lastolite ezybox

Dan7312

I've got the small 8.6" Lastolite Ezybox http://www.bhphotovideo.com/c/search?ci=1337&N=4276734332+4291375550+4276734556 on 580EX-II with a Canon 7d and the 24-70L. I'm trying to understand how the Ezbox effects eTTL.

What I have found is that with eTTL and the Ezybox on I have to push the flash compensation to +3 or the images just come out very dark. If I use the flash without the Ezybox the exposure is in the ballpark with FC set to 0.

All of the were with 1/200th shutter, 5.6. 580exII on the camera hot shoe.

I understand that that the Ezybox absorbs some of the light from the flash. What I don't understand is that eTTL should be measuring the light coming back from the scene and boosting up the output to compensate for what the Exbox absorbs.

What is different about using eTTL with the Ezybox?

Thanks in advance



Ezybox on flash with FC 0




Ezybox on flash with FC +3



Bare flash with FC 0

ziggy53

When both camera and flash support E-TTL II, as in your Canon 7D and (I presume) a modern Canon EX series flash, and when the flash is pointed forward and when you use a lens which supplies distance information, the E-TTL II program automation puts extra emphasis on the guide number of the flash and the distance to subject. The flash does not know about any modifier and it will "not completely" compensate for light loss incurred by a flash modifier.

If the flash modifier is used consistently and if you determine a suitable EC offset, it is perfectly appropriate to use that offset if it gets you consistent results.

If you tilt the flash or swivel the flash, the flash program should revert to basic E-TTL which does not use distance information. In this situation the flash exposure is determined by the measuring pre-flash and factoring in the metering program settings and ambient light contribution.

It is for this reason that I do not use flash modifiers on an E-TTL II flash (in E-TTL II mode) which require a straight-ahead orientation for operation.

Dan7312

Thanks Ziggy!

That explains what I'm seeing and it makes sense to me that the flash should work that way.

ziggy53 wrote: »

When both camera and flash support E-TTL II, as in your Canon 7D and (I presume) a modern Canon EX series flash, and when the flash is pointed forward and when you use a lens which supplies distance information, the E-TTL II program automation puts extra emphasis on the guide number of the flash and the distance to subject. The flash does not know about any modifier and it will "not completely" compensate for light loss incurred by a flash modifier.

If the flash modifier is used consistently and if you determine a suitable EC offset, it is perfectly appropriate to use that offset if it gets you consistent results.

If you tilt the flash or swivel the flash, the flash program, should revert to basic E-TTL which does not use distance information. In this situation the flash exposure is determined by the measuring pre-flash and factoring in the metering program settings and ambient light contribution.

It is for this reason that I do not use flash modifiers on an E-TTL II flash (in E-TTL II mode) which require a straight-ahead orientation for operation.

Dan7312

By experimentation I've found that if I use FEL then press the shutter button the camera seems to ignore the distance in calculating the exposure. That is the images with the modifier on appear to have the same brightness as just pressing the shutter button when there is no modifier, though of course the histograms have a different shape.

The Pathfinder references hinted that this might be the case and it does seem to be.

ziggy53 wrote: »

Some Canon lenses also lack distance information. I am not sure where there might be a comprehensive listing of lenses that have distance information.

Please reread my post. I have emphasized the important portions. The E-TTL II does not ignore the TTL component of flash automation but it does put primary flash exposure emphasis on the guide number and distance calculation. The more a flash modifier negatively affects the flash's output, the more you will see underexposure.

Both the exposure mode and the metering program will impact the calculations. I tend to use Aperture priority mode and Evaluative/Matrix metering myself, with some Manual mode thrown in.

I would have to see Joe's comments before I could comment on what he said.



I do believe that Nikon was the innovator of using guide number/distance information in their i-TTL. I am less sure of the exact implications. Since no flash can know the distance from flash to subject in the case of bounced flash I believe that a Nikon flash only allows i-TTL in flash forward position and they revert to Nikon TTL in bounce orientation. Yes, Nikon i-TTL should also be affected by a flash modifier used in forward orientation. I don't know how their exposure and metering modes are affected in any detail.

Check out Pathfinder's sources for Canon E-TTL II information:

http://www.dgrin.com/showthread.php?t=70330&highlight=fill+flash+pathfinder

If we want to pursue the technical aspects any more it would be best to open a thread in the Techniques forum.

ziggy53

Dan7312 wrote: »

By experimentation I've found that if I use FEL then press the shutter button the camera seems to ignore the distance in calculating the exposure. That is the images with the modifier on appear to have the same brightness as just pressing the shutter button when there is no modifier, though of course the histograms have a different shape.

The Pathfinder references hinted that this might be the case and it does seem to be.

Good to know, thanks.

ziggy53

I broke apart the Nikon CLS and Nikon i-TTL discussion and you can find it here:

http://dgrin.com/showthread.php?t=198555