Originally posted by BruceBanner ....
I know, sounds silly to compare the two, but really.. I hardly ever toggle out of matrix and just wondered if there was something else missing than I can't get from my constant EV Compensation use. I mean I do occasionally toggle to spot for those kinda events that it's really important (public speaking, concerts) where I just want the singers/speakers head exposed well and to hell with the surroundings etc, but yeh...
TIA!
Bruce
My experience of matrix both Pentax and Nikon is that generally you will get a perfectly acceptable result under a fairly wide range of conditions. Sometimes we just have to accept that the exposure may be somewhat less than optimal, but with modern sensors the issues of underexposure and noise is nowhere near as bad as it was with some older cameras. Clipping of IMPORTANT highlights of course is another matter
Applying EV compensation to matrix on the fly is a good way to go, as is chimping (although you will be likely underexposing if you are trying to judge by histogram or look on camera LCD) and reducing exposure until highlights protected. The problem may be that doing this you miss the 'decisive moment' as it occurs between shots.
Metering a specific ROI and applying simple compensation can often get us closer to the optimal exposure. One method is to spot meter the ROI, lets say it happens to be the brightest highlight that we wish to retain detail, then with knowledge of our metering system we can apply the required exposure compensation (either pre set EV shift or quick mental calc.).
The first problem I suspect is that we need to make sure that the ROI fills completely the spot meter area in camera. Your camera may not actually display an equivalent of the spot area and you may just have a vague notion of the area occupying a 2-5% ? circle based on your current focus point. The second issue that needs to be dealt with is the amount of compensation required for a given metering of a ROI. This will depend on how the cameras metering system has been calibrated by the manufacturer. I suspect that it is likely that Pentax follows the current ISO standards for exposure meter calibration and that this will mean that the meter is calibrated to about 12.5%.
IF 12.5% is the camera calibration point then by aiming our spot meter at an important highlight (one we require to hold detail - not specular!) and increasing exposure by +3EV we should have held detail in that particular highlight. Should the metering system calibration point be different then the exposure compensation must also change. For instance (and I think it unlikely) if the manufacturers calibration point is 18% then +3EV will clip highlights as the correct adjustment would need to be +2.47 EV (so practically +2.33 EV).
So as already mentioned to make the most of metering (spot particularly) then some practical testing of what your meters calibration point is will reap rewards.
A quick and dirty method applied by some/many 'old school' photographers was to meter a known value and increase the indicated exposure by the required amount to reach optimal exposure/sensor saturation. Grey card is obvious, but we do not always have one to hand or the time or inclination to use. But we do carry a known value with us at all times, namely our hand. By metering our palm (only) in the same orientation and light as our subject matter and increasing exposure by 1 stop will get us close to optimal exposure - check your own palm values first though.
As long as you do your research/testing on your camera metering system first and assuming you have the time and experience to implement your findings you may find that you have a liking for the precise nature of spot reading over pre calculated values and assumptions of matrix and centre weighted sytems. YMMV of course and as long as it catches what you require then one method over another may not be considered worhtwhile