shutter speeds for long exposures

marky.b

marky.b

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when using bulb setting for long exposures is there-an easy way to calculate the shutter speed needed without guessing
also with regards to in camera noise reduction i now switched mine off as on exposures ive done that go in to minutes, its a real pain waiting the same time to shoot the black frame to go with it. how practical is it to shoot the black frames after returning home. ie: if the exp was say 3 mins at f16, shoot a black frame with the same settings. either when getting home or at a later date
 
Nope you guess. Experience wins out on this one. You take some, then some more and more again and you learn. It all depends on what you are shooting, how fast it's moving and how much light there is.

Dont know what you mean with noise reduction. In camera noise reduction is OK to a point, but if you are going to astronomical photography then there are all sorts of techniques that can be used to remove camera/sensor/heat noise
 
If it's not too dark, you could meter a shot in aperture priority (perhaps even take a test shot or two) with your aperture wide open and your ISO turned up and then calculate from there, based upon the exposure time calculated by your camera.
 
the long exposures would be landscape only ie; moonscapes etc
with the black frame question, ive heard that when camera does the noise reduction it shoots a black frame at the same settings of the photo that you just took and overlays it on to the photo to remove noise etc
read somwere that shooting a black frame later ie: shoot with lens cap. same settings as the photo and then overlaying it in photoshop to remove long exposure noise. was just wondering how this compared to using in camera settings
 
mr_pants said:
If it's not too dark, you could meter a shot in aperture priority (perhaps even take a test shot or two) with your aperture wide open and your ISO turned up and then calculate from there, based upon the exposure time calculated by your camera.
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i think this is what i was getting at, but not sure how to do the calculations
any ( simple ) tips on how to do it
i normally crank up to 3200 iso at first to check on composition and focusing
 
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Moon shots don't require a long exposure, in fact its surprisingly bright, unless of course your talking about a moonlit landscape.

Dark frames should really be taken at the same time as shooting, that way the camera is at the same temperature etc.

Dark frames are normally put into astro software along with the main shot and then subtracted from it, try registax its free and covers dark and flat frames.
 
iancandler said:
Moon shots don't require a long exposure, in fact its surprisingly bright...
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Agreed - the bit of the moon that you can see is actually in extremely bright sunlight. It's just the black bit around it confuddles the metering on the camera. Start off in manual with settings of 1/250 s at F/8, ISO 200 tripod mounted and adjust from there.
 
thanks for all your reply s
however i you are all misunderstanding what i meant.
not photographing the moon or astro photography.
im talking about doing say, normal landscapes but doing them after dark rather than in the daytime. using moonlight instead of sunlight .
when 30 sec is not enough its time to switch to bulb. just wanted to know how to calculate what shutter time would be required rather than guessing.
for example if i do a sample shot at 3200 iso to check composition and focusing
and say it give a shutter of say 20 sec @ f8 and iso 3200 how do i work out what shutter would be for iso 100 at f8
the same technique would be used to photograph landscapes with star trails
 
divide 3200 by 2 until you get to 100 and times the shutter speed by the same factor

so:

3200
1600
800
400
200
100 = factor of 5

double the shutter speed 5 times to get the equivalent.
 
marky.b said:
thanks for all your reply s
however i you are all misunderstanding what i meant.
not photographing the moon or astro photography.
im talking about doing say, normal landscapes but doing them after dark rather than in the daytime. using moonlight instead of sunlight .
when 30 sec is not enough its time to switch to bulb. just wanted to know how to calculate what shutter time would be required rather than guessing.
for example if i do a sample shot at 3200 iso to check composition and focusing
and say it give a shutter of say 20 sec @ f8 and iso 3200 how do i work out what shutter would be for iso 100 at f8
the same technique would be used to photograph landscapes with star trails
Click to expand...

I thought that my guess was close :)

Anyway, for each halving of the ISO setting, you'll need to double your exposure time. For your example, ISO 3200->1600 means that shutter speed goes from 20 secs to 40 secs, 1600->800 means 40secs becomes 80 secs, etc. Comes out at 640 seconds when I do it in my head.

Don't forget that you can always do your metering and test shots using a wider aperture and factor that into your calculations, too.
 
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right im sort of understanding it
so every time you lower the iso the speed doubles. im ok with that bit
i dont understand using the wider aperture in to the calculation.

and bomberman im a bit confused by your calculations
 
so every time you lower the iso the speed doubles
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Not exactly - every time you HALVE the iso the shutter speed doubles.

In my example i've had to halve the iso 5 times to get from 3200 to 100, so the shutter speed doubles 5 times (or doubles by a factor of 5)
 
OK, a 'stop' is a doubling or halving of the total amount of light (near enough). If you establish equilibrium with a set of settings and then alter one of them, one of the others has to change to reestablish that equilibrium. Halving or doubling the ISO setting means that you would have to double or halve (respectively) your exposure time. If you change your aperture, then the numbers get a bit more complicated. Each stop (wrt aperture) is a halving or doubling of the area, which means that it is a reduction (or increase) in the diameter of the actual aperture of a factor of 1.4 (square root of two). So that the aperture series goes: 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16....

Once you know this, you can apply it. So, if you had shot your test picture at f/2.8 and wanted to shoot at f/8, then you'd need to double your exposure time three times i.e multiply it by 8.


Now I've reread what I've written, it looks most unhelpful. I hope it makes more sense to you than it does to me.
 
ok ive read it
im now going to sleep on it and then ill have another look at it tomorrow
hopefully it will sink in
thanks
ill let you know how i get on with it
 
Sat the 14th's issue of amateur photographer has a piece on moonlight photography including how to calculate exposures.

It should still be in the shops as I got my issue today
 
marky.b said:
when using bulb setting for long exposures is there-an easy way to calculate the shutter speed needed without guessing
also with regards to in camera noise reduction i now switched mine off as on exposures ive done that go in to minutes, its a real pain waiting the same time to shoot the black frame to go with it. how practical is it to shoot the black frames after returning home. ie: if the exp was say 3 mins at f16, shoot a black frame with the same settings. either when getting home or at a later date
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Why the rush to get the shot?? Long exposure night photography is one of the most demanding styles of photography out there, but also one of the most satisfying when you get it right.. Take your time, slow down and enjoy the experience..

Best way is to shooting, chimp, adjust, shoot, chimp, adjust, shoot, chimp and so on until you get it right..

Shoot RAW and turn the any in camera noise reduction off..

With street scenes I usually start at 30 seconds at f/11 at 200 ISO..
 
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