[Ptr_Mrtn]

Apparently you've got your EV step set to 1/3 stop.
If you change it to 1/2 stop, you can select 1/180s as a shutter speed.
BTW, achieving illumination of the full frame (without black bars) is possible by using an HSS-capable flash connected to the camera and using its flash output as a trigger signal for one or more off-camera flashes.
You then got two alternatives:Use regular flashes at full power. At full power, most flashes generate a flash with duration 1/125s (not 1/800s, as you seem to believe). This is long enough (longer than 1/180s) to illuminate the full frame. You'll get a fall-off towards the top of the frame, though, as the flash pulse is not uniform but loses power exponentially towards the end. Use a flash that is capable of enabling an HSS-mode manually. Have a look at the respective description of the Cactus RF60. By using such HSS-bursts, you'll get even illumination across the frame. I always use my Cactus V6 and trigger it optically from an on-camera HSS flash. Up to 1/2000s this works by triggering on the main flash; if you need higher-shutter speeds, you need to trigger on the pre-flash and use a trigger delay.
There is one more alternative which is to trigger the camera and the flashes simultaneously with a remote trigger. However, due to the camera's shutter lag, you again need to use a trigger that supports a trigger delay (for the flash, to bring it in sync with the camera). I wouldn't go down that path, because the camera's lag is not always 100% the same (even when set to MF), so you'd probably get a number of unsuccessful attempts.

Thank you! So when using HSS, can you shoot on manual exposure? Or do you have to use exposure compensation to allow for other manual flashes to add to the exposure?? I heard you have to shoot PTTL when using HSS. Though this would be pretty illogical, it's also illogical that you cannot fire the flash past sync speed without didicated HSS

p.s. Some flashes are slower and some are faster at full power. My Yongnuo flashes fire at 320th of a second at full power and the old Vivitar 285s fire at around 800th at full power.

[clackers]

I heard you have to shoot PTTL when using HSS.

???

Where did you hear that?

Edit: I think you could be right.

Doing HSS in Manual camera mode is different from HSS in Manual flash mode ... Digitalis has pointed out the P-TTL info is used by the flash to work out its pulsing pattern.

[Class A]

So when using HSS, can you shoot on manual exposure?

Yes, no problem.

I heard you have to shoot PTTL when using HSS.

The on-camera flash has to be in P-TTL mode, P-TTL HSS to be exact.

Other than that, I'm not aware of any limitations.

p.s. Some flashes are slower and some are faster at full power. My Yongnuo flashes fire at 320th of a second at full power and the old Vivitar 285s fire at around 800th at full power.

Be careful to distinguish between T.1 and T.5 times.

Many manufacturers provide T.5 times (the time for the flash output to fall below 50%). This time is shorter than the more useful T.1 times (the time for the flash output to fall below 10%).

A less powerful flash will have a shorter full power output pulse, but flashes with approximately the same output power will have approximately the same output duration. It just takes some time for the capacitor to fully discharge. Note that at 1/180s, you will cut off a tiny bit of the full power of most flashes, as they are unable to deliver all of it in such a short period.

[Ptr_Mrtn]

Thank you Class A! You have been very helpful. I am going to buy a dedicated HSS flash and try this technique

[Oldbayrunner]

Thank you Class A! You have been very helpful. I am going to buy a dedicated HSS flash and try this technique

Just remember with only 1 Pttl HHS capable flash you will be restricted to on camera hot shoe flash for higher sync speeds. Otherwise for off camera you will need at least two, one needs to be able to do Pttl Hss in control mode and two or more need to be capable of Hss in slave mode. I have a Sigma 610 super I use as a Pttl hss controller, since it wont do Hss in slave mode, and two 540fgz's that will as hss slaves , so those for me work as a nice combination unless outdoors in very bright light.