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Archive 2011 · Total noob with flash photography, need help with vignett...
  
 
rosskykerphoto
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p.1 #1 · p.1 #1 · Total noob with flash photography, need help with vignetting issue


Ok so here's the deal I'm trying to teach myself flash photography and I'm already puzzled haha! One of my friends recommended me to this site and there sure are some amazing photographers on here, hopefully one of you will be able to help

So I setup shop in my office with two FJ Westcott Strobelights with softboxes and asked my girlfriend to have a seat against the white wall just for tests. I took a meter reading from her face at iso 100 and it said that 1/4 sec at f13 was the correct exposure so I fired away and the photo looked great! But since she was against a flat wall I didn't feel like I needed such a great depth of field so I tinkered around until the meter said that 1/800 sec at f9 was correct and half her face was missing from a dark black shadow... The half that wasn't in the shadow looks perfect, but the other half is pitch black. I took the photo from the same location and position as the previous. So I changed the shutter speed by 3 stops to 1/400 of a sec and now she's visible again but starting to look a little white washed... Any ideas why this is happening?

Thanks to all who can help in advance!



Dec 13, 2011 at 05:36 AM
alohadave
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p.1 #2 · p.1 #2 · Total noob with flash photography, need help with vignetting issue


When you shot at 1/4 second, you had lots of ambient light contributing to the shot. By changing to 1/800 you completely eliminated the ambient from your shot, and the flash was providing all the light to expose the face.

You should go over to www.strobist.com and read Lighting 101 and Lighting 102 and do all the exercises in them. They will cover everything you need to know to understand lighting.



Dec 13, 2011 at 06:11 AM
BrianO
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p.1 #3 · p.1 #3 · Total noob with flash photography, need help with vignetting issue


rosskykerphoto wrote:
...since she was against a flat wall I didn't feel like I needed such a great depth of field so I tinkered around until the meter said that 1/800 sec at f9 was correct and half her face was missing from a dark black shadow... The half that wasn't in the shadow looks perfect, but the other half is pitch black.


You've just learned your first lesson about flash photography: sync speed.

At slower shutter speeds the first curtain of the shutter opens all the way, then the flash fires, then the second curtain closes.

But at faster speeds the shutter blades can't move fast enough, so the system pulls a clever trick; the second curtain starts to close before the first curtain is all the way open, creating a slit that moves across the film or sensor.

With continuous light, like the sun or incandescent lights, the light doesn't change over time, so the moving slit exposes the whole image to the same amount of light as it moves.

With flash, though, the burst of light is so short that only the part of the sensor that is currently exposed will get the flash exposure, and then the flash dies out and the rest of the sensor only gets exposed to the room light.

So, when using flash you need to keep the shutter speed at or below the flash sync speed. For most DSLRs that's 1/200 to 1/250. At 1/800, only part of your picture got flash exposure, and the rest was dark.

The second issue is metering. Unless you were using a flash meter, the numbers you were given were for the existing light in the room. When you then added flash to the mix you overexposed the image.

You can buy a flash meter, or you can use manual power adjustments on the flash units and start with a low power setting, check the camera's histogram, and increase power until you get the proper level.

Shutter speeds at or below sync speed have no effect on the amount of flash exposure; only changes of aperture affect that. Shutter speed will affect the amount of continuous light recorded, and so we usually (in a studio-type setting) use the fastest shutter speed we can in order to minimize the effect of ambient so we can use placement of our flash and use of flash modifiers (soft boxes, beauty dishes, etc.) to maximum effect.

[Edit] I see from your profile that you have a Sekonic flash meter. Set the shutter speed of your camera to maximum sync speed as stated in your manual, and set the shutter speed on the meter to the same speed. Then adjust the power of the strobes until test firings match your desired aperture for the amount of depth of field you want.



Dec 13, 2011 at 06:22 AM
rosskykerphoto
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p.1 #4 · p.1 #4 · Total noob with flash photography, need help with vignetting issue


Thanks Dave, I'll check it out!

Brian thanks for all the info and it makes perfect sense! My camera is currently set to a 1/250 sync speed. I forgot to include a little info in my original post I shut off all of the lights in my office and only used the strobes (with modeling lamps on so I didn't hang either of us on all of the cords) and I am actually using a Sekonic L-358 for the metering. So essentially I want to use a shutter speed of 1/250 or slower and adjust the power of the strobes up and down to get the f-stop I desire?



Dec 13, 2011 at 06:42 AM
 

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BrianO
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p.1 #5 · p.1 #5 · Total noob with flash photography, need help with vignetting issue


rosskykerphoto wrote:
...I shut off all of the lights in my office and only used the strobes (with modeling lamps on so I didn't hang either of us on all of the cords) and I am actually using a Sekonic L-358 for the metering. So essentially I want to use a shutter speed of 1/250 or slower and adjust the power of the strobes up and down to get the f-stop I desire?


Correct, but just use 1/250. No need for slower speeds unless you're mixing flash and ambient, which is a more advanced technique.

Also make sure your meter is set for one of the flash modes (see illustration below) and not for continuous light.









Dec 13, 2011 at 06:52 AM
cgardner
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p.1 #6 · p.1 #6 · Total noob with flash photography, need help with vignetting issue


You may find these tutorials of mine helpful:

Lighting Concepts:

http://photo.nova.org/CluelessToCompetent/
http://photo.nova.org/FourLightExercise/
http://photo.nova.org/Fill/

Metering (I also use a Sekonic L-358):
http://photo.nova.org/Ratios/

One of the simpler ways to understand lighting ratios and get good results is to use a "butterfly" pattern with both lights back around the camera 8ft. from the subject centered just below the lens around subject chin level as "fill" and the other "key" light which creates the highlights over the fill up over the subject's head. This is a side view of what I'm suggesting:







Light Placement Concepts: A "key" concept to grasp is that natural light which is our perceptual baseline for 3D modeling of faces and objects comes from overhead most of the time, hence artificial lighting will seem more natural when the key light hits the face at a downward 45 angle. The ideal fill is flat and shadowless when viewed through the lens which is why you want it very close to the lens most of the time. Anywhere the fill doesn't reach you (because the cheek or some other body part shades it) will find very dark unfilled shadows.

Ratios: The ratio convention used for portraits such as 2:1 expresses that 2x more light reflects off the highlight side of the face than the shadow side. Ratios are confusing because they express reflected light but are measured with an incident meter.

With the suggested butterfly pattern above both lights wind up a similar distance from the face. If you put both on 1/2 power they will create a 2:1 ratio on the face BECAUSE THEY OVERLAP. The ratio math is simpler when shown like this:

__ H:S__
F: 1:1 Fill light is even on entire front of face and falls off front > back
K: 1:0 Key light is same strength but only hits part of the face.
=======
R: 2:1 The resulting ratio is 2:1 because 2x more light reflects in from the highlights.

Exposure:

With the flash meter you put the dome up, place meter in front of the subject's face where both lights hit, aim dome at lens of camera (not at either light) and fire both lights. The dome averages the key and fill on its 3D shape similar to how a 3D face reflects and the resulting reading is what you set the aperture to.

1/2 power was just suggested as a starting point. Ideally you want the resulting meter reading for both lights to be in the range of f/8 to f/2.8 depending on how much DOF you want on the face. That varies with personal preference. I like to keep the entire head in focus at capture and shoot at f/8. Other prefer the front of the face to be sharp at capture with the ears out of focus and shoot at f/2.8 or even wider. Starting out you'll find f/5.6... f/8 gives you more margin for AF errors in keeping the eyes and mouth sharp, so I suggest that as a starting baseline when learning.

So take a meter reading at 1/2 power then just adjust the power of both lights equally (to maintain the 2:1 ratio set via equal distance and power) until the reading is in the f/5.6 to f/8 range. I use this target when setting up my lights. I use lights in front and back and the white/ black towels allow me to see shadow and highlight detail on both sides of 3D objects visually in the playback. The base is a Kodak 8 x 10 gray card I can use to set Custom WB. The color chart is a MacBeth color checker which allows me to more objectively judge exposure and color when editing.







I'll rough in the lighting by eye with the modeling lights, take an overall exposure reading with the meter, then tweek the lights based on test shots until I can see the flat centered fill revealing the detail in the folds of the black towel and the accent and key lights creating highlight modeling but not clipping and blowing them. The on a stand target allows me to get the light ratio and exposure set before the subject even arrives. When they do I hand them the target and take a test shot to both confirm the settings and serve as an editing reference:







The results from the suggested 2:1 "butterfly" will look similar to this...





















It's not the most dramatic lighting because the ratio is low and the lights are far away and fall off gradually front > back, but it depicts faces naturally similar to how you see them in person most of the time.

I usually start my portrait session with that type of butterfly set-up because it allows a great deal of movement on the part of the subject without the nose casting dark unflattering shadow anywhere on the face.












It is especially effective with kids because I just have them goof off in front of the camera to start out which relaxes them and often produces some great candid captures and ideas for poses.












The second shot above wound up on the neighbor's Christmas card a few years ago. The little bother did that when horsing around and when we settled down to do the serious shooting we refined it.

The lesson in that shot is that in portraits the lighting is secondary; its the expressions which create the emotional reaction. The main role of the lighting is to: 1) contrast the front of the face with the background so it is easy to find, and; 2) model the face 3D shape of the face with a natural looking and flattering pattern without any dark distracting shadows hanging off the noses.

The set-up above works great for groups and any situation where you can't precisely control the angle of nose to key light which more than anything defines the lighting pattern. From that starting 2:1 ratio butterfly set-up you can learn by experimentation and comparison with the results to alter the ratio to change the mood and move the key light around to change the modeling as the face angle to the camera changes. If you just change one variable at a time you'll grasp what that variable is actually doing faster.

Chuck



Dec 13, 2011 at 02:48 PM
Garry Burton
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p.1 #7 · p.1 #7 · Total noob with flash photography, need help with vignetting issue


WOW!! New images ...


Dec 15, 2011 at 08:23 AM
scubacrazy
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p.1 #8 · p.1 #8 · Total noob with flash photography, need help with vignetting issue


That has to be one of the most concise, useful and helpful posts I have ever seen on here.
Thanks for taking the time to post it.
This one of reasons I like this forum so much.



Dec 15, 2011 at 02:17 PM





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