Help With Flash Photography - DPChallenge Forums

Sony 16-50mm f/3.5-5.6 E-mount

11/06/2003 11:18:16 AM · #26

The 1/60th is not going to be a problem for exposing a subject correctly, given that range. As said above and as I'm sure you know it's possible to lock the shutter speed at 1/200th and let the flash expose properly. I've had no problems myself with the aforementioned 1/200th, f/5.6 and ISO 100, which would require much more flash output than John's shots. Even the 420EX is VERY powerful...it should have absolutely no problem exposing at 1/60th and F/3.5. Although I can't remember where I was that I read it I think the 10D will select ISO 100 for external flash shots in the basic modes.

My belief after reading his posts is than he didn't lock exposure on his subject and the camera metered on the curtains/glass, causing underexposure.

Originally posted by Gordon:

Originally posted by jmsetzler:
I was using the 'green box' point and shoot mode... not the P mode. As noted earlier, the only difference in exposure was that, when in this mode, the camera with the onboard flash set the ISO to 400 and it only chose 100 with the 420 on the camera. That was my first curiosity after it was brought to my attention.

The way I had the camera setup, I would have expected the first and second shots in the set to be almost identical. The difference, however, is that the first one was ISO 400 and the second was ISO 100. Two stops of ISO difference explains the underexposure, but WHY the camera didn't choose ISO 400 for the second shot is the part that is confusing me.

The green box mode is even more basic than P mode. But essentially the problem is the same - you are shooting in a mode that limits your shutter speed to 1/60s or faster. You are shooting in essentially a dark room and the camera is trying to use the flash as the sole exposure source. Your lens is quite slow for that situation and the exposures are all pushed right up against the limits of your equipment.

The fact that you shot straight at a highly reflective subject probably further confused the camera meter. You might get better results if you use flash exposure lock/ pre-flash, but I doubt it.

Message edited by author 2003-11-06 11:34:26.

jmsetzler

Sony Alpha a6000

11/06/2003 02:13:21 PM · #27

Tonight, I will setup some sort of simple still life that I can work with. I will try some various exposure modes to see what results are possible.

Gordon

RIM BlackBerry Curve

Canon EF 85mm f/1.8 USM

11/06/2003 02:27:41 PM · #28

Originally posted by jimmythefish:

My belief after reading his posts is than he didn't lock exposure on his subject and the camera metered on the curtains/glass, causing underexposure.

Yup, could well be the main culprit - though the restricited shutter speed has meant that the camera was forced to underexpose. The flash shut off early because of the reflected/ non pre-metered light, and couldn't go slow enough to really expose the background.

11/06/2003 02:44:25 PM · #29

In that mode it doesn't take ambient exposure into account. It assumes that the flash is the main light source and meters solely on the preflash. The shutter speed is largely meaningless for shots taken in that mode given a suitably dark scenario. The flash burst is what is actually exposing the subject, which is a lot quicker than 1/60th. My guess is that you're hardly getting any ambient light at all in that shot. What really caused the underexposure is bouncing the light off the good reflective, white surface of the glass/curtain combo. The E-TTl system likely received a lot of light back, and fired a very weak flash. It could very well be that the onboard flash used ISO 400 as John simply fluked out and had the focus point on the couch instead of the window for that shot. That's the only plausible explanation, I think.

Originally posted by Gordon:

Originally posted by jimmythefish:

My belief after reading his posts is than he didn't lock exposure on his subject and the camera metered on the curtains/glass, causing underexposure.

Yup, could well be the main culprit - though the restricited shutter speed has meant that the camera was forced to underexpose. The flash shut off early because of the reflected/ non pre-metered light, and couldn't go slow enough to really expose the background.

Message edited by author 2003-11-06 14:46:42.

Gordon

RIM BlackBerry Curve

Canon EF 85mm f/1.8 USM

11/06/2003 03:15:47 PM · #30

Yup, that's probably a good assessment. When you use flash, do you ever use the auto or P modes with TTL ? I found it was fairly reliable way to get bad results, but get consistently good results in the Av, Tv and M modes

Sony 16-50mm f/3.5-5.6 E-mount

11/06/2003 03:19:54 PM · #31

I get the best, most consistent results in Av mode with it locked to 1/200th, and bouncing the flash or using the omnibounce, tilted at about a 45 degree angle. That way I can still fiddle with aperture and the flash will expose accordingly. The 1/200th lock will prevent motion blur that would otherwise occur in that mode due to the ambient light metering rather than the flash metering. With the shutter speed lock the camera meters for flash exposure.

Originally posted by Gordon:

Message edited by author 2003-11-06 15:21:19.

jmsetzler

Sony Alpha a6000

11/06/2003 10:50:31 PM · #32

New test shots...

//www.pbase.com/jmsetzler/420ex_flash

I shot all of these at f/8 and 1/125" and I think this series helps me understand how this thing works now :) Thanks for everyone's input.

Natator

Canon EOS-5D

Canon EF 24-105mm f/4.0L IS

11/06/2003 10:57:25 PM · #33

Very interesting series of pics there.

In manual mode what influence does e-ttl have? Does it do anything?

With my limited knowledge what I see with Mr Gnome is:
Everything the same in each shot, except the ISO changing. As "film" becomes faster the pics get lighter (as you would expect if you ignore the flash).

Now, with that happening it would look to me, in my very limited experience, that the flash fires the same everytime, hence pics getting lighter. If the flash was firing stronger to give more light for the slower "film" I would have expected it to have balances out more.

Obviously there is something I do not understand about e-ttl, or maybe it is the bounced flash that has me confuzzled.

So, experts, care to enlighten me? (no pun intended)

jmsetzler

Sony Alpha a6000

Sony 16-50mm f/3.5-5.6 E-mount

11/06/2003 11:08:43 PM · #34

Originally posted by Natator:

E-TTL works the same no matter what mode you are in. It fires a pre-flash, evaluates the light, then adjusts the flash output power based on that metering.

In these shots, the flash is probably firing at the same output level each time. The iso shift causes the shot to get lighter each time because the 'film' is more sensitive to light with each bump in ISO.

I could have achieved the same effect by slowing down the shutter instead of bumping the iso.

Natator

Canon EOS-5D

Canon EF 24-105mm f/4.0L IS

11/07/2003 12:31:02 AM · #35

Originally posted by jmsetzler:

That was what I thought.

Soooooo why is the flash firing at the same level and not being adjusted. Is it that the 10D can't take the ISO into effect? I would have expected the flash to fire stronger at the lower ISO's to give additional light.

(Sorry if these are really stupid questions)

Canon EF 24-105mm f/4.0L IS

11/07/2003 12:50:02 AM · #36

'Cause what you're really seeing with those shots is ambient exposure plus flash exposure. In manual mode, you're setting the ambient exposure (think background) by setting the shutter speed, aperture and ISO. If you were to take a shot without the flash on, the exposure of the garden gnome would be different depending on the different ISO settings. Now, the E-TTL flash fires a pre-flash to determine how much flash it's gonna need to expose the area it's metering, which is the focal point. If you combine these two exposures, you get the total exposure. Remember that even while the flash is firing to expose the gnome, you're still exposing the gnome with ambient light as well. Two exposures. Flash photography is always involving two exposures. Think that way and you'll have an easier time understanding it.

The easiest way to think about it is simply to look at it in terms of ambient exposure compensation combined with flash exposure compensation. Fiddle with the manual control so that the ambient exposure is metered the way you want it (visible to +/- 2 stops on the meter) and fiddle with the flash exposure so the area around your subject is exposed the way you want it (again, +/- 2 stops). It's all about the look you want.

If you want a bright subject and a dark background, the flash exposure might be, say, +1 stop and the ambient metering might be set to -1 stop. In manual mode you have to set both aperture and shutter speed to get your EV, but you can get the same effect in aperture priority mode, and set the EV to positive or negative values and shutter speed will be adjusted accordingly. Flash exposure compensation will be set the same. The flash exposure compensation is a big reason to get a 10D over a 300D.

Originally posted by Natator:

Soooooo why is the flash firing at the same level and not being adjusted. Is it that the 10D can't take the ISO into effect? I would have expected the flash to fire stronger at the lower ISO's to give additional light.

Message edited by author 2003-11-07 00:53:35.

Natator

Canon EOS-5D

11/07/2003 02:50:41 AM · #37

Excellent explanation there, thank you muchly Jim.

Slowly it is all becoming far clearer, thanks to the help from people here and also John's photos.

(Sorry if I have highjacked some of the thread here John, but the answers I seek are probably relevant to many others as well).

Adrian Tung