Home · Register · Search · View Winners · Software · Hosting · Software · Join Upload & Sell

Moderated by: Fred Miranda
Username   Password

  New fredmiranda.com Mobile Site
  

FM Forums | Lighting & Studio Techniques | Join Upload & Sell

  

Archive 2012 · Shooting TTL on an SB-910
  
 
friscoron
Offline
• • • •
Upload & Sell: Off
p.1 #1 · Shooting TTL on an SB-910



I shoot with a D4 and D700, and like the concept of shooting TTL with my SB-910, but when I do, my shots are always badly underexposed. I often shoot at 1/160, exposure at f/4 to f/5.6, and shutter speeds ranging from 1/20 (to capture ambient movement) to 1/200, depending on the lighting.

I'm concerned that there's a setting on the SB-910 that's throwing it off. Or maybe on my D4?

I've attached a sample pic. She was fairly close to me as I shot this at 38mm, ISO 3200, f/3.5 and 1/160 shutter.

Thoughts?








Jul 05, 2012 at 10:33 PM
Gregg Heckler
Offline
• • •
Upload & Sell: On
p.1 #2 · Shooting TTL on an SB-910


You definitely have something off at that distance and those settings. You didn't say of you were using a light modifier or just the straight flash? Then why were you using flash at ISO 3200 and f/3.5? At this distance those setting the SB-910 would have completely blown her out.

First, pick something in your living room or a person with medium tones to it or there dress (no all back or a lot of white). Get about 5 or 6' from it or them. Set your camera to it's native ISO and about f/5.6 or 8 and 1/60. If you are using your D700 make sure you don't have any negative compensation dialed into the on-board flash (that will affect the SB-910 also). Pick a normal focal length lens or set the flash head zoom to about 35 or 50 MM. Set your camera meter on Matrix and pick the center focus point. Take the picture. If it's still way underexposed then there is definitely something wrong.



Jul 06, 2012 at 01:26 AM
friscoron
Offline
• • • •
Upload & Sell: Off
p.1 #3 · Shooting TTL on an SB-910



Nope, just a straight flash. No need for a modifier when your flash is this weak.

It has to be a setting on my D4 as it does really well in TTL on my D700.



Jul 06, 2012 at 01:37 AM
c2thew
Offline
• •
Upload & Sell: Off
p.1 #4 · Shooting TTL on an SB-910


from what I see, it looks like the flash exposure is turned down by 2 stops. I'm not familiar with nikon's menu system, but I know canon allows you to control the flash in camera.


Jul 06, 2012 at 01:45 AM
friscoron
Offline
• • • •
Upload & Sell: Off
p.1 #5 · Shooting TTL on an SB-910



I changed the Exposure Compensation for Flash to "Background Only." It was set to Entire Frame. It seems to have improved.



Jul 06, 2012 at 02:59 AM
cgardner
Offline
• • • • •
Upload & Sell: Off
p.1 #6 · Shooting TTL on an SB-910


I'm a Canon user but see the same thing in high ISO flash shots. At high ISO the flash metering, which also includes a baseline ambient reading for comparison, cuts back flash because to avoid overpowering the ambient set shutter/aperture/ISO for.

All TTL metering is at best a logical evaluation of what is in the metering zones and the camera settings to try to guess the intent of the photographer. The logic appears to work like this. When low ISOs are used the flash metering figures the photographer wants the flash to dominate and the ambient to be a secondary concern and will bias exposure on the flash lit foreground. The opposite is true in high ISO situations. Why are you using high ISO? Not for the foreground, but for the background ambience. So the flash metering cuts flash so not to overpower the ambient.

The fact the dress was shiny satin and bouncing light back into the camera like a mirror and there is a closer guy in the white shirt on the left may also have been a factor in the under-exposure in that shot. Evaluating in Levels I found that the shiny white dress in the foreground started clipping with only about 1/3 stop more exposure. By the time I corrected exposure to the point the face was correctly exposed (starting to clip in red in specular highlights) the dress was blown out in all channels:







The flash metering, seeing and reacting to the light reflecting off the shiny dress underexposed what you want to be correct, the face. The camera metering can't know that the face is more important, it can only react to the light it sees. Had she been wearing less reflective black dress the metering seeing less pre-flash coming back would have metered out more main flash. Had you better understood how TTL works and cropped the guy in the white shirt out of the photo the metering also would have seen and reacted to less pre-flash coming back and exposed it better, but you still would have needed to override with + flash compensation to handle the brighter than average white dress biasing the metering.

When composing flash shots, both in Manual or TTL, you need constant situation awareness of subject distance to the flash. In TTL things like closer guy in the white shirt or shiny satin dress, or even a mirror on the wall in the background throw off the metering because the algorithms assume the photographer knows to avoid situations like than or will compensate for them. The laws of physics being what they are had you been using manual flash as set it via guide number for correct exposure on the woman's face her closer lighter dress would be overexposed and clipping as in the Levels corrected edit. Flash can only be correct in the highlights at one distance from the flash. With TTL the metering finds brightest metering zone in photo and sets flash power so as not to clip it. Everything further way gets less flash because it falls off per the inverse-square law regardless of how it's metered. The metering worked correctly per it's programming, you simply composed the shot poorly for flash by including something highly reflective in the foreground closer than the face you wanted to have "normal" exposure. But had you used flash compensation to override the metering's best guess to the point of exposing the face of the woman correctly her dress. The solution when people are wearing white clothing? Compose the shot in way that the face winds up closer to the flash than the clothing.

Different metering modes might help improve results but the biggest problem in this shot were the composition decisions (white dress and white shirt in foreground) and unrealistic expectations of what the camera metering is capable of. With flash you need to learn to compose shots so what you want correctly exposed is closest to the flash. With TTL you need to compensate manually with lighter and darker than average clothing. If you see a white dress filling the center of the frame you can anticipate the metering seeing more than average pre-flash coming back will underexpose the flash will need + flash compensation. If you a subject is wearing a long sleeved black dress you can anticipate you will need to dial in minus flash compensation to avoid overexposing the face.




Jul 06, 2012 at 11:43 AM
 

Search in Used Dept. 



friscoron
Offline
• • • •
Upload & Sell: Off
p.1 #7 · Shooting TTL on an SB-910



Thanks, Chuck, but you're completely off the mark here. This was just one example of every picture taken that evening. Not everyone was wearing shiny dresses. Not every shot had some guy in the foreground confusing my camera's interpretation of TTL.

I do not have unrealistic expectations of what TTL can do. I'm well aware of what it can do, just need to get my D4 settings correct to take advantage of it.



Jul 06, 2012 at 03:34 PM
RJKphoto
Offline
• • •
Upload & Sell: Off
p.1 #8 · Shooting TTL on an SB-910


Is your flash mode set for balanced fill (a "BL" after the TTL)?




Jul 06, 2012 at 03:50 PM
friscoron
Offline
• • • •
Upload & Sell: Off
p.1 #9 · Shooting TTL on an SB-910



On my D700, it sometimes switches to BL without my doing anything. On the D4, no, it just shows the TTL.



Jul 06, 2012 at 04:47 PM
Jimsokay
Offline
• • •
Upload & Sell: Off
p.1 #10 · Shooting TTL on an SB-910


What was your camera metering and your flash settings?

Where you in continuous,single or manual focus?




Jul 08, 2012 at 05:37 PM
williamkazak
Offline
• • • • •
Upload & Sell: Off
p.1 #11 · Shooting TTL on an SB-910


cgardner wrote:
I'm a Canon user but see the same thing in high ISO flash shots. At high ISO the flash metering, which also includes a baseline ambient reading for comparison, cuts back flash because to avoid overpowering the ambient set shutter/aperture/ISO for.

All TTL metering is at best a logical evaluation of what is in the metering zones and the camera settings to try to guess the intent of the photographer. The logic appears to work like this. When low ISOs are used the flash metering figures the photographer wants the flash to dominate and the ambient to be a secondary concern
...Show more
Nice comments, Chuck. Putting the face closer to the flash then the clothes? Huh? Can you elaborate on that? I have been shooting my SB800 flash with D300 with the flash set on A. That way, the flash is doing the work. The flash is not "talking" to the camera and, therefore, the camera is not compensating what the flash is doing. Any compensation is made by me either at the flash head or at the aperture on the lens. Comments, please.



Jul 09, 2012 at 10:31 PM
unknown_photog
Offline

Upload & Sell: Off
p.1 #12 · Shooting TTL on an SB-910


Hi! This is one of the reasons I hate TTL, it's so inconsistent. You have to remember that when you are firing your flash you are dealing with two exposures, the ambient light and the flash light.
When you are using TTL, the camera is actually metering the scene and trying to adjust the flash's power to compensate. If you are in Manual mode in the camera, it will try to balance out the flash with the ambient exposure. The reason the flash is underexposed is because you are in a dimly lit room from the looks of it. The camera didn't want to throw out too much flash so that you are able to capture as much ambient light as possible, this is the reason the flash looks underexposed....the camera made a compromise.



Jul 18, 2012 at 01:49 AM





FM Forums | Lighting & Studio Techniques | Join Upload & Sell

    
 

You are not logged in. Login or Register

Username   Password    Retrive password