Hi all
I feel I need to apologize rest of the list for prolonging this
subject. I know Thomas and Bob are clever and I'm not dumb either
but maybe there is something in this discussion where we don't
understand each others perfectly... or I just don't get it ;-)
But I'd be happy to continue this with private emails after this
if necessary.
In fact, this thread actually is not even about foreground vs.
background lighting but about flash vs. ambient light in Av-mode.
Here are some further comments on comments on comments...
1) ----- P-mode -------------------------
> > It does? So you mean in P-mode the shutter speed never goes slower
> > than 1/focal length (with flash)?
> > Oh boy... forgot that possibility. 8-|
> > I remembered P-mode works the same way with or without a flash.
>
>With A-TTL type bodies at least, P mode will NOT prevent shutter speeds
>longer than 1/focal length. Instead it will choose a shutter speed
>between 1/60 second and the flash sync speed. There's also no way to
>use program shift. Don't know about the E-TTL generation, though ;-)
>All this is for use with flash of course.
Well, for most cases I had in my mind this is good enough as the first
aid. E.g. for lenses not longer than 135mm.
If flash is in FP-mode is the P-mode still limiting shutter speed
to sync speed in the fast end?
2) ----- Av + Fixed vs. limited shutter speed, rant 1 -----------
>Again, we were talking AV mode and a fixed shutter
>speed, with flash. As soon as you turn on the flash,
>the flash metering system controls exposure of the
>subject, regardless of metering mode. In AV mode
>without a fixed shutter speed, the camera will vary
>the shutter speed to properly expose the background,
>but that's just what the original questioner wanted to
>avoid.
Well, I (the originator of this thread) was NOT talking about
"fixed shutter speed", I was talking about *limited* shutter
speed to prevent camera shake in case where the subject or
background is poorly illuminated BUT to expose the
subject/background properly when suddenly there *is* more light.
E.g. with a 35mm lens I might want to set the limit to 1/30
seconds because I know my subject is not moving very fast
and 1/30 would be fast enough even if the is enough ambient light.
So the camera would have room to change the shutter between
1/30 and sync speed (e.g. 1/200) or even 1/x000 in flash FP-mode.
3) ----- Fixed vs. limited shutter speed, rant 2 --------------
>>If I could limit the slowest shutter speed in Av
>>mode to what I want
>>(e.g. 1/focal length) when flash is on and ready I
>>could set
>>the aperture to what I like and flash and Av mode
>>together would
>>take care of the exposure, both for foreground (Av
>>and flash) and
>>for background (mostly Av mode).
>
>We're back to square one. You get EXACTLY the same
>effect by selecting manual, setting the shutter speed
>to 1/focal length, and adjusting the aperture to what
>you want. This is exactly how AV mode with the
>ability to limit the shutter speed would work. But
>the flash system CANNOT, in this situation, expose for
>both the background and forground. Background
>exposure is set by the combination of shutter speed an
>aperture chosen, and foreground exposure is controlled
>by the flash.
>
>The ONLY way you could get both exposed properly is if
>the background is essentially right behind your
>subject.
I have to agree and disagree. I brought us back to square one
because I feel we didn't understand each others perfectly in the
very beginning ;-).
You're (of course) right, if the background is poorly illuminated.
But what if the background (or foreground) lighting is changing?
I'm talking about limiting the shutter speed (slow limit), not
fixing it to some predefined value (with flash on, that is).
So using M-mode and Av-mode-with-*limited*-shutter-speed would
differ in the case where the background (or even the main subject)
for some reason suddenly has more light than what is needed to
expose it correctly with the selected aperture and the selected
(M-mode) or limited ("Limited Av" mode) shutter speed. Av mode
would expose it correctly by shortening the shutter speed but
M-mode (without keeping eye on and adjusting it) would overexpose
it.
4) ----- You said it! -----------------
>>Then again, is there really a need for 1/focal
>>length rule when using flash?
>>When flash is the main light source, the flash will
>>freeze the subject.
>
>That all depends on how much ambient light there is.
>I've got plenty of shots in gyms where the main image
>of the subject is frozen by the flash, but the gym
>lighting is bright enough to expose a blurred ghost
>image around the subject. Occasionally this gives a
>very interesting effect. Usually it creates junk.
>
>And in the same situation, even if the subject is
>still, camera shake could be a problem.
That's a good example of what I mean except that 1/focal length
limit wouldn't be good enough. Instead the shutter speed limit
should be user defined (to avoid the blurred chost image with
e.g. 35mm or 50mm lenses).
Another example is city street by night. Your subject may be
in darkness so you need flash for it/him/her. The subject might
be moving so sometimes there are city lights in the background
and sometimes not, resulting e.g. in these three *background*
exposures, each giving good results (exposure vice):
- 1/125 with f2.8
- 1/30 sec with f2.8
- 1/8 sec with f2.8
In most cases 1/125 and 1/30 would be fine but 1/8 too slow to
handhold or to freeze the subject motion. Let's say I'm using a
35/1.4 lens and want to use aperture f2.8.
If the limit was set to 1/30 the 1/8 exposure would have dark
background as expected but the other two would be fine.
Sorry for the long mail.
Vesa
_________________________________________________________________________
Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.
*
****
*******
***********************************************************
* For list instructions, including unsubscribe, see:
* http://www.a1.nl/phomepag/markerink/eos_list.htm
***********************************************************
