Advice on using 580ex with 50mm f/1.8

[verwoodspring]

Hi,

This is my first post. I am not overly technical, but know some of the basics.

However I could do with some advice/clarification that I have understood some of my equipment.

I have a Canon 350d camera (with the usual standard zoom lens), a 580EX Mk2 flash and today I took delivery of a 50mm f/1.8 mk2 lens. I purchased the lens because I wanted something fairly inexpensive - which could take reasonable portraits with a small depth of field.

OK, so here goes. The flash confuses me. Every time I take photos indoors, I get very dark backgrounds. I have done some research - and I think I now understand the settings a little better to avoid this - please can you confirm that the following points are true:

1. If I take pictures indoors in fully-auto mode (green square) my backgrounds turn out dark because the camera forces 60th sec, and the camera puts all its attention on the main subject – true/false?
2. If I take pics indoors, Av/Tv works with the object AND the background - but if the aperture or shutter number flashes, there is still not enough light or speed (also, if I am in Tv mode, do I ignore the flashing aperture number, and assume the flash will sort everything out?)
3, If I decide to use the camera outside (with the flash) - but set the flash to "high sync mode" - and use the camera in Av mode - the flash works as a "fill in" and no longer tries to light everything up

The above points are my understanding - please can you clarify I'm on the right track. I know the flash is capable of much more, but I just want to do basic stuff to start with!

Thanks so much - hopefully when I get more experience, I can help others out in return!!

 

[estel]

3, If I decide to use the camera outside (with the flash) - but set the flash to "high sync mode" - and use the camera in Av mode - the flash works as a "fill in" and no longer tries to light everything up

But this is what you normally WANT isn't it? It's unclear what you are trying to achieve. If there is a foreground object and if the flash tries to light "everything up" assuming background is already dark enough to need the flash, foreground object will be blown out.

It's likely though that metering gets things wrong. Assuming there's nothing in foreground that would be blown out, did you try adjusting the exposure compensation to a positive value to see if it works?

 

[J-Chan]

1. True
2. Av/Tv mode meters for ambient, so if either values flashes in the viewfinder the correct ambient exposure can't be achieved (ie underexposed) but with the magic of E-TTL the 580EXII delivers the correct exposure for the subject.
3. Yup.

Just to add on, you'll need to understand that shutter speed doesn't affect your flash exposure.

 

[GavinTing]

Bounce your flash or use a higher ISO.

 

[verwoodspring]

Thank you.

Although I'm not too sure what you meant by "Just to add on, you'll need to understand that shutter speed doesn't affect your flash exposure."??

I thought if I used a slower shutter speed, the flash would give out less light?

 

[ssping83]

in a nutshell..

flash exposure is determined by aperture size..
ambient exposure is determined by aperture size and shutter speeds..

above all else is the ttl flash metering system.. which corrects the power of the flash output.. which may be a god send.. or a nuisance.. depending on what you want to achieve..