so if you can't get everything to fit your histogram, err on the side of leaving dark parts rather than bright parts.

When exposing for the right edge, make sure that you use the RGB histogram and not the average luminance histogram. The former shows you a histogram for each of the three sensor colors. The latter averages them together and shows just the average. If you take a picture of a bright red flower, you can easily blow out the red pixels while the average luminance still looks OK. You don't end up with white pixels there, but you do lose detail in the red colors, which is almost as bad.

Some older digital SLRs have only an average luminance histogram, so you don't have a choice. With those, you have to guess or bracket.

 

[extreme8]

Now ya done it Mark.
Get ready for the "how do I know the difference between RGB & Average Luminance histogram on my camera" posts

Great post. I'm sure many will find it helpful.