Calculating exposure

[Paul Ozzello]

Stupid question and I think I know the answer - but I tested a roll of velvia 50 and noticed that the best exposure on the roll was an accidental double exposure. Does that equate to 1 extra stop? So would two overlapped shots at f16 @ 1/30 be the same as one single image exposed at f11 @ 1/30th?

Paul

 

[BrianShaw]

Basically, yes... that's one way to do that.

 

[Chess]

Yes or f16 @ 1/15th
Just check the other frames all look like they are 1 stop underexposed consistently. If yes, then next time you can add this extra stop to all your exposures.

 

[Dwayne Martin]

You actually have to move to f/8 to double the exposure. 1 whole stop is always a doubling. The better question to ask is what gave you the incorrect meter reading in the first place.

 

[NB23]

You actually have to move to f/8 to double the exposure. 1 whole stop is always a doubling. The better question to ask is what gave you the incorrect meter reading in the first place.

Two things I see: A camera that underexposes by one stop at all speeds (two of my Rolleiflexes do that). And reflective metering instead of incident. Reflective metering will often give under exposed values.

 

[BrianShaw]

You actually have to move (from f/16) to f/8 to double the exposure. 1 whole stop is always a doubling.

Nope… doubling of light, certainly, but not always a doubling of the index number. Read about the difference between designation of a stop (doubling or halving) for shutter speed and film speed vs that for aperture.

https://www.photographymad.com/pages/view/what-is-a-stop-of-exposure-in-photography

 

[Dwayne Martin]

Nope… doubling of light, certainly, but not always a doubling of the index number. Read about the difference between designation of a stop (doubling or halving) for shutter speed and film speed vs that for aperture.

https://www.photographymad.com/pages/view/what-is-a-stop-of-exposure-in-photography

I stand corrected.

 

[pentaxuser]

Brian's link is a good explanation on the aperture number being the exception to the rule of doubling or halving but the other problem is that the article was written as if only digital cameras exist so this statement becomes suspect if we are talking about film ISO , doesn't it?

The quote from the article says:
"You could open the aperture wider to let in more light - moving from f/8 to f/5.6 is an increase of 1 stop, so we've got back to our original exposure. Alternatively you could double the ISO speed from 200 to 400, again resulting in a 1 stop increase"

I wonder at times if all newcomers to film realise that changing the ISO rating on the dial does not transform a 100 film into a 1600 film as if this were another alternative adjustment to changing shutter speed or aperture aperture

pentaxuser

 

[BrianShaw]

I wonder the same as you wonder.

Good catch on the quote. Poor wording, to be sure.

 

[wiltw]

So would two overlapped shots at f16 @ 1/30 be the same as one single image exposed at f11 @ 1/30th?

1. For ISO values, HALF the value to be -1EV less sensitive... 800, 400, 200, 100, 50...each step down is 1/2 as sensitive to a given amount of light
2. For shutter speeds, DOUBLE the value to be -1EV less light hitting the sensor/film... 125, 250, 500, 1000, 2000 -- which really is 1/125, 1/250, 1/500, 1/1000. 1/2000
3. For aperture values, multiple the value by approximately 1.414 to let -1EV less light going thru lens to hit the sensor/film... 4, 5.6, 8, 11, 16, 22

Two exposures of 1/60 f/16 = same total as one 1/30 f/16
So two exposures of 1/30 f/16 = same total as one exposure of 1/30 f/11

 

[faberryman]

I wonder at times if all newcomers to film realise that changing the ISO rating on the dial does not transform a 100 film into a 1600 film as if this were another alternative adjustment to changing shutter speed or aperture aperture

That works for digital so film newcomers used to shooting digital may have to learn the hard way.

A few years ago I took a Film Photography 101 course at my local community college so I had access to a darkroom while I was re-fitting mine. You would be surprised the stuff newcomers to film don't know: how to open the camera, how to load film, the necessity of advancing the film and cocking the shutter after making an exposure, the necessity of rewinding the film at the end of a roll before opening the camera.... And that's before learning the mystery of how to determine the correct exposure. I mean all this stuff is obvious after shooting film for fifty years or whatever, but to a film newcomer it is like the first day in your quantum mechanics class. Remember when you had to learn how to open your first flip phone. I remember flicking my wrist to open my first flip phone like Captain Kirk opening his communicator, and not being entirely successful.

 

[Auer]

I wonder at times if all newcomers to film realise that changing the ISO rating on the dial does not transform a 100 film into a 1600 film as if this were another alternative adjustment to changing shutter speed or aperture aperture

pentaxuser

The ISO settings matter if you have a camera with a built in light meter, If no meter then the camera doesnt even need an "ISO setting" unless it is just to remind you what you have loaded.