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Why so much +ev comp needed?

Discussion in 'General flash photography, lighting, and technique' started by keko, Jul 12, 2008.

  1. keko

    keko

    143
    Jul 20, 2007
    Barcelona
    Just received my brand new Sb-800 and Sb-600...

    Firing a few test shots around the house using the D300 popup as comander and the speedlights remotely, I seem to need at least 1 stop of +ev consistently to get a decent exposure in TTL mode.

    Am I doing something wrong or is this to be expected. BTW both units are seeing the commander and firing correctly...

    Thanks.
     
  2. It might have something to do with your metering mode, or the background. Show a sample with exif data and maybe we can help you figure it out.
     
  3. If they are not the same distance from the subject as your camera is the metering will not be right - if they are twice the distance the amount of light will be 1/4 of what it should be .[ as an example ]
     
  4. keko

    keko

    143
    Jul 20, 2007
    Barcelona
    Thanks guys!

    That makes a lot of sense!

    To tell you the truth I've been an all natural light kinda guy until I ran into Strobist, joined the Café and saw all these amazing pics taken with CLS and got curious.

    And you guys with your humbleness, make it seem so easy, as if your skills didn't make a difference.

    So I'll just take this as yet another challenge and opportunity to understand exposure and learn to use it for my photography. Looks like the learning curve will have to be a steeper one than anticipated.

    Gotta go and do some strobist reading...

    Thanks!
     
  5. What you say would be true under certain conditions if the OP were using strictly manual flash, but he indicated he was using "TTL". Therefore, your advice does NOT apply. The flashes can be any reasonable distance from the subject (the two need not be the same) and the subject to camera distance has nothing to do with achieving a proper flash exposure.

    With his equipment, TTL means he is using Nikon's very sophisticated CLS system which includes Advanced Wireless Lighting.

    Through a series of preflashes the scene reflectivity is measured and the wireless slave flashes are commanded to produce the proper duration (power) for a proper exposure.

    To the OP, check your camera menu and be sure both your slaves are in TTL mode and be sure you haven't inadvertently dialed in negative flash compensation. I don't have your exact camera model so this next tip may not apply, but be sure you haven't dialed in negative flash compensation via the pop up button either.

    If the flash is still too weak, consider dialing in positive flash compensation on one or both of your slaves rather than positive exposure compensation. Of course, you might be asking the flashes to put out more power than they're capable of producing. Are they firing at full power? If so, raise your ISO, open your lens, etc. etc..... you get the idea.

    By the way, the fewer the slaves and the closer to the lens axis you position them, the more likely you can get a good exposure using the default settings. Use more slaves, position them way off axis and/or use a lot of light modifiers and you should not be surprised to use some sort of flash and/or exposure compensation. In other words, the more complex the lighting set up is, the more difficult the challenge.

    Multi light studio lighting is not simple. Think about how the "real guys" do it. They have all sorts of modeling lights, light meters & flash meters, and especially in the film days, Polaroid backs because they were (are) never certain of making the perfect shot the first time.

    The Nikon Advanced Wireless Lighting system is VERY good, but under difficult circumstances a certain amount of exposure bias is nothing to worry about.
     
  6. Bob, on behalf of the Cafe management I wanted to tell you thanks for your willingness to share good and valuable information for those that are new to flash or are trying to increase their skill level. I would commend any and all posts you have made in this particular forum as your well thought out advice is always spot on.
     
  7. Does it make the calculations based on the built in flash or does it also take the distance of the off camera flashes into consideration ?
     
  8. The camera tells the built in flash to command the remotes to fire a low power test burst of measured value. The camera looks at the result through the lens, evaluates it, and computes how much more power it would take from each remote to illuminate the scene properly. Then it sends instructions to each remote, via coded bursts of light from the built-in flash. The remotes lock in those instructions, and produce the indicated amount of photons when the built in flash issues the "fire" command.

    All of this communication and calculation takes place in a matter of thousandths of a second. Amazing stuff.
     
    Last edited by a moderator: Jul 13, 2008
  9. Hmmm , I've been trying to work out why I get much weaker flash when the remotes are fired into umbrellas in ttl mode ? You would think it would make compensation for the lost power . I'll have to do some more tests . [I had thought it did its calculations based on the built in speedlight only ]
     
  10. smodak

    smodak

    Jun 11, 2007
    Franklin MA US

    This has been my experience as well...ttl off camera required +ev...I do not use ttl off camera anymore...manual cls if fun!!!
     
  11. TTL off camera depends on what you are metering (spot, center weighted, matrix) and where, in relation to your camera, the subject is located. TTL can be quite accurate if you think through these things before you take the picture. I am not knocking CLS as it is quite good and does its best to balance the background and the foreground.
     
  12. ok , I've cleared the doubts in my mind now :smile:
    I did some tests on my 'model' .
    bracket010.jpg
    Subscribe to see EXIF info for this image (if available)


    [not the same shot but it will do ] .
    I set the flash up on wireless about 2 feet from the subject using my D70S which REALLY showed up the preflash coming from the remote flash ! I kept the subject framed the same with my 18-200 at f5.6 , 1/30th iso 200 [manual] and took a few shots as I slowly backed away and zoomed in . When I was at 200mm the exposure was exactly the same [ histogram ] as the 50mm exposure ... well I learned something new today :redface:
     
  13. Gee....... I'm flattered.:redface:

    Now I suppose the pressure is on, right? I'm going to have to pay particular attention to what I post in the future and try to ensure that at least some of it is true.:rolleyes: 

    On another subject, does anyone here have any connection with child protective services in NZ? I'm concerned about the health of Desmond's baby. I notice that Desmond's child always has that goofy grin and a sort of glassy eyed look. It's hard to tell from a still shot, but the baby looks somewhat lethargic; it doesn't seem to be growing very fast either. This baby even came with instructions, but it appears to me that Desmond may not be feeding it properly. On the other hand, the child does have beautiful skin tone and rosy cheeks, so perhaps I'm worrying over nothing.:biggrin:
     
  14. Some have mentioned that the skintones look a bit ''plasticy'' :smile:
    Maybe I've been feeding it too many artificial additives ????
     
  15. Montec

    Montec

    752
    Jul 26, 2007
    British Columbia
    One thing I have learned is that ttl is not very accurate with smaller aperture settings like f/8 and smaller. The pre-flashes are very weak and at these small f/ stops they do no register accurately. ttl is best used at f/ 5.6 and larger.

    Another thing to keep in mind is where you are focusing. ttl takes the reading from that point and adjusts the output accordingly. So if you are just focusing into open rooms around the house like you mentioned you may not be getting the full benefit of ttl.

    Your best bet with ttl is to use spot focus and large f/stops if possible for your most accurate exposures.

    I just completed watching the TTL training videos from Will Crockett over at shootsmarter.com and they are very worthwhile to have a look at in my opinion.
     
  16. gvk

    gvk

    388
    Jun 17, 2005
    Mystic, CT
    With iTTL (unlike the earlier TTL previously used on film cameras) pre-flashes are sensed by the camera before exposure while the aperture is still wide open, no matter what actual aperture is used for exposure. The problem with using small apertures is that, depending on subject to flash distance, the maximum output of the flash may be insufficient for the required exposure. When this happens the red light on an SB-800 or SB-600 flashes to indicate possible underexposure. At closer distances, such as in close-up or macro shooting, I have used iTTL successfully at effective apertures as small as f/32 without any problems.
     
  17. Montec

    Montec

    752
    Jul 26, 2007
    British Columbia
    I am not sure I understand...you are saying even if you stop down your lens to f/32 that your camera still senses the pre-flashes at the lens wide open setting? How does it do that?
     
  18. When you stop down your lens to f/32, it actually stays wide open until you trip the shutter. Focus is acquired at the widest aperture the lens is capable of, and so is the measured test flash.
     
  19. Montec

    Montec

    752
    Jul 26, 2007
    British Columbia
    Thanks for that info. I was not aware of how that actually worked.

    Cheers,
     
  20. You'll notice the effect when you push the depth-of-field preview button on your camera [ if it has one ] , the lens closes down to the aperture you have set and everything goes dark[er] .
     
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