sensitometry

[Christian Tanner]

hi guys!

 

i actually thought i know how to read a curve - but it turns out i might not...

attached is the curve of the super8 64t ektachrome.

 

am i right by stating that this film has a latitude of only four stops? where's my mistake?

 

thanx in advance!

 

tanner

[Dominic Case]

I guess you are looking at the strictly linear part of the curve.

 

The beauty of film emulsions is that soft roll-off at either end of the scale, which of course reduces contrast in the ectreme highlights and shadows, but nevertheless reaches out and reproduces a wider range of brightnesses.

 

The term "latitude" really refers to the amount you can vary the exposure of a given shot and still cature the tonal range you want: for example an emulsion that can record a range of ten stops has three stops latitude when the scene itself has a brightness range of seven stops.

 

So strictly, you should use the term "Useful Exposure Range" to describe the range of brightnesses that the emulsion can record. That is, from the exposure that just records anything at all that is different from black, up to the exposure that gives a tone that can just be distinguished from complete white.

 

Looking at the curve you posted, the shadow sensitivity starts at about bar3.9, (that is, -2.1 in more familiar terminology), and the highlights go on to about 0.2. It's not all straight line, but you would see differential detail at those values. That's a total range of about 2.3, or a little under 8 stops.

[John Atala]

the shadow sensitivity starts at about bar3.9, (that is, -2.1 in more familiar terminology), and the highlights go on to about 0.2. It's not all straight line, but you would see differential detail at those values. That's a total range of about 2.3, or a little under 8 stops.

 

Hi!

How did you convert these values? When I analyze curves like that the only ones that make any sense are the ones with camera stops......

 

thanks!

John