HSS simply does not work on this flash. It does implement the continuous flash, fast shutter speed works, but there are no means to control or adjust the flash power. The material below is overdone, but I was trying to figure out what I was seeing.
On the D300 camera, 1/250 second is regular speedlight flash mode. 1/320 second Auto FP shifts into HSS mode, and full power level is reduced to about 2 1/3 stops down in order to run continuously (HSS is Not the same as speedlight mode full power). Then 1/4 power level has to be 1/4 of that reduced level. It is a very different system than for regular speedlight mode.
But the bottom line, on this NW985N flash in HSS mode, no matter what power level is selected, you get full HSS power (except strangely, 1/128 power is down slightly, but nowhere near seven stops). To have any understanding of HSS mode, you have to realize it becomes continuous light, and acts like sunlight, and shutter speed seriously truncates continuous light (but equivalent exposures work). See explanation of HSS flash mode.
Re Shutter speed: Regular flash mode does not care about shutter speed, its brief pulse is much quicker than the shutter opening. But HSS is continuous light, is just on, like the sun, or like an incandescent light bulb. So in HSS Manual flash mode, faster shutters pass even less light, one stop loss at each increased shutter stop (same as sunlight). That is not the flash, it is normal, because it is continuous light. In HSS manual flash mode, we should be compensating by also opening the aperture, to maintain equivalent exposures in continuous light (same as we do in sunlight, also continuous). In TTL mode, the TTL metering tries to produce the correct exposure no matter what, boosting the flash power as necessary to do it, if it has power to do it.
The NW985N HSS is not working right. Its HSS mode does make flash be reduced continuous light, and a fast shutter speed can be used, but then all power settings from Manual or TTL flash are ignored. We always only get that one level of power, at best, a slight hint of a change instead of the full change. No control of flash power level. Plus there is a banding issue at fastest shutter speeds.
I was not much concerned with a proper exposure or white balance below, just trying to show differences, or lack of expected differences. The flash is in a hot shoe extension cord, in a near reflected umbrella, fabric at nearly four feet from subject, distance chosen to be more or less ballpark acceptable results for what the NW985N can do. If the flash were at any other distance, its results would be radically different, underexposed or overexposed. White Balance here is just standard Flash WB, not accurate, but not corrected. Of course, HSS always seems pointless indoors, so my subject is a stupid choice to use HSS... we don't need the shutter speed, and we seriously need the extra power instead.
A Nikon SB-800 is also shown for comparison, to show correct behavior too. All are with D300 (sync speed 1/250 second, FP HSS is faster), ISO 200, f/8. Nothing changed during the test except swapping the flash and the settings noted.
First, Nikon below (for comparison): Increasing shutter speed reduces exposure of continuous light (same as sunlight). This is Not the flash doing this, it is effect of ordinary shutter speed on any continuous light. We compensate with wider aperture for same Equivalent Exposure (not done here). All are HSS Full manual power.
Nikon below: Increasing shutter speed should not affect TTL, which meters and adjusts power level to remain constant (providing it has enough power to do it). However, I was not compensating with a wider aperture (for an equivalent exposure), and the power demands of 1/4000 f/8 ISO 200 was not at all equivalent to slower values, so TTL ran out of flash power trying. The flash could not deliver (my fault). The SB-800 was warning that I was asking for 1/3 stop more power than available at 1/2000 second, which is really handy. NW985N does not warn of this, but it is not trying to control HSS TTL exposure.
Nikon below: Decreasing power level reduces exposure of manual flash. All are 1/320 second HSS.
HSS mode has to reduce maximum power by about 2 1/3 stops to be able to run continuously during the shutter travel.
This is just a comparison of what that lower power level difference would look like. HSS is about 20% power maximum.
I realize I made these many images too small, thinking it was only about brightness. At right is a bigger view of the banding that develops at fastest shutter speeds below, shown a little brighter here. And still a little bit of banding down at 1/2000.
This flash is Not a suitable HSS solution.
NW985N below: Increasing shutter speed reduces exposure of continuous light (same as sunlight). This is Not the flash doing this, it is effect of ordinary shutter speed on any continuous light. We compensate with wider aperture for same Equivalent Exposure. All of this row are HSS Full manual power.
NW985N below: Increasing shutter speed should not affect TTL, which meters and adjusts power to remain constant at any setting. However, that is not what is happening below. Neewer NW985N HSS stays constant power regardless of any level setting. The last two are down a little, but the SB-800 runs out of power there and goes black.
See the problem, above and below? To be continuous, Nikon HSS flashes "tens of thousands of times a second", I think something like 70 KHz. The NW985N is pulsing much slower, showing intensity variation at the fastest shutter speeds (the narrow shutter slit sort of freezes the action). It is not varying the flash power anyway, but if it were responding, it would run out of power at these same speeds too. HSS power is extremely different than speedlight mode. Speedlight mode just truncates the single full power flash pulse to reduce power. HSS has to flash continuously, so it needs a real way to lower power. Maybe there is something in there trying and straining, but it is not getting to the output.
NW985N below: Decreasing power OUGHT TO reduce exposure of manual flash. But strangely, power level has no effect here. 1/128 power does seems affected slightly, but it should be down seven stops (very black). All are ISO 200 f/8 1/320 second HSS.
The NW985N does necessarily reduce maximum power in HSS mode by a couple of stops of power, in order to run continuously. But then it simply just leaves it there, and does not adust for the power level setting, not for manual flash, not for TTL flash. ANY selected power level is ignored, and everything is at its maximum HSS power, and always gives the same result (no power selection is honored). We can control the exposure with shutter speed and aperture (like we control sunlight), but the flash offers no control of HSS maximum power. The umbrella distance was adjusted so that the NW985N HSS exposure did come out about ballpark right, only in a situation when about 1/4 manual power would be correct.
We cannot adjust the intensity of the Sun either, and still we learn to make do. But this is NOT a regular HSS feature, it needs a new name. I hear other customers mentioning the same problems, and it concerns me that they are willing to market and ship this flaw.
Nikon AWL with two remote wireless TTL flashes in two umbrellas. Point&Shoot TTL. Routinely with Commander, +1 EV Flash Compensation (affects both flashes) is needed, and certainly all this white in this scene needs even more too. I set +3 EV total here (+1 FC, +2 EC), which seemed a lot to me.
The Neewer NW985N is wireless remote group B on camera right (N slave mode). A Nikon SB-800 is wireless remote group A on camera left. Both are zoomed to 24 mm in white reflected 45 inch umbrellas (at full shaft length, both placed fabric at 45 inches). D300 Commander, ISO 200, f/5.6, 1/160 second (Not HSS). The NW985N has a power level problem in TTL mode with the Commander.
I am unhappy, does not look right. A little ratio always helps the tonal gradient shading, it is better lighting. The NW985N is just not cooperating here. The Commanders job is to set both TTL groups equal at the subject, and then we compensate one to create a lighting ratio. Notice the shadow on right above (table and base and head) from left Nikon, and no shadow on left from right NW985N. The NW985N is weak, not making any shadow, not contributing its share.
Wondering about this, I investigated to see how dim the NW985N was. Manual power can do f/22 here, which is f/5.6 + 4 EV. So just to be sure, these next four are done at f/2.8, which should reach +6 EV. The NW985N is just not trying. The flash menu shows TTL mode from Commander, but always shows Zero compensation (when it's not). But it does react to compensation (not correctly), and even the first one with zero Group B compensation is not right either. Dunno why, but TTL on Commander is not satisfactory. Manual flash seems fine.
Some effect of compensation (seen in how it fills the trigger shadow), but power level is way down. There is necessarily a shadow from one single flash. The extra background shadow is from the camera commander trigger signal. The camera is up on end, so the commander is in fact on the left. The internal flash is disabled, and the trigger is fairly weak, and easily washed out. The Nikon filter SG-3IR panel can prevent it. FWIW, at ISO 200, the trigger is metering f/2.8 (but camera is only at 3.5 feet). Can't meter TTL due to the preceding preflash and command, but NW985N seems not much more - it cannot obliterate the weak trigger shadow. The NW985N is 2 stops less than the standalone Nikon picture below. That's not right, only 25% of the power. The flashes are supposed to be equal here.
The Groups have zero added compensation, but with two Nikons working together (two equal flashes working together is 2x power, or one more stop), I had to back off on the camera compensation, to only +2 EV camera compensation (not unexpected on all the white).
Now equal left and right shadows on table and base, both filled by the other. How it is supposed to be.
Or rather... How it is supposed to be is that the lighting is always much better with a lighting ratio, one light about one stop lower than the other. Makes pleasing tonal gradients, less flat. But what I meant, in the case of two lights metered and set equal, equal shadows is how it is supposed to be.
One last look at f/8. SB-800 left, NW985N right. First two below are Manual mode in Commander, next two are TTL again. No camera compensation in this pass. I'm looking at the shadows. Commanders tries to set all TTL groups equal at the subject, until we compensate one for ratio. Here, they should look equal. NW985N TTL doesn't.
The Neewer NW985N Remote N mode does work with the Commander, but I'm very unhappy with its TTL power in this mode, it doesn't respond right. So close, but yet so far. The first pictures towards top of page (and the Manual pictures here) shows it has equal power to the Nikon, but something happens in this Slave N TTL mode. Manual Commander mode appears to work OK.
White Balance Cards: FWIW, the two white balance cards in pictures above are the Porta Brace White Balance card ($5 at B&H) and the more expensive WhiBal White Balance card ($20 and $30). Clicking one with the raw White Balance tool instantly corrects the color, which can be pretty bad until you do. You can click the pictures individually (done here, because each case was a different flash power, even a different flash, they varied quite a bit - see HSS section, which was not corrected, some pink, some blue). Or you can click one test picture (with card in it), and have it apply to all following pictures in the same lighting situation (like a portrait session). It makes color correction be very easy, and fast, and good ... extremely desirable.
I find the two cards to be interchangeable, equally good. I tend to use the Porta Brace card. Both normally vary about 50K clicking around on the same card, but normally they are very close to each other. Sometimes though, in some light, including the pictures above, now and then one card might differ up to 250K, sometimes one card higher, sometimes the other. But usually very near the same. Seems to make no real difference, but either card is tremendously useful.
NW985N Part 3 - Continued - Exposure Comparisons