Board index Photography Technical Questions Flash Photography Question

Technical Questions

Flash Photography Question

Discuss technical aspects of photography
mdecaprio
 
Posts: 32

Flash Photography Question

Post Sat May 10, 2008 10:34 pm


I am having a lot of trouble understanding how my flash works with my camera. I currently shoot w/ a canon Rebel XT. I have seldom used the pop up flash. But, recently I purchased the canon 430EX flash.

I generally shoot in Av, Tv, or M modes. But I noticed a difference in exposure setting when using the flash in P mode vs the other modes. For example, in a recent test, when in P mode with the flash on exposure settings were automatically set to 1/60 at f4. Keeping the flash on and metering the same subject in Tv mode with shutter set at 1/60 I get f2.8 flashing (indicating it will be underexposed). Likewise if I got to Av and set to f4 I get a shutter speed of 1/10. In M mode if I set the camera to 1/60 @ f4 I get the light meter saying it will be under exposed (but if I take the shot it looks pretty good). When I take the shot in Tv or Av the photo looks good (although tripod needed for Av).

I am just trying to understand how the camera is metering in these different modes so that I can properly use my flash when needed. I know this is an amature question but I am still learning. I appreciate any insights.

Thank you,
Mike
Mike
Canon 40D
Canon EOS 350D
EF 70-200/f4 L
EF-S 17-55 f2.8
EF 100/f2.8 macro
EF 50/f1.8
EF-S 18-55

bclaypole
 
Posts: 410

Re: Flash Photography Question

Post Sat May 10, 2008 10:58 pm


Theres some great material on the Canon website that helped me.
http://web.canon.jp/imaging/flashwork/index.html

prinothcat
 
Posts: 662

Re: Flash Photography Question

Post Sun May 11, 2008 12:06 am


It's actually not a bad question, since flash systems are somewhat complex these days. The Canon pages are probably a good place to start. You might also wander through Strobist. It's a site devoted to flash photography. While it may be beyond what you seek at the current time, it has a lot of relevant content to make your flash photography better.
I'm gonna guess that in P mode your flash is trying to provide the primary light source based on a sync speed of 1/60 sec. What you want to read up on is the use of what is known as fill flash. Here the camera sets exposure based on what the meter reads and adds additional illumination with the flash unit. So in Av or Tv it may well be that the meter values are correct, and the flash will only provide enough light to make the exposure correct at those values. You probably want to start with the manual and find out the sync speed(s) at which your camera will operate some will do only 1/60 or 1/125. Others will go much faster.
Hope this is helpful,
Chris

dang
 
Posts: 3780

Re: Flash Photography Question

Post Sun May 11, 2008 1:51 am


I shoot with XT's most of the time & agree. It doesn't generally matter which mode setting you use on the XT, since the external flash is controlling the overall exposure. The camera meters the same as if it wasn't there, and the reason you'll see warnings in the viewfinder. However, you have access to flash exposure compensation in your second menu tool set, and in custom functions you can set AV mode to flash at 1/200th.

You can refresh about the basic Mode settings here: http://www.dpreview.com/reviews/canoneos350d/page7.asp

Also, the link to Canon posted by bclaypole should answer other questions.
If using a Canon flash, be sure and check your manual for additional settings the flash might allow, since they vary from model to model.

The link prinothcat posted will give you a good basis for how to use flash, and explain some of your questions on how flash exposure works in various situations. It has example photos which help you remember. It's a good read.

Also, if you search with Google, you'll find more information than you can probably absorb. Much is redundant, but every now & again you'll hit gold. There's certainly a lot more to flash than point & click if you want to get the best from it.


Board index Photography Technical Questions Flash Photography Question

Who is online

Users browsing this forum: No registered users and 2 guests