exposure questions

[freddie bonfanti]

hi

 

when pushing the film, say a 200 ASA stock to 320 ASA, you just need to set the meter to the new ei number and shoot normally, making sure you notify the change of speed on the magazine once exposed, right? and thats a way to get an extra stop in low light situations, with increased grain as result. why then i often hear about people doing the other way around, when a 320 ASA stock is rated 200 ASA? why doing so? to get finer grain? whats visually the result of changin the speed of the film to a lower number?

[David Mullen ASC]

You request to the lab that they push or pull-process film in stops, i.e. PUSH ONE STOP. You don't tell them what ASA ratings you were using -- that's pretty much meaningless to them.

 

So you may take a 200 ASA stock and rate it a 400 ASA, underexposing by one stop, and have the lab push it by one stop. Or you may rate it at 320 ASA, underexposing it by 2/3's of a stop, and have the lab push it by one stop. This can be smart because it leaves you with 1/3 of a stop extra density (like overexposure) but also because pushing is not an exact science and you may not get exactly one-stop more density when asking for a one-stop push, so you are giving them some leeway.

 

Now however you rate it, if you shoot the grey scale in the same conditions, let's say rated at 320 ASA for a 200 ASA filmstock that is going to be pushed one-stop, then if that grey scale comes up 1/3 of a stop too bright, the timer / colorist doing the dailies will bring it down to normal looking in terms of brightness.

 

In terms of rating a stock slower than recommended, often processing normal (not compensating with development) so that the negative ends up denser than normal (overexposed), that is to reduce the appearance of graininess, add more shadow detail, and improve the blacks in the print, since when printing a denser negative "down" to normal brightness, you end up using higher printer light numbers. Above one-stop overexposure, however, you get into problems -- you are now starting to expose too much highlight information on the shoulder of the characteristic curve, you may start to hit the top limit of 50 printer light points (the scale is 0 to 50), plus if you really wanted to reduce grain, you might as well switch to the next slower-speed stock rather than overexpose a faster stock that much. Hence why most people stick to either a 1/3 or 2/3 of a stop overexposure (i.e. rate a 200 ASA stock at 160 or 125 ASA.)

 

Color negative film is made up of a fast and slow-speed layer for each color, and overexposing slightly causes more of the smaller, slower grains to get exposed (the larger grains always get exposed first because they have a bigger surface area exposed to the light -- that's why faster film is grainier.)

[Filip Plesha]

Pushing film doesn't REALLY give you an extra stop of speed.

 

It is a sort of an amplifying technique which boosts every recorded density by one stop, including the fog level and grain. So what you get is no more than you would have if you exposed it normally, but it's not amplified. If something is not recorded on film at all under normal exposure it can't be recorded when pushing either.

[freddie bonfanti]

You request to the lab that they push or pull-process film in stops, i.e. PUSH ONE STOP. You don't tell them what ASA ratings you were using -- that's pretty much meaningless to them.

 

thanks

 

i thought it was the same as still photography, where you tell the lab to develop the film at a given speed. but now everythings clearer. one more question: i read you always expose your negatives 2\3 of a stop slower, is that true? i mean in any situation? even if your lights and lenses would allow you to shoot normally?

 

thanks david

Edited May 18, 2006 by federico bonfanti

[David Mullen ASC]

Well, it depends on the project, but generally, yes, I basically treat the stock as if it were 2/3's of a stop slower, so that the processed negative is overall a little denser than normal.

 

On "Northfork" I rated the stocks normally but this was because I was flashing the negative to soften the blacks and colors, and then using a skip-bleach process to the prints to increase contrast, deepen the blacks, and soften the colors even more. So I didn't want a denser-than-normal negative because I didn't want it to get too snappy-looking -- I wanted a more muted look because the "snap" was going to be added by the printing process. Plus I shot most of the movie on 125 ASA Fuji stock, so overexposing to reduce graininess wasn't so important to me -- I didn't mind a little graininess and 125T stock is not particularly grainy.

 

But on something like "Akeelah and the Bee" I just shot & printed the movie conventionally, and rated the stocks (Kodak) 2/3's of a stop slower so that my printing lights would be higher than normal. And 2/3's of a stop is not much overexposure -- it only causes my printer lights to jump up about 4 to 5 points at the most (if a normally-exposed stock printed to look normal in brightness prints at 25-25-25, let's say, then I was printing more at 30-30-30.) Also, with a largely African-American cast, I felt safer by placing more low-level information on the negative by overexposing everything slightly. But I regularly rate stocks 2/3's of a stop slower anyway. But most of what I shoot ends up being printed.

[freddie bonfanti]

But I regularly rate stocks 2/3's of a stop slower anyway. But most of what I shoot ends up being printed.

 

 

one last question, david

 

would you treat 16 or s16 stocks the same way? can the film handle the 2/3rds of underexposure the same way?

 

cheers

[David Mullen ASC]

would you treat 16 or s16 stocks the same way? can the film handle the 2/3rds of underexposure the same way?

 

Yes, color negative stocks can. But it's OVER-exposure when you rate a stock slower, not underexposure.

[John Pytlak RIP]

would you treat 16 or s16 stocks the same way? can the film handle the 2/3rds of underexposure the same way?

 

Although the effect of exposure on tone scale and color reproduction is NOT dependent on the format (image area), the increase in graininess that you get with underexposure or push processing IS more critical with smaller formats. So proper exposure is a bit more critical for Regular-16 than Super-16, since any increase in granularity will be magnified more.