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Mark1616 Apr 14, 2010 10:56 AM

Some Flash Questions
 
Hi, I was asked these questions in a PM by a Canon shooter (I mention this as not all settings are identical across system) but as many people might be wondering similar things I thought i would post them here and include my answers.

"Thinking about the Av mode. So lets say i am not in a well lit place and the camera is indicating that in need to use a lower f number. But i know that with the flash i shouldn't have go as low. Is there any way to make the camera use the "pre-flash" to correctly calculate what the f value should be when the shot is taken WITH the flash? this happened last night in a poorly lit room in my house. with the 18-55 lens at f4. f4 was flashing which indicates that i needed more light as far as i understand


second, fill flash means that the flash head itself will point directly towards the subject, right? anything else would be a bounce flash?"

OK, so question one, using Av mode. With a Canon camera in Av mode the camera will always expose for the scene with the correct shutter speed for the lighting conditions. This is why I only ever shoot Av and flash in good light, and even then more often that not I will shoot M which I do with nearly all flash shots.

So, Av and flash is great if you want an exposed background with ambient light and then addition fill flash, it's not great when the ambient light is too low and you are really having to drag the shutter. Point of note, if you are shooting outdoors in good light in Av and with the aperture pretty wide you generally need to select High Speed Sync on the flash otherwise the shutter speed is limited to normally 1/200s or 1/250s depending on the camera so you can easily get vastly over exposed shots.

Back to the indoor low light question, I will shoot manual mode and set and exposure (no flash currently) that will give me about 1-2 stops under..... it depends on your desired effect you can play around. This usually means that even with flash photography I'm using quite high ISO settings to give the mix if light.

Now even with the flash in auto you should find a pretty nice shot of your subject with some background detail and your subject exposed as desired. Now if the subject is wearing something light or something dark this can throw off the metering so you might want to adjust your flash compensation a little. I was wearing a white shirt a few days ago and my fiancee was in black so I had to add a stop of additional flash compensation for me as the camera thought I was already well lit.

Now if you were feeling clever then you could start looking at manual flash settings, however I only use these in controlled conditions and not when shooting people rapidly.

Onto the 2nd question about the term fill flash, this is any time flash is used to fill in shadows and it can be done by direct, bounce or combination of both. Usually when I bounce I will put the white catch-light card up that is built into the Canon 580 and 580II, if your flash has this that can help put more light forward so it isn't wasted out the back. There are also various options for diffusers etc that can be added. I'm naughty as I always shoot naked..... well, I shoot with nothing to diffuse the light, it's something I should do but never had got to as yet.

I hope that helps and feel free to ask for clarification or if there is anything else on your mind.

shoturtle Apr 14, 2010 11:16 AM

Think this would make a good sticky

Mark1616 Apr 14, 2010 11:20 AM

Quote:

Originally Posted by shoturtle (Post 1079647)
Think this would make a good sticky

I won't go that way for now as I want to (and have been planning to for a year or so) create a detailed flash post to help people take it to the next level with flash use. I have a flash on my camera in most situations be it outside or in (not always used I will add, but it's ready to go) as it is helpful to be able to control another element of the light. Let's see what other people are interested in knowing and this might just build into a useful thread.... or might not LOL.

shoturtle Apr 14, 2010 11:24 AM

That would be a very good thing with a how to flash post. It will be very useful I think.

Mark1616 Apr 14, 2010 11:31 AM

Let's leave this running for now and see if anyone has other burning questions about using flash in different environments, areas they've struggled with etc and then I will know what to use to build something useful in the future. I'm not saying I know everything about flash, and I have loads of things I would like to learn, but if used well it can really help out a photo.

shoturtle Apr 14, 2010 11:49 AM

Mark you are being very modest, you do some great flash work.

Giving you some of the treatment Hards have been receivings in other thread;) but honestly I really think you have some great skills with flash photography and that allot of us can learn form you. :)

Mark1616 Apr 14, 2010 11:55 AM

Thanks, it's all relative, there is someone better and someone worse, I read a lot of lighting information from places like http://www.strobist.blogspot.com/ and there is so much that can be done with practise and the kit. When I'm back in the UK I plan to start work on this more, I would like to use the time I have while here to play but I don't have the triggers, stands etc that I need and don't want to buy them here (even if I could) as it is a waste.

So I do OK, but there is a long way to go ;)

ronin2307 Apr 14, 2010 1:46 PM

since i am the guilty Canon shooter, let me throw this at you:

from what i am reading now on the site i linked in my PM to you, it appears that HSS would do exactly what i asked in the OP.
am i mistaken? Again?

Mark1616 Apr 14, 2010 1:58 PM

HSS is only for when you are shooting in bright light rather than low light. It is to allow the camera to break the shutter sync speed (probably 1/200s on your camera) so you can reduce exposure in bright conditions.

I use this feature quite a lot when outdoors but it does decrease flash power but you get the ability to shoot with wider apertures and still have flash so it is a trade off.

ronin2307 Apr 14, 2010 2:00 PM

crap. i am having a serious info overload. everything is mixing up. my mind would give a great blurry background to any picture atm.
thx for clearing it up....again


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