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Tue Dec 09, 2014 11:28 am

Joined: Tue Dec 09, 2014 11:18 am
Posts: 3

Hi,

I have read a similar discussion on this forum yet haven t find an answer to this i.e the darker center spot I have when the deflector and the grid are mounted together ( on a E640). The "shadow" projected by the deflector is kind of 0.7/1 stop darker than the outer light. Of course the effect is more pronounced when the BD is closer ( 3-4 feet) to the subject ( smaller spot yet darker) I have tried to vary the distance of the deflector plate inside but I couldn t get rid of this shadowy area .

Is anything wrong ma I doing? any help? thanx.




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Tue Dec 09, 2014 3:48 pm

Site Admin
Joined: Tue Dec 08, 2009 10:43 am
Posts: 5266

When the deflector is is installed on a beauty dish, there is an area where light is blocked. As you back out, the larger area of light around the blocker starts to spread filling in the shaded area. Back off further, even more light fills in, until you get to the point it is all effectively homogenized.

(http://en.wikipedia.org/wiki/Umbra,_pen ... d_antumbra)

When you add a grid, the larger area of light is does not spread as quickly as with no grid, so the dish will need to be moved back farther. The tighter the grid, the more it will need to be moved back.

Which Beauty Dish and which grid are you using?




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Tue Dec 09, 2014 7:33 pm

Joined: Tue Dec 09, 2014 11:18 am
Posts: 3

thank you so much for your answer. I have the 22" silver HOBD and the 30 deg grid.




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Wed Dec 10, 2014 2:44 pm

Joined: Thu Jan 27, 2011 12:33 am
Posts: 101

I have an older 20" model and I've been toying with the idea of replacing that aluminum shield (dark spot) with a Lexan clear circular piece and maybe a layer of ND filter attached to it held by the nut. Glad you mentioned about one stop as I think Lee or Rosco make them in heat-proof sheets for theater lights, maybe. Might let a little more light in the middle and not so dark there.




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Wed Dec 10, 2014 7:27 pm

Joined: Tue Dec 09, 2014 11:18 am
Posts: 3

Technical Support wrote:
When the deflector is is installed on a beauty dish, there is an area where light is blocked. As you back out, the larger area of light around the blocker starts to spread filling in the shaded area. The tighter the grid, the more it will need to be moved back.

Which Beauty Dish and which grid are you using?


Hi I have run a few tests. Yes , situation improve by backing the deflector. Yet photographing directly into the BD you can clearly see a quite amazing circular are just outside the deflector that is lighter in tone (less intense) This area stops when the beauty dish changes its shape i.e when th bottom start to close to make the shape it has. By projecting on a white wall and measuring with a sekonic this lighter area is a 1/3 of a stop lower. When I use the 30 grid the situation is more dramatic. Even if I back the deflector almost to the end of its pole, the darker spot is 2/3 of a stop lower with respect to the outer light ring projected outside. Is this thing bother just me? I haven t heard of any other BD having this same beahaviour. Actiually using a gridded bD into a face in a close up results in quite evident underesposure. Can anyone suggest a solution?




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