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-   -   Canon 40D & The * Key for Auto Focus (http://www.railpictures.net/forums/showthread.php?t=6911)

Wizzo 03-16-2008 03:57 PM

Canon 40D & The * Key for Auto Focus
 
Bonus time has rolled around again, so yesterday I finally laid my hands on a Canon 40D. Unfortunately, thats all I got hold of as the 24-105 F4 L is currently out of stock and awaiting a delivery from Canon.

I've been ploughing through the manual, so far there isn't too much I want to change from default, especially as I'll primarily be shooting RAW, but I do want to use the * key to do one shot auto focusing rather than pressing the shutter button halfway. This way I'll pre focus the camera in advance of the shot and not worry about getting an AF lock at the last second.

I've searched the forum and found the following from Alan Crotty

Quote:

Originally Posted by alan-crotty
I have found it better to set my custom function (CF4 option 3) to transfer the AF to the star button on the rear of the camera.

Don't forget that the star key operates the AF and not the shutter release.

Alan


On the 40D CF4 Option 3 is "SET button when shooting" and none of the options looks correct for an AF function, so my question to all you Canon users is exactly which CF function sets the * to be the AF button and disables the press shutter halfway AF, and which option under that function is the correct one ? The manual is less than helpful.


Thanks

devights 03-16-2008 09:15 PM

I can't seem to find a list of custom function settings for the 40D, but looking at my 20D you will want to look for an option labeled "Shutter button/AE lock button" and set it to "AE lock/AF". Basically that means that a half depress of the shutter locks the exposure and pressing the AE lock button (*) will lock the auto focus.

alan-crotty 03-16-2008 09:36 PM

40D * key
 
Hi Steve,

I don't have 40D, but a friend does, I'll ask him tomorrow and post for you if no answer in meantime.

Alan

alan-crotty 03-16-2008 09:53 PM

40D AF on button
 
Hi Steve,

Just DLed the pdf manual for your camera

http://www.the-digital-picture.com/O...40D-Manual.pdf

Looks like you need to set CF4/1/3

Your camera has a specific button for AF on, not the * key, although this can be used in place of AF ON button CF4/2

Hope this helps you

Alan

Wizzo 03-17-2008 10:18 AM

Quote:

Originally Posted by alan-crotty
Hi Steve,
Looks like you need to set CF4/1/3

Your camera has a specific button for AF on, not the * key, although this can be used in place of AF ON button CF4/2

Hope this helps you

Alan

Thanks - yes that looks right. Use AF-ON for AF and metering, and presumably while pressing that, if required, press the shutter halfway for AE lock. Since I'll be using full manual mode most of the time AE lock will largely be irrelevent, the important thing is to prevent the pressing of the shutter halfway resulting in refocusing.

Can't wait for the lense to turn up now

PS - which metering mode do you find works best with railway subjects on your EOS 1D ?

milwman 03-17-2008 11:09 AM

PS - which metering mode do you find works best with railway subjects on your EOS 1D ?[/quote]

Ok you didn't ask me, spot metering works if you know what your doing. Or Evaluative But what works for me is, Meter your hand, set it to that, make your test shot, look at the Histogram, Adjust if needed.

alan-crotty 03-17-2008 12:58 PM

Metering mode?
 
Hi Steve,

For railway snaps I use spot metering from a neutral area, grass or grey road etc. camera set to manual

For general use I use evaluative metering, either av or tv.

However I am always guided by the histogram and will normally make a test exposure in tricky lighting conditions.

Alan

Wizzo 03-17-2008 01:27 PM

Quote:

Originally Posted by alan-crotty
Hi Steve,

For railway snaps I use spot metering from a neutral area, grass or grey road etc. camera set to manual

For general use I use evaluative metering, either av or tv.

However I am always guided by the histogram and will normally make a test exposure in tricky lighting conditions.

Alan

Thanks - I'll try them all and see what works best for me. I couldn't get on with spot metering with my Fuji (tended to wildly over expose with railway subjects) and found the average mode worked best. Maybe the Canon will be different.

alan-crotty 03-17-2008 03:27 PM

In The Zone
 
Steve,
When using SPOT metering it's most important to understand lighting 'zones'.

Camera meters are stupid and are calibrated to assume they are pointing at an 18% grey image (supposedly that's the shade you get if all the colours/shads of an average scene are blended together).

So you must either spot meter from an 18% grey area, or know how many f stops lighter or darker than 18% your target is.

See

http://en.wikipedia.org/wiki/Zone_system

For a detailed explanation.

I just meter from green grass or grey road.

Also you need to understand the Dynamic range of your camera, 40D will be about 7 f stops.


Alan

Wizzo 03-17-2008 03:36 PM

Quote:

Originally Posted by alan-crotty
So you must either spot meter from an 18% grey area, or know how many f stops lighter or darker than 18% your target is.

See

http://en.wikipedia.org/wiki/Zone_system

For a detailed explanation.
Alan

Thats an interesting read - thanks

Estimating how much darker or lighter a target will be is certainly a challenge with the livery variations around at the moment :)


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