Topic #2, Light Metering, White Balance, JPEG vs RAW formats

Discussion in 'Photography Beginners' Forum' started by Dominantly, Jan 6, 2010.

  1. Dominantly

    Dominantly TPF Noob!

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    Intro:

    This will be round number two of the basics.
    References will be:
    Google
    Lighting by Chris Bucher
    Photography Field Guide by Bryan Peterson
    Digital Photography: Top 100 tips and tricks by Rob Sheppard

    Just in case you want to expand on anything I type here, all my info and technical knowledge has come from them. So a couple days later and you could be all caught up:p

    Topic #1 can be found here http://www.thephotoforum.com/forum/...9084-exposure-your-photographic-triangle.html


    Light Metering:


    Alright, so in the last "lesson" we talked a little bit about light metering and the fact it plays a very important role in your goal of capturing a proper exposure. I'll try and expand on here a bit more here, because I feel it's pretty important to understand.

    Most (if not all) modern cameras have some sort of light metering capability built in. Back in the day, in order to be successful at dialing in your exposure, you had to carry an external light meter to aide you. They could meter ambient light falling on your subject (have you seen those small hand held devices with the small white half sphere?) or reflective light by pointing it at your subject and reading it.
    With your cameras meter all you have to do is point your camera at your subject and your camera will continuously meter and assist you in your exposure (or do it all for you minus hit the shutter in Auto modes).
    The built in meter is called a Through The Lens (TTL) meter. You may have heard of i-TTL or intelligent Through The Lens Metering which uses the in camera meter and an external flash to pick the appropriate amount of light for any given scene, at any setting.

    -The way this metering stuff works is it measures the amount of light reflected off your subject. Your camera is calibrated to want to see the luminance of reflected light coming off a subject of middle/neutral gray (with a reflectance of 10-18% depending on your manufacturer/model), when it does this it's the happy, properly exposed, point.
    So what about trying to photograph two extremes together? For example if you are photographing a black object in front of a white backdrop with strong, even lighting falling on both; you will get different metering results on both if you zoom in and focus on them, even though they are lit the very same way. The reason this occurs because dark colors absorb light while brighter colors (like white) will reflect it. Your white background will reflect approx 40% of the light, and your black object will only reflect 10%.
    The important thing to do in a situation like this is meter off the subject, and use a mode that allows you to meter specifically off that (modes described below). Your camera freaks out at those extremes and will want to render them gray if you don't step in and take creative control of the metering and settings.
    The Gray card Can be found here will allow you to get proper exposure when shooting dark or bright subjects.
    It's pretty simple to do, you place the card in front of the camera with the same light hitting it that is hitting your subject. Then you place your camera (should already be there ) in manual and adjust your settings until your camera tells you that you have a correct exposure. Then just remove the card and shoot away.

    For daylight we have the Sunny 16 rule. This rule just gets you in the right direction, and shouldn't be taken as gospel.
    So for a middle of the day exposure, set your aperture to f/16 and then match your ISO and Shutter Speed as close as possible. SO for example f/16 ISO 100 1/125, or f/16 ISO 400 shutter 1/500..... SO shutter speed = ISO for this rule of thumb.



    Modes:

    For Nikon we have Matrix Metering (Canon calls it Evaluative
    Light Metering), Center weighted, and spot modes.

    -Matrix
    works by evaluating the entire frame and set the exposure based on the distribution of brightness, color, distance, and composition. The Cameras internal processor chip references thousands of images with greatly varying contrast and brightness (think snow to city nights) and references what you are metering and picks a "like" reference image to reference for your images exposure settings. This is the safe setting, and will work well in a large majority of exposures, and will give you pretty consistent results.

    -Center weighted still evaluates the entire scene, it just shifts its priority to a 6, 8, or 10mm circle in the center of the screen then tapers outward(user adjusted, Canon may vary)..This is a very common metering method for portraits, and the standard for cameras without an evaluative/Matrix metering mode.

    -Spot metering is just as it sounds, it meters off one little tiny dot, the rest of the scene be damned. It will meter 2.5% of the frame, or 3.5mm/0.14in on average. Spot meter will probably be something you learn to use in very specific situations, and not a whole lot in between them. One example of a great time to use your spot meter would be when photographing the moon.




    White Balance:


    What you see before you at a photo shoot with your very own eyes, and what your cameras see are very different. Your fancy brain compensates for different color temperatures (measured in degrees Kelvin (K) ), and allows you to see various lighting conditions which may be intermixed, as normal. That's why it's sometimes hard to try and recreate that awesome lighting you may be seeing with your eyes, in your exposure. Lets see if we can break down how White Balance and Color temperature are intertwined.

    So it may seem backasswards but in Kelvin, Cooler colors have a HIGHER temperature then their warmer counterparts (lower temperature). Thats confusing so I will break it down a bit more:

    WARM- Candle light, Fire light, etc..... Color Temp- 1500K to 1900K
    WARM- Incandescent Bulbs................. Color Temp- 2500K to 3000K
    WARM Studio Tungsten................. Color Temp- 3400K

    Neutral- Daylight (midday)................. Color Temp- 5000K to 5500K

    Cloudy day, Shade, .......... Color Temp- 6000K to 7500K
    Various other blue lighting....... Color Temp- up to about 11000K

    So you can see that the red/yellow/orange; warm light, has the lower Kelvin number, and the bluer cool lighting has the higher Kelvin number.

    As a general theory/rule/feeling, warmer tones actually draw out better emotions from people Vs cooler, blue tones. Most people can imagine an orange, warm, beautiful sunset, and all the good feelings/awe it draws. It's just something to think about when setting up your white balance. For reference, Bryan Peterson states he sets his camera in Cloudy mode and shoots away. He spends most of his time shooting outdoors with natural lighting, and enjoys the color and warmth the Cloudy setting gives. If it doesnt work out, you can always change it in Raw (thats why you shoot in raw, right?).
    What your camera does with Auto White Balance..... It just adds and mixes colors.If the blue light in your scene rises, your camera will add orange to balance. If it is shot under fluorescent (which appear greenish) it will add magenta. It will mix and match to try and get your colors correct, your whites white with no tint (doesnt always work that way, you can end up with peach colored whites, or dull gray whites).
    Auto white balance will work the majority of the time, but it can be fooled so if you want to nail the white balance and save time, you can use an 8"x10" bright white card at your shoot. Once you have your lighting set up, take your shot of the white card to set the white balance for that specific time. Your meter can be fooled with large amounts of the same color, especially blue, and will try and compensate for it, even though you want the blue as blue as you can get it.

    Courtesy of IgsEMT when I had specific topic questions:: (THANK YOU!)



    For MANUAL WHITE BALANCE (D90 specific instructions)
    You might also want to try and adjust your white balance using your gray card.

    If you are shooting with a D90, so this is how you would do it. Grab your gray card, do the same thing mentioned above in regards to filling your field of view with the card and subjecting it to the same light source. Then hold your WB button and turn your main command dial to "PRE". Now hold the WB button down; PrE will flash on your LCD. Take a photo of your gray card. GOOD will flash if the shot was acceptable. After GOOD flashes, press the WB button again, and you are now good to go with your custom white balance.
    Now if you go under your shooting menu, the 5th option down is White Balance (should say PRE), press the right arrow into, then the right arrow again at the PRE submenu. You will see your WB reference photo labeled d-0, you can store up to 5 (d-0 thru d-4). You can edit comments/labels for each reference, and you can go in and fine tune them.



    Raw vs JPEG


    Shoot Raw. Well, let me expand on that. If you are taking photos that you care about, want to come out perfect, and cant easily do a re-shoot (or don't care to); you want to shoot raw. If you are taking a snapshot and could care less about the results, OR you just don't care to hassle with the processing of a raw file, then by all means shoot a fine JPEG.

    JPEG's are processed files that have been run through your cameras image processor, then compressed and saved to disk. The problem with these files is that when the processor is compressing the data, it will average similar colors and similar contrast. Also when you you load the JPEG to your computer, you are pretty much done with it. If you plan on editing the photo, you will be limited as to what you can do, and you can only do it once (without more loss). When you go to save that file, save it as Image Quality 12 and let it be. Every time you open it after that and edit it, you will compress it further upon saving it. One way to handle this is saving the file as .Tif right away, Tif's are loss-less files so they will not compress and lose data with each subsequent save.
    RAW is just that, a RAW file of all the image information from your camera. It is quite a bit larger (3 times) then your average JPG, but that's understandable as it contains more color and contrast information, in a minimally processed file. You can change 2-3 stop Underexposures and 2-3 Over exposures into perfect examples, using a raw file. Maybe you didn't nail the exposure in the camera, but with raw you can go back and make it a perfect exposure in most cases (as long as you were in the ball park).



    Thanks for looking. I will try and do some photo examples and post them in this post, in the next couple days. If anyone has any good example shots covering metering or white balance, and you want to add them, PM me...

    :thumbup:
     
    Last edited: Feb 9, 2010
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  2. IgsEMT

    IgsEMT No longer a newbie, moving up!

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    In my defense, I was tired when was writing this and apologize for spelling/grammer mistakes, plus I'm ESL :lmao:
     
  3. Dominantly

    Dominantly TPF Noob!

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    Same here, except I'm EFL :meh:
     
  4. Craig G

    Craig G TPF Noob!

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    I enjoyed your first write up (didn't care where it came from) and was looking foward to #2. Thanks:thumbup:
     
  5. AfroKen

    AfroKen TPF Noob!

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    I just wanted to say thanks for writing that.
     
  6. keith foster

    keith foster TPF Noob!

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    Thank you for this. Good stuff.
     
  7. KalaMarie

    KalaMarie TPF Noob!

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    :thumbup: Very useful info. I gave the link to this thread to someone who just bought a dSLR and has questions re: RAW v JPEG etc.
     
  8. TylerF

    TylerF TPF Noob!

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    thanks for taking time to write these Topics out.

    maybe you could touch upon how to fix WB, exposure and other things when shooting in RAW. many people say they use a gray card and then use an eye dropper to fix the WB. i dont know what that means lol.

    also, if i am shooting RAW, should i really fuss over settings and try getting them perfect, or should i just aim to get close? i usually shoot jpeg, but plan on shooting concerts where i most likely wont have correct setting all the time and cannot re-shoot.
     
  9. Josh66

    Josh66 Been spending a lot of time on here!

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    Not sure if Nikon has an equivalent, but on Canon bodies there is also Partial.

    Partial is pretty much the same thing as spot, but the spot is bigger.

    Spot metering uses a small spot, like you said - 2.5% or something like that.
    Partial will do the same thing, but the spot is maybe 7% (not sure on the exact size).
     
    Last edited: Jan 8, 2010
  10. Josh66

    Josh66 Been spending a lot of time on here!

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    In many PP programs there is a dropper tool for WB.

    You just select the tool and click on something that should be neutral.

    If you take a reference picture of something that you know is neutral, fixing your WB in PP only takes 2 clicks. You can then apply those settings to any other pictures that were shot under the same lighting conditions.
     
  11. Dominantly

    Dominantly TPF Noob!

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    Thanks for the idea on what to think about posting next.

    If you shoot raw, you should still do your best to nail the exposure the first time. You can't fix everything with a Raw file, for example if you shoot and have areas that are blown out (face from spotlights), or that are black/underexposed, you can't pull detail from them. The reason for that is, there isn't any detail to pull. So picking your creative exposure, I mean deciding what in the photo is important to you, and setting your camera up to record this the first time, is very important. I mean maybe you want dramatic lighting, half the face to fade to shadow, or maybe you want the opposite with hot lighting and skin tones- just decide and set the camera up as close to it for the first few shots and let her go.
     
  12. Dominantly

    Dominantly TPF Noob!

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    I just went through the User manual to check for a partial comparison for Nikon, and came up with nothing.
    From the way you describe it, it sounds an awfully like our Center Weighted, which is adjustable from 6,8,10mm. I mean spot is just that, narrow, spot specific, where the center weighted seems more partial with it's highest priority the center, yet still taking into account a little outside as it feathers to the edges.
     

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