Parabolic reflectors in the studio

Started Jan 21, 2018 | Discussions thread
Sailor Blue
Sailor Blue Forum Pro • Posts: 14,046
Re: Parabolic reflectors in the studio

I use classical shallow umbrellas and double diffused softboxes. My most used softboxes have a flush front diffuser but I have one set with recessed front diffusers and grids. I don't have any parabolic reflectors but some information about them is given below.

Some general concepts for anyone who isn't familiar with umbrellas and softboxes.

Shoot through umbrellas are light grenades, blasting light out in a sphere around the umbrella and potentially causing all sorts of stray light problems. Shoot through mode is best used when the subject to any nearby surface or the background distance is much larger than the subject to umbrella distance so stray light interference is reduced according to the inverse square.

A shoot through umbrella produces a hot spot and the closer the umbrella is to the subject the more evident a hot spot will be. The light on the subject from a shoot through umbrella drops off to the sides faster than it does with a reflection umbrella because of the convex shape of the light source.

A reflection umbrella with a black backing reduces the stray light problem by more than 1/2. Light still spreads out in a hemisphere around the umbrella opening but the intensity drops off smoothly to the sides. The light on the subject is more even from a reflection umbrella than a shoot through umbrella but if you get too close there is a darker central area, the shadow of the body of the light.

Silver reflection umbrellas produce more specular light than white ones. This means a silver umbrella produces a greater difference between highlights and shadows and somewhat harder light. How specular and hard the light is depends on whether the umbrella lining is shiny, matte, or pebbled.

Depending on the design a deep reflection mode umbrella should have a faster fall off to the sides than a standard reflection umbrella. Many are poorly designed.

A true parabolic reflector beams light at the subject. Whether the light is focused to an area smaller than the reflector, the same size as the reflector, or greater than the reflector depends on the position of the light inside the reflector and how close the shape of the reflector is to a true parabolic reflector.

Almost all umbrella parabolic reflectors are not even close to being parabolic in shape and do a poor job of focusing the light.  Many so called parabolic umbrellas are just deep umbrellas.

Adding a sock makes an umbrella into a softbox, sometimes called a brollybox. Reflection of the light off the inside of the umbrella is the first way the light is diffused, the sock is the second way the light is diffused.

A classical softbox has the light outside the umbrella and aimed toward the front opening. The light is usually diffused twice by inner and outer pieces of fabric.

If the front diffuser of a softbox is flush the light spreads out to the sides very much like it does with an umbrella or brollybox. This type of softbox and a brolly box basically work the same for photography. Adding a grid is more difficult than if the front diffuser is recessed.

If the front diffuser of a softbox is recessed you get less spread of light to the sides, giving you a bit better control of subject and background lighting since the amount of stray light is reduced. Adding a grid to the front of a recessed front diffuser softbox is easy.

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