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FORUMS General Gear Talk Flash and Studio Lighting 
Thread started 17 Jul 2008 (Thursday) 05:41
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ISO with flash-help I'm so confused!!!

 
fidelis
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Jul 17, 2008 05:41 |  #1

Hi everyone,

I'm new to flash photography & have been reading different articles concerning it over the past week or so. I'm hoping that I may be able to gain a better understanding of it & how to apply it when natural light just isn't an option, say I was photographing someone indoors & it's just too dark to gain acceptable results by shooting at a higher iso (because of grain). By the way I shoot with a Canon 10D which is particularly noisy at high iso's. So I don't really want to shoot any higher than iso 400, is there anyway around this or is it possible to shoot at any iso when using flash indoors (i do apologise if this is a silly question, i still have a lot to learn)!


  
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PaulBradley
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Jul 17, 2008 06:06 |  #2

It's possible to shoot at any ISO when using flash, providing that everything you want the flash to illuminate is within range, so when you're using ISO 100 the flash has less "reach" than at ISO 400 for example, but that said in most indoor situations you'll find you can shoot at ISO 100 if you want.

One reason you might want to use a higher ISO is to avoid the "black hole" look where things that are illuminated with the flash are well lit but the background is too dark for your tastes - then you might want to go to say ISO 400 and use a slow shutter speed like 1/10 so you not only get the flash lit parts in, but also pick up a bit of the ambient illumination to show more of the background. Don't worry about blurry pictures from the slow shutter speed when doing this, the flash happens fast and will "freeze" your subject, provided that the ambient exposure you set underexposes by a couple of stops.

For more flash info (lots of great stuff) google "lighting 101" and "lighting 102" for the strobist tutorials.




  
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Derbyshire ­ Weddings
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Jul 17, 2008 06:13 |  #3

Paul covered what I would have said!




  
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martinsmith
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Jul 17, 2008 07:07 |  #4

Or buy more powerful flash or flashes.

I use 580 exii and 2 Noink SB-28s. Seems to work ok for my needs although studio strobes kick out a fair bit more power.


[SIZE=1]ms-imaging (external link)

  
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DDCSD
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Jul 17, 2008 07:28 |  #5

Here is an amazing resource on flash photography:
http://planetneil.com …h-photography-techniques/ (external link)

Paul summed things up quite nicely.


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fidelis
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Jul 17, 2008 07:44 |  #6

Thanks for the explanantion, that's great! Ok, so I don't want the dark cave look to my images & need to expose for ambient light too, how do i go about doing this? Set my camera to Manual mode (I'm using a 420ex) by the way, so can only control it via my fec on my camera, I then choose what aperture I need & shutter speed, does it not matter that my light meter inside my camera is not reading for a well exposed image I presume not as the meter is metering ambient light & not taking into account my flash? So do i ignore my in camera light meter & just use my histogram when using flash? Sorry just trying to work this all out in my own mind.

Can someone share their starting points with what they set their camera/flash to when shooting indoors on M mode. I know they can't be exact as it depends upon the sitaution but a starting point would be useful.

Thanks guys for all your help, I really appreciate it!


  
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AB8ND
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Jul 17, 2008 08:21 as a reply to  @ fidelis's post |  #7

If you can you should try to let your 420 be dominate by 1 to 1 1/2 steps. Meaning you need to measure the ambient light then letting the flash, if I remember the 420 is only TTL or ETTL, light the subject. Say you measure the ambient getting at iso400 1/30th at f/4, now set the camera to 1/30th at f/5.6 the flash should now light the subject fine with the surrounding area just a bit underexposed. You can use your camera get a meter reading, but a small hand held incident meter will give much more accurate readings. Now if the ambient is too dark or you don't want to go much higher with the ISO you probably will just have to deal with the black hole. If you bounce the flash indoors the fall off should light some of the surrounding area.

Jack




  
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fidelis
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Jul 17, 2008 08:49 |  #8

Thanks Jack yeah the 420ex is ETTL & your explanantion makes alot of sense, so thanks for taking the time to respond to this thread.:D


  
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PaulBradley
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Jul 17, 2008 12:01 |  #9

Jack said it right. Using M mode is best, but if the ambient is changing and you want in-camera metering to adjust your exposure you could go into Av mode, set the aperture and ISO you want, then dial in -2 stops (or thereabouts) of exposure compensation (not FEC, just normal EC), then the flash will light the subject and the camera will expose for the ambient at 2 stops under. The reason for underexposing the ambient is that if you don't you will get "ghosting" from subject and camera movement, but when the ambient is underexposed a fair bit the trails from the shake will be unnoticable since the flash exposure dominates them. Of course this only applies in poor ambient light where you are at a slower shutter speed than you'd usually like - in good light you can just "balance" the exposure and expose normally for the ambient, using the flash to fill in the shadows. Another creative option you may not have considered yet is to try grossly underexposing the ambient outdoors in good light (like -3 stops or more) and then using the flash to light the subject giving you a properly lit subject against, for example, a really saturated and moody sky.

So EC adjusts the ambient exposure, and FEC adjusts the flash exposure - simple and elegant once you get the hang of it, and it gives you two different regions of exposure to play with within the image giving a lot of options.

Again though, unless there is some good reason not to (like fast changing light) do what Jack said and use M mode.

Also, if you are new to flash, do the other thing Jack mentioned and practice bouncing it off surfaces both in and out doors - don't just limit yourself to the ceiling as so many newer flash users seem to (I used to), think about all your options - often bouncing off a side wall or a corner in a room gives light that looks much more natural since it is slightly more directional but still softened by bouncing it. When you are bouncing be aware that the flash is not only being spread out by diffusing off the wall/ceiling/whatever, but is also having to go further, so to avoid working the flash too hard you may want to up your ISO a bit or open up the aperture, or both.




  
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fidelis
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Jul 17, 2008 12:11 |  #10

Thanks Paul for your comments, I will do as is suggested here & use M mode but experiment bouncing the flash off different surfaces & see what results I get, thanks again.


  
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DDCSD
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Jul 17, 2008 12:45 |  #11

I highly recommend having a couple of good reads of the link that I posted earlier. It was the single most important thing that helped me using a flash.


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fidelis
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Jul 17, 2008 13:03 |  #12

Thanks DDCSD, I have started to take a look at the link you posted for planetneil.com & it does look like an excellant resource, I'll be sure to read it all ASAP to help me in my quest to become better at flash photography! Cheers.


  
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DC ­ Fan
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Jul 17, 2008 14:42 |  #13

fidelis wrote in post #5927764 (external link)
I don't want the dark cave look to my images & need to expose for ambient light too, how do i go about doing this?

With flash and a subject in close range, say up to 20 feet away, shutter speed decides ambient light and aperture decides subject exposure. If ambient light is low, slow shutter speeds increase the amount of ambient light in the imge. However, that doesn't get you to the questions of how to hand-hold a camera at 1/20 and avoid flash ghosting, or what happens when the ambient light doesn't match flash white balance...




  
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fidelis
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Jul 17, 2008 15:29 |  #14

Hi DC Fan,

Thanks for that, yeah so if I do have to use slow shutter speeds to allow more ambient light in, I'm presuming I'd have to use a tripod as I wouldn't be able to hand hold at say 1/20, I'm not that steady;)

Although did I not read that the flash would freeze any action & prevent ghosting provided that the ambient exposure I set underexposes by a couple of stops?

Also whats that about- ambient light doesn't match flash white balance?

Oh my goodness I have so much to learn about flash! :o


  
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DDCSD
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Jul 17, 2008 17:01 |  #15

fidelis wrote in post #5930632 (external link)
Also whats that about- ambient light doesn't match flash white balance?

Gels.

http://strobist.blogsp​ot.com …sing-gels-to-correct.html (external link)


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ISO with flash-help I'm so confused!!!
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