Thanks Wayne. Much of your response prompted me to review flash photography principles which helped me see where my problems were here. Let me run what I think is correct through you and others.
First off, I don't get when you say you use EC to boost flash power when you need more than +1. For that to work for me on the D7100, I would have to be out of manual mode such that I was changing ISO or Aperture thus affecting the effective flash power (larger aperture or higher ISO). If I am in M mode, changing EC does nothing but move the meter needle (the digital representation of it that is). You do say that is true of Nikon's (not Canon's) early on in your response. So you must be in a different mode or using a Canon to use EC to boost your flash more than the +1 FC gives you.
No, EC always affects the TTL flash, including camera manual mode. -- (Oops!) Coming back up to this line, your D7100 E4 menu is a choice to make that be not true, see below. I was writing up here before I got to E4 below.
Probably more than anyone wants to know...
In manual mode, EC does move the meter, but the meter meters ambient, the meter is not about flash. This is hard to explain... + EC raises the exposure target goal point. If not manual mode, the camera controls react to reach that goal for ambient. The TTL flash power ALSO reacts to that goal, however not speaking of the meter, the meter meters ambient, which is likely far down indoors.
FC affects ONLY the TTL flash, and TTL is automatic in any camera mode.
EC affects auto ambient and TTL flash (also auto). EC and FC add at the flash (again, see E4 exception below). Nothing affects Manual flash mode of course.
Canon separates them, EC means only ambient, and FC means only flash. There are Pros and Cons either way. For Nikon, outdoors in Sun where ambient really counts, the TTL BL flash does Balanced Fill Flash (TTL BL flash is probably down about -2 EV for fill in bright sun). Point and shoot balanced fill flash. Then if we want the result a bit different, EC adjusts both darker or brighter, in one operation. Canon is two operations.
However, in Nikons, if you want to underexpose ambient 1 stop using EC, then you have to add +1 back in FC. Pros and cons.
The latest two or three Nikon models have a new menu E4 to separate them or not, Canon style or Nikon style, so to speak.
So, now my reasoning after reading your response, If I use the settings i say in the U1 mode for indoor flash photography, most of the time i get good exposures. If I don't or I want a different look I can do the following:
1) use FC to increase or decrease flash power (-3 to +1). If I need more than +1, I would increase ISO or open the Aperture. Then to balance ambient if needed I would reduce the shutter speed the same f stop amount.
Yes, or could also add some EC, it adds to the FC. Or the flash body has FC on it too, you could add that. All of these sources add to a total FC. (again, E4...)
I find it best to adopt one system (EC or flash body) to help me remember when resetting them off. I don't use camera body much, because we have icons in camera top LCD that shows if EC and FC is on, and shows FC on Nikon speedlights, but probably not in third party.
2) If I want to increase or decrease ambient light, I change shutter speed (faster - less ambient, slower- more). I think this was the problem I was having when I was adjusted FC and I thought it was affecting the ambient background. At the settings I was using, there was no significant ambient. I believe that is what you were trying to tell me correct??
Yes, I would not expect to see any indoor ambient at ISO 400 1/250 f4. Could say no significant ambient, but I really think it will be jet black.
Speedlights, I usually back off a bit on shutter speed, just a bit of ambient warms it and can be pleasing if not overdone.
But studio sessions, ISO 100 and 1/250 and probably f/8, to keep absolutely all orange ambient out. Even the modeling lights.
I don't know what happened when I was increasing shutter speed from 1/250th to 1/30th with direct flash; it did change the subject exposure dramatically. It probably was my set up. I was shooting a colorful pillow on the middle of a bed propped upright from the end of the bed. The ambient light comes from a light on a nightstand at the head of the bed so I was evaluating the light and the wall right behind it as the non-subject background light. So when I changed shutter speeds from 1/250th to 1/30th without changing anything else, it was changing the entire exposure, the pillow and the wall (and the light of the light) got much brighter.
1/30 second ought to affect anything the ambient light was on. But not the flash.
Two more things come to mind that fit in this post.
1) why the difference in Auto FP (1/250 Auto FP or 1/320 Auto FP)??? Is there an advantage in using one or the other? Isn't this just the shutter speed that Auto FP kicks in at so why wouldn't you want it to kick in at 1/320 or higher and use 1/250 as your max shutter sync speed??
The 1/250 and 1/320 seem interchangeable to me for flash. Nikon always warns that the flash range might be decreased at 1/320.
This is my notion, the way I interpret it. In this class of camera body, the shutter can obviously do 1/320 sync. Simply obviously does it, very well. No question about it.
But Nikon "specs' the shutter at 1/250, and the spec chart says 1/250.
Speedlights are slow at full maximum power. The SB-700 spec chart (page H-17) says 1/1042 second at full power. Full power is truncated shorter at lower power levels, but at full power, it has the normal trailing tail as the power fades away. This is impossible to measure. When is it gone? at 10%? 5% 1%? It is basically a horizontal line on the graph, and getting to zero takes a very long time, relatively, a few milliseconds.
That duration in flash specs in general is the half power points (called T.5 measurement), the time the power is above 50% of the peak (standard engineering practice, which can be measured). The full trailing tail takes longer, and does contribute. The 1/10 power points (T.1 method), the time the power is above 10%, is better suited for photography, but they are engineers, you know?
Commonly accepted engineering practice is that T.1 is 3 times longer than T.5. That makes 1/1042 second T.5 be 1/347 second T.1. And 10% is not zero, so there is still a bit more... hard to say for how long. The remainder does not contribute much, but it is not zero.
So at full maximum power, it is likely that the 1/320 second shutter speed truncates part of that weak trailing tail, and less power does reduce flash range.
IMO, it is negligible. Only true of maximum power level. The other levels are vastly shorter duration. The other levels are truncated duration for lower power, but very fast duration. They are all surely already shorter than T.1.
I think Nikon is being super-cautious about the specs for the 1/320 second sync. The shutter is obviously that fast. The speedlight maximum power level might not quite always be. But it simply just works.
2) The D7100 has the option to have EC change just the background (affects just EC) or the entire frame (affects EC and FC). It doesn't say what it is doing but I would imagine if you have it set to Background only, it is only changing shutter speed; in contrast, if it is set to entire frame, I would assume it changes aperture or ISO affecting both ambient and effective flash power. Is that what this menu option on the D7100 is all about?? If that is the case, I don't need to worry about it in M mode indoor photography like I have set on U1. It does come into action when I am outdoors in TTL-BL mode doing fill flash in P mode. In this case I guess I would want it on only background and then use FC to adjust flash power. Then you have individual control of each variable (Flash Power and Ambient light). Is this reasonable thinking??
OK, that is the new E4 menu I mentioned. Very few models have it, only the most recent 2 or 3 models. It didn't register in time that your D7100 was one of them.
It is not about shutter speed. You can select if EC affects only ambient (called background), or the old standard way, affects both ambient and flash. I suppose the manuals can't confuse the most rank newbies with words like ambient.
E4 is something else in the D7000... not one of the most recent models.
So if you have so selected your E4, to "background only", then you're right, EC does not affect flash.
I guess the last scenario is when you are in in-between lighting. In this case, all I need to do is kill the ambient and go with indoor flash techniques. Or if I want ambient light, use the balance flash on P mode and play with the FC and EC until you get what you want (or I guess you can also adjust shutter speed, ISO, and aperture in in the P mode pretty easily on the D7100).
I think that covers it for now. Please correct any aberrant thinking i have!!
Balanced flash (TTL BL, default for SB-700 unless Spot metering) does automatic fill flash, meaning automatic flash reduction in brighter ambient.
TTL flash mode (Spot metering) does whatever the flash actually meters, regardless of any ambient.
That means, outdoor with fill flash in bright sunlight...
TTL BL probably does it right automatically, probably applies (invisible, not seen in LCD menus) about -2EV flash compensation. Probably comes out good, fill in bright sun.
TTL mode (spot metering) for fill in bright sun, has to be manually set to about -2 EV flash compensation. The old standard value is -1.7 EV.
If the automatic camera ambient metering meters the subject normally, and if TTL mode flash meters the subject normally, and both do their normal thing,
then that is two normal exposures on the subject, adding to 2x, or one stop overexposed by definition.
TTL mode has to be backed off manually, and TTL BL mode backs off automatically.
And fill ought to be a bit weaker anyway.
It is just that indoors (no significant ambient), TTL BL sometimes seems to back off a bit anyway.
And the Commander (also TTL BL) is for multiple flashes, and they add and combine too, but the Commander meters them individually, does not see how they combine.
So the Commander seems to back off, just in case they might add. I routinely set +1 EV FC for the Commander, and it normally works out well.
TTL BL in one hot shoe flash may not need anything. Or it might at times... We do what we see we have to do.
