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FORUMS General Gear Talk Flash and Studio Lighting 
Thread started 25 Dec 2013 (Wednesday) 08:25
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Stofen and ETTL?

 
Roxie2401
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Dec 25, 2013 08:25 |  #1

What effect does using a diffuser like a Stofen have on a Speedlight (580EX II) and ETTL?

I just noticed that my exposures are much darker when I have the Stofen on the flash (pointed straight ahead). I'm assuming that since the flash does not "know" that the diffuser is on the head, it is still calculating flash output as it would if there was nothing on the flash. Does that make sense, hence, the "loss of light" or darker exposures?

Is there a set formula/technique for compensating for using the Stofen?

UPDATE: The exposure seems "just ok" with the lens wide (24mm) but really dark exposure when zoomed (105 end) with the Stofen. Really confused about ETTL now.

I'm using 580EX II, Canon 5D MK III, 24-105, and shooting in Manual mode (typical f/8 @ 100-160).


Related question, but does ETTL still work when the flash is in "bounce" mode (up to the ceiling)?

Thanks very much. Sorry for the very basic questions - but I'm really new to speedlight use.




  
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SkipD
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Dec 25, 2013 09:08 |  #2

Roxie2401 wrote in post #16552866 (external link)
What effect does using a diffuser like a Stofen have on a Speedlight (580EX II) and ETTL?

Unless you have nearby (preferably white) surfaces such as walls and ceiling, the net effect of any of the 'tupperware' diffusers is simply reducing the output of the Speedlite and wasting battery energy. This is because the diffuser does nothing more than scatter the available light from the Speedlite in all directions. Any of that light that is not reflected back toward the subject is lost forever.

Roxie2401 wrote in post #16552866 (external link)
I just noticed that my exposures are much darker when I have the Stofen on the flash (pointed straight ahead). I'm assuming that since the flash does not "know" that the diffuser is on the head, it is still calculating flash output as it would if there was nothing on the flash. Does that make sense, hence, the "loss of light" or darker exposures?

If you are using ETTL with the Stofen mounted to the flash and still have under-exposed images, you're probably too far from the subject (see above comment).

You apparently don't understand the way ETTL works. When you push the shutter release button, the flash emits a "pre-flash" burst that is analyzed by the camera. Then, the camera tells the Speedlite how long to stay on (up to 100% of its normal burst - there is no more) to properly expose the subject. If you are too far from the subject (or if the output of the Speedlite is limited by something like the Stofen attached to it), there simply may not be enough light from the Speedlite (or Speedlite/diffuser combination) to properly illuminate the subject with the currently selected ISO setting in the camera.

Roxie2401 wrote in post #16552866 (external link)
Related question, but does ETTL still work when the flash is in "bounce" mode (up to the ceiling)?

Yes. Read the comment above.


Skip Douglas
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Roxie2401
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Dec 25, 2013 09:46 as a reply to  @ SkipD's post |  #3

Skip,

Thanks. If I'm correct, my eye won't see the pre-flash?

Simple situation - medium sized living room, dog laying at far end. With Stofen attached and flash pointed straight ahead - @ 24mm I get good exposure but @105mm really dark exposure. Remove the Stofen and both ends of the lens are good image exposure.

I sort of figured the Stofen was reducing the output but why only at the far end did I see a reduction?

Guess I was trying to soften the light by using the "tupperware" device but based on your comments - throw the thing away and let the camera and flash work together?

Its strange that you tend to see the "Pros" all using the diffuser...........to what end?

Appreciate your response. 19 degrees here - hope its better where you are.

Tom




  
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Roxie2401
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Dec 25, 2013 10:07 as a reply to  @ Roxie2401's post |  #4

Skip,

One more question - is it possible that the Stofen is actually spreading/diffusing the pre-flash, too?

Or, could there be something that is reflecting the pre-flash differently when I zoom in on the subject that is telling the ETTL reading to reduce the flash power - for example, a TV screen in the frame when @24mm vs @105 - its reflection is more affecting for the ETTL reading?

I keep looking around the room and see shiny objects (brass, or even lights on the tree) that may reflect more on the tighter frame...........




  
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Dec 25, 2013 10:25 |  #5

ETTL II doesn't care what modifier you have on there, it will still work. However like SkipD said you may be throwing away too much light with the modifier which means you aren't getting enough light on your subject.

Your preflash will be affected by the same modifiers the main flash is affected by, it's all coming out of the same place.


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Hoppy1
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Dec 25, 2013 10:52 |  #6

When the flash is pointing straight ahead, as you say, E-TTL uses focusing distance information as a priority factor in exposure calculation, overriding the pre-flash feedback. Which is normally a very accurate way of measuring direct flash - unless of course, there is a Stofen fitted that the camera doesn't know about.

Try this: press the tilt/swivel release button and check the distance scale on the gun's LCD. It should go out, as it now thinks you are tilting and bouncing the flash and distance information is therefore useless for exposure calcs. Keep the button held in while the picture is taken, and this will force the camera to use only pre-flash feedback. Good exposure will be restored :)

BTW, a Stofen should never be used pointing directly forward, but upright to the ceiling, or angled slightly forward if there's a bit more distance to the subject.


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Roxie2401
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Dec 25, 2013 11:11 as a reply to  @ Hoppy1's post |  #7

Hoppy1,

Thanks - your one comment - "BTW, a Stofen should never be used pointing directly forward,"

Can you say why? I keep seeing what I'll call "Press Photo" people using the Stofen and its usually straight forward.

You got me curious.

As to all the other responses - I sincerely appreciate them and am going to spend more time today reading about diffusers and ETTL.

Thanks to all for taking the time to respond.




  
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Snydremark
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Dec 25, 2013 11:22 |  #8

IMO, the Stofen should just never be used....it doesn't even do what it's purported to do.

TTL on a 580EXII; 35mm, 7D, Flash WB - exposed to kill ambient and only show results of modifications to the flash light production:

Straight flash:

IMAGE: https://dl.dropboxusercontent.com/u/60553404/Photos/samples/Bare%20flash%20direct-9518.jpg

Straight flash with Stofen:
IMAGE: https://dl.dropboxusercontent.com/u/60553404/Photos/samples/Stofen%20direct-9519.jpg

Note that it didn't change or soften the shadows at all; the only effect it had was warming the image up noticeably

Bounced flash, bare:
IMAGE: https://dl.dropboxusercontent.com/u/60553404/Photos/samples/Bare%20flash%20bounced-9520.jpg

Bounced flash w/ Stofen:
IMAGE: https://dl.dropboxusercontent.com/u/60553404/Photos/samples/Stofen%20bounced-9521.jpg

Here, it actually creates harsher shadows than the bare flash. Oddly enough, it also cooled the image compared to the bare flash. This result did, honestly, surprise me to the point that I shot a handful of follow up shots to see if it was repeatable; which it was. Odd.

- Eric S.: My Birds/Wildlife (external link) (7D MkII/5D IV, Canon 10-22 f/3.5-4.5, Canon 24-105L f/4 IS, Canon 70-200L f/2.8 IS MkII, Canon 100-400L f/4.5-5.6 IS I/II)
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SkipD
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Dec 25, 2013 13:56 |  #9

Roxie2401 wrote in post #16553137 (external link)
Can you say why? I keep seeing what I'll call "Press Photo" people using the Stofen and its usually straight forward.

Based on my observations, I think that a LOT of folks - even a fair percentage of the working pros using on-camera flash - don't have a clue about what a diffuser stuck on a Speedlite flash unit actually does. The marketing folks tend to bamboozle a lot of folks into becoming paying customers.

The ONLY thing that "softens" shadows is a larger light source. A reflection off a large surface such as a wall creates that larger source. A silly piece of plastic attached to the flash that does not increase the effective area of the flash source (and without nearby reflective surfaces to return a significant amount of the "diffused" light to the subject) does absolutely nothing to soften shadows.


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Hoppy1
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Dec 25, 2013 15:21 |  #10

Roxie2401 wrote in post #16553137 (external link)
Hoppy1,

Thanks - your one comment - "BTW, a Stofen should never be used pointing directly forward,"

Can you say why? I keep seeing what I'll call "Press Photo" people using the Stofen and its usually straight forward.

You got me curious.

As to all the other responses - I sincerely appreciate them and am going to spend more time today reading about diffusers and ETTL.

Thanks to all for taking the time to respond.

What Skip said really - even some professionals don't know how their kits works ;)

All flash 'diffusers' and bounce devices work in the same basic way, and are almost totally dependent on the environment they're used in for the quality of results (though marketers usually forget to mention this). They soften the light by spreading it all around so that a lot of it bounces off surrounding surfaces, making them effectively large light sources, and that's what really softens the light and lightens the shadows.

Easy test - take a portrait outdoors when it's dark. There will be no light bouncing back as there are no nearby surfaces for it to bounce off, and given that a Stofen doesn't actually increase the size of the flash head significantly, the result will be exactly the same as using direct flash without the Stofen. Then take the subject indoors and shoot the same picture in a smallish room with light-toned walls and white ceiling. Aim the gun straight up, and the result will be dramatically different/better/softe​r. While you're at it, take the same shot with the flash pointing forwards at 45 degrees, and again with it pointing straight at the subject. See how the result changes.

The reason why Stofens should not be pointed straight at the subject, but directly towards the primary bounce surface (ie, preferably a normal height white ceiling) is because they have another good trick to play. They're designed to send most of the light towards the bounce surface, and at the same time send a small proportion directly towards the subject. So you get nice soft light from above, but the direct component lifts the shadows under eyes and chins and puts a nice sparkle in the eyes. Using the pull-out bounce card built in to the flash head works in much the same way.

In the right environment, Stofens work pretty well. There are better devices, offering better results and more versatility (eg Lumiquest QuikBounce) but nothing else is as cheap or easy/foolproof, or as small and robust in a press scrum.


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Roxie2401
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Dec 25, 2013 15:31 |  #11

Hoppy1 wrote in post #16553521 (external link)
What Skip said really - even some professionals don't know how their kits works ;)

The reason why Stofens should not be pointed straight at the subject, but directly towards the primary bounce surface (ie, preferably a normal height white ceiling) is because they have another good trick to play. They're designed to send most of the light towards the bounce surface, and at the same time send a small proportion directly towards the subject. So you get nice soft light from above, but the direct component lifts the shadows under eyes and chins and puts a nice sparkle in the eyes. Using the pull-out bounce card built in to the flash head works in much the same way.


If I'm reading this correctly, isn't this the same effect I get if I don't use the Stofen and point the flash head up at the ceiling and pull the little white card up on the flash? Isn't that little card sending some of the light forward?

As to your tests - are they with the Stofen or without?




  
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Hoppy1
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Dec 25, 2013 15:40 |  #12

Roxie2401 wrote in post #16553531 (external link)
If I'm reading this correctly, isn't this the same effect I get if I don't use the Stofen and point the flash head up at the ceiling and pull the little white card up on the flash? Isn't that little card sending some of the light forward?

As to your tests - are they with the Stofen or without?

Yes, to both questions.


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CliveyBoy
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Dec 25, 2013 15:55 |  #13

Snydremark wrote in post #16553159 (external link)
IMO, the Stofen should just never be used.

Here are two uses: as a weak light source in a table lamp, and as a shadow-reducer behind furniture. Both off-camera in architectural shots. It's contribution here is to disperse, not diffuse the light.

IMO, the plastic cap diffuser is of little value - it makes only a tiny increase in the apparent light source. Something like the Lumiquest ProMax reflector increases the light source to almost the width of the human face, and helps avoid high-contrasting of pimples, etc.


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Roxie2401
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Dec 25, 2013 17:49 as a reply to  @ CliveyBoy's post |  #14

Going back to Skip's original comments about the pre-flash and the Stofen reducing the amount of output, I found this comment about the LumiQuest Promax and now I'm totally confused:

"No exposure compensation is required when shooting with TTL exposure control, but SoftBox III will interfere with the on flash auto exposure sensor and autofocus assist. Approximate light loss is 1.25 stops."

If this device (and I assume the Stofen, too) reduces light, as in "light loss is 1.25 stops" how do they explain the "No exposure compensation is required when shooting with TTL"?

Does the modifier reduce the pre-flash by the same amount and therefore, no compensation for the final output?

Sorry, I guess I really don't understand, but unless the pre-flash is reduced, I don't see how the ETTL calculation "knows" there is a diffuser attached.

Based on the Promax statement, I would think you would need to bump the FEC up by 1.25 stops - unless, as Skip said, it was already at 100% and there just isn't anymore power available.

What am I missing?




  
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Snydremark
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Dec 25, 2013 17:49 |  #15

Even behind furniture it would seem better to just bounce it off the base of a nearby wall, I'd think. Just doesn't appear to do anything useful that can't be done cheaper by other methods.

As for pointing the Stofen toward the primary bounce surface, that isn't even born out in the test I did above. It actually performed worse, by giving the same result as direct flash, more like what you described in your outdoor scenario. My replacement for that ill-informed decision was, in fact, the Lumiquest bundle, too. I was going to play around with it today, but folks showed up before I could.


- Eric S.: My Birds/Wildlife (external link) (7D MkII/5D IV, Canon 10-22 f/3.5-4.5, Canon 24-105L f/4 IS, Canon 70-200L f/2.8 IS MkII, Canon 100-400L f/4.5-5.6 IS I/II)
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Stofen and ETTL?
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