How big of softbox with my speedlight???

We often see discussions by lighting novices who want to put their speedlight into a very large softbox. This thread addresses that desire, and how well/poorly that can be achieved.

First some principles...

• Many studio flashes use a bare bulb (reflectorless) head to spread light more evenly within a softbox, so that the sides of the box are used to scatter light more evenly across the front face of the softbox and avoid hotspots.
  
• Most speedlights achieve variable coverage angles thru lhe front lens, and 24mm (FF) FL coverage is the normal max without a supplementary lens; with supplementary lenses, some speedlights achieve 20mm Fl coverage.
  
• Some, but not all, softboxes employ 'double diffusion', in which a diffusion panel is placed between the flash and the front panel, in an effort to reduce hotspots from forward facing flash heads

Before I broke down the softbox, I decided to put the double diffusion panel back inside, and shoot with the 30mm standard coverage angle of the 45CT, to see how it improves upon coverage (it doesn't really do an adequate job) and reduction of hotspots (it does eliminate the star pattern)

Here is another reference on the subject
Link

I have been told that the X pattern in your diffusion panel is from the wrong type on ripstop nylon being used. This is typical from lighting products with a China origin.

ElliotD wrote in post #15265007
Here is another reference on the subject
Link

I have been told that the X pattern in your diffusion panel is from the wrong type on ripstop nylon being used. This is typical from lighting products with a China origin.

Like most of the name brand modifiers arent made in china...

Guess it depends on what you call "Name Brand"
Some brands have been used in the photo and film industries in the USA for decades.
I think Elinchrome is made in India

Wilt thanks for your tests. I was wondering though. Can't you underexpose even the most expensive studio strobe in a softbox to show the flash tube/hot spot.

ElliotD wrote in post #15265207
Guess it depends on what you call "Name Brand"
Some brands have been used in the photo and film industries in the USA for decades.
I think Elinchrome is made in India

Wilt thanks for your tests. I was wondering though. Can't you underexpose even the most expensive studio strobe in a softbox to show the flash tube/hot spot.

Dont confuse USA companies with USA made.

gonzogolf wrote in post #15265223
Dont confuse USA companies with USA made.

Of course not
Plume, Larson and Chimera are not made in China. Neither is Elinchrome I believe they are made in India.

In this test, I mentioned that I used a well recognized name brand which has long been associated with quality affordable softboxes -- Photoflex, located about 90 minutes from where I live. Looking at the softboxes, country of origin is not sewn on, and the boxes went to the recycle bin decades ago.

Yes, that is the point...showing how well speedlights fill softboxes! Notice the severe vertical cutoff without double diffusion when the flash lens fails to fill the front panel, and notice that there is no apparent vertical cutoff with the same lens coverage angle used with the double diffusion helping to bounce the light around before it strikes the front panel.
Doing such a test with a rear facing bare tube studio flash would show the superiority in evenness of illumination.

The same tests repeated with a variety of brands and quality levels would certainly show which designs do a better job, and how poorly some might fare.

Pretty sure Photoflex is made in China. Not a bad company IMO.I would see about a replacement panel because that X pattern is not normal for a quality nylon diffusion material. Sounds like your softbox is old. Maybe they upgraded the material.

Inverse square law explains the fall off with one panel @ 24 mm. The light is closer to the center of the panel than the edges. It could never be completely even with a forward facing flash head. Two panels create and larger light source inside the box making the distance from the center to the edge shorter. Not sure what softboxes do not come with a inner panel but I agree those will not work well for even light, regardless of the flash head used.

Which leads me to ponder the 50" Westcott Apollo... where the Speedlite is directed toward the back of the softbox and light is reflected back toward the front panel for more even illumination. An obvious trade off is the efficiency of the reflected material (i.e. how much light is lost via the reflected light)... Has anyone used the 50" with Speedlite(s)? I don't know that I've heard of too many people with it. I've got the 28" and based off it's output, I'd want to say the 50" would be a setup that may need a tri-flash bracket...

With a LiteDome XTC, there is no removable and replaceable front panel...it is sewn on. That is probably about 20 years old.

It's my understanding that Joe McNalley uses a Stofen on his speedlites to even out the front panel.
That should help. (Can't remember where I saw that, I think on this forum.)

The biggest problem for any light source inside a modifier is the size, shape and position, relative to a reflector, of the flash tube. Monolights have benefit of relatively large circular flash tubes that are in front of any reflector built into the head.

Quantum and a couple of others, have a flash tube that takes a couple of twists inside a protector. These tubes stick a couple of inches out from the head and a reflector.

Speedlites have the disadvantage of having the tube flat, recessed into a reflector. The only way to get the light forward is to zoom it to widest angle and drop the wide angle fresnel. Joe McNalley, apparently, thinks that adding the stofen turns the source into more of a bare bulb. Since the light is embedded in a modifier that seems to be a good solution that won't degrade the light quantity excessively.

dmward wrote in post #15267843
It's my understanding that Joe McNalley uses a Stofen on his speedlites to even out the front panel.
That should help. (Can't remember where I saw that, I think on this forum.)

The biggest problem for any light source inside a modifier is the size, shape and position, relative to a reflector, of the flash tube. Monolights have benefit of relatively large circular flash tubes that are in front of any reflector built into the head.

Quantum and a couple of others, have a flash tube that takes a couple of twists inside a protector. These tubes stick a couple of inches out from the head and a reflector.

Speedlites have the disadvantage of having the tube flat, recessed into a reflector. The only way to get the light forward is to zoom it to widest angle and drop the wide angle fresnel. Joe McNalley, apparently, thinks that adding the stofen turns the source into more of a bare bulb. Since the light is embedded in a modifier that seems to be a good solution that won't degrade the light quantity excessively.

I could certainly see the reasoning behind that, obviously getting a more even spread from the Speedlite. However, it also comes at a cost of losing a stop (?)...

drvnbysound wrote in post #15268522
I could certainly see the reasoning behind that, obviously getting a more even spread from the Speedlite. However, it also comes at a cost of losing a stop (?)...

That's what I don't know for sure. Since all the light is bouncing around in the box and eventually coming out the diffusion panel maybe not that bad.

OK,
Did a quick test. Primarily to see impact of stofen bare bulb dome on the output in a soft box.

All the exposures were made at same camera settings; 1/160, F16, ISO 200, 50mm on 24-70 lens. The raw images were imported into Lightroom using my standard import preset;
Custom camera profile for 5DIII by serial number; Exposure 0, contrast 0, Highlights -50, Shadows +50, Whites -50, Blacks +25, Clarity +15, Strong tone curve.
With these setting none of the images had highlight or shadow clipping indications.
Removing the preset settings from the Upper and Lower left images did not cause any clipping in highlights or shadows and did raise the brightness readings about 8% at the four corners and the middle.

Soft box is a 90cm Westcott knockoff with a YN-560 at 1/4 power.

Upper left is with flash zoomed to 50mm, upper right is flash zoomed to 24mm.
Middle left is zoomed to 24 with wide angle fresnel lens down.
Middle right is 24 zoom, wide angle fresnel and stofen dome.
Lower left is 24mm zoom, no wide angle fresnel and stofen dome.
Lower right is with front diffusion panel pulled back half way to show how light is setup.

For all the images but the last, the readings in Lightroom develop module were 90% plus or minus 3% along a line from the dark spot where the RF-602 is touching the diffusion panel. All four corners are within 10% of the center point. The brightest area on the silvered back of the soft box in a similar spot to the other tests measured 98%.

It appears, at least when using this type soft box, that the stofen dome does not cost an appreciable amount of light. It also does not add appreciably to evening the light which is already quite even across the soft box face.