Way overexposing with Omnibounce diffuser & Sigma EF500

[NeoteriX]

For some reason, when I try using bounce shots with my Sigma EF500 Super I just got in plus the Omnibounce diffuser, the shots seem to be really overexposing. When I take a shot with the setup, you can hear the capacitor fully discharge and the whine of it recycling. When I take a bounce shot or otherwise without the diffuser, it's a typical shot and doesn't overexpose. I have to turn the on flash FEC to like -2 for it to resemble a diffuserless shot.

Also, an aside question -- is the FEC adjustment on camera and the one on flash one and the same or are they adjusting different things?

[David1943]

Are you covering the sensor on the front of your flash gun with anything (perhaps your hand) when you have the diffuser attached? If the sensor is ubstructed, it won't be able to detect light reflected back from your subject and will allow maximum exposure from the flash.

Regards, David :)

[NeoteriX]

Are you covering the sensor on the front of your flash gun with anything (perhaps your hand) when you have the diffuser attached? If the sensor is ubstructed, it won't be able to detect light reflected back from your subject and will allow maximum exposure from the flash.

Regards, David :)

David, thanks for the response -- I've checked and it doesn't appear that I am covering anything. If I take a shot with the flash without the diffuser and take the same shot w/ the diffuser, holding the camera the same way, there's a clear difference in exposure -- and it's not underexposure like you would think. I'll post up 2 pics in a little bit.

Edit: Added pics below. 1st shot is a bounced flash w/out diffuser. 2nd shot is a bounced flash w/ Omnibounce diffuser. 3rd shot is of the flash with the diffuser on it.

http://www.pbase.com/neoterix/image/46468490/original.jpg
http://www.pbase.com/neoterix/image/46468491/original.jpg
http://www.pbase.com/neoterix/image/46468492/original.jpg

[David1943]

Yes, there is a big difference in the two pictures and, like you, I'm now at a loss to suggest anything. Hopefully, some others will be able to help.

I'm interested myself because I'm thinking about getting an Omnibounce to use with my Canon 550EX.

Regards, David :)

[glenhead]

I ran into the same issue with my 540EZ on my A2E, and learned the answer from another forum. When you put a Speedlight or equivalent in vertical mode, it loses its zoom, and it flashes at top power. With just the flash on bounce, you're depending on the somewhat-reflective surfaces surrounding the subject to provide illumination, and you really don't get any direct lighting onto the subject. When you put the Omnibounce on it, the diffusion redirects enough light straight ahead that it can really smack a fairly close subject, especially with the inherent power of the 500 Super. You have a few options: back off from your subject (if possible), experiment with flach compensation, or swivel the head of the flash (with the Omnibounce on it) and tilt it a bit to decrease the forward-blasting light. I ended up turning the head of my 540EZ around 180 degrees and just barely tilting it back from straight vertical to make it work - with a film camera, it wasn't much fun experimenting. I eventually went with a Lumiquest ProMax bounce to get the finer control over shots. I still use the Omnibounce to soften the flash for other uses, though.

HTH!

[Jon]

Assuming the helmet's white, the first shot looks underexposed and the second looks better. White is white and black shows some details. You're losing shadows on the helmet with the Omnibounce because it's throwing some light directly at the helmet, and it's basically functioning as a bare bulb, not really bouncing off the ceiling which is why it's running at full power.

[NeoteriX]

Jon,

Looking at the pics again with a CRT monitor at work instead of my usual LCD, the pics do look as you describe -- underexposed on the first and correctly exposed on the bottom. However, in the histogram when shooting the two, there is a huge spike in the shot with the Omnibounce in the far right -- that there is a large portion of the shot that is completely blown out. I'll try posting up the histograms to see if that helps.

[lostdoggy]

Its should be unstandable that you re getting a "huge spike on the right" since the helmet is white. The right side represents the white and the left side represents the black and the middle is midtones that are neither of the extreme.
Does the flash actually fire at full power??? or does the ETTL control the exposure??? The preflash should've measure the exposure, which is the distance of the flash to the ceiling down to the subject and bouncing it to the Exposure sensor, that is a long distance to travel. So yes it is at full power. Try shooting the same subject but with a smaller aperature.

[jdouglas003]

I have had the Sigma EF500 and Canon 20d for about 6 months and I have been having problems with the flash consitantly underexposing by about one stop. I have use the Stofen Omnibounce and Lumiquest Pocket Bouce and while using each the flash seem to gain a stop, which worked for me because was having the underexposure problem.

I have since determined that even using the flip down diffusion screen that came with the flash causes it to gain a stop or so. Additionally, I have come to the conclusion that whenever the flash is used with any type of on flash diffusion it gains a stop or so. This is not scientific but it seems to be true for my flash.

I also rented a Canon 550 and the same was true with it as well as using the Sigma flash with my 300 digital rebel.

I have just ordered another Sigma flash and I expect the same will be true with it also.

I have just learned to work around this oddity. At least it's fairly consistent and predictable.

If someone could explain this though it would be great.

[willg]

my guess is that a lot of your light without the diffuser is being lost to the ceiling and when you have the diffuser on it spreads the light more evenly around so you actually get some head on to the subject....picture for reference...red is without diffuser, blue is with a diffuser

http://www.spideronthefloor.com/upload/files/flash.jpg



(i have no idea why i made that picture...its late and i should go to sleep)

[AjP]

my thoughts is that helmet white with black, hardest thing to photograph, same things during weddings, try to play with custom WB, greay card and of cause different setting of flash

[glenhead]

The example with the red and blue arrows is pretty much what I was talking about - the diffuser actually makes some of the light go forwards. Prove it to yourself - put the flash in bounce position without the Omnibounce, hold it with the top edge of the flash above eye level (where you can't see the lens on the flash), look at the top edge of the flash (where you would mount the Omnibounce) and trigger it. It'll make a nice flash in the room, but you won't have an after-image of the flash. Put the Omnibounce on, hold it at the same level, and look at the same spot on the edge of the flash. Trigger it again, and be ready to have a nice after-image of the Omnibounce in your vision for a while - there's a huge difference in the light that comes forward.

Messing with FEC and/or tilt/swivel is the surest way to get used to what the Omnibounce does. It's a really good little widget, and you can get some really nicely-lit subjects, but you do have to figure out how it acts at what distance with your particular setup. Take a couple of dozen shots at varying angles and distances, document what you did, and see which you like best. That's what I did many moon ago with my Elan IIe - just be glad you're not doing it with film!

[NeoteriX]

Wow, thanks for the explaination guys, the visual really helps :) Your insomnia is well appreciated, WillG

[Jwreich]

I am having the same issue. It is great to read this post. It makes good sense when the flash is in a bounce angle that it will increase the output. Come to think about it, I always keep mine in a bounce angle thinking I reducing the amount of light on my subject. I always keep my FEC @ -2 because at 0 FEC it is over exposed.

HMM, I must do some more tests...

[scottbergerphoto]

Adding an Omnibounce reduces a flash's max capacity by two stops so you can't explain this by the light being thrown forward by the omnibounce. If that was the case, the Omnibounce would increase your flash capacity. Remember that flash output is controlled by ETTL. That means that the amount of Preflash that returns to the camera from the subject determines the flash output. Less preflash return means more flash output. I suspect that what's happening is that the omnibounce in diffusing the preflash, is causing less preflash to return to the camera. That results in a larger flash output. To test this, put your flash in Manual mode to eliminate the preflash and see which power setting is needed with and without the diffuser to get an adequate exposure. I'd bet that without the Omnibounce you need less flash power by about 2 stops, the opposite of what you are seeing in ETTL.

[Jwreich]

I'll give it a try and see what happens. You know I can't even tell that my I have a "Pre Flash"...

[scottbergerphoto]

I'll give it a try and see what happens. You know I can't even tell that my I have a "Pre Flash"...
If you want to seee a preflash, hit FEL, that sets off the preflash in advance of the shutter button. You can also set your camera to second curtain sync, with a long exposure time (1/2 sec).

[Jwreich]

Scott,

Bad News for me! I pull off the omni bounce and load fresh batteries into my Sigma and a borrowed 550ex. I set both to full auto. Every shot taken with the sigma straight on the subject is so blown out, it almost looks completely white.

Every shot with the 550ex looks great. Long zoom, short zoom anything looks good.

I am very SAD. If I bounce the Sigma it shows 50mm focal length and the shots look better. When I have the flash in bounce mode with the omni bounce and FEC @ 0 it looks like the Canon.

I'm so beside myself I don't know what to try next. Can you please give me some advice.

[gmaize]

For some reason, when I try using bounce shots with my Sigma EF500 Super I just got in plus the Omnibounce diffuser, the shots seem to be really overexposing. When I take a shot with the setup, you can hear the capacitor fully discharge and the whine of it recycling. When I take a bounce shot or otherwise without the diffuser, it's a typical shot and doesn't overexpose. I have to turn the on flash FEC to like -2 for it to resemble a diffuserless shot.

Also, an aside question -- is the FEC adjustment on camera and the one on flash one and the same or are they adjusting different things?


Does anyone have an answer to NeoteriX's second question. I have often wondered the same thing about FEC on camera vs. on flash.

Thanks much!

--gmaize

[Jwreich]

FEC on the camera is the same as the one on the flash. If your flash is set to Auto, it will take direction from the camera. The FEC on the Flash is for tweaking or Manual operation.

[gmaize]

Jwreich,

Thanks for the clarity

[jdouglas003]

scottburgerphoto wrote-
I suspect that what's happening is that the omnibounce in diffusing the preflash, is causing less preflash to return to the camera. That results in a larger flash output.

If I diffuse by bouncing directly off of the ceiling without the Omnibounce or Pocketbouncer my Sigma flashes consistently underexposes, just as they do with direct flash. It would seem that by bouncing directly off of a ceiling could cause even less preflash to return. If I diffuse using any type of on flash diffusion (Pocketbouncer, Omnibounce, builtin flip down panel) the Sigma flashes consistently gain about one stop. With this in mind I don't see how your theory could be valid (just guessing:)).

Jwreich-
I have two Sigma flashes and neither one of them ever overexposes without fec or my on camera setting being off. They generally underexpose by about one stop. This is consitent on both my 20d and my 300 rebel. I've also rented a Canon 550ex and it behaved exactly as the Sigma flashes. If your flash is overexposing there may be something set wrong on your camera or your flash may be defective but I'm just guessing. I have read many posts on various forums about the Canon flash systems and I can't recall any having overexposure problems, most all that I've seen have underexposure problems.

[Jwreich]

Jdouglas003,

With the omnibounce off of my flash, I'm happy with the results compared to the 550ex. My Sigma even looks good with the Fong LSII. The Omni Bounce ontheotherhand, really stops down the preflash and causes the flash to trigger at max power. This is the only thing I can think of. It appears the LSII may be my answer as it provided consistant results...

[robertwgross]

I ran into the same issue with my 540EZ on my A2E, and learned the answer from another forum. When you put a Speedlight or equivalent in vertical mode, it loses its zoom, and it flashes at top power.

A Speedlight is a Nikon flash unit. Is that what you are using?

A Speedlite is a Canon flash unit. Your 540EZ is typical of the flash units made a few years ago for film cameras. The newer Speedlites, such as 550EX for digital cameras, do not have any zoom problem in vertical mode.

---Bob Gross---

[scottbergerphoto]

FEC on the camera is the same as the one on the flash. If your flash is set to Auto, it will take direction from the camera. The FEC on the Flash is for tweaking or Manual operation.
That is incorrect. FEC set on the 550EX overrides any setting on the camera. FEC=FEC regardless of where it is set.

[scottbergerphoto]

scottburgerphoto wrote-
I suspect that what's happening is that the omnibounce in diffusing the preflash, is causing less preflash to return to the camera. That results in a larger flash output.

If I diffuse by bouncing directly off of the ceiling without the Omnibounce or Pocketbouncer my Sigma flashes consistently underexposes, just as they do with direct flash. It would seem that by bouncing directly off of a ceiling could cause even less preflash to return. If I diffuse using any type of on flash diffusion (Pocketbouncer, Omnibounce, builtin flip down panel) the Sigma flashes consistently gain about one stop. With this in mind I don't see how your theory could be valid (just guessing:)).


That proves my point. Go back to my original post. You are using the Omnibounce as a diffuser. It costs you 2 stops of light in total flash output and preflash. That means that via loss of power and diffusuion less direct light is striking the subject to be reflected back to the camera. As long as you stay within the reduced range of the flash, that results in a brighter flash output. You won't see any reduction in the actual flash until you exceed the reduced Guide Number of the flash. It's really simple if you think about how the flash is regulated.
Your non diffused shots are slightly underexposed because ETTL is set up to give you a slight underexposure. I routinely have to add about 1 stop to my shots.

Here's a simple test: Take your camera, flash and some non flammable diffusion material. Put the diffusion material over the flash head, press FEL, remove the material and take a picture. Next without the diffusion material press FEL, and take the same picture. Which one is brighter?
The Preflash is reduced in intensity by the diffusion material resulting in a brighter picture.

By the way, I haven't seen anyone report back on the previous test I suggested, to take the same pictures in Manual Flash mode. If you put the flash in Manual Mode, the same power setting for both shots, bounce position, one shot with Omnibounce and one without, the results will be exactly the opposite of what you get in ETTL. The shot with the Omnibounce will be darker. Why? No Preflash in Manual Mode.

So stop guessing and take some pictures. ;)

[Jwreich]

That is incorrect. FEC set on the 550EX overrides any setting on the camera. FEC=FEC regardless of where it is set.

Scott, Is what I was trying to say. I just didn't get my point across in a clear manner.

Regards,