AF point affects metering?

[Javelin]

Decided to start a new thread on this because it didn't belong where the subject came up. It's been said that the AF point selected affects metering. I did some test pictures where I don't see it. Actually I really would like to know how to make the AF point meter I thnk this would be handy if it worked. I tried this with spot too and got the same results. This is a small window in the front door looking out (no it's not green shag)> I was expecting a drop in shutter speed like in the 3rd picture.

Centre focus point

1/200"
F3.2
Aperture priority
400


Far left focus point on the corner of the molding around the window

1/200"
F3.2
Aperture priority
400

Exposure locked on corner focus point and recomposed

1/5"
F3.2
Aperture priority
400

[bfitzgerald]

AF point is def part of it..go outside and do a WA shot..vary the AF point position...try highlight areas, and shadow ones.
Variables as well, distance to subject..in or out of focus..etc etc

[Javelin]

surely it would have showed up in these pictures? i'll have to wait for it to stop raining to do this sort of thing with a wide angle outside..

[01af]

It's been said that the AF point selected affects metering.

In pattern metering mode, it does. In integral and spot metering modes, it doesn't.

-- Olaf

[Javelin]

these were shot with pattern metering. is the scene too contrasty? what conditions make it work?

[David Kilpatrick]

It's loaded with a database of scene examples and compares them against this, as well as using algorithms. I guess it recognises a window/doorway situation because the database has included that kind of scene ever since the first Minolta honeycomb metering with 40 segments was introduced. The old 14-segment even has some simple weighting, it knows where skies are likely to be (and therefore gets some shots wrong).

David

[Javelin]

ok that makes this sort uf untestable unless you happen to hit one of the scenes in the database where it yanks up the exposure on the dark areas. sort of makes it unpredictable doesn't it?

It's loaded with a database of scene examples and compares them against this, as well as using algorithms. I guess it recognises a window/doorway situation because the database has included that kind of scene ever since the first Minolta honeycomb metering with 40 segments was introduced. The old 14-segment even has some simple weighting, it knows where skies are likely to be (and therefore gets some shots wrong).

David

[bfitzgerald]

AF point net curtain..

AF point DVD cases

If I place the DVD case bang in the middle of the frame..the metering is less influenced by that.
Obviously if you use MF, then the AF point is no longer a factor. I suspect (but don't know for sure), that the pattern metering is based more on a central one for MF.

Some basic stuff here..
http://www.geocities.com/minolta507si60 ... ist04.html" onclick="window.open(this.href);return false;


Honeycomb should be backlighting aware, capable of knowing in or out of focus areas..distance to subject also. Without any tech docs, we won't know exactly how it works though.

I guess the logic of it is, that you are most likely to place the AF point on your subject of interest. The only weak point to that, is for WA landscapes etc. Where most likely there is no specific point of interest. I believe it's aimed at reducing exposure compensation in some situations..or avoiding the old CW metering AEL re-compose thing.

[Greg Beetham]

With the KM5D and A100 (I assume it's still the same for the A700), the metering 'segment' is tied too the AF point in Multi-Segment metering mode (and Spot metering), only when you use AF-S and AF-A, Autofocus modes, you can also select from nine AF/metering points with 'Focus Area Select' mode, with the multi controller.
Greg

[Javelin]

I just haven't see this feature actually work so it's hard to understan whats going on untill it happens on something i've shot. I don't often use local the local focus points so I haven;t run across it. When barry mentioned this I wanted to know all about it.

[Greg Beetham]

You can even steal an exposure from one focus point and focus with another one via the AEL button (set to toggle works best), focus area select, and rear controller pad, if you want, but the idea is really only useful when working off a tripod with a wide angle lens, ie. scenic type shots where you have a fair amount of bright highlights that might need looking after, I don't think it's something that you can practically use with offhand type shots, in any case with offhand shooting it's just as easy too grab the exposure you want with the centre focus/exposure point from wherever in the scene, toggle AEL button it, and then recompose/focus with the centre point again at the desired whatever and shoot with the preserved exposure, only problem with that is remembering that that AEL button is still on toggle and resetting it back to normal when finished with it.
Greg

[Javelin]

I use spot toggle all the time (the *) in the viewfinder is a good reminder so i've nver left it on inadvertantly. i'll play wih the AE lock and focus points. it may make it easier to see the effect than what i've tried already. I haven;t been able to reproduce barry has no matter what with a regular non set up scene. another grain of info was the wide angle point you mentioned .. the 90mm might be to narrow for the scenes I tried.

[Greg Beetham]

Yep, if you do it from a tripod you'll see it easily, especially if you have the composure arranged so there is a few stops of exposure difference between separate focus points, it's really handy if you want too preserve fine detail on the edges of a tree against the sky for example, just AEL toggle the sky and re-aim (if necessary) and shoot the tree, or the edge of the tree against the sky...it's an absolute must here in summer with the sky so bright in the background.
Greg

[Javelin]

Handy for portraits or product shots too. for example if your subject needs 1.5 stops of shadow you could adjust your lights without having to disturb your setup to meter around the scene like when you use the spot meter.

[Greg Beetham]

BTW I have tried doing it two ways, select focus point with rear controller, then half press the shutter, then AEL button....and by the manual, keep the directional controller pressed and then AEL button, I think I like the shutter button method the best, then you know for sure it is metering on the illuminated focus point when it actually focusses on 'that' point in focus area select mode, I think there are a few metering segments under each focus point though, and cover an area quite a bit bigger than the focus point itself, I also get the impression that those segments are averaged if they are registering a range of individual exposures.
Greg