canoli
03-20-2010, 05:44 PM
Hi Folks - Can I get some advice on shooting a landscapes in very low light?
My question comes down to this - given 2 "equal" exposures, is it better to use a shorter one or a longer one?
Start with a tripod-mounted 40D at ISO 100. From there I can choose any number of Av/Tv values to get the exposure I'm looking for. But which ones are better? Is it better to leave the shutter open longer and use a small aperture, or the other way around?
Usually you make that decision based on your desired DOF and/or whether you can (or want to) freeze the motion in the scene, right?
For instance, focusing 100 feet away on a boat in a lake. There's a slight breeze that causes the boat to drift slightly ... ideally you'd freeze the motion of the boat to get a sharp image.
On the 40D using a 50mm lens @ f/2.8 gives me over 200 feet DOF. Above f/4.5 it's infinite. (0.030 CoC) So I can take DOF out of the equation right? The point of interest is the boat, there's plenty of DOF to get it all in focus, and the foreground/background will fade into OOF. (let's leave aside the aesthetic value of such an image...lol)
About the movement, the slight drift from the breeze in the scene - I'd prefer to freeze it and get a sharp image. But the cost of freezing the motion may be a high level of noise if I'm forced to use an ISO above ~400. So unless I'm going for a high-key image, none of the higher ISOs (above 400) work very well.
So - DOF isn't part of the equation; freezing the motion isn't part of the equation. I'm left with (let's say) f/2.8 at 1 sec or f/11 at 4 secs. Is one better than the other? How do I choose?
Thanks you guys, for any thoughts you'd care to share. I know it was a lengthy setup, hopefully you were able to follow it alright...
My question comes down to this - given 2 "equal" exposures, is it better to use a shorter one or a longer one?
Start with a tripod-mounted 40D at ISO 100. From there I can choose any number of Av/Tv values to get the exposure I'm looking for. But which ones are better? Is it better to leave the shutter open longer and use a small aperture, or the other way around?
Usually you make that decision based on your desired DOF and/or whether you can (or want to) freeze the motion in the scene, right?
For instance, focusing 100 feet away on a boat in a lake. There's a slight breeze that causes the boat to drift slightly ... ideally you'd freeze the motion of the boat to get a sharp image.
On the 40D using a 50mm lens @ f/2.8 gives me over 200 feet DOF. Above f/4.5 it's infinite. (0.030 CoC) So I can take DOF out of the equation right? The point of interest is the boat, there's plenty of DOF to get it all in focus, and the foreground/background will fade into OOF. (let's leave aside the aesthetic value of such an image...lol)
About the movement, the slight drift from the breeze in the scene - I'd prefer to freeze it and get a sharp image. But the cost of freezing the motion may be a high level of noise if I'm forced to use an ISO above ~400. So unless I'm going for a high-key image, none of the higher ISOs (above 400) work very well.
So - DOF isn't part of the equation; freezing the motion isn't part of the equation. I'm left with (let's say) f/2.8 at 1 sec or f/11 at 4 secs. Is one better than the other? How do I choose?
Thanks you guys, for any thoughts you'd care to share. I know it was a lengthy setup, hopefully you were able to follow it alright...