HDR using wireless nikon flash for rim light

[thinkpic]

Hi everyone,

This is my first post so I hope this is the right place for this question. I am experienced in the visual field but relatively new to flash and HDR photography.

I am trying to do a series of tripod based fine art photographs of a full sized artist dummy in various poses using HDR photography. I have a D700 and a couple of SB600 wireless flsh units. Outside of a HDR context I have no problem using the wireless Nikon system (flash on the camera set to commander with the built in flash set to -3 with the 2 groups set to ch3 and the SB600s set to C -> {flash arrow}).

In CS4 (soon to be CS5) I have been successfully automating HDR bracketted sets (shot with the shutter set to high speed continuous). Up until now I have been using available light.

However I now want to use the wireless flashes to add 2 strong rim /side lights to the dummy/subject. The dummy is already in a high contrast situation and for various cretive reasons I want to continue to use HDR.

The problem is I cannot figure out how to set the camera/SB600s so that the flash units sync/fire at a controlled and constant level as the camera (set to aperture priority) automatically brackets the exposure. (Also I have to set the camera to something other than continuous shutter as the flash needs time to re-charge).

Can this be done and if so can anyone help with this? Thanks...

[mistermonday]

Thinkpic, not sure if you have tried Oloneo Photoengine HDR software but it contains a module called Relight. Instead of lighting the entire scene in each bracketed shot, you selectively turn on one or more light sources per frame. Then when you run them through Relight, when the s/w merges the bracketed frames, each light source is isolated and you can change each light sources intensity and color. Not sure if this will solve your problem but you can check it out at Oloneo.com.
Regards, Murray

[thinkpic]

Thanks I will look into it

[RobertAsh]

Originally Posted by thinkpic

The problem is I cannot figure out how to set the camera/SB600s so that the flash units sync/fire at a controlled and constant level as the camera (set to aperture priority) automatically brackets the exposure. (Also I have to set the camera to something other than continuous shutter as the flash needs time to re-charge).

Can this be done and if so can anyone help with this? Thanks...

Have you tried setting your flashes to Manual mode? In Manual mode the flashes should put out the same amount of light every time they flash, then you adjust your aperture larger or smaller to over- or under-expose the image as you prefer.

Or am I misunderstanding your question?

[TheDrift-]

Originally Posted by RobertAsh

Have you tried setting your flashes to Manual mode? In Manual mode the flashes should put out the same amount of light every time they flash, then you adjust your aperture larger or smaller to over- or under-expose the image as you prefer.

Or am I misunderstanding your question?

+1 that was what I was thinking too

[thinkpic]

Thanks for your suggestion but something strange is hapenning. With autobracketing turned off, in the camera's commander menu I set group A to "M" at 1/4 strength. I then set the camera to M with a speed of 1/250th. The wireless SB600 (set to group A) was set up to the side of the subject. I took an exposure. I then changed the shutter speed on the camera to 1/50th and took another shot. The exposure did not appear to change. The metadata shows the speed change from 1/250th to 1/50th but also strangely shows the aperture to have shifted from f5.6 to f5.3 and exposure compensation to have shifted from nothing at 1/50th to +2 at 1/50th. I have duplicated this experiment twice with the same result. Immediately after taking the first exposure the aperture and exposure compensation have automatically reset for the second shot. I never touched either!

Stranger than strange.....I can't figure out what's going on??? Anybody???

[TheDrift-]

I shoot canon so i don't know a lot about nikons, are you shooting the camera and the flash in manual? Sounds like full manual is the way to go here?

[RobertAsh]

Stay in full manual mode for both camera and flash like it seems you're doing, that's the right thing to do. Then you need to change your aperture, not your shutter speed.

--Aperture controls the brightness of the flash.
--Shutter speed controls the brightness of the ambient light.

You use longer shutter speeds if you want to mix some of the ambient light in with the flash, e.g. the background light from a room or a landscape or background outside. You use shorter shutter speeds if you want to black out the ambient light and light only with the flash.

[thinkpic]

Thanks for that.I didn't know this but in this case I don't think this will work. won't changing the aperture change the depth of field? I need all of the images to be identical for the HDR to work properly.

Also, out of curiosity I wonder why, when a) the camera is set in manual mode b) the built-in flash is up and set to commander and c) the flash group is set to manual, the camera is automatically changing aperture and exposure compensation?

[RobertAsh]

Originally Posted by thinkpic

Thanks for that.I didn't know this but in this case I don't think this will work. won't changing the aperture change the depth of field? I need all of the images to be identical for the HDR to work properly.

Also, out of curiosity I wonder why, when a) the camera is set in manual mode b) the built-in flash is up and set to commander and c) the flash group is set to manual, the camera is automatically changing aperture and exposure compensation?

Ok. Then change your flash output to 1/2 or 1/4 power or whatever works from one shot to the next, or change your ISO. And your flashes should not be changing their light output if you wait until they're fully charged before making another exposure.

I think you have to still have something still set to some auto-setting. If you're shooting with your camera set to M and your flashes on full Manual mode with no flash or exposure compensation in the camera or any of the flashes then your camera shouldn't be changing aperture, shutter speed or ISO.

That said, i have had issues with the Commander mode of my D300 on-camera flash actually adding light to the scene at very close distances, which is why I now use Pocket Wizards. I use studio strobes much more than small flashes so I haven't bothered to figure out what's causing that, but I really should get to the bottom of it before I really need multiple small flashes for something....

[mistermonday]

Thinkpic, with HDR you want to keep the aperature fixed. As for the strange behavior, go into your Shooting menu and make sure that Auto ISO is disabled.
Regards, Murray

[thinkpic]

The mystery of the changing aperture and exposure compensation has been solved. I am embarrassed but it seems I forgot to turn off bracketing on the D700 so that was resorting to exposure compensation for the bracketing. I will understand if you all ignore my posts from now on, but there are so many peramaters I fell into the trap of making such a rudimentary mistake!!

Having said that I can't understand what exposure compensation was actually doing in autobracket mode - while I was manually setting the shutter speed from 1/250th to 1/50th the aperture only altered by a fraction of a stop yet the ambient light stayed basically constant.

Also, I still do not have a solution for bracketing these shots with wireless flash induced rim light but maybe Nikon can help. Thaks again everyone for your interest and help.

[RobertAsh]

You need to manually turn down the power of your flash(es) between each exposure. First exposure, full power. 2nd at 1/2 or 1/4 power, etc.

For auto-bracket the camera is likely remembering the previous settings and going from there. Also, as Murray suggested, it might have been resetting the ISO. You might want to check the EXIF information of one of the bracketed series you shot, that might tell you.

[thinkpic]

With everyone's help and some perseverance I have finally cracked it!

It takes a very detailed approach. I must have been overlooking one thing or another until now but here is the solution for a 5 exposure bracket with each exposure seperated by 1 stop. For my test I was using a small sculpture with the flash 3/4 back for the rim and shooting inside (it was a small subject, the flash was close and I was shooting in low ambient light to the flash had to be dialled right back to -128 but I suppose the principal would remain the same no matter what and where I was shooting:

Setting on the camera:

1. Set exposure mode to manual.
2. Set speed to 1/250th
3. Turn off auto ISO
4. Flash sync speed set to 1/250th
5. Flash shutter speed set to 1/60th.
6. Flash control for built in flash set to commander mode
7. Commander mode set as follows:
- Built in flash set to TTL -3.0 compensation
- Group A set to M with compensation set very low (in my case to 1/128th)
8. Autobracketing set to 0F - which I believe means it is off.
9. White balance set to something constant
10. No exposure compensation

Settings on the flash:

1. Set to commander mode.

To Shoot:

1. Set ISO and aperture so that image is underexposed by 2 stops at 1/250th of a second.

Actuate. (2 stops under)

Reduce speed to 1/125th

Actuate (1 stop under)

Reduce speed to 1/60th

Actuate (correct exposure)

Reduce Speed to 1/30th

Actuate (1 stop over)

Reduce Speed to 1/15th

Actuate (2 stops over)

And there you have it a 5 pix bracket with nikon wireless flash providing rim light suitable for HDR photography.

Thanks Robert adn Murray again for your help

[RobertAsh]

Ahhh. Ok. So if I understand you correctly what you're doing is HDR'ing for the background and maybe as well for the statue's shadows, not for the statue highlights. That part I didn't know I was assuming you were HDR'ing only the statue.

Well, whatcha waitin' for? Post some results!!

[thinkpic]

I've just got my smoking new i7 with an ssdscratch disk and 16 gigs of ram. I'm configuring it then doing some test and then I will have ago at this. Thanks for the help.