Flash photos in AV canon 30d

Keltic Ice Man said:
So you do :D - long day I think; what is the slowest shutter speed you could hand hold with a flash, with say a 24 - 70 on a cropped sensor?
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The hand holding rules stay much the same - or it's safest to treat them that way. If you're using say a 50mm lens and a shutter speed of anything much less (slower) than that then there's a real danger if the ambient light is strong enough that you're not only going to get secondary ambient light images from possible subject movement, but you're almost certain to get them from camera shake.

You can prove all this to yourself with a few test shots in just the same way you took your polar bear shot earlier. :)

EDIT

sorry mate, so with a 24 to 70 zoom you should really match your minimum safe shutter speed to whatever focal length the lens is zoomed to if you're hand holding - 1/24 at the short end up to 1/70 at the long end. Far better to use a tripod really if you can.
 
:D You guys make my head hurt!!


:lol: :bonk:
 
Keltic Ice Man said:
Kev - If I had dropped the Aperture - with 2 lines of kids I wouldn't have had enough DOF would I?
I Couldn't drop the Shutter Speed - as I was in AV and had told it to set to 200, maybe I should have gone to Manual on the Camera.
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Depends on what your focal length was and how far away the kids were. I suspect you could have gone bigger on the aperture with the right combination. If you've got a nifty fifty type lens and shoot at F1.7 for a close up on the face you know you'll get a really shallow DOF but people use the same lens and aperture for doing full length shots at gigs where the DOF is sufficient for a full length person shot.
 
Janice said:
why when you make the aperture smaller will the flash not have enough power?

cider hasnt quite worn off yet either! ;)
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You know how the shutter+aperture combination works for an exposure without flash don't you. When your not using flash the ambient light is there for the whole time of the exposure. The light from a flashgun is there from something between 1/1000-1/4000 depending on the output from the flash (unless we're talking about HSS which is a whole other thread). So given that the flash duration is so much shorter then the size of the aperture is what counts. Bigger the aperture the more effective the flash light is.
 
Anton Roland said:
:D You guys make my head hurt!!


:lol: :bonk:
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Its killing me too!! I dont see how I can make all those calculations every time I take a shot at a wedding! :eek:

Expose for the background: Outside, the background is going to be pretty light...... if I want to use F4 for a head shot but use flash to fill in shadows on that face......the shutter speed keeps flashing on the camera telling me it needs to be faster than the 1/250" that the camera will let me when there is a flash attached. So therefore it isnt exposed properly if it stops at 1/250" is it..when it actually needs to be faster......the resulting exposure of the background will be too bright.
 
Janice would it help if I discussed shutter dragging flash photography with you now??:D :D :D
 
Anton Roland said:
Janice would it help if I discussed shutter dragging flash photography with you now??:D :D :D
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crazy1no.gif




I dont understand how I can have such a mental block about this when everyone else seems to understand it.

I'm not thick by any means..... but it just doesnt all fall into place. :(
 
Dont worry Janice, I dont understand it either :nuts:
 
Janice said:
Its killing me too!! I dont see how I can make all those calculations every time I take a shot at a wedding! :eek:

Expose for the background: Outside, the background is going to be pretty light...... if I want to use F4 for a head shot but use flash to fill in shadows on that face......the shutter speed keeps flashing on the camera telling me it needs to be faster than the 1/250" that the camera will let me when there is a flash attached. So therefore it isnt exposed properly if it stops at 1/250" is it..when it actually needs to be faster......the resulting exposure of the background will be too bright.
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This is where High Speed Sync (HSS) is used.

1/250th is the X-sync speed which means it's the highest shutter speed where the entire sensor is exposed all at once. Higher speeds and the rear curtain follows behind the front curtain so only part of the sensor is exposed as the two curtains move across it.

HSS fires the flash in multiple bursts so that all of the sensor gets to see the flash as the two curtains move.

Just turn on HSS on your flash and you'll be able to select a faster shutter speed.
 
If you need to go faster than the normal sync speed janice then you have to turn HSS on. This will let you shoot faster speeds bit dramatically reduces the working distance of the flash.
 
Janice said:
Its killing me too!! I dont see how I can make all those calculations every time I take a shot at a wedding!

Expose for the background: Outside, the background is going to be pretty light...... if I want to use F4 for a head shot but use flash to fill in shadows on that face......the shutter speed keeps flashing on the camera telling me it needs to be faster than the 1/250" that the camera will let me when there is a flash attached. So therefore it isnt exposed properly if it stops at 1/250" is it..when it actually needs to be faster......the resulting exposure of the background will be too bright.
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1.Increase the ISO? or ...

2.Stop down the lens? or...

3. A combination of both?

I don't think you're thick Janice, or anyone else having trouble with this for that matter, I know how difficult it is to get your head round this, but you're actually creating your own problem here by specifying f4 out of doors in what we are assuming is quite bright light.

The technically correct answer to this problem if you really want to use f4, is that here you really do need to switch the flash to Manual Mode - calculate the Guide No for the ISO you're using - divide 4 (f4) into the Guide No to give you the correct flash- to -subject distance to enable you to use f4 with the flash providing fill in on your subject. BUT you're absolutely tied to this distance - you're talking about a head shot, and at f4 it's likely to be quite a distance from your subject so you'll also need to consider which focal length lens you use to frame the shot as you'd like. Flash isn't an exact science either - that guide no is only a rough guide, you'll probably need to reduce power to get the result you want - those face shadows just lightly brightened - otherwise the shot can still look over-flashed. Pre digital togs used to spend a fortune on polaroid shots to get this right before they took the shots for real.

Just stop down a little, that's what I'd do, you get a bit more DOF but choose your backgrounds carefully which you should be doing anyway for the posed shots.

Hope that's helped a bit?
 
CT said:
Just stop down a little, that's what I'd do, you get a bit more DOF but choose your backgrounds carefully which you should be doing anyway for the posed shots.

Hope that's helped a bit?
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Now that has helped a lot, CT....thank you. I was trying to achieve something that wasnt easily achievable...thereby creating problems!
F11 outdoors for me then!! :thumbs:

Just a couple more things....

1. some people say "expose for the background"....i assume this means only the trees etc etc that are behind.....using MATRIX?

2. others say "expose for the ambient light".... this isnt the same as exposing for the background is it. ambient light includes your subject too doesnt it...so if your bride is in white..that alters the exposure completely.

3. if you expose for the background or ambient with the flash on your camera turned ON...wont the camera take into account that you have a flash and will be lighting with it and thereby give you not an ambient exposure but one which will include a zap of flash too?
 
Janice said:
1. some people say "expose for the background"....

2. others say "expose for the ambient light"....

3. if you expose for the background or ambient with the flash on your camera turned ON...wont the camera take into account that you have a flash and will be lighting with it and thereby give you not an ambient exposure but one which will include a zap of flash too?
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1 and 2 are really the same thing - it's up to you to decide how much of the existing light you want to expose for - it could be a sunset behind the subject or just street lights in the background. Whatever it is the principal is the same, expose for that and the flash does the rest.

3: The camera doesn't take the flash into account when it meters a scene. The calculation for the flash exposure is only done when you fire the shutter. The flash then fires a low level burst which is used to determine how much power to use for a second burst - this all happens so quickly that is seems like only a single burst.
 
Janice said:
Just a couple more things....

1. some people say "expose for the background"....i assume this means only the trees etc etc that are behind.....using MATRIX?

2. others say "expose for the ambient light".... this isnt the same as exposing for the background is it. ambient light includes your subject too doesnt it...so if your bride is in white..that alters the exposure completely
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Let's take a camera meter which just uses full frame average metering to try to understand these metering modes. All a full frame average meter does is mix all the tones in the scene projected onto your focusing screen down to 18% grey , which is just the same as metering on a grey card. I know you understand that you'd use this reading direct unless there were elements in the scene which were unusually light or dark, in which case you'd adjust exposure accordingly if those elements were important in the shot such as they patently would be with a white dress.

'Matrix' metering is actually a Nikon system, Canon's version is similar but is called 'Evaluative'. With these systems the screen is divided up into a number of different zones which are each metered independantly of each other, the camera software gathers the info and calculates what it considers to be the best exposure for all those different parts of the scene. It's a far more accurate system and I'd have no hesitation in using it for a wedding job. Just make sure that the white dress is included in the viewfinder, but plenty of the background too. I'm not saying you can trust the system completely in this situation you may still need to stop down a little after some judicious chimping. ;) I know lots of pros who simply use 'P' and auto flash for weddings, I've done so myself on occasions and you'd be surprised how well it works. Just keep an eye on that preview screen and adjust if you need to. :)

With regard to metering in Evaluative Mode, just meter the whole scene including your foreground figures.

3. if you expose for the background or ambient with the flash on your camera turned ON...wont the camera take into account that you have a flash and will be lighting with it and thereby give you not an ambient exposure but one which will include a zap of flash too?
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LOL.Janice you're really thinking about this aren't you? :lol:

No it wont. You can set your mind at rest about this right now - take an ambient reading with the flash turned on and again with it turned off and you'll see that the meter reading doesn't change. When you take the shot the flash just provides the fill in for the ambient light settings - as long as you're using ETTL Mode on the flash.
 
Janice,

Here's an example of using High Speed Sync for fill flash.

First here's a shot without flash, I metered for the garden outside:

no_flash.jpg


This next shot I used my 430ex is HSS mode everything else was the same:

flash.jpg


Both shot were:

ISO 1600
1/800s
f/4

There's a slight difference in WB but I was in auto mode. HSS mode is ideal for the kind of shot you described because although the power of the flash is reduced you only need enough for fill light as you're not trying to light an entire scene with it.

I can't remember how you turn on HSS on the Sigma but I know it does support it...
 
Good example of Hi Speed Sync there from pxl8 which is another option for you. :thumbs:

The nice thing about HSS at least as far as the Canon 580 EX is concerned is that once it's set on the flash it stays set (but isn't used) even when you reduce shutter speed to normal sync speeds and engages again if you increase the shutter speed. You get a warning symbol 'Hi' at the bottom of the viewfinder when it's active.
 
I can only thank you all again for being patient!

Im afraid its a rather bad character trait.... if I start to find out how something works before I use it.....I need to know it ALL!!
I cant just USE IT..... I have to be able to understand WHY it happens!!

I did want to use P mode with flash, CT, but with the Canons the shift mode in P is disabled when using flash so its 1/60" permanently... and no chance of changing aperture either. I thought that might be a bit restrictive.

I am going to be taking a million test shots throughout July then....with my lads at gunpoint one dressed in black and one in white (God help the one in the white dress! :D )

Thanks Rayfin. I actually have that article in my favourites from before.

For anyone else wanting to know more there is also THIS: http://www.planetneil.com/faq/flash-techniques.html

And thanks again all you patient people! :thumbs:
 
I know I'm joining this late but thanks for all the good advice in this thread. It's filled in quite a few gaps in my understanding of flash techniques.
 
I might just throw one more thing into the mix, not to complicate things but because it may prove pertinent......

Flash exposure compensation is vital sometimes, especially if what you're shooting is predominantly white or black. If the scene is bright then the flash will underpower and make everything underexposed, if it's dark it will overpower and black things become grey.

I learn this the hard way from the couple of weddings I did last year, and it's proved helpful when shooting peoples houses too.


Generaly though, whatever I'm shooting, I tend to use matrix metering and then just let the flash sort itself out. Very rarely does it get it wrong!
 
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