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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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Jul 21, 2015 04:59 |  #16

My Rime Lite Grand Softbox 120cm is .... not parabolic .. :)


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Jul 21, 2015 12:37 |  #17
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GregDunn wrote in post #17620828 (external link)
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Heck... what's that? A new kind of reflector called a spotdark?


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nixland
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Jul 22, 2015 04:57 |  #18

Let's go to some nerdy stuff ... :)

If mounted backward, the Godox AD360 with Bowens S-mount bracket has the advantage for the light spread angle, especially for deep parabolic modifiers.

Looking at the strobe head design (other than Godox and Quantum strobe), Broncolor has more protruding head while others have shallow ones.
Mounting them in the bracket will reduce the angle more.
Even by trimming the adapter as what I did in the picture below for my bowens mount strobe, the angle of light is still too narrow.

Correct me if there is something I missed.


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nixland
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Jul 22, 2015 04:59 |  #19

Or maybe we could use Fotodiox mount where no adapter attached around the strobe head :)


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Jul 23, 2015 13:05 |  #20

Alveric wrote in post #17639160 (external link)
Heck... what's that? A new kind of reflector called a spotdark?

Good name. ;-)a They say it's more like a wide angle reflector when you don't have the bulb extender installed, but I haven't tried to use it for photos like that...


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Aug 03, 2015 11:13 |  #21

Another brand to check?


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Aug 25, 2015 01:23 |  #22

nixland wrote in post #17640091 (external link)
Or maybe we could use Fotodiox mount where no adapter attached around the strobe head :)


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what is this Fotodiox mount called?


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nixland
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Aug 25, 2015 06:47 |  #23

PhilF wrote in post #17681985 (external link)
what is this Fotodiox mount called?

Hi Phil, I don't know and I think it's not sold separately.




  
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Nov 05, 2015 08:59 |  #24

nixland wrote in post #17617812 (external link)
I just found this site :

http://onemediacenter.​com/ (external link)

where we can draw a parabolic curve with variation parameters.
So I tried to google some of the parabolic modifiers and find a matching curve for each of them.
The black dot in the axis line is the location of focus point (our barebulb strobe).

As you can see in the picture, the Broncolor, PLM and Rime Lite are quite parabolic while the Westcott Zeppelin and Profoto umbrella are not.

I have the Paul Buff PLM, Rime Lite 120cm and Aurora Tera D (same as Westcott Zeppelin).
Though the Aurora is not true parabolic, I like its light output.

Any other parabolic modifiers I should check? :)

Very interesting find, nixland.

Yes, could you please take a look at the CheetahStand RB-90 and RB-120 modifiers?

If it helps, here are photos of the RB-90 and RB-120 from their site.


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nixland
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Nov 06, 2015 09:37 as a reply to  @ Ulysses01's post |  #25

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 :)




  
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Nov 06, 2015 23:00 |  #26

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 :)

Great! I look forward to seeing what you find out. :-)

You make a great point. Just because a modifier is not parabolic does not mean that it is a poor modifier. In fact, it can still suit the need very nicely.




  
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Nov 09, 2015 16:33 |  #27

Ulysses01 wrote in post #17774978 (external link)
You make a great point. Just because a modifier is not parabolic does not mean that it is a poor modifier. In fact, it can still suit the need very nicely.

I was wondering about the point of this thread, as it relates to this observation. Are these photographic analyses of the various modifiers just academic musing, or is there some actual quality issue at stake here?

A perfectly-reflective, perfectly-parabolic mirror with the strobe's flash tube right at the focus would not be ideal, because it would project more of a donut or halo shape than a smooth circle of light with nice falloff, simply because the parallel nature of the rays would mean that the strobe head itself would cast a shadow if set up in the umbrella way where it is aimed backwards into the modifier, or the shadow of the small internal reflector dish if the strobe is firing in from the rear. A small deviation from a true parabola, along with a diffuse reflective surface, would work together to prevent an obvious dark spot in the center, which would be more visible when there is no front diffusion layer (i.e. when the octa is being used like a silver umbrella, rather than softbox). That is to say, the fact that some of these modifiers are not perfectly parabolic is very likely deliberate engineering.


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Nov 09, 2015 19:21 |  #28

Ulysses01 wrote in post #17774978 (external link)
Great! I look forward to seeing what you find out. :-)

You make a great point. Just because a modifier is not parabolic does not mean that it is a poor modifier. In fact, it can still suit the need very nicely.

BUT..... by knowing if its true parabolic or not, you will avoid the fact of buying a modifier that can replicate what your modifiers that you currently have.

For example...why would you buy modifier A when your existing modifier X can do what modifier A can?

OR... If you buy modifier A and it can do what 2 of your modifers (x and Y) can do. .... you might as well buy and bring modifier A to shoots rather than lugging modifiers x and y.


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Nov 09, 2015 22:53 |  #29

PhilF wrote in post #17777949 (external link)
BUT..... by knowing if its true parabolic or not, you will avoid the fact of buying a modifier that can replicate what your modifiers that you currently have.

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.


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Nov 09, 2015 23:57 |  #30

absplastic wrote in post #17777774 (external link)
I was wondering about the point of this thread, as it relates to this observation. Are these photographic analyses of the various modifiers just academic musing, or is there some actual quality issue at stake here?

I posted this topic at first for just sharing my findings of how close to parabolic shape are the curve of the rod of some modifiers.

Along the way, I thought that this could be useful gor someone who need a parabolic modifiers, at least very close to parabolic shape.

When I said about non parabolic still give the very good light, my intension is that I dont want this thread to become a parabolic fan boy or zealotist :) which think that : parabolic = good, non parabolic bad. No.


A perfectly-reflective, perfectly-parabolic mirror with the strobe's flash tube right at the focus would not be ideal, because it would project more of a donut or halo shape than a smooth circle of light with nice falloff, simply because the parallel nature of the rays would mean that the strobe head itself would cast a shadow if set up in the umbrella way where it is aimed backwards into the modifier, or the shadow of the small internal reflector dish if the strobe is firing in from the rear. A small deviation from a true parabola, along with a diffuse reflective surface, would work together to prevent an obvious dark spot in the center, which would be more visible when there is no front diffusion layer (i.e. when the octa is being used like a silver umbrella, rather than softbox). That is to say, the fact that some of these modifiers are not perfectly parabolic is very likely deliberate engineering.

The strobe size is very very small compared to the diameter size of the modifiers shown above. I have done several testing of that modifiers and the shadow of the strobe is negligible.

The design of those non true parabolic is from deliberate design? Yes, it could be. But then we dont call it parabolic modifiers right? :)

Also with using diffuse reflective surface the light will not focus on tight spot and so its not a parabolic modifiers. Again, the comparison above could help someone who needs the true parabolic modifiers where the light comes out parallel from the center to the edge.




  
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How much parabolic are parabolic light modifiers ...
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