Technical Question

[silverturtle]

Ok im tryin got understand off camera flashes and metering more from a technical prespective, im an engineer so i need to understand how stuff work.

Tkae this picture (taken from another thread, not mine)

http://zsuttonphoto.com/Alex/1.jpg

i got the picture from here
http://photography-on-the.net/forum/showthread.php?t=412392&page=110


Here obviouly a flash was used creativly to fill in the person, but the picture is metered for the sky, if it was metered for the person, the sky would have been overblown ot too bright, so please correct me if im wrong. but the only way to do with would be to:

put the flash on manual and adjust camera settings as needed.
turn on auto focus, focus the lens to the person, then shut of auto focus(or just manual focus from the start)
Aim the camera at the sky so it meters to that, then shoot the comporisition you require. So you are fooling the camera to think it is taking a picture of the sky, but the manual flash brings in the person with the correct exposure, but because the camera and flash are in manual, the camera does not compensate for the flash, and just assumes it is picturing the sky.


Am i correct, is there any other way of shooting a picture like this.

My question has always been, if you want to use autofocus, is there a way to focus on one part of the picture , while metering on another ?

[Wilt]

This photo was done in two parts...
1. Meter the sky and set the camera on M, to permit selection of f/stop and shutter speed to net a -1EV (or less, probably less in this case) underexposure for ambient lighting.
The shutter speed was probably at max X-synch speed for a non-HSS flash, or it was above X-synch speed with and HSS-capable flash. The power handicap from use of HSS was inconsequential because of the close shooting distance to the subject.
2. For the selected f/stop the flash was put on ETTL. (or a manually controlled power output flash was metered so that the output power matched the chosen f/stop_.

Aim and shoot after the two steps.

You can focus on one and meter on another simply by moving the AF control away from the shutter button. You can then use Exposure Lock to hold the exposure (for example when using Spot mode) and then reframe and shoot, using the pre-set focus and locked exposure setting.

[bobbyz]

I would put a link to the picture as it is not yours.

To do it,

1. Camera in manual mode set to exposure for the bg.
2. Flash in etTL mode

Simple.

Not sure why you need to focus on/off and other things.

[silverturtle]

I think my confusion is ttl, and how it works. I though if you metered the bg in this shot then ttl would calculate that flash isn't really needed and would reduce the power drastically making it not very usefull ?


I got the pic from the one strobe ceartve thread I'll post a link


I think I also choose a bad example as I want one with off camera flash I'll find another

[Wilt]

I think my confusion is ttl, and how it works. I though if you metered the bg in this shot then ttl would calculate that flash isn't really needed and would reduce the power drastically making it not very usefull ?


I got the pic from the one strobe ceartve thread I'll post a link


I think I also choose a bad example as I want one with off camera flash I'll find another


But you UNDERexposed per the ambient light, and the ETTL flash is making up for that! Also, by not using P mode, the logic of using flash or not -- based upon ambient -- is gone.

[silverturtle]

ok lets take another example

http://farm4.static.flickr.com/3499/3793994819_6100679004_b.jpg
from here:
http://photography-on-the.net/forum/showthread.php?t=412392&page=92


in this picture, the camera is focused on the girl, the camera is meters for the night background, thr flash is off camera on to the right of the camera i assume, would you still use ttl for this? would you still have to manually adjust EV on the camera. If you where using a non TTL radion controller for this, would it just be trial and error till you figure out which flash settings are the best ?


im assuming you would use something like f2.8 maybe f4, shuuter at 1/250 to match the flash sync. and the flash to the side, with an umbrella or a diffuser at 3/4 power?

i need to play around in an environment like these and learn from there i guess.

[Wilt]

You are trying to hard to learn the 'school solution' of flash vs. ambient. Go shoot and learn by direct experience, and it will fall into place faster than trying to gobble up via rote learning on POTN. When we used to have to suffer the cost of film and processing, and the delay to see results, it made far more sense to ask first, then shoot. "DIGITAL IS FREE", take advantage of that. To mimic is to learn, to try to mimic is equally to learn.

[silverturtle]

i agree, its just finding a person willing to give up their time for you to practise is difficult

[Yamaha451]

i agree, its just finding a person willing to give up their time for you to practise is difficult

Self portrait FTW!

[Wilt]

That's why your goal should be to get a wife or girlfriend! ;)

BTW, gray cards make fine subjects when the teaching point is simply balancing light!

[ToddR]

I just got a mannequin head from the lady that cuts my mother's hair. Now I just need to experiment with my lights by taking a bunch of test shots of it.

At least she won't complain about "holding still." It even has a C-clamp/ball head gizmo on it in lieu of a throat.

[TMR Design]

How about an 18% gray cutout of a girlfriend ? :D

I'm kidding but if you think about it, a full length cardboard subject that is 18% gray would not only help with balancing foreground flash with background ambient but would also let you explore light falloff, feathering of light, and understanding the relationship between the size of the modifier, size of the subject and distance of modifier to subject.

You could make them in a Barbie version and a Ken version. :lol:

[bobbyz]

ok lets take another example

http://farm4.static.flickr.com/3499/3793994819_6100679004_b.jpg
from here:
http://photography-on-the.net/forum/showthread.php?t=412392&page=92


in this picture, the camera is focused on the girl, the camera is meters for the night background, thr flash is off camera on to the right of the camera i assume, would you still use ttl for this? would you still have to manually adjust EV on the camera. If you where using a non TTL radion controller for this, would it just be trial and error till you figure out which flash settings are the best ?


im assuming you would use something like f2.8 maybe f4, shuuter at 1/250 to match the flash sync. and the flash to the side, with an umbrella or a diffuser at 3/4 power?

i need to play around in an environment like these and learn from there i guess.

I would suggest some more reading on

http://www.planetneil.com/tangents/
http://strobist.blogspot.com/

and here on POTN. And like others said, go and test for yourself.

[Dirk Lately]

I just got a mannequin head from the lady that cuts my mother's hair. Now I just need to experiment with my lights by taking a bunch of test shots of it.

At least she won't complain about "holding still." It even has a C-clamp/ball head gizmo on it in lieu of a throat.


That just sounds so dirty. :lol:

[ToddR]

That just sounds so dirty. :lol:

Agreed. :cool:

Mom reports that she got some funny looks exiting the mall with a "head" under her arm.

The head was apparently some sort of haircut practice dummy, so it had hair, but it had all been shorn to Sinéad O'Connor length.

[Dirk Lately]

Agreed. :cool:

Mom reports that she got some funny looks exiting the mall with a "head" under her arm.

The head was apparently some sort of haircut practice dummy, so it had hair, but it had all been shorn to Sinéad O'Connor length.

hahahahah! And how did your Mom know you needed an extra head? Perhaps you were sitting around together, and apropos of nothing, she says, "Son, if you ever need a disembodied mannequin head with closely shorn hair and a ball-head throat, well, I can hook you right up!"

Or, perhaps she just collects heads wherever she finds them?

I really have no idea why I find this so entertaining.

[ToddR]

hahahahah! And how did your Mom know you needed an extra head? Perhaps you were sitting around together, and apropos of nothing, she says, "Son, if you ever need a disembodied mannequin head with closely shorn hair and a ball-head throat, well, I can hook you right up!"

Or, perhaps she just collects heads wherever she finds them?

I really have no idea why I find this so entertaining.

No, nothing so macabre. :p I just had been trying to find one to play with as I'm certainly not going to get my wife to sit still while I fiddle with lights, modifiers, and camera. The woman who cuts my hair didn't have anything (I asked) so I had Mom do the same because she's friends with her hair lady.

I've seen examples of lighting configurations here on POTN that involved a mannequin head, so I figured I could play, too.

[daver777]

google OneLight and get their DVD - explains all you need to know.

[shart717]

I wouldn't use e-ttl in this case, because the ambient is brighter than the pre flash, giving you incorrect information for the flash exposure.

[Titus213]

I've found E-TTL to be quite good at dealing with back light situations. Proximity, as in the case of the sample image, also allows the use of HSS as already mentioned.