ETTL-II average or evaluative?

[Janice]

Can someone please explain the difference between EVALUATIVE and AVERAGE flash ETTL-II, in the custom functions of the Canon 350D?
Which is best to use?

 

[Marcel]

I *think* Average basically meters to light the whole scene, and Evaluative meters to put just enough flash where it's needed (ie fill in flash)....if that makes sense.

 

[Janice]

so is this something I need to change and look at with each shot??

 

[Marcel]

Quick, someone else jump in! I'm out of my depth.

 

[Warspite]

Lol @ Marcel (although Im also out of my depth) - See if this helps:

From - The Magic Lantern Guide for the 350D

C.Fn-8 E-TTL II

This is a simple control that lets you choose a different way of metering electronic flash.
0. Evaluative - this uses fully automatic Evaluative metering for all conditions.

1. Average - this setting averages the flash exposure readings over the entire area covered by the flash. Flash exposure compensation will not work with this setting.

Hope this helps

 

[Pete E]

Janice,

if you take a look at the Web Links forum, I've posted a link to a Canon Flash site...Its not the lightest of reading (excuse the pun!) but there maybe some info in there which you'll find useful...

Regards,

Pete

 

[CT]

so is this something I need to change and look at with each shot??

Basically it's something you need to consider with each shot -yes.

I'll try to keep this as simple as possible Janice.

Average Metering.

Early TTL metering cameras had average metering. All this system does is mix all the tones on your focusing screen down a single tone which it calls '18% Grey' It will give exactly the same result as a reflective reading from an 18% grey card or taking an incident light reading using the white cone on an exposure meter. Our photographic forebears found that an 18% reading gives a good result for the majority of subjects. Obviously though if YOUR MAIN SUBJECT is substantially lighter or darker than 18% grey then you need to give exposure compensation to account for it.

Evaluative Metering.

With this system the screen is divided into a number of small zones (which you can't see) and the metering system reads the exposure within each of those zones, probably mixing all the tones in those zones down to a single tone. Each zone will probably end up with a different tone. The onboard software then compares each of these zones and comes up with an exposure to suit all of them as best it can, using on board logic as to where the most important zones are likely to be in the frame, probably biasing importance towards the centre of the frame and downwards to avoid being over-influenced by bright skies, but using lots of other parameters too. The Nikon F5 actually had thousands of example images stored in memory which it ran through before deciding on an exposure based on it's own Matrix System readings. (Their name for the evaluative system)

Evaluative metering should give good results in the vast majority of cases but it can sometimes get it wrong. The best thing to do on those occasions is to use a spot meter to meter on a key tone in the scene, or (if you can) move in, fill the frame with the key tone, set the exposure, then move back and take the shot.

Hope that helps a bit?

 

[Janice]

Thanks CT, isnt that the in-camera evaluative/average metering (for ordinary shots) though?

Im assuming I can have the camera set on partial metering as I always do.....but have the flash metering in the custom functions set at evaluative?

 

[CT]

Thanks CT, isnt that the in-camera evaluative/average metering (for ordinary shots) though?

Yes it is. The reason I went to such lengths to explain that was that in normal ETTL useage, the flash and camera are so completely integrated. All the exposure info is fed into the flash from the camera metering itself.

Im assuming I can have the camera set on partial metering as I always do.....but have the flash metering in the custom functions set at evaluative?

Yes, I don't see why not. This is the bit where it starts to get complicated though. The camera body has a number of flash sensor/meters, probably about three with top end cameras, which can either be integrated with or independent of the cameras ambient metering system, which is why you have those custom settings.

Canon and Nikon et al have made flash photography much easier than it used to be, but unfortunately they're not very good at explaining to us the intricacies of how it all works. The average manual will leave you wanting to throw it at the wall! I think if you have a look at the link Pete-E posted, it's the most in depth explanation of Canon guns you're going to find, so it's worth sitting down and really wading through it. You'll see so much depends on what mode you're using, even which AF point you're using, and whether the metering is linked to the AF point!

FWIW I've never felt the need to change that function - mine is on evaluative.