exposure

[freddie bonfanti]

hi all

 

my question is simple..given a EI number, say 200, how do you know what fstop will be the "middle gray", the fstop that places right in the middle of the curve?

 

thanks

 

freddy bonfanti

 

edinburgh college of art

[Stephen Williams]

hi all

 

my question is simple..given a EI number, say 200, how do you know what fstop will be the "middle gray", the fstop that places right in the middle of the curve?

 

thanks

 

freddy bonfanti

 

edinburgh college of art

 

Hi,

 

Using a light meter is a good start! Light meters are calibrated to between 12% and 18%.

If you have not got one and its a sunny day try f32 at 25 fps.

 

Stephen

[David Mullen ASC]

Don't you have a light meter?

 

If you're in full sunlight, I know it's always about f/16 to f/16.5 at 50 ASA / 24 fps / 180 degree shutter.

 

The other rule is that 100 footcandles = f/2.8 with 100 ASA film (24 fps / 180 degrees). But even that rule requires a light meter.

[K Borowski]

If you don't have a stand-alone lightmeter, you can use the onboard lightmeter of a 35mm SLR; they work just as well. Also, if you really want to nail down exposure, you can rent a professional polaroid camera, a MF camera with a pola back, or use a DSLR set at the same or near ISO to the stock you're using to evaluate its exposure characteristics. IMO polaroids are the quickest for really nailing down what aperture you want. If you have time though, you can do all kinds of specialized tests to really nail down lighting. SHoot a test roll with the same sky conditions that you'll want to shoot the actual shot with is the surest way to know that you'll get exactly what you want.

 

Regards.

~Karl Borowski

[Chris Keth]

If you don't have a stand-alone lightmeter, you can use the onboard lightmeter of a 35mm SLR; they work just as well. Also, if you really want to nail down exposure, you can rent a professional polaroid camera, a MF camera with a pola back, or use a DSLR set at the same or near ISO to the stock you're using to evaluate its exposure characteristics. IMO polaroids are the quickest for really nailing down what aperture you want. If you have time though, you can do all kinds of specialized tests to really nail down lighting. SHoot a test roll with the same sky conditions that you'll want to shoot the actual shot with is the surest way to know that you'll get exactly what you want.

 

Regards.

~Karl Borowski

 

 

The polaroids and DSLRs will help you to evaluate exposure, but be aware that both have exposure lattitude different than that of negative film.

[freddie bonfanti]

i do have a light meter, the only thing i didnt quite understand is that on the first measurement the reading was 2.8 so i have been suggested to get more light in order to achieve a reading of 4.0 ... thats what i didnt understand, why do i need a 4.0? is it maybe because of the lens i was using? (9 millimiter wide angle for a 16 mill arri sr2) maybe having a 4.0 was good to get more darker zones and therefore have a balanced shot...i think that must be the reason, i didnt ask why i just wanted to shoot since we had not time at all. having the aperture at 2.8 would have got me a overexposed shot since the middle grey would have been one stop more than the maximum aperture...

 

i am definitely loving my hard way to get to all this knowledge but i just need someone to tell me that was the case and my assumption was right

 

thanks

[David Mullen ASC]

Well, it all depends on how and what you are metering, but assuming it was an incident meter and you were reading the main light on the subject, if it said "f/2.8" then that's the correct exposure for an average brightness where 18% gray would read as 18% gray, etc.

 

Now perhaps your particular lens did not look particularly good at f/2.8, hence the advice to get the key light up to f/4. Or perhaps your subject was a little dark compared to the surrondings, hence adding more light would have balanced it with the background. Once you added more light and then metered it and got an "f/4" then that would be the "correct" exposure to render the subject at average brightness.

[freddie bonfanti]

Well, it all depends on how and what you are metering, but assuming it was an incident meter and you were reading the main light on the subject, if it said "f/2.8" then that's the correct exposure for an average brightness where 18% gray would read as 18% gray, etc.

 

Now perhaps your particular lens did not look particularly good at f/2.8, hence the advice to get the key light up to f/4. Or perhaps your subject was a little dark compared to the surrondings, hence adding more light would have balanced it with the background. Once you added more light and then metered it and got an "f/4" then that would be the "correct" exposure to render the subject at average brightness.

 

 

 

 

thanks mr mullen,

 

but if the right exposure was 2.8 i reckon i would have had the background out of focus so thats why they told me to get a 4.0, to get more depth of field..NOW I GET IT...i feel so stupid actually, it was so clear!

 

its always reveting and inspiring to get you people's replies, i feel like this forum is a sort of a teaching class!