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10-24-2012, 10:01 PM   #1
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Light metering from c -> m


I have a film camera Pentax P30 which only supports one light metering method (center-weighted aka c). Is there a way to convert any result by that method to Matrix style? (This may vary and depend on camera. I am asking for P30, and if possible, Kr).

Auto-settings from camera P30 isn't good esp for landscape shooting. Here are two pictures taken with my P30 (almost at the same time). The first one is very bright (and it's good to me).

Th?o C?m Vin Si Gn | Di?u's FineArt
SaiGon Zoo | Di?u's FineArt

Thank you for your helps!

10-26-2012, 09:51 AM - 1 Like   #2
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Matrix metering takes light measurements from several locations in the frame. Pentax DSLRs use either 16 segments or 77 depending on the camera. The measurements are compared to a database of light readings from well-exposed images, and an exposure is chosen from the best possible match. It should recognize a scene like a backlit portrait and adjust automatically. Some other computer magic is factored in, especially for DSLRs, to minimize the areas where no detail would be recorded. The inner workings are all up to the manufacturer and not available to the user. So it's more or less impossible to know exactly what the camera is thinking all the time. With the instant feedback of digital, you can tell when it's not giving you the results you want.

Center-weighted may not be right any more often, but you can see how it works and adjust to that. There is a graph that shows its sensitivity to light in the camera's manual. The meter will suggest a setting to expose the center of the frame at 18% gray. The further away from the center of the frame, the less sensitive the meter is to light. For a backlit portrait, you could center the face in the frame, lock exposure with the AE-L button, then recompose and shoot.

The P30 is going to limit the amount of adjustments you can make because it doesn't have many. It only has M and P modes, and P only if you have a KA mount lens. There's no exposure compensation. The only input you have in P is the AE-L button. In M mode, you can only choose shutter speeds in full stops.
10-26-2012, 11:27 AM - 1 Like   #3
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I don't understand what you mean by converting a center-weighted meter reading to a matrix style. However considering the fact that you've obviously outgrown your P30, the way I see it you have a few options:
1. Either dump your P30 and get a used film camera with a better metering system. Film cameras are dirt cheap, even those that were $1,500 "pro" bodies can be had for a few hundred bucks. Or, better yet, keep it as a back up or as 2nd body so can shoot color in one body and B&W or another speed in the other body.
2. Keep what you have and adapt to the camera's limits. For example, you could meter off a grey card and transfer those setting in M mode. If keeping a gray card on you is inconvenient, then meter off of healthy green grass or evergreen trees which are also very close to 18% gray. When I shot slide film, I'd just meter off of my palm in auto mode (I'm Caucasian) and then transfer the exposure in manual mode, increase the exposure by one stop, shift the aperture/shutter speeds for the scene and shoot. With this method my highlight exposures were almost always dead on.
3. Purchase a hand-held meter that reads both reflective and ambient light. Sekonic makes great light meters. Getting one with a built-in spot meter is preferred. Getting one that also reads flash is great, but not necessary.

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