1)Does metering accuracy increase with no. of metering zones? It appears that 35-zone metering in eos rebel 2000 is more than enough! 2)How does E-TTL work?What is the difference between TTL and A-TTL in autoflash metering system? 3)why do some cheap eos have such slow X-syn. speed as 1/90 s?and why do they lack spot metering ? 4)What does it mean by 'serial' and 'slave' in flash photography?thanks very much

-- albert (fibrebundle@hutchcity.com), April 16, 2001

Answers

1) Yes the accuracy of metering does increase with the no. of metering zones. This is because the field of view is divided into smaller sections all of which can then be averaged - it's statistical, the larger sample size you have, the more accurate your result. But I don't really think that having any more than 35 is necessary. I also use a Rebel 2000 and find it ok. More to the point I usually use a hand-held spot meter instead of the camera's metering system.

2) E-TTL works by the camera firing a pre-flash a fraction of a second before the main flash. On EOS-dedicated speedlites this is at 1/32 of full power. From this the camera works out the correct flash exposure and the main flash output/aperture is set accordingly. A- TTL is where the camera measures the amount of light coming into the lens and sends a cut off signal to the flash when enough light has reached the film. 3) Dunno really. Probably to do with how fast the shutters work. They lack spot metering because Canon assume that the average Joe blogs who buys a cheap EOS only wants to take (expensive) snapshots and doesn't need to use exposure lock. 4) A slave flash is a flash that is triggered by another flash. It has a sensor that detects another flash going off and triggers the slave unit. Dunno what 'serial' is.

-- Chris Jewell (vs0u8055@liv.ac.uk), April 16, 2001.

Let me modify some of Chris' comments:

1) If everything else was equal, more zones = better metering, but other things are seldom equal. The metering system uses programing that may be superior in one camera or another. I doubt that the 35 point metering system in the Rebel 2000 is actually superior to the 16 zones in the 1N.

"2) ...A- TTL is where the camera measures the amount of light coming into the lens and sends a cut off signal to the flash when enough light has reached the film."

That's actually TTL metering. A-TTL metering adds a preflash (usually IR) primarily to determine a proper aperture for the lens. The Rebel 2000 isn't capable of using A-TTL which is just fine since it was nearly worthless anyway.

3a)The cheap cameras offer a slow sync speed to entice you to spend more money to buy a better camera. It does take a better shutter to do this, but Canon's sneaky little truth is, the EOS 1000/500/300/Rebels (all of them) are limited to 1/90 by the programing of the camera only. Their shutters are all capable of 1/125. This can be checked easily with a non dedicated flash.

3b) They lack spot metering because of the same reason, (Makes you want to buy n EOS 3 doesn't it?) but also because it does cost a couple of bucks more to put a true spot meter into the system. Chris seems to think that spot metering is tied to exposure lock. It isn't and the Rebel 2000 does offer exposure lock, unfortunately it is tied to partial metering with this model. Upscale models seperate the functions.

-- Jim Strutz (jimstrutz@juno.com), April 16, 2001.

Ok, so how is partial metering different to spot metering - is it just that spot metering uses a smaller area than the middle 9% of the viewer? And I agree, having it linked to AEL is annoying at times although with patience it can be got around.

-- Chris Jewell (vs0u8055@liv.ac.uk), April 16, 2001.

Partial metering uses the existing central portion of the evaluative meter. A true spot meter is a seperate meter that is built into cameras like the EOS 3. In use the difference is simply the amount of area used. The EOS 300/Rebel 2000 and EOS 30/Elan 7 uses a partial meter that is 9-10% of the area. The EOS 3 has a partial meter area of 8.5% and a spot meter of 2.4%

-- Jim Strutz (jimstrutz@juno.com), April 16, 2001.