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Archive 2015 · D750, auto, and flash

  
 
pr4photos
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p.1 #1 · p.1 #1 · D750, auto, and flash


If I have my D750 set to auto ISO and on program it all works fine. But, if I attach a flash and want to use ttl to fill in, it doesn't work. It sets the whole exposure to underexpose by about a stop.
Is there a way for the camera to keep the ambient exposure correct and me being able to use the flash to fill in, without resorting to manual exposure on the camera?



Nov 09, 2015 at 08:58 AM
wellsjt
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p.1 #2 · p.1 #2 · D750, auto, and flash


I assume you've checked to ensure you don't have some negative flash compensation dialed in? Is it that the background is dark but the subject is properly exposed? Or is everything underexposed?

I use auto ISO a lot, but I really dislike it with flash. Without flash, it's just math: given the selected shutter and aperture and meter reading, what ISO is required for a correct exposure. With flash, the camera can't just calculate it because it doesn't know how you want to balance the ambient with the flash. A correct exposure could a black background and a well exposed subject. It could also be a bright background and a well exposed subject. Or a slightly underexposed background... etc.

This is why I prefer to turn off auto ISO when using flash, and ideally go manual mode to have total control over shutter, aperture, and ISO, and let bounced TTL flash take care of the subject.



Nov 09, 2015 at 12:02 PM
swainsons
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p.1 #3 · p.1 #3 · D750, auto, and flash


I just hate using auto anything and flash, but I would check EV settings on camera and on flash.

Is it under exposing background and subject or just subject. If its just subject ride you FEC (Flash exposure comp).

Also, I can't recall exact setting but you can set EV to under or over expose background and subject simultaneously. I don't like it, but check that setting.

After that, go manual.

Good luck

Regards



Nov 09, 2015 at 12:09 PM
chuhsi1
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p.1 #4 · p.1 #4 · D750, auto, and flash


yeah, auto-iso and flash is a bad combo.


Nov 09, 2015 at 06:22 PM
morris
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p.1 #5 · p.1 #5 · D750, auto, and flash


For fill flash set matrix metering on your body and TTL BL on your flash

TTL BL is for balanced light aka fill
Matrix metering is required for TTL BL

Have fun,

Morris



Nov 09, 2015 at 10:29 PM
pr4photos
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p.1 #6 · p.1 #6 · D750, auto, and flash


If I set the camera on a tripod and point it at a subject I get an ambient exposure which is perfect. If I then switch the flash on, the meter says it will underexpose the ambient image. This is without me even clicking the shutter. Both the camera and the flash are set to 0 exposure compensation. I have no problem with using manual, but am curious as to why there is an apparent problem when it is set to auto everything


Nov 10, 2015 at 07:50 AM
jbouchard
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p.1 #7 · p.1 #7 · D750, auto, and flash


What flash are you using? That could be relevant.

I expect your D750 works like my D700 when you aren't in AUTO mode. On my D700 when I turn on my SB700, or any flash AFAIK, it works like this...
- the AUTO ISO automatically goes down to my preset ISO, effectively disabling auto ISO.
- my shutter speed is automatically changed to 1/60 as a sync speed (changeable, but that's default)
- Since I'm in Aperture preferred mode (A) 98% of the time, the aperture is what I've set it to, like f2.8.
- Now my ISO, shutter speed and aperture are all chosen, regardless of how light or dark the setting is.
- The only variable left is the TTL system in the body/flash, which will throw as much light as it needs to when the photo is being taken.
- So, what's my exposure meter doing during all this? It does what exposure meters do... it shows me if I'm going to underexpose or overexpose with these settings and ambient light. It has no idea what the flash is going to do, so that doesn't enter the equation.
- If it's showing overexposed then that means ambient light is too bright for my settings, and I have to make an adjustment, or it will definitely overexpose.
- If it shows underexposed, that tells me what my ambient to fill-flash ratio is going to be like. If it's -1, then I'll have a nice bit of fill flash. If it's pegged on the negative side, it's going to be "mostly flash" and potentially a very dark background. I can change my settings if I like.
- BTW, I typically use "center weighted" and "aperture preferred" rather than "matrix" and "program" because I'm frequently using Ai lenses. Then even if I'm using CPU lenses, I leave it there because it's easier than switching back and forth.



Nov 10, 2015 at 12:57 PM
wellsjt
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p.1 #8 · p.1 #8 · D750, auto, and flash


jbouchard wrote:
- the AUTO ISO automatically goes down to my preset ISO, effectively disabling auto ISO.


It doesn't work that way anymore on Nikon bodies, and I really think that's the main issue as I posted earlier. Auto ISO definitely plays a big part here.

The OP mentioned P mode and auto ISO. Quick experiment: On my D800, flash turned off, base ISO set to 100 with auto ISO turned on, matrix metering, P mode, 24mm, focusing on my wife from 6 feet away, it is suggesting 1/100 at f/2.8 at ISO 6400. When I turn on the flash, it wants 1/100 at f/5.6 at ISO 400. Clearly, the ambient exposure will be dramatically underexposed with the flash compared to without.

The problem is that auto ISO has no clue what you want to do in terms of balancing the ambient and the flash. Its suggestion may be totally acceptable to some people: a lower noise ISO and a well exposed subject. Others may want just a slightly underexposed ambient and a well exposed subject.

The solution is to turn off auto ISO and take back control of setting it.



Nov 10, 2015 at 08:00 PM





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