# How to calculate very long exposures

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#### icelava

##### New Member
So i was reading this article on how one may use one's camera to suggest and determine the appropriate exposure duration. I got confused with Plan B - how does one extra stop stretch the exposure from 1 min to 32 min?

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#### catchlights

##### Moderator
Staff member
for the example quoted in plan B, is moving six stops for the shutter speed, for compensating on one stops at aperture plus five stops at the ISO, so it is this way

from ISO 3200, f11, 30sec
to ISO 1600, f11 1mins (60sec)
to ISO 800, f11, 2mins
to ISO 400, f11, 4mins
to ISO 200, f11, 8mins
to ISO 100, f11, 16 mins
to ISO 100, f16, 32 mins

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#### night86mare

##### Deregistered
yes, what uncle catchlights said, use STOPS to determine.

1 stop roughly doubles, so if you look at his post,

1: ISO3200 , f11, 30 seconds

when you HALF the ISO, that is one stop less, you have compensate by doubling exposure time to 60 seconds, the next line
2: ISO1600, f11, 60 seconds

similarly, for f-stops, the same applies. multiplying by 2 is really easy.

as to how to determine, just shoot at very high iso, if the histogram looks right, then adjust accordingly.

if the light is changing, then best to compensate a little, for example, if it is transiting into darkness, remember to expose more. long exposures are no joke, you don't want to wait 32 minutes to get nothing out of your wasted time, just because you didn't know what you were doing.

#### icelava

##### New Member
oh i see where i got "misled"; I was looking at Plan A's timings and thought 1 min was the max exposure at 5 stops, and took that as the baseline for Plan B. That is not correct, as Plan A was able to "stabilise" with a 2-second exposure, whereas Plan B was still asking for more than 30 seconds since there's not enough light. thanks

#### giantcanopy

##### Senior Member
If using film look out for reciprocal failure. The longer u expose the less sensitive the film. Usually they will come with charts to calculate the correction.

For digital .. calculate and shoot away!

Ryan

#### jnet6

##### Senior Member
can also use light meter.

But lots of testing need to be done on digital and it's "free" just lose 1 shutter count for each test. :bsmilie:

#### giantcanopy

##### Senior Member
But lots of testing need to be done on digital and it's "free" just lose 1 shutter count for each test. :bsmilie:
no joke leh especially for very long exposures, a few 10 + min test shot seems forever. .. .

I need to listen to a few mp3s on my ipod and slap some mosquitoes i between :bsmilie:

Ryan

#### jnet6

##### Senior Member
no joke leh especially for very long exposures, a few 10 + min test shot seems forever. .. .

I need to listen to a few mp3s on my ipod and slap some mosquitoes i between :bsmilie:

Ryan
Ya, that's true.... so i tried "shorter exposure" first with higher iso then work backwards for the actual shoot to get near satisfactory results for me.

#### night86mare

##### Deregistered
can also use light meter.

But lots of testing need to be done on digital and it's "free" just lose 1 shutter count for each test. :bsmilie:
shutter count is one thing.......

wait there for 10 minutes is another thing.....

when your camera cannot turn off noise processing is ANOTHER THING........... :sweat::sweat:

#### jnet6

##### Senior Member
shutter count is one thing.......

wait there for 10 minutes is another thing.....

when your camera cannot turn off noise processing is ANOTHER THING........... :sweat::sweat:
So total 3 "things" hehehe
Let's stop here, sorry for OTing.

#### shunzi

##### New Member
something like the triangle which DP school teach. balance is the key..

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