Need help on using flash in Manual Mode

[girod]

Hello Keith and others,

I have not ever used any flash in manual mode, so please help me. This coming Saturday (4/24/10, 5 -7PM), Simon and Garfunkel are performing here at New Orleans Jazzfest. The stage is covered but the foreground is open. I planned to be there by 11AM when the Fairground opens to be able to secure a place in front and in the center relative to the stage - the nearest distance allowed from the stage is about 20 - 25 meters. My only gear for this occasion: D700+MB-D10, 70-200mm/2.8 VRI, TC-2.0 III, and the SB900 flash. I figured that if I have to use the SB900, it has to be in manual mode(). The SB900's GN=34m/111.5ft @ ISO 100, if I use ISO 800 it can reach to 95m/312.2ft (x2.8 factor). Using the GN=Aperture x Distance (@ ISO 800), f/2.4 will give me 34m reach; f/4=24m; f/5.6=17m; f/8=11m and so on. I plan for a 1/60s shutter speed to get some ambient light but avoid ghosting. Is this right? what's the best way?

I also have the Fx-6 Flash X-tender that I have never tried yet, would this help?

jaime

[keithsnell]

Hello Keith and others,

I have not ever used any flash in manual mode, so please help me. This coming Saturday (4/24/10, 5 -7PM), Simon and Garfunkel are performing here at New Orleans Jazzfest. The stage is covered but the foreground is open. I planned to be there by 11AM when the Fairground opens to be able to secure a place in front and in the center relative to the stage - the nearest distance allowed from the stage is about 20 - 25 meters. My only gear for this occasion: D700+MB-D10, 70-200mm/2.8 VRI, TC-2.0 III, and the SB900 flash. I figured that if I have to use the SB900, it has to be in manual mode(). The SB900's GN=34m/111.5ft @ ISO 100, if I use ISO 800 it can reach to 95m/312.2ft (x2.8 factor). Using the GN=Aperture x Distance (@ ISO 800), f/2.4 will give me 34m reach; f/4=24m; f/5.6=17m; f/8=11m and so on. I plan for a 1/60s shutter speed to get some ambient light but avoid ghosting. Is this right? what's the best way?

I also have the Fx-6 Flash X-tender that I have never tried yet, would this help?

jaime

Hi Jaime,

Thanks for asking.  The SB-900s guide number varies with the zoom position, so given that you will probably be at the long end of the zoom, the most applicable guide number is probably 183.7 (ft) at a zoom position of 200mm.  So the range at an ISO of 100 would be 184 (rounded) divided by the effective aperture (with the TC 2.0) of f5.6 = 32.8 ft.  The range will double for each time you quadruple the ISO, so at an ISO of 400, the range will be 65.6 ft, and at ISO 800 the range will be 65.6 x 1.4 = 91.8 ft (or 28 meters).  Given this, you should have enough flash range to reach the stage.  If you wanted to be safe (and potentially better balance ambient and flash exposure), you could bump up the ISO to 1600 without too much loss in image quality.  

The Better Beamer Flash extender will double the range of the flash when it is set to the 50mm zoom setting.  The guide number at 50mm is 131.2, so the range at ISO 100 would be 131.2/5.6 = 23.4 ft.  Using the Better Beamer the flash range would double to 46.8 ft, which is a bit better than the range with just the flash at the 200mm zoom setting.  One reason for this difference is that the Better Beamer concentrates the flash so that it only covers the field of view for a 300mm lens (so if you use a shorter focal length, the flash illumination will be uneven across the frame).  Using the same math we used before, the better beamer will give you a flash range at ISO 800 of 46.8 x 2 x 1.4 = 131 ft (40 meters) which should be plenty of range.  If you are consistently shooting at a focal length greater than 300mm, it might work best to use the Better Beamer.  If you do, be sure and set your flash zoom manually at a position of 50mm, since this is what the fresnel lens is optimized for.  If you let the flash zoom on auto while using the Better Beamer, you won't get optimum results.  In addition to extending your flash range, the Better Beamer should also allow you to have a faster recycle time (since you won't need to fire the flash at full power) and conserve batteries as well.

You can use the flash in manual mode, if you want, but you don't have to.  TTL should work just fine with just the flash, and should actually work OK with the Better Beamer too, since the flash will adjust it's output based on what return it measures from the pre-flash.  You probably will get more consistent results if you set the flash in manual and adjust the power to get the range you want.  The range displayed on the LCD will be correct for the flash by itself, and should indicate close to the proper range if you are indeed 25 meters from the stage.  You can reduce the flash range by a factor of 1.4 by setting 1/2 power (a 1-stop increment), or you can reduce the range in finer increments by adjusting your aperture in 1/3 stop increments.  The range display should update appropriately on your flash in conjunction with your changes in aperture, so you won't have to do the math in your head.  If you are using the Better Beamer, just remember that the fresnel lens will double the effective range of the flash compared to what is being shown on the flash display, so if your distance from the stage is 25 meters, just ensure the display is showing an effective range of around 12.5 meters and you should be OK.

Does all this make sense?  If not, please ask additional questions and I will try to clarify this explanation.

Keith

P.S.
Yes, using a shutter speed of 1/60 should be a good setting, as long as direct sunlight is not hitting the performers.  (I don't know the setup of the stage, but given the time of the concert, I suppose there could still be some sun illuminating the stage.)  If direct sunlight is hitting the performers, you will probably need to shoot at a higher shutter speed in order to control the ambient exposures.

[girod]

Thank you very much Keith. I will have to re-read your explanation several more times to make sure that I really comprehend it and can implement it very smoothly. I will practice as much as I could before Saturday.

I've read in dpreview forum that the 70-200/2.8 VRI + TC-2.0E III combo becomes really sharp starting at f/7.1. I only got mine 2 weeks ago and didn't really have enough shoots to find it for myself. Should I use f/8? Should I even use it (TC-2.0) on Saturday? What's your advice Keith?

jaime

[Michele]

Wow, they are playing together again?  That is going to be pretty cool.  I have seen Paul Simon three times in concert.  Each time he was amazing.  Let us know how it went.  Good luck with the flash.

Michèle

[keithsnell]

Thank you very much Keith. I will have to re-read your explanation several more times to make sure that I really comprehend it and can implement it very smoothly. I will practice as much as I could before Saturday.

I've read in dpreview forum that the 70-200/2.8 VRI + TC-2.0E III combo becomes really sharp starting at f/7.1. I only got mine 2 weeks ago and didn't really have enough shoots to find it for myself. Should I use f/8? Should I even use it (TC-2.0) on Saturday? What's your advice Keith?

jaime

Hi Jaime,

I'm sure the TC-2.0E III is an improvement over the previous version; however, that said, I've never been a fan of the 2.0 teleconverters.  It seems that with each new iteration, there is a lot of hype about how good they are in combination with XX lens, but after I've tested them personally I always end up selling the TC 2.0.  I suppose the TC 2.0 III could be different; however, there are still basic laws of physics to contend with, and I seriously doubt that Nikon has found a way to modify the laws of physics.

If you do end up using the TC-2.0 in order to get the range you need, then yes, using f8.0, and the Better Beamer will probably be a necessity for sharp images.  You should have plenty of range with the Better Beamer, but won't have enough range with just the bare flash (in conjunction with the TC 2.0), unless you shoot wide open, which I wouldn't recommend.

If you have the opportunity, shoot some with the TC, and some without.  Past experience tells me that your "keeper" rate will be lower with the TC, so I would recommend shooting a few shots without the TC for "insurance."

Please let us know how it all works out.  

Keith

[girod]

Thanks Keith. I will have to decide (+/-TC; which flash mode) before the appearance of Simon and Garfunkel because with the crowd, I don't think I will have a space to do those maneuvers. I will let you know.

[girod]

Thanks Michelle....will share some pictures.....that is, if I get lucky.

[girod]

Just a quick feedback from Simon and Garfunkel concert: 1) I didn't have to use a flash (though the SB900+extender was mounted and ready for use), ISO 800 and 1600 did it. 2) I shot worth 8GB images just for the Duo (14-bit NEF, lossless compressed. 3) In terms of sharpness and exposure - with 70-200mm/2.8+TC-2.0E III @ f/8 all the way, mostly @ 400mm - my estimated taker is about 95-98% (of course, this is according to my standard); I was able to use the Benro C-269+B1 tripod-ballhead (made to function as a monopod) 90% of the time with VR off, about 10% handheld (VR on).

I have tons of images to be developed......but most of all, this is one of my happiest days!

[keithsnell]

Hi Jaime,

Thank you for letting us know how it went.  It sounds like the TC-2.0E III worked very well for you.  We'll look forward to seeing some of your images once you find the time to process them.  It sounds like you had a wonderful time at the concert, and will have some nice images to remember it by.

Keith

[Michele]

That is so cool.  I am very happy for you and I can't wait to see the shots.

Michèle