I just saw an "interesting" thread in a lighting group on Facebook. Basically, the original author said that it didn't matter if you used a speedlight or a strobe head in a modifier. Most of the replies said he was crazy, and that this would never work.

It just so happens that I have a large (48x72-inch or 120x200-cm) softbox set up with both its internal and front diffuser panels for a project I am working on. So, before jumping into the fray, I thought I would do something I wish more people would do. I tried it for myself!

My instruments of choice were a Canon 430EXii speed light and an Interfit Honey Badger strobe.

I started with the Canon set to full power and manually zoomed to the 35mm position. Sitting about 2 feet from the softbox this gave me a meter reading of f/10 at ISO 100. Pretty impressive for that little speed light.

Then I switched to the Honey Badger, which is a 320ws unit with a frosted glass dome over the flash tube. To get a reading of f/10 I had to set the power to 8, which would be the equivalent of two stops down from full power, or 80ws, or 1/4 power if you are used to working with speed lights and fractions. 

I present to you here selfies made with each light source in the large softbox. Apologies for my appearance as it was around 6am and I had just got out of bed when I read the message thread and decided to try it out. Can you tell which of these was made with the speed light vs the strobe head? The color temperature between them is quite different. The camera was set to "daylight" and no changes were made in post processing for this first pair. 

compare speedlight strobe 1

I also measured the front of the softbox at the center and at the top, bottom, and sides. And I photographed the front surface of the softbox to see the light pattern from the light source. For the strobe the surface read f/14 at the center and f/13 at the other points. 1/3 stop falloff from center to edges. With the speedlight the center read f/18 with three other points reading f/13 and one reading f/14, so about one stop falloff from center to the edges. Kind of expected as the speedlight has a fresnel lens that tends to concentrate the light coming out of it, even when set to a wider coverage (35mm in this case).

compare speedlight strobe 2

At this point I know a lot of people are going to start shouting HOT SPOT, HOT SPOT! My response to that is, so what!?! Unless I am photographing the surface of the softbox or some super shiny surface like a glass bottle or a polished stainless steel appliance which shows a direct reflection of the light source, this isn't going to have much, if any, effect on a portrait. Over the years there have even been asymmetrical softboxes on the market for portrait photographers to emphasize a hotter area of the light output. And for highly reflective product photography I would prefer to use "hard" boxes. That is a box with a plexiglass diffuser so there won't be any wrinkles showing or irregularities in the edges of the light source in the reflection.

Back to the original pair of photos. The one on the left (A) was made with the strobe and the one on the right (B) with the speed light. 

All-in-all, the strobe does win out. It has a bright modeling lamp available and recycle time is around one second. The speed light doesn't have a modeling lamp and at full power can take a few seconds to recycle between exposures. But still I say it is pretty impressive for that little speed light.

Thanks for following along!