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Exposing for highlights confusion

Christopher Thompson , Jul 08, 2010; 10:48 p.m.

The other day I wanted to practice exposing for highlights to capture enough detail to be visible but avoid blowing/clipping. I found a reasonably compliant subject, a white duck at the zoo. My understanding of this is thus: in spot meter mode a reading of a brilliantly white region should render these values at the infamous 18% gray. To obtain the level of white I want for these values I should adjust by + 1-2 stops (decreasing shutter speed in this case). What I found in reality was that I could not avoid blowing/clipping highlights unless I was shooting at with 0 or even minus exposure from what the meter was reading (shooting in manual mode). I'm not worried at this juncture about the dynamic range of the entire scene, I just want to place the whites where I want them. So, I guess I'm confused and just not understanding what I'm missing about this. Seems reasonably simple, and I've read in so many different places that this is the 'correct' procedure for exposing for highlights. I'm using a D80 by the way, did not have additional exposure compensation dialed in. My metering technique was to place the focus point over the area I wanted to hold detail in and then adjust shutter speed until the meter in the view finder indicated I was at +1 or +2 (it adjusts in 1/3 stop intervals, so 6 'clicks' of the command dial towards the plus side of the exposure scale). Ultimately I have to be an empiricist and go with what works, but it bugs me that I can't seem to replicate a procedure that seems well documented.


white duck, metered for whites, no + or - adjustments

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Mark L. Cooper -- Junction City, Ohio , Jul 08, 2010; 11:16 p.m.

Christopher - I've not messed with this too much, but I believe to keep the highlights you should underexpose a certain amount. My D300 is set to adjust EV in 1/3 stop steps. I would try -1/3, then, -2/3, then -1 just to get a feel for things. I think the display would read -.3/-.7/-1 in this instance. This is a case where digital will give you instant feedback if you can run off 3 shots, then view on computer.

Hope I'm not confusing things more. Mark

Matt Laur , Jul 08, 2010; 11:39 p.m.

And... were you spot metering, or matrix metering, etc?

Christopher Thompson , Jul 08, 2010; 11:48 p.m.

yes, sorry I didn't make that more clear - spot metering. @ Mark - this is exactly the confusion that I'm having - what you suggest seems to fly in the face of the written material but seems to prove out empirically.

Kevin Delson , Jul 08, 2010; 11:52 p.m.

but it bugs me that I can't seem to replicate a procedure that seems well documented.

It appears to me you are making too many assumptions.

1) The image is white?
2) You've achieved critical focus?
3) You believe +1 or +2 exp comp will render a white object white?
4) You believe your white balance is correct?
5) You are spot metering from what luminance value of the target?

I just want to place the whites where I want them

Where would that be?

I'm not worried at this juncture about the dynamic range of the entire scene

Perhaps you should be concerned about the limited dynamic range for a certain area of the duck? The duck has no areas of luminance above a level of 235. (I've uploaded your image to illustrate)
You are not even close to blown hi-lites; so your problem must be elsewhere; yes?

The +1 to +2 exp comp is something that has been thrown around to approximate the compensation (usually) required for fresh fallen snow in full high sun exposure.

I usually don't like to simply give answers to this type of question as I feel students understand concepts better when hints are given, forcing them to re-think the problem. The above assumptions I cited should help you solve your mystery. Hint: #2

..and to help a tad more.

A ducks feathers may indeed be white, but certainly not all over the breadth and width of the feathers.
So; if you are hand holding and spot metering, you have little control at the moment of exposure to what your meter was actually seeing. You could have been looking at a level from 200 to 240. That alone will make quite a difference in camera white point settings.

Try this next time, use center weighted metering on what you believe to be the whitest portion of your subject. Now open up +1 to +2..be sure to get critical focus.


Duck

Kevin Delson , Jul 09, 2010; 12:10 a.m.

Perhaps this image will help a tad....

There was no way for me to capture the entire range of luminance in this image unless I shot it in a more controlled lighting environment...i.e (Studio)

Notice the sun/shadow positions and where I indicated blown hi-lites and not blown. Both areas are white. Hopefully you now understand the relationship of source illumination, position subject shape vs light reflection.

Large photo attachment:
(Seagull -- 564 x 850 photo)

Christopher Thompson , Jul 09, 2010; 01:24 a.m.

@ kevin:
1) The image is white?
I believe the area I was metering is white
2) You've achieved critical focus?
The image is soft so perhaps I can do better next time I try this to make sure focus is correct. The attached image is a 700x700 crop from the original
3) You believe +1 or +2 exp comp will render a white object white?
As you note about fresh fallen snow I have been taught that white subjects (perhaps the duck isn't as white as snow perhaps (another reference to #1 above?) will tend to render detail without being blown at +1 to +2 exposure comp from metered values
4) You believe your white balance is correct?
White balance is on Auto WB so this could have an impact - there was bright sun falling on the duck at the time but possibly one might consider that setting to be open shade too.
5) You are spot metering from what luminance value of the target?
since I don't know what the luminance values of the duck are, I'm not sure how to respond here - I'm metering on the whitest/brightest portion of the duck which is where you've marked it as a value of 235
I think what you're suggesting is that what i am perceiving as white actually may not be as white as I think. Your point about the area that has a luminance value of 235 being the brightest part of the image is well taken. I guess what I'm questioning here is that that spot is actually where I was metering - so shouldn't that region have taken on lesser values? I'm thinking in terms of zone system concepts where this area, what I wanted to achieve, was to show at very bright levels.. perhaps my concept of what bright or high luminance is needs to shift. I'm not sure I intended to suggest that the whole of the duck should be brilliant white or the same luminance all over - thats not it at all. However, conventional 'wisdom' would suggest that i could meter the area you've indicated, add exposure to the tune of 1 or 2 stops and have a white that still holds detail (provided some of the assumptions you raise are met).
With regard to your second post, the gull, I would agree that both parts you have indicated are 'white', that these reflect different quantities of light, and that taken as a whole the luminance range of the scene is too great to capture in one image. My question really is about how you meter and expose for that portion you identify as blown in that image

Dieter Schaefer , Jul 09, 2010; 01:48 a.m.

You are making your life way too complicated - the one place to look for and learn from is the histogram; it's free and right there at your fingertips. It tells you all there is to know about the exposure and which way you need to correct and by approximately how much. The one for your duck looks very nice and certainly couldn't take anymore positive exposure compensation than +1/3 stop (and that will push some areas into overexposure already).
Initially, I also used spot metering for white birds - with quite mixed results. Now I am using matrix metering and have learned how to adjust the exposure to get the result I want. It depends on how large the white bird is in the frame and what brightness/darkness the background has. When in doubt and given the time, I check the histogram - or rely on the "blinking highlight warning" on the LCD.
Your image has quite a green cast that takes a little effort to correct -I just went only as far as making white white:


green color cast removed

Elliot Bernstein , Jul 09, 2010; 01:54 a.m.

I say this as a former D80 owner - I found could not to trust the D80's meter reading some of the time, especially when dealing with subject matter where there was a lot of light areas. I found the camera's meter often tended to overexpose.

Shooting RAW and ignoring the meter (meaning check your display for blown out highlights using whatever method you choose to insure good exposure) will yield the best results. Using programs like Photoshop, you can more easily bring out the detail of darker areas than you can retrieve blown out areas, especially with JPG files. RAW files give you more latitude in correcting both blown out areas and shadows but I still prefer to get the bright areas exposed properly and fix the darker areas during post processing.

Your shot looks exposed correctly so I am not sure what your issue is? You seem to have got it right.

Dieter Schaefer , Jul 09, 2010; 02:10 a.m.

Couldn't give it a rest - this is the same image with a +1/3 EV exposure compensation - just at the limit were none of the pixels is blow (i.e. 255). Depending on your monitor and monitor settings, some areas might already look blown - the histogram verifies that they are not.
If you really want to make this into a science - than use a gray card and a white sheet of paper under uniform lighting conditions and see what results you get as a function of exposure mode and correction. You would have a very simple histogram - ideally just a single peak that you can move around with different exposure settings to your hearts content.


+1/3 EV exposure compensation

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