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Inverse square law

slravenphotoslravenphoto Member
edited May 2013 in flash & lighting
Hi again

Another image from me, another from my charity event.

This is an outtake, a test from the event.

24-70 f/2.8 L MKI @ 45mm
1/200 / f/5.6 / ISO 2000
580 EX II @ FEC 0

Flash bounced behind me, although I was close to the bounce surface (I suspect this last fact is actually the key here).

I was hoping that the inverse square law would work to my advantage here and light the back of the room as evenly as the foreground... any idea why it's darker?

I did take another and increase the FEC, which largely worked, but it caused the foreground to blow out!

Any suggestions here? Specifically, do I completely misunderstand the inverse square law? And, any tips on increasing the range without blowing out the foreground.



  • The inverse square law actually is very noticeable here: You can see the light quickly fall off as the distance from the flash increases. That's how it works. For this kind of a wide shot, I probably would have gone to f/2.8, a slower shutter speed (maybe 1/100?) and bounced straight up or up and slightly forward for more even downlighting in the entire shot. If you were getting people portraits standing 6 feet away from them or something, then I would go with bouncing up and behind you like you did. It's when you are trying to light the whole room, you can't just blast the light into one corner or wall. My $0.02 anyway, good luck!
  • jhilgersjhilgers Member
    edited May 2013
    I completely agree with Nikonguy here. On a separate note I would ask you this:

    "What is the subject of this photo suppose to be?"
    - Is it the lady in the front lower right or is it the whole room overall?
    - I ask you this because depending on what your subject is suppose to be, will determine what your best settings to use will be (in my opinion).

    If the lady in the lower right is your subject, then I agree with the f5.64 choice, but I would have framed more of her and not so much of the room.

    If your subject is the whole room and the overall banquet "feel" appearance, I would have gone to a smaller aperture and boosted by ISO a lot more to compensate. Then I would have bounced my flash as Nikonguy recommended doing. WIll a smaller aperture more of the complete room area would be in focus.

    I can see why most of the picture is not sharp, it is because you have such a wide view of the room and you are using f5.6. To me that is the only issue really and it is not really an "issue", just choice of framing and settings use.

    Don't get me wrong, I have had to use an aperture of f2.8 and an ISO of 3200 or more, at night time for taking photos after sunset and not all of the photo was completely sharp because of it. I had to deal with it because I did not want to crank my ISO too high and risk too much ISO noise.

    Your lens is doing what it is suppose to be doing at f5.6 and at that angle and view in my opinion. I would have maybe used f8 or maybe even f11 if you could compensate enough with a higer ISO and then through the use of flash to clean up the over all remainder of the low light you were working with. Keep in mind your flash is going to have to dump a lot more juice at such apertures though. High ISO and maybe using your flash in manual mode full power (for such a large area) may be an option.
  • Neil vNNeil vN Administrator
    It looks like you used a diffuser cup or something similar, on your flash. That will largely negate the benefits you will get from bouncing the bare flash behind you ... especially in terms of opening up your background.
  • ZenonZenon Member
    In this situation especially bouncing with an on camera flash there is a point fall off is completely gone. On camera flash is too weak for that environment. Here is where you need to crank up the ISO way up to bring in as much ambient as possible for correct exposure and the flash just sweetens your subject/s. If you shot in RAW that image can be easily balanced using ACR or LR.

  • slravenphotoslravenphoto Member
    edited May 2013
    Neil, I didn't use a diffuser.

    Also I'm pretty sure that I did just bounce upwards - because behind me was a red curtain which would have given a dreadful colour cast. I know I said it was behind, but I'm thinking about it now and I'm not so sure.

    There is no subject to the image, like I said it was just a test shot.
  • nicktnickt Member
    Maybe using a bounce card might have helped.
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