Speedlight in 7' Westcott

[Deleted member 49428]

So I bought this white reflective 7' umbrella with diffusion panel to use with my AD360.
Then I thought it could be fun to try and measure how much falloff on the panel I'd have with a TT685.ø, WA panel out and dome mounted. I pointed the dome of a second 308B at the panel trying to maintain same distance of approx 5cm giving -1/2 stop at top, -2/3 stop at sides and - almost a stop at bottom of umbrella.
Possible causes of error.
Dome pics up light from a larger area and my be affected from more direct light from flash. But trying with bare season on meter yielded same results.
More?

 

[Phil V]

So I bought this white reflective 7' umbrella with diffusion panel to use with my AD360.
Then I thought it could be fun to try and measure how much falloff on the panel I'd have with a TT685.ø, WA panel out and dome mounted. I pointed the dome of a second 308B at the panel trying to maintain same distance of approx 5cm giving -1/2 stop at top, -2/3 stop at sides and - almost a stop at bottom of umbrella.
Possible causes of error.
Dome pics up light from a larger area and my be affected from more direct light from flash. But trying with bare season on meter yielded same results.
More?

To measure the light coming off it, I'd point it square at a wall and then measure the light by holding the meter flat to the wall at various points.

You haven't described your bracket, but I'd guess that the flash tube sits above the centre of the umbrella.

Frankly I'd be gobsmacked if a speedlight could get close to evenly lighting a brolly that size.

You're using a tiny flash tube, with a small highly polished reflector, through 2 fresnel lenses and a dome, there's no 'design' to that light pattern, it's a random bunch of 'stuff'.

 

[Deleted member 49428]

I'm using the godox S-bracket
I know I have an accessory pouch with a flat "dome" for the meter. I'll try and find that one and do another test.

 

[Deleted member 49428]

The way the flash and umbrella are placed in relation due to the bracket is an obvious source to some of the difference found

 

[Deleted member 49428]

Spend the afternoon working on the test design using the ultra milenum liquid candy cooled computer working out this hi-tech solution measuring through the tube just touching the fabric.



Oddly the difference are still the same. Less than a stop difference. I'm making a mistake somehow but where?
What numbers should I get?

 

[Phil V]

I'm confused as to why you think you've got it wrong

I gave you the 'best practice' test method earlier.

I also suggested why I'd expect to see something close to the results you've got.

I don't understand the question at all (given the above)

 

[Deleted member 49428]

I'm confused as to why you think you've got it wrong

I gave you the 'best practice' test method earlier.

I also suggested why I'd expect to see something close to the results you've got.

I don't understand the question at all (given the above)

Ok thanks I just didn't expect a speedlight would be able to do this.

 

[Phil V]

Ok thanks I just didn't expect a speedlight would be able to do this.

Well it doesn't, you're getting a stop difference in light across a modifier, whilst it's usable it's not 'right'.

To use the brolly for its intended purpose, I'd expect 1/2 stop fall off. Though I've never tested, I tend to stick to a bare bulb when using large or specialist modifiers.

 

[Deleted member 49428]

Yes the ad 360 is closer to 1/2 stop. I must say though that getting 1/2 to 2/3 of a stop across most of such a big modifier, only the bottom shows up to th full stop, is darned acceptable. Maybe not all of the modifier will give the "right" output but most of it will be within the acceptable so while the barebulb ad360 will be the flash of choice for this umbrella I won't have second thoughts of using it with a speedlight in a pinch.

 

[Phil V]

Yes the ad 360 is closer to 1/2 stop. I must say though that getting 1/2 to 2/3 of a stop across most of such a big modifier, only the bottom shows up to th full stop, is darned acceptable. Maybe not all of the modifier will give the "right" output but most of it will be within the acceptable so while the barebulb ad360 will be the flash of choice for this umbrella I won't have second thoughts of using it with a speedlight in a pinch.

The other issue though would be how much power you can get at 7' from the modifier from only a speedlight. (Which is why I'd have used that method for measuring)

 

[Deleted member 49428]

The other issue though would be how much power you can get at 7' from the modifier from only a speedlight. (Which is why I'd have used that method for measuring)

Yes but it will be the softest candle in the universe

 

[Garry Edwards]

Ok thanks I just didn't expect a speedlight would be able to do this.

It can't. You've tested it with a barebulb flash, which gives reasonably good results. The lighting will be very uneven if you use any flashgun fitted with a built in reflector - try it.

 

[Deleted member 49428]

It can't. You've tested it with a barebulb flash, which gives reasonably good results. The lighting will be very uneven if you use any flashgun fitted with a built in reflector - try it.

Eh I used a Godox TT685S. To my knowledge that is a regular speedlight. I did however use the wide angle fresnell thing and a white dome on it.

Hmm now you mention it maybe I should try @24mm setting and 14mm setting without the dome.

 

[sk66]

I'm not particularly surprised that you can get it that close to even being that it's a reflective umbrella... what I find a bit more surprising is that it's just about as uneven with a bare bulb. I would guess the light source is placed too far from the umbrella; probably necessary w/ the speedlight...

 

[Deleted member 49428]

Yes the barebulb flash need to get deep into the umbrella then we talk 1/3 stop max maybe even no difference at all. I seem to have misplaced my measuring tube so these were just done at the diffuser material.