Canon ettl Help

[jdcpa]

The environment:
I placed a tarp over the deep end of our pool, so that I would not have a stark white environment. With it, the light was not bad, but not great. Obviously the water was clear and no particulate matter.

The Camera Setup:
Canon 40D, with 100mm macro f2.8 lens, dual DS-125 Ikelite strobes in an Ikelite housing, with dual sync cord. Strobes were set to ttl.

The subject:
I placed small plastic fish on the bottom of the pool to shoot pictures. My intent was to work on depth of filed underwater.

The Problem:
Shooting at a distance of three feet or less I got the following problems.
Set to a shutter speed of 1/160, the camera determined an f stop of between 2.8 and 3.5. Obviously too open for good depth of field.
Set to an aperture of f9, the camera determined a shutter speed of 1/60 or less. At f11, it was down to as low as 1/15. Too slow for hand held.
Set to manual at 1/125 and f/11, the camera read underexpose by at least two stops. But, the pictures were perfectly exposed, good histogram. Good depth of field.
It was the same answer with all metering settings.
With the M settings, I was even getting the camera attempting to reset the shutter speed in some instances and the strobes were short firing.
I could not get the camera to read the light correctly.

The Solution:
Beats the heck out of me. Any suggestions would be greatly appreciated.
How do I trick the camera while it is trying to trick me?
What am I doing wrong?
Thanks for the help.

PSAny pros in the Tampa Bay area?)

 

[gogums]

I think the issue here is you were in Av or Tv mode and the camera is metering for the amount of available ambient light. The camera is doing exactly what you told it to do. You set shutter speed (1/160) in Tv and camera gives you a f/stop (f/2.8) that will produce a properly exposed image using available ambient light. Albeit with too shallow a DOF.

In Av, you set the f/stop to f/9 for increased DOF so now you are telling the camera to set the proper shutter speed to give you a properly exposed image using available ambient light. Which it did. It centered the needle on the meter at 1/15th of a second. Too slow to stop motion or eliminate camera shake.

In both these modes the camera is metering for ambient light only. The camera has no idea you are about to add light to the scene via a strobe, it expects the light it "sees" reflected back through the lens to be the only source of light for the image.

What you want to do is minimize or eliminate the amount to ambient light hitting your sensor and expose the scene soley with light from your strobe. There simply just isn't enough available ambient light to properly expose a macro scene that requires large DOF and enough shutter speed to eliminate camera shake and freeze action.

Best way to do that is camera in Manual mode. So in your example when you went to M mode and set a shutter speed of 1/125 and f/11 the little indicator line on your meter scale was probably pushed all the way to the left and most likely blinking. Essentially telling you if you trip the shutter you will be rewarded with a black picture.
Again that is because the camera has no idea you are about to add flash to the scene and it is strictly relaying info to you on the amount of available light it sees reflected back through the lens. At 1/125 and f/11 the camera is screaming at you that it is pitch black! Not a problem, because you know something the camera doesn't. You know you'll be adding artificial light to the illuminate the scene once the shutter opens.

By going full M on the camera you control how much ambient light you want to register on the sensor, which is many cases, means little to none. Thus I'd recommend staying in M mode and keeping shutter speeds at sync level (1/250 for 40D I believe) and aperture at f/8 to f/11. This will most likely eliminate any ambient contribution and allow the flash in ETTL to properly expose the image.

Your meter will only jump around in M mode if you are swinging your camera around to areas of light then dark areas. In M mode the camera isn't trying to give you the proper exposure it simply reads the ambient like reflected off whatever you have the camera pointed at and the needle responds appropriately. Point it at a bright subject needle jumps towards the center or to the right. Point it at a dark subject it stays buried on the left side of the scale.

Hope this makes a little sense and I haven't wasted your time telling you something you already know! Good luck you have an awesome rig. I'm trying to get into the rig for my 5D!

Aloha,
Greg

The environment:
I placed a tarp over the deep end of our pool, so that I would not have a stark white environment. With it, the light was not bad, but not great. Obviously the water was clear and no particulate matter.

The Camera Setup:
Canon 40D, with 100mm macro f2.8 lens, dual DS-125 Ikelite strobes in an Ikelite housing, with dual sync cord. Strobes were set to ttl.

The subject:
I placed small plastic fish on the bottom of the pool to shoot pictures. My intent was to work on depth of filed underwater.

The Problem:
Shooting at a distance of three feet or less I got the following problems.
Set to a shutter speed of 1/160, the camera determined an f stop of between 2.8 and 3.5. Obviously too open for good depth of field.
Set to an aperture of f9, the camera determined a shutter speed of 1/60 or less. At f11, it was down to as low as 1/15. Too slow for hand held.
Set to manual at 1/125 and f/11, the camera read underexpose by at least two stops. But, the pictures were perfectly exposed, good histogram. Good depth of field.
It was the same answer with all metering settings.
With the M settings, I was even getting the camera attempting to reset the shutter speed in some instances and the strobes were short firing.
I could not get the camera to read the light correctly.

The Solution:
Beats the heck out of me. Any suggestions would be greatly appreciated.
How do I trick the camera while it is trying to trick me?
What am I doing wrong?
Thanks for the help.

PSAny pros in the Tampa Bay area?)

 

[jdcpa]

Thanks.

I apprecaite the help.