how to count "bulb" speed?


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tirza

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#1
hi guys

im confused about this lately.. :bsmilie:

lets say, i use my camera metering to meter a scenery.. its says for perfect exposure i need to expose with 30secs f/2.8.. (maybe its very dark at midnight)
then i wanna put an nd400 filter and use f/22 instead of f/2.8.. so i gotta use bulb..
then come the question.. how long should i expose for it?

wondering if there is a kinda formula to count this? :think:

thankss
 

ElectronZ

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#2
A shutter speed's stop is in steps of *2. Compensate for the difference in Aperture stops and multiply it to the time. And technically u would have the same exposure. Correct me if i am mistaken =)
 

megaweb

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#3
hi guys

im confused about this lately.. :bsmilie:

lets say, i use my camera metering to meter a scenery.. its says for perfect exposure i need to expose with 30secs f/2.8.. (maybe its very dark at midnight)
then i wanna put an nd400 filter and use f/22 instead of f/2.8.. so i gotta use bulb..
then come the question.. how long should i expose for it?

wondering if there is a kinda formula to count this? :think:

thankss
f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22
f/2.8 to f/22 is 6 stops

ND400 is 9 stops ND filter

So 6 + 9 stops = 15 stops :eek:

30sec, 1 min, 2 min, 4 min , 8min, _________________
 

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Dream Merchant

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#4
f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22
f/2.8 to f/22 is 6 stops

ND400 is 9 stops ND filter

So 6 + 9 stops = 15 stops :eek:

30sec, 1 min, 2 min, 4 min , 8min, _________________
I've never done suoer long exposure in digital, but does reciprocity failure apply to digital?
 

Prismatic

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#6
I've never done suoer long exposure in digital, but does reciprocity failure apply to digital?
Don't think reciprocity failure is much of an issue as compared to noise. In astro, splitting up the exposure and then stacking usually gives a more controllable result unless the subject is very very dim.
 

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#8
hi guys

im confused about this lately.. :bsmilie:

lets say, i use my camera metering to meter a scenery.. its says for perfect exposure i need to expose with 30secs f/2.8.. (maybe its very dark at midnight)
then i wanna put an nd400 filter and use f/22 instead of f/2.8.. so i gotta use bulb..
then come the question.. how long should i expose for it?

wondering if there is a kinda formula to count this? :think:

thankss
In the first place, why would you want to add a ND400 filter when it's already so dark!

f/2.8 is 6 stops from f/22, so simply add 6 stops to the shutter speed. By adding the ND400, you need to decrease the shutter speed even further, leading to hours long exposure even...

Samuel
 

ExplorerZ

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#9
f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22
f/2.8 to f/22 is 6 stops

ND400 is 9 stops ND filter

So 6 + 9 stops = 15 stops :eek:

30sec, 1 min, 2 min, 4 min , 8min, _________________
and god, its 240hr, i think either ur sensor will just go burst first or u run out of juice. :bsmilie:
:nono: to ur poor camera. :sweat:
 

tirza

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Jul 26, 2007
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#11
f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22
f/2.8 to f/22 is 6 stops

ND400 is 9 stops ND filter

So 6 + 9 stops = 15 stops :eek:

30sec, 1 min, 2 min, 4 min , 8min, _________________
oww i think i get it
so one change of aperture, one change of stop..
and when multiplying the speed by 2.. it is also one stop change..
izit sumthing like that?

- alternatve n ExplorerZ, haha this is just an example.. wont try it to my camera though.. the answer is 240hours?? :bsmilie:



btw thanks for all the replies ;)
 

Dream Merchant

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#12
I think TS was just asking, as an example, of how to calculate ... not really thinking of putting a 9-stop ND filter on.:cool:

Thanks guys, for answering ab reciprocity law failure in digital. Exposure stacking does sounds interesting! Time to do more research!
 

ExplorerZ

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#13
I think TS was just asking, as an example, of how to calculate ... not really thinking of putting a 9-stop ND filter on.:cool:

Thanks guys, for answering ab reciprocity law failure in digital. Exposure stacking does sounds interesting! Time to do more research!
:bsmilie: i think most of us were just kidding about it, don even think he can even see anything thru his VF with that kind of lighting+nd400. :sticktong
 

Dream Merchant

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#14
:bsmilie: i think most of us were just kidding about it, don even think he can even see anything thru his VF with that kind of lighting+nd400. :sticktong
Hmm ... yu'll be surprised what some people would do ... just for the sake of experimentation! :bsmilie: :embrass: Faded memories of climbing up on other people's roof-tops and taking one hundred and twenty minute exposures in the dead of night while walking up and down the entire block of houses out of sheer boredom and 'exploring' other neighbor's gardens and houses from a different perspective ... hahahaha!
 

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