AF point affects metering?

Discussion of all digital SLR cameras under the Minolta and Konica Minolta brands
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Javelin
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Re: AF point affects metering?

Unread post by 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.
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Greg Beetham
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Re: AF point affects metering?

Unread post by 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.
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bfitzgerald
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Re: AF point affects metering?

Unread post by bfitzgerald »

Interesting observation, the A57 isn't biased to the AF point in use. That's a pro and a con (ok for scenic, not so much portraits) however if you enable face detection it does bias the metering to the person, "if it detects them"

Not sure how other SLT Models work but that's my observation here
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Greg Beetham
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Re: AF point affects metering?

Unread post by Greg Beetham »

Geez Baz now I’ve forgotten what I was talking about, I’ll have to go back in the thread and refresh my memory. :lol: On the face of it it sounds peculiar that the A57 doesn’t have exposure for the AF point in segmented metering mode? I thought that would be set in stone?
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bfitzgerald
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Re: AF point affects metering?

Unread post by bfitzgerald »

I thought it odd, but I've done real world shooting and testing and it's no question not adjusting it's exposure on the AF point in use. Not sure if all the SLT's do this...previous Sony DSLR's were based on the AF point just like the KM ones.

Just an observation. Metering is a bit cautious as per previous Sony Alpha's I've used, but fairly consistent (unlike the D7k I had all over the place)
Winkler Prins
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Re: AF point affects metering?

Unread post by Winkler Prins »

Javelin wrote:It's been said that the AF point selected affects metering. I did some test pictures where I don't see it.
I can't tell what camera you are using? Can make quite a difference ofcourse.

Fact is, in your second image, the whole glass window is in focus. My guess is: exposure will adjust to (all) area's where focus points tell the camera the image is in focus.

Otherwise read the manual that was supplied with your camera.
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bfitzgerald
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Re: AF point affects metering?

Unread post by bfitzgerald »

There are only small bits of information around such as this:
http://www.reocities.com/minolta507si60 ... ist04.html

(you can see the groups DK is talking about ie patterns)

Sony's 40 segment is basically the same with more areas over the original. but very little information about how it works
http://www.sony-mea.com/microsite/dslr/ ... ure02.html

There is some variation between models though (7d and 5d react quite differently in multi segment metering mode)
The best way I've found out what it's doing is actually using the 7 film body, because it tells you what segments are being used and what they are reading (bar the outer segment)
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I've no detailed information on the newer SLT models (bar it's off the image sensor), DK's write up says the A77 is AF point based (I don't doubt that I've only tried one briefly and didn't look at the metering)
Just about every Sony I've used has been more cautious with metering. The Km5d actually is one of the better cameras for metering, tad aggressive at default it does a good job even in very low light situations.
D7k was all over the place (over and under)
Pentax not so great (older metering newer one is much better)
D90 was quite good actually metering wise
Canon 5dMkII prone to underexposure a bit at times, Canon's newer metering is quite a bit better than the older one.

Sony's are fairly consistent though the ones I've used are a bit exposure shy in low light and tend to underexpose. They can overexpose at times too. I did expect better metering as it's off the sensor on the SLT's. It's better than the A200 but then so was the Km5d ;-)

I've personally found this to be true, don't judge the metering purely on specs, but real world shooting
Almost all of the makers go by the AF point in multi segment (Pentax have an option to link or unlink it) Nikon's spot metering works off the the active AF point being used (rather than the small central area on most makers)
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Greg Beetham
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Re: AF point affects metering?

Unread post by Greg Beetham »

The A700 user guide says much the same as the KM5D’s on metering, (comparing Sony to Minolta) only the method of switching between metering and AF modes is different on the A700, you use a selector switch instead of selecting a menu item. (press the [Fn] button on the KM5D)
A700 user guide basically says (KM5D as well):
Segmented metering is connected to the focus point only when [AF-A] and [AF-S] focus modes are used, and the exposure is locked. (it doesn’t say so but I’m assuming it means that when the shutter button is half pressed, the exposure setting doesn’t happen and isn’t locked until the shutter button is half pressed).

Actually playing with the cameras:
When [AF-C] is used with segmented metering on both cameras both the focus and exposure changes while moving the cameras about with the shutter button at half press aiming near and far, lighter/darker subjects (with centre focus point selected, you can freely change the focus point with the multi selector and doing that can alter the exposure/focus).
So in effect the metering zone and the focus point is still connected using [AF-C] but neither is locked at half press. (the user guide doesn’t explain it properly)

[DMF] with segmented metering on the KM5D seems to be similar to [AF-S] (the exposure and focus is ‘set’ at half press) but the big difference is the focus ring can be moved after AF is achieved, the focus ring does not move on the KM24-105 in any focus mode but by comparison it does on the KM18-200. (except [MF] of course)
The A700 doesn’t have a [DMF] focus mode that you can set but it does have an AF/MF button instead. It’s six of one or half a dozen of the other, [DMF] on the KM5D is good and the AF/MF button on the A700 is good too…flip a coin on that one.
Greg
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mikeriach
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Re: AF point affects metering?

Unread post by mikeriach »

Using the matrix metering on both the A77 and A99 I generally find images are slightly underexposed especially in cloudy/overcast conditions.
In LR, I often add between 0.3 or 0.7 to the exposure.
The alternative is to set this on the camera compensation. This is more important on the A77 where noise is more of an issue in shadow areas of lightened shots.

Mike
All my Sony SLT gear gone. Still got my RX100 though.
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