Welcome to the forum!

As an adjunct to the Tangents blog, the intention with this forum is to answer any questions, and allow a diverse discussion of topics related photography. With that, see it as an open invitation to just climb in and start threads and to respond to any threads.

OFF camera flash: smaller aperture = softer light ?

CedCed Member
edited December 2013 in flash & lighting
Hello,
I'd like to know if that makes sense.

I noticed that quite often while setting up an off camera flash and using TTL, my subject was over-exposed, even with FEC dialed down to max. So I guess my umbrella was to close to the subject even with the minimal output power of the flash.

I had a concern moving the light further away from the subject because I wanted soft light and light contrast, and increasing the distance would increase the contrast.

So, instead I used smaller aperture.


The umbrella was less than 1 meter away from the subject (less than 3 feet ?), I started at f4 and increased To f6.3

Does this make sense or something looks wrong, not correct (way to do)?

My conclusion was that at max aperture it is not possible to get as soft light as with small aperture, without using nd filter.
Tagged:

Comments

  • ETTL is not perfect so when you are stopping down ( at FEC -3) the light that the flash is putting out is less so the shadows will be richer since less light is bouncing around. The f stop value has nothing to do with the softness of the light. You can have soft light at 1.2 as long as you have proper light placement, proper light setting, etc.

    So, to answer your question: No, you can get soft light at at any f stop, even at 1.0. Use manual flash mode, it is easier to control flash output. If the lowest setting is still too much, buy ND gels for the flash heads.

    Rudy
  • hi ced,
    in what ambient situation is this? did u take an "ambient only" test shot to be sure its not the ambient light that was overexposing the subject? it sounds a bit strange to me that a speedlight in an umbrella at f/4 couldnt lower its power enough that it should not over expose the subject. try it again with the speedlight set to manual at its lowest power (1/128 or 1/64)
  • CedCed Member
    edited November 2013
    I took the photo indoor at 1/250s , iso 100, ambient light was not contributing. I will try again with manual, always used ttl so far. If you say that is not normal that is was over-exposed even with FEC at -3 I will try again also in ttl.

    So what I meant is that given the same source light, a small aperture of f8 will allow a softer light than a big aperture of f2.8 because the light can be placed closer to the subject without over-exposing. Is that correct, in theory ?



  • MikeZMikeZ Member
    edited November 2013
    There would have to be an increase in flash "power" to compensate for the f8. I understand what you are asking. Ttl is going to do whatever it thinks it needs to do to make the exposure at 100iso and f8. A lot of dark in the frame will cause the flash to boost on most ttl setups. So maybe the ambient was not contributing but the tonality was depending on your metering mode. Changing the aperture from f4 to f8, for example, with manual flash, will cut the amount of light entering the camera. So, in terms of your question, the light would appear softer but in reality only less light is getting in. The shadows would probably be very contrasty. In turn your flash will be working hard for no reason. I would just use manual flash with the aperture you desire and adjust the light power. It will be very consistent that way. I really only use ttl in fast paced situations where there is no time for setup.

  • Neil vNNeil vN Administrator
    If the umbrella is less than 3 ft away from your subject, I think you're dealing with simple over-exposure here?
  • I did some test shots with someone really really patient, my teddy bear, and I think I have the start of an explanation, unfortunately it also raised more questions :).

    The tests I did with my teddy bear got me really confused, because I placed the flash really close to it (less than 2 feet), at f8 till f2.0, and using ETTL and FEC I could always get correct exposure.

    Then, I tried manual mode, and then was the first surprise, at f2.0 and flash power at min 1/128, teddy bear was over-exposed (whearas in TTL and FEC exposure was correct) !

    I have tried with 2 different flashes and it gave same result. Is this normal ? So with TTL the flash output can be less than the minimum power that can be set in manual mode ?

    So, TTL mode could not explain the issue I got, until I added a second flash in TTL mode for rim light,using two groups A:B with a ratio of 4:1 , A group being the key light, B group being the rim light.

    I think this is what happened during the shooting where I added a second speedlite for the background, using B group and different ratios.

    My intention was to light the background a little, but maybe the rim light in ttl was boosted because it tried to get correct subject exposure by bouncing light on the background. I am not really sure...

    In my teddy bear tests I tried to use the C group and it was better, not ideal in ttl, but better than using the B group.


    o Is this a sensible explanation ?
    o Is it normal to observe that TTL flash output can be less than minimum manual power of 1/128 ?


Sign In or Register to comment.