Is 0.9 ND what I need?

Based on pictures that I shot yesterday (without an ND filter), I believe that I need a 0.9 ND filter in order to shoot portraits outdoors with an HSS strobe while at f/1.4.

I suspect that if I shoot at noon during summer, this will increase to 1.2-1.5 ND value.

Does my evaluation seem correct?

According to the sunny f/16 rule, you could move your shutter speed to 1/8000 and just need 1 stop (0.3 reduction) - see below. You could also consider a variable ND filter since this calculation would not account for the additional light your strobe would provide. You may want to consider shooting in open shade or using a scrim to reduce the light.


Sunny f/16 = f/16 ISO 100 S/S – 125

f/16 – f/11, f/8, f/5.6, f/4, f/2,8, f/2, f/1.4 = 7 stops

S/S 1/125 – 1/250, 1/500, 1/1000, 1/2000, 1/4000, 1/8000 = 6 stops

1 stop reduction = .3

Hmm, that's odd. I needed to be at f/3.5, 100, 1/3200. And it's winter.

EDIT: But maybe it was just my technique. I didn't use a gobo.

icor1031 wrote in post #18999280
EDIT: But maybe it was just my technique. I didn't use a gobo.

Not sure what a gobo would have to do with this. Gobo is a term normally used to describe something that would produce a specific light/shadow pattern (Example: window blinds, palm leaves, etc.)

bob_r wrote in post #18999501
Not sure what a gobo would have to do with this. Gobo is a term normally used to describe something that would produce a specific light/shadow pattern (Example: window blinds, palm leaves, etc.)

Interesting. That's not how the book I read on lighting used the term, and I'm not saying he was correct.

icor1031 wrote in post #18999644
Interesting. That's not how the book I read on lighting used the term, and I'm not saying he was correct.

I bought my first SLR over 60 years ago and I think of all the changes that have occurred in photography since then and it probably makes sense that a word's meaning may have evolved over that time too. I haven't read a photography book in quite a few years, so perhaps an alternative meaning for the term gobo has also evolved into something with which I'm unfamiliar. If so, I apologize for my comment.

bob_r wrote in post #18999694
I bought my first SLR over 60 years ago and I think of all the changes that have occurred in photography since then and it probably makes sense that a word's meaning may have evolved over that time too. I haven't read a photography book in quite a few years, so perhaps an alternative meaning for the term gobo has also evolved into something with which I'm unfamiliar. If so, I apologize for my comment.

Nah, don't apologize. As I understand it, a gobo is something that's used to block light -- typically with no pattern effect intended, though sometimes it includes that. So if you want to block sunlight from hitting the subject's face, you'll put up a large black card or such.

icor1031 wrote in post #19000044
Nah, don't apologize. As I understand it, a gobo is something that's used to block light -- typically with no pattern effect intended, though sometimes it includes that. So if you want to block sunlight from hitting the subject's face, you'll put up a large black card or such.

'gobo' is indeed a generalized term for something that 'goes between' to obscure some light...more specifically,

• to block light from a portion of the scene it is a 'flag' and
  
• when it casts a pattern (think 'stencil') it is a 'cucoloris'
  

icor1031 wrote in post #19000044
Nah, don't apologize. As I understand it, a gobo is something that's used to block light -- typically with no pattern effect intended, though sometimes it includes that. So if you want to block sunlight from hitting the subject's face, you'll put up a large black card or such.

I had not heard of a gobo being used in that context so I decided to look it up on Wikipedia to see how they defined it.
Here is a link to their description if you want to read the whole article: https://en.wikipedia.o​rg/wiki/Gobo_(lighting)

"A gobo is a stencil or template placed inside or in front of a light source to control the shape of the emitted light. Lighting designers typically use them with stage lighting instruments to manipulate the shape of the light cast over a space or object—for example to produce a pattern of leaves on a stage floor. Sources

The term "gobo" has come to sometimes refer to any device that produces patterns of light and shadow, and various pieces of equipment that go before a light (such as a gobo arm or gobo head).[1] In theatrical lighting, however, the term more specifically refers to a device placed in 'the gate' or at the 'point of focus' between the light source, called a lamp and the lenses (or other optics). This placement is important because it produces a crisp, sharp edged pattern or design (of logos, fine detail, architecture, etc.). Gobos placed after the optics do not produce a finely focused image, and are more precisely called "flags" or "cucoloris" ("cookies")."

At the bottom of the description they stated the following:
"Other usages
The term "gobo" also is used to describe black panels of different sizes or shapes placed between a light source and photographic subject (such as between sun light and a portrait model) to control the modeling effect of the existing light.[citation needed] It is the opposite of a photographer using a "reflector" to redirect light into a shadow, which is "additive" lighting and most commonly used. Use of a gobo subtracts light from a portion of an overall shaded subject and creates a contrast between one side of the face and another. It allows the photographer to expose with wider open apertures giving soft natural transitions between the sharp subject and unsharp background, called bokeh."

The "Other usages" seems to describe your definition and I was not aware of the term being used in that context. Thanks for the info.

Wilt wrote in post #19000173
'gobo' is indeed a generalized term for something that 'goes between' to obscure some light...more specifically,

• to block light from a portion of the scene it is a 'flag' and
  
• when it casts a pattern (think 'stencil') it is a 'cucoloris'
  

Correcting my own understanding!...

gobo is a stencil used INSIDE the theatrical lighting devices to cast a pattern/shape
cucoloris is stencil put in the path between the light source and the subject, to cast a patttern/shaoe
flag goes in the path between light source and subject, to block light from striking an area of the scene