Depth of field

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keyrex

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Michael
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If I take a photo at f1.4 with a fast exposure I get a shallow depth of field, if I take a photo at f1.4 with a longer exposure does it increase the depth of field or just ruin the picture? I am thinking specifically of night time pictures.
I know I could use a smaller aperture and long exposure and get good results but that needs everything to stay still for te entirety of the exposure so photographing a church at night,for example, would be relatively straight forward because it doesn't move but living things do, such as trees in the wind. I'm wondering whether I could open the lens up and reduce the the exposure time and still get the result I want. If you see what I mean?
 
Yes.. depth of field is a product of aperture and does not change with shutter speed. On a quiet night though, a few blurred leaves wouldn't ruin your shot, surely. Edge sharpness suffers badly with most lenses wide open. Do you need a shallow DOF for the shot?
 
was just hypothesising about whether it would work,
 
keyrex said:
was just hypothesising about whether it would work,
Click to expand...

It really depends on what you're trying to achieve.

In your example of wanting to do a night shot, chances are you'll need to leave the shutter open for a few seconds to get enough light in to get any kind of shot, even at f1.4

The best advice would be wait for a still night.

It's already been said that shutter speed has no influence over DoF so use the aperture you need to give you the DoF you require and/or the shutter speed you need.

For example, using f1.4 you may need a shutter speed of 2 seconds to expose correctly. This will give you a narrow DoF but reduce the chance of "moving" stuff spoiling the shot.

If you go up to f8.0 you'll need around 10 seconds to get the same exposure (of course you could adjust ISO too)
 
keyrex said:
If I take a photo at f1.4 with a fast exposure I get a shallow depth of field, if I take a photo at f1.4 with a longer exposure does it increase the depth of field or just ruin the picture? I am thinking specifically of night time pictures.
I know I could use a smaller aperture and long exposure and get good results but that needs everything to stay still for te entirety of the exposure so photographing a church at night,for example, would be relatively straight forward because it doesn't move but living things do, such as trees in the wind. I'm wondering whether I could open the lens up and reduce the the exposure time and still get the result I want. If you see what I mean?
Click to expand...

if you take a photo at f1.4 with a long exposure then you will allow in more light, so this is only okay if you have less light in this situation.
the alternative is to change the ISO..either make the sensor more or less sensitive to the available light.

The variables are typically:
The amount of incident light
the aperture
the exposure time
how sensitive the camera is to light

if you have two constants, then you can balance off the other two in order to get your exposure right, for example, in a fixed lighting situation (no flash all ambient light) and fixing your DOF (via aperture) then you can balance the other two.
If that makes sense and if I've read your question correctly,
 
Russ77 said:
For example, using f1.4 you may need a shutter speed of 2 seconds to expose correctly. This will give you a narrow DoF but reduce the chance of "moving" stuff spoiling the shot.

If you go up to f8.0 you'll need around 10 seconds to get the same exposure (of course you could adjust ISO too)
Click to expand...

Maybe a typo on your part but I make this around 60 seconds. Just didn't want to cause the OP any confusion.
 
Thanks Diz

As I saidi was thinking about whether it would work or not but clearly from your explanation it won't and i was way off with my thinking.
I knew the DoF is affected by the aperture but wasn't sure if it was also connected to the shutter speed in the way I asked (ie. longer shutter speed and bigger aperture)
Guess ill leave the theorising to those who what they are theorising about lol
Thanks for all your comments and help
 
Gad

How did you work out that it was 60 seconds and not the 10 seconds that was mentioned in the other post?
What is the rule to use to establish the exposure length at different apertures?
 
Not sure of the formula, I'm afraid but a correct exposure will always be a product using f no., shutter speed and ISO. Open up the aperture or raise the ISO and the shutter speed will be faster; raise the shutter speed and ISO will need to be raised or the aperture will need to be opened up (smaller number). When the camera meters, it calculates the exposure value (EV), then the clever electronics work their magic and calculate the necessary values for any paramaters not set by the user. I used to have an old Weston cine light meter which reported the EV rather than the shutter speed/aperture required for the chosen ISO but I then had to refer to a table to work out the correct exposure and that was a faff (although necessary to get well exposed results!). I hope that hasn't confused me as much as it did me when I was trying to word it in vaguely layman's terms!

Basically, for each stop difference in f stop, the shutter speed needs to be either halved or doubled, depending on whether the aperture (f stop adjuster) has been opened or closed.
 
I like it when people talk in 'basically' terms, those are the ones I understand!

I think I know what you mean, I'll try reading the setting with my camera on auto and see if I can work it out from there.
 
keyrex said:
Gad

How did you work out that it was 60 seconds and not the 10 seconds that was mentioned in the other post?
What is the rule to use to establish the exposure length at different apertures?
Click to expand...

Well, it's quite a big subject but basically full aperture f-stops go along the lines of:

f/1
f/1.4
f/2
f/2.8
f/4
f/5.6
f/8
f/11
f/16
f/22

For each step (or stop) change in the above, half the amount of light is let onto the sensor. In order to keep the exposure constant we'd therefore need to open the shutter for twice as long. The alternative would be to double the iso as that would amplify the light two fold but I'll ignore that for now as it confuses things.

In the example earlier we said an aperture at f/1.4 might need a 2 second shutter speed to get the exposure you want. Therefore if we'd closed the aperture to f/2, we'd need 4 seconds. If we closed it to f/2.8 we'd need 8 seconds, f/4 = 16 seconds (more likely 15 on most cameras), f/5.6 = 32 seconds (30 seconds on most cameras) and f/8 would be 64 seconds or approximated to 1 minute. I hope that helps and hasn't just confused the hell out of you!
 
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It is only the aperture numbers that are confusing as they come from a division.
Always thought it would be more straight forward if they also just doubled to perform in the same way as Shutter and ISO but realise life is not as simple as that!
 
Thanks Gad, that didn't confuse the hell out of me, like I said, I like 'basically' I know you didn't say that's but that's what was implied from what you wrote, it makes perfect sense.
Only been on here a week or so and learnt so much already, thanks all round
Now to get my head around all the other tech stuff?!?!?

:rolling eyes:
 
ernesto said:
It is only the aperture numbers that are confusing as they come from a division.
Always thought it would be more straight forward if they also just doubled to perform in the same way as Shutter and ISO but realise life is not as simple as that!
Click to expand...

Since they basically relate to the area of the aperture rather than the radius or diameter, they go up in multiples of square root of 2, rounded down to 1.4. Not quite as easy as plain doubling but easy enough - if they confuse you, print gad-westy's list or remember that odd stops start at 1 and double each step to the next odd one (1, 2, 4, 8 etc) and evens start at 1.4 and double every step to the next even step (1.4, 2.8, 5.6, 11 (rounded down from 11.2) etc.)

In my rather old copy of Michael Langford's Basic Photography, there's a table showing the relationship between EV, aperture and shutter speed. Copyright means I'm not going to reproduce it but I expect more modern editions have the same (or similar) charts.
 
Yes, they are easy enough to understand once the logic is explained. To those new to photography I can see why they are not as straightforward as simple doubling of shutter speeds.
 
gad-westy said:
Maybe a typo on your part but I make this around 60 seconds. Just didn't want to cause the OP any confusion.
Click to expand...

Minor brainfart whilst trying to do other things..... 5 extra stops on the aperture so multiplied 2 by 5 which I know is wrong :lol:
 
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