Flash Diffuser

Discussion in 'Beyond the Basics' started by fotogenik, Jun 22, 2006.

  1. fotogenik

    fotogenik TPF Noob!

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    Hello All,

    I recently purchased an omni bounce flash diffuser for my SB600. I figured it would help me with a wedding I am shooting in the coming weeks.

    Outdoor, in the evening with ffading light, I figure I am gonna need flash most of the time.

    Anyway. I am not seeing a lot of difference in my shots with and without the diffuser and am curious what others have seen from them. It is a Stofen Omni-Bounce Diffuser and everyone I have spoken to about them just raves. Maybe I am not looking for the right thing but it just seems very unmodified to me other than a change in color temperature.

    Here are two shots taken from the exact same spot with the exact same settings with and without the diffuser on my flash. Am I doing something wrong? Do I need to adjust my exposure?

    1) With Diffuser



    [​IMG]

    2) Without Diffuser

    [​IMG]

    Anyone take a stab and tell me a correction for what I am seeing?

    EXIF Data is attached to these files in case anyone wants to check the settings. White Balance was set for flash, Aperture Priority with an Aperture of 5.6, Focal Length was zoomed all the way in on my small zoomer lens at 80mm. Interestingly the shutter time was not recorded in exif but it was 1/60th.

    No edits in PS other than resizing for display on the forum and this is full frame no crop. Flash was my SB600 and was not bounced, I aimed it directly forward.

    Thanks,
     
  2. mysteryscribe

    mysteryscribe TPF Noob!

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    one thing always jumps out at me, you lose a stop of light with a defuser at least. Some of them even more. But you also do that with a white cloth or a piece of bond paper. Oh wait they do the same things never mind.

    I personally don't see a lot of difference but most people swear by them. I also don't see a lot of difference in bounce light but it is supposed to be the same kind of light as defusion. Bounce light in my opinion, which isn't worth much, mostly changes the angle of the light and lowers the intensity. Im not all that fond of lowering the intesity but the angle is nice. You can also do that with a very long handled L bracket. But you keep the high intensity of the light. I know I'm hopelessly out of date.

    The other thing that bounce light does is to spread the pattern of light. and defusers do the same. They widen the beam of the light giving you a wider more even coverage of light. So I guess they are okay. You got to compensate for the exposure and shoot it. If you have to shoot a wedding with it, you might have a coverage problem as it cuts the distance your light will carry a bit.

    Let me see if I left out any negative thing. Oh yeah, when you need it, you most likely wont be able to find it. That is the most important one.

    Oh what to do add a stop of exposure to the shot
     
  3. fotogenik

    fotogenik TPF Noob!

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    So maybe try a few shots without the diffuser and see how it goes? I was thinking mostly that the diffuser might be needed for the actually posed shots and I would be fine with any other shots without it.
     
  4. markc

    markc TPF Noob!

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    It's going to be really hard to see the difference in that image. It won't show in the lit areas, but at the edges of shadows, and I only find two that are in the background. Rather than being sharp and harsh, diffuse light will soften the edges. You can see a little of that at the upper right.

    There are several factors that affect how direct or difuse light is. The smaller the source and the further away the source is, the more direct it is. Putting a diffuser on a flash can help, but if it's the same size as the head, the size of the source remains small, so it won't get very diffuse. You can only scatter the light, which weakens it. That's why umbrellas work so well. They become a relatively large light source. And while they do weaken the light, you don't have to scatter the light as much to get the same effect, since they are larger.

    I was having a hard time finding good examples, but here's a couple from this page on the Blender site: http://www.blender.org/documentation/htmlI/x12593.html

    The image under "point light" or "sun light" is a good example of direct, and the image under "area light" is a good example of diffuse.
     
  5. fotogenik

    fotogenik TPF Noob!

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    the thing that struck me the most with the two example photo's was the color shift. Is there a shift or is this something I am simply seeing on a non calibrated monitor at work?

    The diffuser seems to impart a brownish cast to the entire image.
     
  6. markc

    markc TPF Noob!

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    With the diffuser on, you are getting more ambient light into the mix, which is warmer than the flash that the white balance is set for. You'll probably have to use a custom white balance based on the room you are in.
     
  7. fotogenik

    fotogenik TPF Noob!

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    interesting, thanks, Something else I need to learn how to do on my camera LOL.

    Cheers,
     
  8. mysteryscribe

    mysteryscribe TPF Noob!

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    again I have given advice based on film... in film the color shift you see is called being muddy.. it is caused by the shot being underexposed which happens almost all the time with diffusers that aren't compensated for.

    The amount/intensity of light from the flash is less after it is diffused. In the case of film if you dont compensate, you get a thin negative which makes the colors dark and drab. Evidently in digital (which I didn't know, since I know very little about digital) the balance between strobe and daylight changes most likely for the sort of the same reason, the flash is not as powerful as in the first shot so doesn't override the ambient light.

    I would think you could use the strobe on auto and use the manual setting to dial in the exposure for the strobe /defused and not have to worry about custom white balance. I would expect that the ttl function is where you are getting the ambient light. Since the camera is trying to balance the two light sources.

    I would think that if you set an auto strobe up as you would on a film manual camera and compensated the exposure for the defuser you would get exactly the same color in both shots. I tried this when digital got to the 4mpx state and it worked that way for me. But the cameras were much less automated that I tried it on.

    Am I wrong on this, I am seriously curious now. By the way my son in law who is a very serious digital photographer says TTL is very dangerous to the subtle difference so you need to be careful using it. I think he does use it most of the time though. I know he bounces all his flash last wedding was interesting it was in a traditional catholic church. I think he had a little trouble with the 40 foot ceilings lol.
     
  9. markc

    markc TPF Noob!

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    From my understanding, underexposure wouldn't cause a color shift like this. It is a bit muddier, but to me that only means darker, not more brown. You would see the same color shift in film if you used daylght balanced film. White balance isn't something new to digital, just the fact that you can change it on the fly and you can pick a custom one, whereas with film, you can only get what the manufacturers make (usually just daylight/strobe and incandescent).

    If you boost the flash output to compensate for the diffuser, then the color balance will be the same, but that's because you will have the same balance of strobe vs. ambient in both images, just one will have diffuse light.

    Im not sure what he means by "TTL is dangerous". TTL is Through The Lens. It means the light is being measured after it passes through the lens, and not just on some sensor on the flash. It's a much more accurate way to measure the light reaching the film/sensor.
     
  10. Digital Matt

    Digital Matt alter ego: Analog Matt

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    I made a simple diffuser for my flash from a 1 quart soup container (won ton soup). I cut a hole in the lid that is the shape of my flash head, and when I use it, I point the flash straight up, as if to bounce from the ceiling. The light bounces around the soup container and comes out all directions very soft. You do lose several stops of light however, so the flash power is normally all the way up, and I bracket with my aperture.
     
  11. mysteryscribe

    mysteryscribe TPF Noob!

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    maybe its just me but the colors in the picture look muddy ie dark on my screen and muted. Like I have always said I don't pretend to understand digital differences. but it looks underexposed to me.

    my Sil I think, and im not sure, meant the ttl allows a more balanced approach than setting the strobe on auto and manuel exposure. Therefore the color balance tends to change more often. The way I shot strobe with the digital I tried out, was just like I always did with film and had no problems with white balance. But it did look as though someone had used a stobe. His ideal is to look as though he didn't use one. Probably a differnce in thinking more than anything else.

    The original cameras i tried out had set white balance programs not custom. you could get daylight indoor florescent and maybe something else. But being from a film background I just set it up daylight and used an auto strobe and manual settings. It worked fine for me even with multiple studio lights in the studio. Now I'm quite sure what My SIL does is much better than that, but it worked fine when I did it for what I wanted it to do. I don't fault him for all the balancing act he does, he likes that kind of thing.

    By the way I took the image one into my editor and did just the exposure compensation things to it. When I finished the white were white more or less and there was a warmer tone to the color which I would expect from a thin color negative, but I do know that it isnt the same or maybe it is since the room light might invade in any under exposed shot. The shot with the appropriate software change would be a usable shot, if not a perfect match. With a one stop adjustment to the exposure when it was made It most likely would have exposed for the white light and been fine. Again that is based on a totally different perspective and maybe all wrong. If it was me, I would test it after I read all I could find on it. I never trusted anyones opinion till I verified it.
     
  12. Unimaxium

    Unimaxium TPF Noob!

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    MS: You are right that the first frame is underexposed. According to the exif data, the shot settings were identical in the two shots, except that with the first the flash had the diffuser on which caused it to be less powerful. But a slightly underexposed digital capture is not by itself going to cause a brown tone in the image. I believe mark is right in that when the diffuser was used, the flash was less powerful which meant that it did not overpower the ambient incandescent light as much, causing the incandescent light to be more visible in the frame with the diffuser. And that's what caused the redder tone in the image. It's kind of like mixing a recipe (or diluting photo chemicals if you want to think like that ;-) ). Instead of having something like 2 parts flash to 1 part incandescent light, it was 1 part flash to 1 part incandescent (or whatever it really was; I just made those numbers up).

    But maybe that's what you were saying and I just misunderstood you.


    As for advice for Rashadan: What you might want to do is to try taking the flash and diffuser outside and try it out as a fill flash rather than as the main light source. I think it will be easier to compare your results when all of your light sources are of the same color temperature (i.e. the sun and your flash, since flashes are calibrated to output the same color as the sun). Also, try taking some shots closer to your subject. I can see from the exif data that you used a long focal length for these shots (80mm, which is the 35mm equivalent of 120mm). This is probably why the shadows are about equally as harsh in both images. As you get closer, the relative size of your light source gets larger, which means that your shadows will be softer and you'll likely see more of a difference with the diffuser. These are just my guesses, anyway.
     

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