metering and white balance advice please

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will lattea
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metering and white balance advice please

Post by will lattea » April 3rd, 2012, 8:10 am

I'm trying to wrap my head around the various metering and white balance modes I have to play with. Often times auto just doesn't do what I want it to. I've seen things about carrying an 18% grey or white cards in the field to adjust for spot metering or white balance. Do any of you do something like that? I hate adding gear to my bag but I think I could manage a couple little plastic cards if it makes a difference. I found this article...

http://www.cambridgeincolour.com/tutori ... tering.htm

which explains metering well, but I'm still unsure about how to manually adjust for white balance settings. What do you do? How many cards do you actually need, etc.?

-Will

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chrish
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Re: metering and white balance advice please

Post by chrish » April 3rd, 2012, 10:16 am

Honestly, I understand how white balance and metering work because I've been shooting photos for 30 years, but I mostly just shoot RAW and fix WB and metering issues in Lightroom/Photoshop.

White balance isn't usually worth playing with IMHO. Yes, on an overcast day it makes a difference and when shooting indoors under tungsten or fluourescent light it matters, but frankly I find that I can auto WB on every shot I take. It is a simple matter to adjust white balance on the computer with no real loss of quality.

Exposure/metering is a different issue. Even in RAW, if you underexpose a shot it is hard to recover the details without adding extra pixel noise to the image. If you overexpose, you can usually recover the image pretty well without adding noise. Of course, if you go too far either way it may be a lost cause.
  • The rules to know are simple:

    - if the field of view/subject are dark, the camera is going to try to make them lighter by overexposing them (i.e. it wants to make black things gray). Prevent this using negative exposure compensation (i.e. underexpose the photo).

    - if the field of view/subject is light, the camera is going to try to make them darker by underexposing them (i.e it wants to make white things gray). Prevent this by using positive exposure compensation (i.e. overexpose the photo).
It seems illogical at first, but you want to overexpose bright subjects and underexpose dark subjects. Of course, this is all based on the idea that the camera will screw up the exposure. That assumption may be incorrect.

Years ago when I had a manual film camera, I had to be careful to make sure I understood what the meter was seeing, what it thought it was seeing, and how to correct so it would see it how I wanted. It was a PITA, but it was how photography worked in the 70s and early 80s.

Finally, I got a camera that had good metering (Minolta 400si). I figured out pretty quickly not to try to outsmart the camera most of the time. The camera's center weighted metering tended to hit the exposure straight on. I wasted a lot of slides by trying to dial in exposure compensation when the camera had already figured out the problem and adjusted for it.

And with flash, I think the day that we finally developed a competent TTL flash metering system should go down as one of the seminal days in herp photography. :beer:

Modern cameras have amazingly sophisticated metering. Their meters are so smart that I think it is largely a waste of time to use them in full manual mode and meter yourself. I always suggest to people wanting to learn how it works to use the camera in Aperture priority mode, choose the aperture you want based on what you are trying to achieve, evaluate the scene to make sure it isn't at one extreme or the other (way too light or way too dark) and shoot the photo. Yes, there are times when the camera will be fooled, but not as often as they used to be fooled. My camera nails it most of the time. I have to know when it will have a problem (birds against a bright sky, for example), but I know to watch for that and adjust accordingly.

Remember, it is digital so film is free. Shoot RAW, shoot lots of photos and figure out what your camera does right. And at least you don't have to wait 10 days for your slides to come back to see what you got right and wrong. And we have EXIF data to show us how/why we made the mistakes if we do.

will lattea
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Re: metering and white balance advice please

Post by will lattea » April 3rd, 2012, 11:04 am

Hey Chris, thanks for the reply. I've been shooting manual/ RAW for a bit but I don't have photoshop so my post editing abilities are limited. I shoot in RAW anyway hoping to afford photoshop in the future. I'm still having trouble with certain situations though, and your bird in the sky comment would be a good example. I generally just stick to the center weighted metering... I don't know if that's what's best or not.

Say for example you have a brightly back lit subject where you can't use a flash to get rid of the shaded area- like the bird in the sky or people standing in front of a sunset. Should I switch to spot metering and go off of the shaded subject? If I expose the shaded subject the background will get blown out. If I keep the background lighting natural looking the subject will be under exposed.

Another example of this is when snakes bask with part of their bodies in bright sun while the other part of their body is in some type of shadow... same as above things are either blown out or underexposed.... should I try spot metering in this case? Should I be using some auto metering instead of center weighted? Do I just have to choose between properly exposing the lit parts or the shadowed parts? In some cases a fill flash might be the answer, but I can only afford my camera with an on board flash at the moment.

And on that note, when I try to use my flash and I'm able to get rid of the shadows my photos usually end up with a yellow or brown tinge to them compared to what I can get with natural lighting... is that just because I'm under powered, or can I adjust my white balance? It's similar to the effect that results when shooting indoors i.e. tungsten lighting. I've been shooting with a rebel xti for a couple years and I just upgraded to a t2i, if that helps. I'm trying to see what I can manage without affording a fill flash.

Thanks!!

Will

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kit fox
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Re: metering and white balance advice please

Post by kit fox » April 3rd, 2012, 12:45 pm

Adding flash outdoors, often requires adding a CTO (Color Temperature Orange Gel) to match the ambient light color. I good example would be a snake basking on a rock, during sunrise or sunset. The orange / red sky looks different than the flash color which is whiter.


If you don't have money for Photoshop CS5, consider Elements 9. I had Photoshop CS2, and couldn't afford the newer versions. CS2 couldn't read the raw files from my D90, so I spent $80, and purchased elements 8. I edited the Raw file in Elements, then converted to PSD (photoshop native format) to edit in Photoshop CS2.


Having the ability to adjust color temperature, and hue is extremely important for accurate white balance. On occasion, this wasn't enough, I still had to fix color casts using Curves and Levels.

As for the snake shot where part of the snake is in the shade, and the other part is in the sun, take one exposure for the highlights (part in the sun) and one shot of the shaded snake. Make sure the exposures match the lighting, then blend in Photoshop (when you eventually get there).

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chrish
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Re: metering and white balance advice please

Post by chrish » April 4th, 2012, 3:40 pm

Will,

kitfox has answered most of the questions very well. I have found that some flash diffusers impart a warm (yellowish) tone to some photographs. This is an easy fix in photo software.

If you don't want to shell out the money for Photoshop, you should look at downloading the GIMP. It is an excellent free photo editor that does almost everything photoshop does. http://www.gimp.org/

As for the snake in the sun/shade, the problem is the the dynamic range contained within the shot. DR is the difference between the lightest and darkest areas of a photo. Your eyes are capable of registering more dynamic range than a camera sensor so a camera is either going to make the light areas white or the dark areas black. It can't properly expose both areas.

The fix for this is to use special HDR (High Dynamic Range) techniques. There is lots of information online on HDR photography. Some cameras have a special HDR function that increases the dynamic range of a shot.

One other comment that kit fox made about shooting two shots is a great one, but there is an easier fix. Shoot one RAW shot leaning towards the overexposure of the white areas. Then make an extra copy of the raw file on your computer. Adjust the exposure of one file for the light areas and the other for the dark areas, then combine the two files in the GIMP software.

Chris

will lattea
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Re: metering and white balance advice please

Post by will lattea » April 5th, 2012, 7:15 am

cool, thanks! there were a lot of helpful tips in these couple replies!

I've tried downloading GIMP but I have an older mac and there's some kind of compatibility issue with it that I can't get past. I think the best way to take my photos to the next step will be to save my pennies for better post work.

One thing I'm not sure of though, is how adding orange film to my flash would help get rid of the yellow tint... that seems like the opposite of what I'd want to do... right?

thanks again

:beer:

will

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Hans Breuer (twoton)
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Re: metering and white balance advice please

Post by Hans Breuer (twoton) » April 5th, 2012, 8:58 am

Chris, thank you very much for your wonderful answers! This photo idiot learned a lot today.

I've bookmarked this thread to read it and learn even more tomorrow.

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