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04-21-2007, 06:26 PM   #1
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spot metering

I am trying to get a handle on this setting. My question is what kind of situation would you use it for and what does is do. Rick

04-21-2007, 06:46 PM   #2
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QuoteOriginally posted by wade7060 Quote
I am trying to get a handle on this setting. My question is what kind of situation would you use it for and what does is do. Rick
Hi rick and welcome!

spot metering is just like it suggests.... it takes a small portion of your lens (middle, I think between 2-6% depending on camera) and only uses this center zone to meter lighting, instead of the whole lens like average metering
a situation that you might want to use spot metering.... a lighter subject on a darker background. average metering do a lousy job, averaging the exposure for both. this is a fast example but I am sure others will bring in more info...


04-21-2007, 06:51 PM   #3
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Randy, Thanks for the fast response and the welcome. You have given me a better idea of what it is. Rick
04-21-2007, 07:14 PM   #4
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Instead of looking at the whole scene and trying to compute the best overall exposure, spot metering computes the exposure based on a very small area ("spot", in fact) -- usually the center of the frame, but could be elsewhere. *

You could use it when your subject is small, or to get what you want out of a high-contrast scene. You might combine this with exposure compensation (EV + or -) to make sure the other non-metered areas are with reason -- or you might just leave it and only worry about your subject.

There's another option, center weighted, which, as the name implies, takes the whole scene into account but puts the most importance on the center. I like to work in this mode, with center-point focusing as well. I lock focus and exposure on the subject by pressing the shutter half way (in the K100D, enable the "AE-L with AF locked"), dial in compensation if the background requires it, recompose the image if I don't want the subject dead-center, and then take the shot.

* The K100D has a custom menu item "Link AF Point and AE", which the manual says is used in multi-segmented (i.e. "look at the whole scene") metering mode. It's not clear to me if this setting simply weights the matrix exposure towards that point or whether it uses it as the point for spot metering. Can anyone clear that up?

04-21-2007, 07:31 PM   #5
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Hi rick, remember that what you take a reading of the light meter is going to give you a reading to render it as medium grey (18%) if you read up on the zone system it is a big help. To simplify zone 1 being photographic black and zone 8 textured white, med grey is zone 5 (1 f stop per zone) so if you take a reading of a middle tone you'll be right on or you could take a reading of a white and to put it in the right zone you would add 3 stops (maybe 2 with digital) I'm not real sure. Just something to think about, of course I usually just wing it
04-21-2007, 07:55 PM   #6
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Spot metering is more often than not attached to some form of exposure system; the Zone System of White/Adams/et al or the Beyond the Zone System methodology of Phil Davis. Or a number of hybrid systems of various others emulating the previous.

One thing everybody has right is the small size of the spot. Pentax doesn't give an angular measurement-just that it is the small circle inside the center focus screen indicators.

In the zone system a practitioner memorizes a chart of zones; each zone having a representative object. This PDF contains a small toy which lists the zones and objects (Lower left). By assuming (or empirically testing) the response of the meter to a standard gray card or through the creation of a zone ruler one can meter off an object and place that object in the exposure through adjusting a fixed number of stops.

The Zone System of White/Adams/et al is primarily for B&W (but Adams made some final notes about applying the basic concepts to color film before he passed), and is plagued by three serious flaws: endless testing and retesting, a complete absence of objective standards and reliance on only a small portion of the empirically determined placement zones in making a exposure.

Phil Davis went Beyond the Zone System and beyond what most of the average population can understand and afford with actual sensitometry/densitometry, charts and graphs and the need for draftsmen-like precision in construction of those diagrams. His method requires a computer for most folks, his software, an expensive densitometer, special developing tubes....

Fundamentally he does the same metering as the Adams Zone System-including object placement on desired zones. The process is compounded with the inclusion of something called the Scene Brightness Range-stops from brightest bright to darkest shadow. The book is an interesting read. The system is tedious to perform.

Both of these spot metering systems are more easily performed in the context of large format photography (4 by 5 inches and larger); but for some reason manufacturers included spot metering on SLRs in the 60s and 70s (perhaps sooner). They have become common as have the various methods for using same. There are few true, Zone System practitioners in the SLR/dSLR population.

The one remaining and pervasive item from Zone System days is that chart linked earlier in this post. When all else fails:
  • one assumes the meter will try to put its target at or near zone V-middle gray,
  • meters the target and compensates the required number of stops to put the object on the correct zone;
  • press the shutter button and pray---believe it or not, it works about 95% of the time.
04-22-2007, 04:56 AM   #7
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Thank you all for taking the time to reply in such detail. I do understand more about it now and. Next step is to see how it works in practice. Rick
04-22-2007, 07:25 AM   #8
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A real world example

QuoteOriginally posted by wade7060 Quote
I am trying to get a handle on this setting. My question is what kind of situation would you use it for and what does is do. Rick
Hi Rick, here is a real world example of how I use spot metering. In the summer I go to as many outdoor music festivals as possible. The musicians are always on a shaded stage while all of us are out listening in the sun. If I were to try to take a photo of the musicians, they would be severely underexposed, because of all the bright sunshine around the camera. I use spot metering in this instance to get the musicians properly exposed on their nice shady stage. (of course the audience is now overexposed, but I crop those bits, I'm not terribly interested in the audience )

NaCl(hope that helps)H2O


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