Pop up flash and shutter speeds

Mike D90

Senior Member
I like using fill flash for outdoor photos but I have a question about what it changes.

If I pop up my flash, and it is set to TTL, does it change my shutter speed automatically?

What is the proper way to set the flash to get fill flash and keep a higher shutter speed?
 

Mfrankfort

Senior Member
The flash in TTL will adjust it's output. Not your shutter speed or aperture. That's set by your. If you use M, and lock in your shutter speed (1/200 max), and aperture, the only thing the flash will change is the strength it outputs. If you use "A" mode, the camera will adjust the shutter speed for proper exposure of the background.
 

WayneF

Senior Member
I like using fill flash for outdoor photos but I have a question about what it changes.

If I pop up my flash, and it is set to TTL, does it change my shutter speed automatically?

What is the proper way to set the flash to get fill flash and keep a higher shutter speed?


The camera, in P or A mode, will meter the daylight ambient, and will set the shutter speed for the ambient. The flash does not care about (is not affected by) shutter speed. However, the camera shutter will not sync flash faster than 1/200 second (D90). This is sort of a problem in bright sun.

So... the standard Sunny 16 rule says bright sun exposures will require near 1/200 second at f/16 at ISO 200 (hazy, cloudy, overcast, or shade will need more exposure). However the camera meters it, but that is about ambient. You cannot use 1/400 f/11 equivalent here because camera cannot sync flash faster than 1/200 second (maximum sync speed). The TTL flash has to work with that ambient setting, and it does work ... it simply sets its TTL flash power accordingly to be proper flash exposure. If it has enough power to pull it off.

The popup flash has very little power (guide number about 42), so its range as fill flash in bright sun is only a very few feet, more like 4 or 5 feet, nothing like ten feet. You will do much better using your Sunpak flash (decent power, it might make ten feet in this bright sun setting).

The popup flash will do TTL BL balanced flash, to be point and shoot flash in bright sun. I think the Sunpak will too, but I have no experience with it to be sure. In the unexpected case that it is not balanced flash (saying, if the subject is greatly overexposed in this situation), then use about -1.7 EV Flash Compensation on the camera to correct it. But I would not expect that will be needed, and expect balanced flash will pretty much take care of it. Practice a bit in the back yard before any big event where it needs to work right.

I have to mention that Four Flash Photography Basics we must know - Flash pictures are Double Exposures is about this subject.

You mentioned "higher shutter speed". I think you mean this: Your D90 does have menu E5 to offer Auto FP, which will allow any faster shutter speed with certain flashes, those flashes which also support it. The camera popup does not. The Sunpak does not mention it, so I suspect it does not.

Nikon flashes like SB-600, SB-700, SB-800, and SB-900 do offer high speed sync FP flash (SB-400 does not). They will work with this D90 Auto FP option. Which such a compatible flash, then you could conceivably use f/2.8 and 1/4000 second with flash in bright sun, but at substantially lower power level (still, with those flashes, 10 feet should be possible).
See Four Flash Photography Basics we must know - Auto FP and HSS about Auto FP flash options.
Again, the camera popup flash cannot do this option. My own notion is that f/16 1/200 second works OK for me. ISO 100 allows f/11 1/200 second.
 
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Mike D90

Senior Member
I bought the wrong Sunpak flash. It does not work in TTL with my D90. It will work in manual and I can set its output manually.

So, I guess it will be like you said, use it a few times, and see what happens.
 

WayneF

Senior Member
I bought the wrong Sunpak flash. It does not work in TTL with my D90. It will work in manual and I can set its output manually.

So, I guess it will be like you said, use it a few times, and see what happens.

Well, you can use manual flash for fill in bright sun. Just experiment with it a bit, and set the power level as you see is desired for the result that you want. Do experiment enough to see both 'too much' and 'too little", so you will know the range and the choices. This won't be wasted work. IT WILL BE ABOUT THE SAME NEXT TIME IN SIMILAR SITUATION (it is called experience). Bright sunlight is the same, and you can make your subject distance be the same.


Or.. the flash manual should have a guide number chart, with guide numbers for each zoom value. If for example, you are using it at 50mm zoom, use that column. Multiply the chart ISO 100 values by 1.414 to get ISO 200 values your camera is using. Or divide if converting going the other way.

Then suppose your camera is using f/16 for subject at 8 feet, which is Guide Number 16x8=GN 128 needed (for f/16 at 8 feet, ISO 200). 128/1.414 = GN 90 in ISO 100 chart. Find that GN 90 (or closest value) in the column for the 50mm zoom you are using, and use that power level... Full or 1/2 power maybe. Pretty simple.

However, and here is the thing about it - that is for computing full flash exposure. You only want fill exposure, maybe two stops less than that in bright sun. So instead of 1/2 power indicated, drop two stops to 1/8 power (each half power step is one stop). You can compute 2 stops less fill level by simply dividing this computed GN 90 by 2, to look up power level for GN 45 (which would be fill two stops down). These are the ISO 100 numbers converted to match the power levels in the chart.

You can do this evaluation one time before you leave home, and will have a very good starting point to tweak manual flash. You can also practice this in the backyard, before the actual event. If you want to do it, there certainly is a way.
 
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Mike D90

Senior Member
Just to update this I have been experimenting with the Sunpak flash and you are correct. It works very well when I use its manual capability to dial down the flash and zoom the flash head.
 
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