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FORUMS General Gear Talk Flash and Studio Lighting 
Thread started 02 Jul 2015 (Thursday) 05:28
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How much parabolic are parabolic light modifiers ...

 
nixland
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Nov 10, 2015 00:02 as a reply to  @ post 17778168 |  #31

Thats a good suggestions.
I still find time to do such test for my modifiers.
Lets hope othe members can contribute their findings or test.




  
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PhilF
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Nov 10, 2015 00:25 |  #32

absplastic wrote in post #17778168 (external link)
For comparison purposes, I'd rather see the pattern projected onto a large flat wall than a mathematical analysis of the profile accompanied by speculation. For photography, what matters to me is the visual end result, which has as much to do with the interior reflective surfaces, cross section and diffusion layers as the shape. No parabolic modifiers commonly used are true parabolic surfaces of revolution, no matter how they look in profile, because they have cross sections that are most commonly hexagon, octagon or dodecagon rather than circular. None have mirror surfaces either, they all have diffusely reflective interiors.

for the record... I don't use modifiers on walls. I take portraits of people...and I judge the quality of modifiers on how it works on portraits of people. :-)


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SamFrench
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Nov 10, 2015 00:26 |  #33

PhilF wrote in post #17778256 (external link)
for the record... I don't use modifiers on walls. I take portraits of people...and I judge the quality of modifiers on how it works on portraits of people. :-)

bw!




  
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absplastic
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Post edited over 3 years ago by absplastic. (2 edits in all)
     
Nov 10, 2015 01:47 |  #34

PhilF wrote in post #17778256 (external link)
for the record... I don't use modifiers on walls. I take portraits of people...and I judge the quality of modifiers on how it works on portraits of people. :-)

I do both, actually :-) In fact, I light walls quite a bit with both umbrellas and softboxes, with and without gels.

Also, I suspect that "parabolic" is possibly being used as a sort of layman's term by the manufacturers, because it's a word a lot of people are familiar with. The OP's RiME LITE and the Westcott Zeppelin are, not surprisingly to me considering the purpose and nature of the flexible rods, almost perfectly catenary (black curves, the red are the parabolas), and it would not surprise me to find that the inner reflector is approximately at the locus, sort of like the inverse of a solar collector. This makes more sense to me than a true parabola, considering the goal for these really large modifiers is a large diffuse light source, not a spotlight for calling Batman. You want to be able to move the light back and forth in a smallish space and get a usable difference in coverage. Whether or not this shape is intentional engineering, or more the natural will of the flexed fiberglass rods, we may never know.


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nixland
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Nov 10, 2015 08:34 |  #35

The batman :) focused light might be useful if someone need the maximum output from the "parabolic", let's say for outdoor photoshot.




  
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Nov 10, 2015 20:39 as a reply to  @ nixland's post |  #36

I actually use a Norman Trilite for batman spot lights. It's focusable and you can put gobos too. I think the parabolic modifier cannot do the hard edge arc that a spotlight can do.

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absplastic
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Nov 10, 2015 21:35 |  #37

PhilF wrote in post #17779332 (external link)
I actually use a Norman Trilite for batman spot lights. It's focusable and you can put gobos too. I think the parabolic modifier cannot do the hard edge arc that a spotlight can do.

You're correct. To get actual parallel rays of light and a nice hard edge from a searchlight, the mirror has to be perfectly parabolic and shiny, and the light source has to be as close as a point source as possible. The diffuse (non-mirror-like) nature of the silver insides of photography parabolic modifiers makes their actual shape not critical. In the studio, obviously focusing the light with a lens, as with the Trilite, is more practical for that spotlight look than an actual searchlight, since you don't need a true parallel beam of light, just a cone of light with a well-defined edge.


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Nov 11, 2015 00:44 |  #38

nixland wrote in post #17774269 (external link)
I will check them. But from the shape of the back part I think the 120 is more parabolic.
I think its difficult for small size para to bend the back part to form a parabolic curve unless it has a special back parta design like bronco para 88.

But as I often said, one of my deep round "parabolic" softbox is not true parabolic ..but I like the light that comes out of it :)

Just curious if you had a chance yet to take a look at the Ricebowl modifiers. I'd be curious to see the findings you come up with (and yes, this is more of an intellectual exercise than a practical one. It won't affect whether or not I enjoy the modifier or prevent me from liking its output.) :-)




  
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absplastic
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Nov 11, 2015 01:45 |  #39

I looked at those two right now, since I already had the curves set up in desmos.com, and while the pictures are not perfectly symmetric or exactly in profile, the shape does appear closer to catenary (black) than parabola (red). Neither is quite narrow enough at the back to be a real parabolic shape. I'm pretty sure that this is just the natural shape you get when you bend a thin, uniform flexible rod into an arch.


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RicoTudor
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Nov 11, 2015 01:52 |  #40

That Norman Tri-Lite looks pretty sweet. The hard edge is the aperture (or stop) as focussed onto the target plane and, therefore, requires an optical system. I have the ProZoomSpot, Profoto's version of a followspot, but am not interested in the "Batman" effect. More useful to me is the hard light quality and the extremely uniform light distribution. Other modifiers like parabolic dishes, snoots or grids cannot emulate a projector. Here's the best effort by a Profoto 10° grid:

IMAGE: http://patternassociates.com/rico/fm/prozoomspot1.jpg

Sorry, no beautiful models handy at the moment. :) Light spread of this grid is attractive, and probably more useful in general, but simply cannot produce this effect:

IMAGE: http://patternassociates.com/rico/fm/prozoomspot2.jpg

Gear shots:

IMAGE: http://patternassociates.com/rico/fm/prozoomspot3.jpg

IMAGE: http://patternassociates.com/rico/fm/prozoomspot4.jpg

Canon, Nikon, Contax, Leica, Sony, Profoto.

  
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nixland
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Nov 11, 2015 06:15 as a reply to  @ PhilF's post |  #41

I use lightblaster and speedlite for the sharp edge circle spotlight.




  
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Nov 11, 2015 09:11 |  #42

absplastic wrote in post #17779542 (external link)
Neither is quite narrow enough at the back to be a real parabolic shape. I'm pretty sure that this is just the natural shape you get when you bend a thin, uniform flexible rod into an arch.

This is exactly as I suspected, absplastic. And I was wondering about that same conclusion about the bending rods. Thanks for going to the trouble of taking a look at those. VERY interesting.

I do like those modifiers a lot. Wish they were easier to assemble, but it's not a horrible experience once you get the hang of how do do so. The light they produce is very nice indeed. So I'll hang onto them for now. :-)




  
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absplastic
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Jan 14, 2016 18:38 |  #43

abbadon31 wrote in post #17620505 (external link)
Some bracket inspired by master shom ;)

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Scott, could you clarify what we're looking at here? I'm familiar with Cheetahstand's Ricebowl softboxes, but I thought they were all direct mount softboxes. These mounts look more like the focus tubes on the Broncolor and Breise paras. I also don't see anything like this on Cheetah's website. Are these custom or modded? And if so, what modifier are they meant to be used with?


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absplastic
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Jan 16, 2016 19:51 |  #44

I just ordered a RiceBowl-120 from Cheetah. I'm excited to try this out both as-is, and as a focusable para. This is why I asked specifically about these mounts...


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absplastic
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Post edited over 3 years ago by absplastic.
     
Jan 22, 2016 12:39 |  #45

My RB-120 arrived, and I set it up with no diffusor installed and played around with positioning a 600ex-rt with sto-fen at various points along the center axis, from 2" from the back, all the way to the plane of the front rim. When the light is near the back of the dish, it makes a concentrated hotspot, just like a focusable para. But as the light moves forward, it just illuminates the whole dish interior fairly uniformly. It do not see anything like the characteristic ring of light moving towards the edge of the reflector that you can see quite clearly in a Bron or Briese para as you move the focus tube.

My conclusion is, that while the RB-120 is a great deal and a fantastic light source when used as intended, I don't see any reason to adapt it for indirect mounting or focusing. It's simply not parabolic enough to have a focal point and function like a Broncolor para 133. I'm going to revisit my idea of making a fully DIY deep parabolic.

The one thing I would like to try with the RB-120--since I find that the Broncolors are the most magical when defocused to the point where they are a large ring light source--is replacing the inner white diffusion screen with a round silver reflector (homemade or a popup disc type), ideally black on the non-silver side, snapped in place of the diffusor with the silver side facing the strobe at the rear. If I can get all the light coming from the outer rim of the softbox, perhaps it will have a similar look to the Bron?


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How much parabolic are parabolic light modifiers ...
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