PDA

View Full Version : General Question -> Flash Usage in Av Mode on the Digital Rebel XT

pradeep1
14th of March 2005 (Mon), 00:17
Hello All,

I just got the Digital Rebel XT and have been playing around with it using my 420EX flash. I am still not getting the nice results I used to get with my 420EX + Powershot G3 camera, but that is probably because of something stupid I am doing. I'll investigate that later, but for now, when I am in Av mode, it seems that the flash speed does not automatically lock to anything. I can set Custom Function to 1/200 sec. and it works fine, but when I have Cfn. set to AUTO, the camera does not lock a speed, but just fires the flash at the exposure time indicated.

So I am sitting in a fairly dimly lit room at night and I am shooting something at a fair distance using my 28-105 lens, the exposure reads 1/4 sec. when I dial in f/4.5 in Av mode. The shutter opens, the flash fires quickly...seems to fire at around 1/60 sec. and then the shutter closes after the shown 1/4 sec. elapses. On my G3, when I dial in Av mode f/4.5, it shows that I need an exposure of 1/4, just as with my DREXT. When I turn on the flash, the shutter speed automatically goes to 1/60 sec. and when the photo is taken, the 420 EX fires at 1/60 and all is well.

What am I doing wrong? Is there some setting on the 420EX that needs to be changed between cameras?

Thanks,
KevC
14th of March 2005 (Mon), 00:19
In Av mode, the camera goes into "fill-flash" mode. Always shoot in Manual when using a flash... at least that's what I've read around here...
pradeep1
14th of March 2005 (Mon), 00:24
My eyes just wandered to the top of the page and I see the EOS Flash sticky. Sorry if this has been answered before. I'll look there. If anyone can point me to the right info. quickly, do let me know.
Skip Souza
14th of March 2005 (Mon), 00:29
Congrats on the XT. Waiting for first pix. Hope wife is feeling better. 20D by Wednesday (I hope). Sorry, I can't help you at all with the flash.
CyberDyneSystems
14th of March 2005 (Mon), 00:31
In AV mode,. the camera's shutter does not care that you are using flash,. and the shutter times to get an exposure based on Meter reading. The flash fires as fill.

If you want a faster shutter,. then shoot in manual,. ;)

Definitely check out that Sticky!
pradeep1
14th of March 2005 (Mon), 00:32
Congrats on the XT. Waiting for first pix. Hope wife is feeling better. 20D by Wednesday (I hope). Sorry, I can't help you at all with the flash.

Sorry man, I don't have anything other than test shots to show you. Didn't get to go anywhere this weekend to shoot. Have fun with your 20D! :)
pradeep1
14th of March 2005 (Mon), 00:39
In AV mode,. the camera's shutter does not care that you are using flash,. and the shutter times to get an exposure based on Meter reading. The flash fires as fill.

If you want a faster shutter,. then shoot in manual,. ;)

Definitely check out that Sticky!


Thanks for the info CDS. Now how would I approach this situation? I set my camera to manual. Set the shutter to 1/60 and then choose an aperture that I want, say f/5.6 to maximize a particular lens's sharpness. Now when I shoot this, how do I control the flash output to make sure the scene is properly exposed?
CyberDyneSystems
14th of March 2005 (Mon), 00:43
The flash uses ETTL to autoexpose,. by varying the output of the flash,.. I know it's weird at first to think in these terms,. but the flash does all the work. If it does not seem that the flash is bright enough,. or is too bright, use FEC (flach Exposure Compensation) untill you get the look you want. Most people find they need to add 1 stop or so of exposure comp to the flash to have it bright enough. Other than that,. it does all the work for you.
drisley
14th of March 2005 (Mon), 00:52
When I bought my DRebel after using my G3 and 420ex, I had the same conundrum.
I learned (from this forum) that this is the way DSLR's work with external flash, and I also learned in time that this is in fact much better than the way the G3 worked. Once you get the hang of it, you will love the ETTL-II
pradeep1
14th of March 2005 (Mon), 01:09
Thanks for the info. guys. It just seems odd that I'd have to use FEC to compensate, when we have all of this high-faluting technology behind it. On the G3 it was almost too simple and flawless. I tried out your suggestions and it seems to work. Interesting. :?
pradeep1
14th of March 2005 (Mon), 01:10
My other question to you both...what are you doing up at 2:10 AM on a Sunday night? :)
drisley
14th of March 2005 (Mon), 01:14
The reason is because Canon made the ETTL-2 on it's DSLR's to purposely underexpose slightly to preserve highlight detail. It's up to the user to increase the FEC to his/her liking.
It's just about bed time for me though ;)
CyberDyneSystems
14th of March 2005 (Mon), 01:27
My other question to you both...what are you doing up at 2:10 AM on a Sunday night? :)

Check my signature ;)
pradeep1
14th of March 2005 (Mon), 17:08
Check my signature ;)

Funny. :)