7D and 580 EXII discovery

<span style="font-size: small;"]I went out shooting on Sunday morning and as planned I arrived at my destination 1 hour before sunrise (pitch black). As I looked for a suitable spot to park I noticed a large owl (outline) sitting on a fence post not more than 30 feet away. The owl (Great Horned) I think, gave me the time to open my case, pull my camera and lens out, mount the flash, turn everything on and check settings, get out of my truck and take aim. Dangit, too dark forAF to work and too dark for me to manually focus--the bird flys away, shot missed. At that moment I realized that I didn't know my camera as good as I thought I did because I didn't know how to fire the FE Lock pre-flashnor did I know to focus in the dark. So today, I started reading both the 7D and the flash manual, again.


<span style="font-size: small;"]It took me a while but I did find in the manual where FE lock was the M-fn button---but mine wouldn't work, ultimately, I discovered that the M-fn button was assigned as the AE-lock (I didn't do this). So the FEL issue was an easy fix, I assigned the M-fn to FEL and now it works like a champ.


<span style="font-size: small;"]Here is the discovery: While pushing all of the buttons on the camera, I discovered that theDepth-of-Fieldpreview button would cause the flash to emit a high frequency flash sequence---I assume that this is the red eye reduction, but I couldn't find any reference in the manuals regarding this. So just for fun, I took the camera in a dark room where I couldn't achieve AF by normal means and tried starting this flash sequence while attempting to Auto Focus (AF-ON button)----It worked. I would push the DOF button and quickly press the AF button while the flash was firing, and the camera would achieve focus. I wish I knew this on Sunday[*-)]. I can find nothing in the manuals that would explain this behavior/technique.


<span style="font-size: small;"]Now, one might ask why the AF focus beam (infra-red beam) on the flash didn't work? My guess is that my owl was to far away for the IR beam to work. To confirm effectiveness of my new found (to me) technique for achieving focus on distant subjects in the dark, I plan to try this out in my back yard tonight and see if I can get a distant object in focus.


<span style="font-size: small;"]Anyway, I thought I would share this. I would love to here your comments---Did I miss something obvious in the manuals?, Is this common knowledge that I just missed???---I promise, I really did look!!!.


<span style="font-size: small;"]Bob


<span style="font-size: x-small;"]

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Originally Posted by Bob Williams

I can find nothing in the manuals that would explain this behavior/technique.

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With an external Speedlite attached (and powered on), pressing the DoF Preview button activates a 1-second modeling flash. You're right about it not being in the 7D's manual - although it's mentioned in passing on p. 147 where is says that modeling flash won't work in Live View (nor will FE Lock). It's in the specifications section (under wireless) of the 580EX II manual (and my 430EX II manual, which is where I found it first), and it's also mentioned in the wireless flash section of the text of the manual (there's a section called Modeling Flash). Modeling flash works for wireless and shoe-mounted flash. Note the warning about not firing it more than 10 consecutive times or you risk damage unless you let it cool down for 10 minutes (not sure how real the risk is, but it's not something I want to test to the point of failure, either!).


I don't know that I'd call it common knowledge, but I've seen it mentioned here in these forums (and I found it by accident myself on my T1i). You can set that on the 7D on Shooting Menu 1 &gt; External flash C.Fn setting &gt; C.Fn 2, where you can specify modeling flash to fire with the DoF preview button, the test (Pilot) button on the flash, both, or neither. Selecting Test or Disable restores the DoF preview function of the DoF Preview button with a flash mounted.

Quote:

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Originally Posted by Bob Williams

Now, one might ask why the AF focus beam (infra-red beam) on the flash didn't work?

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The AF assist beam is rated effective out to 10 m (33 ft) in the center, half that distance for peripheral AF points.

Quote:

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Originally Posted by Bob Williams

To confirm effectiveness of my new found (to me) technique for achieving focus on distant subjects in the dark, I plan to try this out in my back yard tonight and see if I can get a distant object in focus.

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Seems like a nice workaround for AF with distant subjects -Thanks for sharing! Please let us know how it turns out, Bob!


--John

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Originally Posted by neuroanatomist

(there's a section called Modeling Flash).

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Thanks, John---Somehow, I knew you would have some answers for me---I looked under, external flash, onboard flash, depth of field, AF, Flash exposure comp, FE lock and a few others, but I never thought to look under "modeling flash"--Duh. But now that you mention it, I recall the warning, but didn't really understand what it meant--Now I do. Thanks. I'll let you know my results here in a few minutes after it gets a little darker.


Bob

OK, This process seems to work surprisingly well. Her are the shots.


This one was taken in almost pitch black conditions about 45 feet from the camera and AF could not be achieved normally.


[img]/cfs-file.ashx/__key/CommunityServer-Discussions-Components-Files/12/8345.IMG_5F00_5422.jpg[/img]





This one was taken at same settings but about 150 feet away:


[img]/cfs-file.ashx/__key/CommunityServer-Discussions-Components-Files/12/3362.IMG_5F00_5423.jpg[/img]


The images aren't optimum because I wasn't worried about the exposure--only the focus, but as you can see focus was achieved hand held and only using the modeling flash.


I would pay attention to the manual in regards to using the modeling flash---No more than 10 cycles without a 15 min rest.


So, if your in a pinch and need to focus in very dark conditions, try using the modeling flash at the same time you hit your AF button---it seems to work.


Hope this is useful,


Bob

Bob


Thanks for sharing. I am away from my camera (business trip) but I

Thanks, Bob! I will try this out myself as soon as I get a chance! This information will be very useful &amp; much appreciated!