Questions about flash with 1D mk3 - help please

combat squirrel

combat squirrel

Messages
1,207
Edit My Images
No
Hi,

Im used to using a 5D mk2 in clubs on P mode or Av with 580 EXII, which normally gives a shutter speed in the reagion of 80, and F2.8 to 3.5, I usually like to bump up the ISO to 1250 to collect ambient light, more atmosphere etc.

However Iv recently got a 1D mk3 and had ago of that last night (want it for its robustness and water proof features) and this behaves quite abit differently.....

Again I hit ISO 1250, but on P mode it seems hell bent on sticking to a 125th/sec shutter speed and anywhere between F2.8 to 5.6, also in Av mode it doesnt seem to want to do 'auto flash' or behave like Av mode does on the 5Dmk2.

Now essentially I want the 1D to 'p mode' to a say 60th'sec shutter speed and keep around F2.8.... obviously I tried this in manual and it works ok but it doesnt compensate for subtle changes in light like say the 5d mk2 would.

All have ETTL-II enabled...but im confused why the 1D will only work with flash in P mode..and behave as though there is no flash in all other modes even though triggering the shutter sets the flash off.

Iv dived into its menus of course but everything seems to be in order....

So obviously im missing something here, of course you could say just use the 5D but I want to master the behavior of the 1D also, thus gaining more knowledge, of course 125th/sec works ok with the 1D and it takes nice pics, but I have noticed a slower shutter lets more ambient in (obviously) and I prefer that, so why does the 5D behave differently? - where am I going wrong here guys ? :)
 
I don't use P mode ever, and with flash I prefer to set a manual exposure, so today I popped my 1D3 into P mode,with flash, and sure enough it seemed to default to 1/125. I've searched the manual and can find nothing documented about this.

However, a had a flash of inspiration and tried lowering the ISO. At 800 ISO it was still stuck at 1/125, but at 400 ISO it dropped to 1/60. I don't understand the design philosophy behind that behaviour, but I don't think you have done anything wrong and I'm not at all sure that you can do anything about it other than avoid P mode with flash. I do know that P mode is designed to help avoid camera shake, because in Av mode (unless you adjust settings to prevent it) the camera will select any shutter speed it wishes, which could end up being dangerously slow - like seconds if that's what it wants. P mode is designed to lower that risk, by llimiting the slowest shutter speed available. I have no idea why Canon thinks there is a greater risk of shake at 800 ISO than at 400 ISO.

If you want to retain the flexibility of autoexposure rather than fixing it manually you could always opt for Tv mode and lock in 1/60 or 1/80 and let the aperture value float instead.
 
tdodd said:
I don't use P mode ever, and with flash I prefer to set a manual exposure, so today I popped my 1D3 into P mode,with flash, and sure enough it seemed to default to 1/125. I've searched the manual and can find nothing documented about this.

However, a had a flash of inspiration and tried lowering the ISO. At 800 ISO it was still stuck at 1/125, but at 400 ISO it dropped to 1/60. I don't understand the design philosophy behind that behaviour, but I don't think you have done anything wrong and I'm not at all sure that you can do anything about it other than avoid P mode with flash. I do know that P mode is designed to help avoid camera shake, because in Av mode (unless you adjust settings to prevent it) the camera will select any shutter speed it wishes, which could end up being dangerously slow - like seconds if that's what it wants. P mode is designed to lower that risk, by llimiting the slowest shutter speed available. I have no idea why Canon thinks there is a greater risk of shake at 800 ISO than at 400 ISO.

If you want to retain the flexibility of autoexposure rather than fixing it manually you could always opt for Tv mode and lock in 1/60 or 1/80 and let the aperture value float instead.
Click to expand...

Thanks for the response :) Yeh tried Tv mode last night and it flashed 2.8 on the LCD - as if to say it wont expose properly, i.e. it wasnt accounting for the flash, but just tried it now and it did adjust the aperture value if I pointed toward a brighter light...........so im not sure whats going on now :bonk:

I guess my only concern is, if its doing this in Tv mode, will it adjust the flash correctly in terms of ETTL-II input data into the camera or will it just fire the flash - if that makes sense.
 
It should adjust the flash perfectly well, within the limitations of the ETTL-II system and the power of the flash.

In any exposure mode the camera is only metering ambient. The aperture flashed at f/2.8 because it wanted more light than was available from the ambient conditions. It isn't until you begin to take the shot that the camera fires a pre-flash, assesses the effect upon the scene, works out how much flash is necessary and then opens the shutter, chucks the light it thinks is required at the scene and completes your combined exposure of ambient and flash. On top of all this, if you are bouncing the flash the camera has no way to know what sort of power you'll get from the flash until it's fired the pre-flash and measured the output reaching the subject. In other words the camera makes no assumptions about what the flash will do to the scene. It has to fire the pre-flash and take it from there.

Obviously, if you are planning to add flash it makes sense that your ambient exposure is set up a little on the low side, otherwise when you add more light from the flash the risk is overexposure. It's also worth noting, although I am sure you are aware, that the flash exposure metering is as vulnerable to extremes of tonal range in the subject/scene as ambient metering. If you've got a dark subject there is a risk of overexposure unless you dial in some negative EC and FEC. With a bright subject you may want a little positive EC and FEC. The advantage of locking the ambient exposure manually is that it's one less variable to fight with. Just fix the ambient exposure to slightly underexpose for the ambient/incident light and then let the ETTL work out how much light to add to bring the levels up
 
I think the only 'proper' way is to use M mode. There is not much thinking there - f/2.8 and whatever shutter speed you like. The camera will then sort out your flash, unless you want to go M there as well.
In P/Av mode with the flash, the cameras aren't as clever as you'd think. By default they will try to expose for foreground (which is damn hard to do at the nightclub) while not exceeding 1/60s, and then fill in. Different metering mode will likely have a dramatic effect. There is a custom setting to force it to max sync speed, but M mode does exactly that.
 
Thanks for the tips guys, M mode leaves things lookin abit flat, I find its defo not a lottery, I bounce the flash with a modifer, P mode is just fine, maybe its more my modifier but M mode is abit, non altering, at least in other modes the cam mildly adjusts for ambient, least what i find.

Anyways ill take all the views on board and try a few things next time :)
 
My understanding is that the 5D2/1D3 is using the available light to "guess" what you want and what you're shooting.
If you have a naturally bright scene (EV13 or higher) then it uses a lower power flash but at 1/60 to harvest more of the available light.
When the scene is darker (EV10 or less) then it ups the flash power to correctly expose the subject in the focus point and modifies the shutter speed accordingly.

It could well be that the two bodies have marginally different algorithms for EV10 or less.

Bob
 
It's for Av mode, not P, and the only options on the 1D3 are Auto or 1/300. It's CFn 1-15. See page 162 of the manual.
 
You must log in or register to reply here.
Back
Top