Godox lighting problem

[Hadron]

Evening all. I’ve come across a bit of a strange issue with my pair of Godox SK400 II lights. I noticed that for some reason the inverse square law had appeared to stop working which clearly is impossible but when lighting at 45° from the left the right hand side of my backdrop was lighter than the closer left hand side (shot with the camera in portrait orientation). I found if I inverted my camera the issue was reversed ie the image always has a gradient going from darker to lighter the same way relative to the camera. The camera is a Lumix S1R and the problem stays regardless of lens. I’ve also tried using an S5II and get the same effect and I’ve also tried dropping the shutter speed to well below the flash sync speed.
Out of frustration more than anything else I tried to replicate the effect with my AD200 Pro and had no issues there so I’ve come to the conclusion it is definitely something to do with the SK400s.
I’m guessing the fault most likely lies with the operator rather than the tools or is this just a glitch you have to put up with with cheapo lights? Image showing the effect below with the light as square on to the background as possible (forgive the garish paper it was the only colour I had in a reasonable size).

Lighting Problem by Jcw Photographic, on Flickr

 

[sk66]

Is this the correct orientation for the image; i.e. the gradient is a the top of the landscape image/bottom of sensor? If so, the flash is firing a hair late. It could be radio delay...

 

[Hadron]

Is this the correct orientation for the image; i.e. the gradient is a the top of the landscape image/bottom of sensor? If so, the flash is firing a hair late. It could be radio delay...

Yes. Straight out of camera. Is a delay something I can alter settings wise? Using a Godox ST-III TTL-T trigger if that makes a difference.
Thanks

 

[Hadron]

Is this the correct orientation for the image; i.e. the gradient is a the top of the landscape image/bottom of sensor? If so, the flash is firing a hair late. It could be radio delay...

Wouldn’t a radio delay also affect the AD200?

 

[sk66]

Wouldn’t a radio delay also affect the AD200?

Not necessarily... it could be a send delay, a react delay, or more likely a combination of both. Sometimes you can add delay to the transmitter, but you can't reduce it AFAIK. Are you in TTL or manual? I don't know if or why there would be a difference, but it's probably possible. If a wired connection solves the issue you know it's radio related.

It can also be positioning related... I.e. most antennas have a "cone of silence" where they don't cover/transmit as well. And the receiver could be in a less than ideal position (partially blocked). Most Godox transmitters have a distance setting as well.

 

[Hadron]

Not necessarily... it could be a send delay, a react delay, or more likely a combination of both. Sometimes you can add delay to the transmitter, but you can't reduce it AFAIK. Are you in TTL or manual? I don't know if or why there would be a difference, but it's probably possible. If a wired connection solves the issue you know it's radio related.

It can also be positioning related... I.e. most antennas have a "cone of silence" where they don't cover/transmit as well. And the receiver could be in a less than ideal position (partially blocked). Most Godox transmitters have a distance setting as well.

I’m shooting in manual. When I tried the AD200 I kept everything else the same (settings, position etc). I think I’ve got an old set of no name/un branded slaves and triggers somewhere. I’ll try and dig them out tomorrow and see if that makes a difference.
Thanks for your help. Really appreciate it as it’s been driving me nuts this afternoon.

 

[Dryce]

I think it would be worth eliminating the SK400 as being the problem.

Try triggering the flash manually in darkness with a very long shutter speed (or bulb) to eliminate the effect of trigger and shutter delay interaction. If the gradient is still present then that would suggest the flash unit illumination is uneven (possibly something to do with the flash bulb itself ?).

If the gradient goes away then that would suggest that the triggering and shutter have interaction.

- slow the shutter time and of the problem goes away then that would suggest it is flash duration and the rear curtain being closed while the flash is still illuminating.

- reduce the flash power and if the problem goes away that would also suggest it is flash duration and that the rear curtain is being closed while the flash is still illuminating.

- otherwise it might suggest that the flash is being affected by the front curtain in some way - which would imply that it is being triggered prematurely.

One other question - is the exposure from the flash consistent as the power changes. Does stepping through the power levels on the flash result in coniststnt steps in exposure. If not that might suggest the flash bulb or the controlling electronics in the flash are faulty.

 

[Hadron]

Thanks.

Try triggering the flash manually in darkness with a very long shutter speed (or bulb) to eliminate the effect of trigger and shutter delay interaction. If the gradient is still present then that would suggest the flash unit illumination is uneven (possibly something to do with the flash bulb itself ?).

I shall certainly try this.

- slow the shutter time and of the problem goes away then that would suggest it is flash duration and the rear curtain being closed while the flash is still illuminating.

- reduce the flash power and if the problem goes away that would also suggest it is flash duration and that the rear curtain is being closed while the flash is still illuminating.

I’ve already dropped the shutter speed in increments down to 1/60th of a second with no effect and also varied the flash power likewise with no effect.

One other question - is the exposure from the flash consistent as the power changes. Does stepping through the power levels on the flash result in coniststnt steps in exposure. If not that might suggest the flash bulb or the controlling electronics in the flash are faulty.

I’m 90% certain that the flash power is changing consistently through the range but again I will check to be 100%

Thanks again for your help

 

[Hadron]

Eeeeerrrrrm. A bit of an update on this. It might just possibly maybe a case of slight operator error. I decided to got through the steps @sk66 and @Dryce suggested and thought it was best to take a reference image using existing kit and settings before I changed anything. As I was doing so I noticed I'd inadvertently knocked the HSS setting on the trigger to on and upon turning it off again my problem appears to have disappeared. Needless to say I now feel a right royal prat but at least I seem to have got to the bottom of it.
Many thanks again to @sk66 and @Dryce for their help, it is very greatly appreciated.
I'm now going to skulk off to a dark corner and hang my head in shame

 

[Faldrax]

Eeeeerrrrrm. A bit of an update on this. It might just possibly maybe a case of slight operator error. I decided to got through the steps @sk66 and @Dryce suggested and thought it was best to take a reference image using existing kit and settings before I changed anything. As I was doing so I noticed I'd inadvertently knocked the HSS setting on the trigger to on and upon turning it off again my problem appears to have disappeared. Needless to say I now feel a right royal prat but at least I seem to have got to the bottom of it.
Many thanks again to @sk66 and @Dryce for their help, it is very greatly appreciated.
I'm now going to skulk off to a dark corner and hang my head in shame

It's amazing how easy it is to look at a problem, mentally tick of the things you 'know' can't be the reason, then spend hours looking for what might be the cause, only to revisit it later and realise it was one of the things you initially had decided were correct.

Glad you have it sorted - and don't feel too bad about it, I'm sure I'm not the only one of us who's done something similar myself.