Details of the G2 centre weighting metering

pengland

New Member
The light metering used by the G2 is described as "centre weighted average light metering" but I cannot find details of the magnitude of centre weighting used. For ex&le, I would be interested to know the weighting given to light received at the centre relative points at the edge of the frame and say, half way between the centre and the edge. It would also be useful to know whether the weighting changes continuously from the centre outwards or whether there is a defined central zone that is given extra weighting.
 

coodeville

Well-Known Member
Philip:
I was wondereing about this too. I found out the best way to figure this out is by experiment. Take some pictures of a subject in front of a well lit white wall. Bracket exposures and see which ones come out best. Then do the opposite with a black wall. From that point on, you will be able to determine how much comp you will have to dial in out on the field. I did the bracket in 1/2 stop intervals with the camera in manual mode. I use this is the reason wnhy you want ot know if the G2 is a 60/40 or a 75/25?
 

afranklin

Well-Known Member
> Someone around her posed a pictue showingh ow center weighted the G2 > is. It's heavy on the center

I would be that someone, and here it is again:

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Austin
 

wilsonlaidlaw

Well-Known Member
Austin,
Thank you for posting that link again. I have had a look at it and printed out a copy for my Contax bits and bobs file. The implications are very interesting, if the plot is correct and I assume it would be, the plot shows, counting the lines that the meter's sensitivity is highest towards the bottom of the picture or possibly the top, if the plot is not reversed to allow for the actual image on the negative being upside down. The sensitivity also extends far further in a vertical plane than it does on the horizontal, being close to spot horizontally and classic centre-weighted vertically. Have you any idea which way up the image is? I may try by putting my G2 on a tripod in a darkish room and looking at a point source (the ultra-bright LED on my keying mini-torch) to see which is more sensitive, the top or the bottom. I will mentally have to make allowances for exposure when taking shots - well maybe, on a good morning, before lunch and for at least one shot. If the meter is more sensitive at the bottom of the shot this is actually very clever as most pictures (other than snow ones where one tends to compensate in any case or even use a graduated filter) are darker at the bottom than the top, with sky or ceilings usually brighter. Also most shots tend to vary more in brightness in a vertical plane than they do in the horizontal. If I have got it right, someone at Zeiss/Kyocera has really had their thinking cap on for this.
Wilson
 

pengland

New Member
Thanks for the graph Austin. Where did you get it from? Is it specifically for the G2 or is it a generic graph to illustrate centre-weighted metering? When I tried a similar empirical approach to the one Wilson suggested in the previous post I got a pattern that could well match the graph. I found almost no sensitivity in the top 1/3 to 1/2 of the field of view with most of the sensitivity concentrated in the centre of the lower 1/2. Pretty useful for many landscapes and outdoor shots and perfectly usable in other situations if used like a blunt spot meter by pointing the sensitive patch at the subject of interest for metering. Incidentally, I have found the G2 metering excellent, to the point that autobracketing is nearly always a wast of film. Of course, I still autobracket for shots that look like they have tricky lighting. Anyway, thanks guys for your help.
 

bimmer

Member
Does anyone find it annoying that Contax neglected to put the centre-weighted metering markings in the viewfinder like an SLR? It may not be dead accurate cos the viewfinder isnt TTL but it might provide some guidelines. And the G1/G2 doesnt have matrix / evaluative metering to negate the use of the said markings. >
 

wilsonlaidlaw

Well-Known Member
John,
I agree it would, in theory, be nice to have the centre weighting marked but it might make for a rather confused viewfinder. Home laboratory results (absolutely no guarantee as to accuracy) from this afternoon. The most sensitive point is just on the bottom edge of the focus window falling off gently upwards and more sharply downwards to close to zero at top and bottom of viewfinder window. Horizontally the sensitivity seems to fall off fairly sharply either side of the focus window markings, so on an empirical basis you now have your centre weighting area without the complication of an extra window. Hope this helps Wilson
 

afranklin

Well-Known Member
> Does anyone find it annoying that Contax neglected to put the > centre-weighted metering markings in the viewfinder like an SLR?

What, exactly, part of the pattern would you mark? It's a gradual falloff...and someone would have to choose a threshold to "place" this mark... A spot meter is easy to indicate, as it has a steep falloff...but an average is much more difficult IMO.

Austin
 

afranklin

Well-Known Member
Hi Phillip,

> Thanks for the graph Austin.

You're welcome!

> Where did you get it from?

G2 product brochure.

> Is it > specifically for the G2 or is it a generic graph to illustrate > centre-weighted metering?

Specific to the G2.

Regards,

Austin
 

afranklin

Well-Known Member
Hi Wilson,

> Thank you for posting that link again.

You're welcome.

> ...if the > plot is not reversed to allow for the actual image on the negative > being upside down.

I believe the meter pattern would be based on the image in the viewfinder.

> Have you any idea > which way up the image is?

I'd say it's a viewfinder image plot. But, your question is certainly a good one. If anyone finds out differently, I'd like to know.

Regards,

Austin
 

bimmer

Member
Austin: According to the graph you posted, perhaps the boundary of the centre-weighted metering would be useful? (ie. where is starts and/or ends) >
 

jsmisc

Well-Known Member
Do SLR's show the metering patterns in the viewfinder? They may indicate whether you are using spot or evaluative or centre weighted but surely they don't show it on the screen or do they? I don't think that my Aria and RX do.
John
 

saspencr

Well-Known Member
if someone really wanted to get a good idea, replicating the graph as a 3d color graph (or a graph like an elevation chart) and then looking at it full scale in the viewfinder would tell you a lot. scott
 

bimmer

Member
> "Posted by John Strain (Jsmisc) on Friday, November 28, 2003 - 7:44 pm: Do SLR's show the metering patterns in the viewfinder? They may indicate whether you are using spot or evaluative or centre weighted but surely they don't show it on the screen or do they? I don't think that my Aria and RX do."

Hi John:

I'm not familiar with Contax Aria and RX as I use Nikon SLR's (AF and MF) - but i can imagine that most SLR's of various makes would have some reference circle in the viewfinder to indicate the centre-weighted metering area. In Nikon's case it would be a 12mm diameter reference circle right smack in the middle of the viewfinder to indicate which part is sensitive to the centre-weighted metering. This is useful to zoom into a particular area where you want to meter (eg. a human face), lock exposure, zoom out to capture environment/background. There is also a smaller ref circle (3mm or 5mm, i forget) for spot metering as well. And there are a separate LCD indicators (in the viewfinder and top plate) for whichever metering mode you are using also.

Regards, another John.
 

jsmisc

Well-Known Member
Hello John,
The Aria and the RX do not have reference circles as such although the spot meter measures, according to both the Aria and the RX handbooks, "only the brightness of the subject in the centre of the viewfinder (microprism area) to determine the exposure value. Its applicable area is within the outer circle in the centre of the viewfinder".
Regards,
this John
 
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