Da... Verification of ASA & fstops

[peter k.]

Shoot one, B&W frame, yesterday.. and didn't check the ASA light meter setting... it was on 200 and was shooting TriX 400, which I usually shoot at 38O, but close enough to 400 for discussion... sooooo ... comparing it to 400...

I was two stops off?
As if I had opened up the aperture two stops say from, f16 to f8... correct?

Rest of the story.. before the next shot, discovered my error, and correctly set the light meter to the normal ASA... so was wondering how far off the first frame was going to be, and picturing the blown high lights in my mind before developing. This the wonder of film, (or for some its short coming), its not instant gratification. ;-)

 

[TimFox]

No, ASA 200 vs. ASA 400 is one stop.
One full stop is a factor of two in total light, which happens with twice the shutter time or 1/1.414 = 0.707 times the f-number (which doubles the aperture area) such as f/16 to f/11.

 

[peter k.]

haha...thanks... getting to be an old 'art, and couldn't remember.
Thanks for the clarification, and the shot may turn out fine. Time will tell.
Life is good!

 

[Thomas Bertilsson]

Develop the film 'normal'. All is well. Negative film is extremely tolerant of extra exposure.

When you look at film speed and f/stops, the logic is as follows:

1. Film speed - if you shoot ISO 400 film, double the speed or half the speed for one stop difference, (200 for one stop more exposure, and 800 for one stop less). Quadruple for two stops less (1,600), and quarter for two stops more (100). Etc etc etc

2. f/stops - works with a factor of roughly 1.4 for one stop correction. If you shoot at f/8 - multiply by 1.4 (8 * 1.4 = 11 -> f/11) for one stop less, divide by 1.4 (8 / 1.4 = 5.6 -> f/5.6) for one stop more. If you go two stops, 1.4 * 1.4 = 1.96, which is equal to 2 for all practical purposes, so TWO stops with the f/stop ring is a double or a half, like going from f/8 to f/16 (8 * 2 = 16, or 8 * 1.4 * 1.4 = 16), and from f/8 to f/4 (8 / 1.4 / 1.4 = 4, or 8 / 2 = 4).

I hope shutter speeds are self explanatory, as they are roughly like the film speed example.

 

[Klainmeister]

I'm sorry, but can you actually see a difference at 380 vs 400? That's such a minuscule difference that your shutter speed variances probably matter more.

 

[gone]

What Thomas said. Develop it normally, you will see a small difference, but if you didn't konw what frame it was on you would have a hard time finding it. That's the deal w/ Tri-X. What a wonderful film!, and it looks so good to boot. You won't see any difference shooting it at 380 either. Tri-X needs a full stop before you will see any difference. Getting your times and temps right, not to mention agitation, will have a bigger influence on how your negs look than a stop or two difference w/ good B&W films.

 

[MattKing]

No problem!

What meter lets you set it to EI 380????

Are you sure you don't mean 320?

320 is just 1/3 of a stop different from 400.

 

[peter k.]

but can you actually see a difference at 380 vs 400?

I doubt it...

What meter lets you set it to EI 380????

Ok you asked fer it. ;-)

Remember dem oldie but goodies.. Weston 9's... with a diode now, to use modern batteries..
vell dar is not an actual spot that says 380, but you can turn the dial just to the left, of 400, and well above the 'tick' mark, that locates 300.
So 380 vrs 400 probably will not be seen, and yes...

times and temps right, not to mention agitation, will have a bigger influence on how your negs look than a stop or two difference

this one, when he started with TriX, tried different ASA's, for the 1946 anniversary "orphan" (3.5x4.5) speed graphic camera, with its older lens.. and found that at 380, (which at that time he did not understand made no difference at all), with the way of my agitating, and time sequence, in the hard water he has to use, liked the results!

Sooooo.. nostalgia .... and have kept it that way. ;-0