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09/15/2011 04:08:48 PM · #1 |
An absolutely elementary question that I should know the answer to, but based on some things I've read, I'm now starting to get confused:
Assume I'm trying to take an image of a stationary object. Absolutely still, no motion whatsoever.
With no filter in place, with my chosen aperture setting the exposure meter reading is 1/250s.
When I place my 10-stop neutral density filter on the lens, I calculate that the required exposure reading is 4s.
My question is: assuming that both images are exposed exactly the same (for the sake of this discussion), will the images have the same amount of detail/texture or will the longer exposure result in more detail?
I've read on a couple of websites that the using longer exposures with ND filters will increase the amount of detail in your subject. But this doesn't make sense since they both theoretically are exposed the same.
Am I missing/misinterpreting something here?
Message edited by author 2011-09-15 16:22:05. |
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09/15/2011 04:14:43 PM · #2 |
Great question and many of us would be curious to get an educated answer!!
(How did you calculate the 4s?) |
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09/15/2011 04:20:58 PM · #3 |
Originally posted by bergiekat:
Great question and many of us would be curious to get an educated answer!!
(How did you calculate the 4s?) |
Used a table I found on-line for determining long exposures. Look at Joel Tjintjelaar's website (one of my favourite long exposure B&W photographers.
Table |
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09/15/2011 04:23:45 PM · #4 |
Absolutely no difference, assuming:
1.) There is no camera shake
2.) The shots are exposed the same, per the histogram
It may in fact be that the longer exposure *will* have more detail, if there is minor camera shake on the shorter exposure that has time to damp out on the longer one.
I often use this to my advantage when shooting with one of my microscope set-ups at work. I will turn down the illumination to ensure that the small shake caused by the shutter opening damps out in the first small portion of the exposure.
The opposite can also be true. The shorter exposure can have more detail if vibration from the exposure is more important than the shutter/mirror action.
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09/15/2011 04:29:04 PM · #5 |
One reason this could be true, if the shot is taken over a sufficient distance and high enough focal length for atmospheric distortion to become a factor, the longer exposure can "even out" some of that distortion and create greater detail, or at least more accurate detail, but the effect isn't super significant...
Otherwise, more glass and longer exposure is a sure recipe for less detail and more noise. |
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09/15/2011 04:37:44 PM · #6 |
Originally posted by Cory:
One reason this could be true, if the shot is taken over a sufficient distance and high enough focal length for atmospheric distortion to become a factor, the longer exposure can "even out" some of that distortion and create greater detail, or at least more accurate detail, but the effect isn't super significant...
Otherwise, more glass and longer exposure is a sure recipe for less detail and more noise. |
Actually, when atmospheric distortion is a factor, the shorter the exposure the better. That's why folks that do planetary photography use web cams, take thousands of frames of video, and sort through for the best ones.
Now, combining multiple exposures is a *whole* 'nother topic!
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09/15/2011 04:40:25 PM · #7 |
Originally posted by kirbic:
Originally posted by Cory:
One reason this could be true, if the shot is taken over a sufficient distance and high enough focal length for atmospheric distortion to become a factor, the longer exposure can "even out" some of that distortion and create greater detail, or at least more accurate detail, but the effect isn't super significant...
Otherwise, more glass and longer exposure is a sure recipe for less detail and more noise. |
Actually, when atmospheric distortion is a factor, the shorter the exposure the better. That's why folks that do planetary photography use web cams, take thousands of frames of video, and sort through for the best ones.
Now, combining multiple exposures is a *whole* 'nother topic! |
That would be why I qualified it as "more accurate".. I've noticed that the lines on buildings will straighten out, at the cost of contrast... maybe I'm just nuts though.. |
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09/15/2011 05:08:50 PM · #8 |
Originally posted by bergiekat:
Great question and many of us would be curious to get an educated answer!!
(How did you calculate the 4s?) |
Charts are handy, but if you don't have one just remember that for every 1 stop loss of light in a scene your shutter speed would double. The same holds true for every 1 stop of light gained....your shutter speed halves to maintain the current exposure. Cameras can't always display the exact perfect halved or doubled values so you set it to the closest shutter speed your camera can shoot at. For instance 1/125 halved would be 1/60 sec.
So in this case 10 stops on a camera that is set to 1/3 stop increments you would double the shutter speed of the initial exposure 10 times.
1/250 sec becomes 1/125, 1/60, 1/30, 1/15, 1/8, 1/4, .5 sec, 1 sec, 2 sec, 4 sec.
So yes, 10 full stops down (loss of light) from 1/250 sec. is 4 seconds.
If you still find that confusing there is yet another way to calculate it which might be the easiest for most. With most DSLR cameras...including entry level models you can set your camera exposure level increments to either 1/3 or 1/2 intervals (I recommend 1/3 increments to get the most control). Depending on what you have your increment set to will determine how this next part works.
One full stop of light is broken up into 1/3 intervals when your camera is set to the 1/3 setting. That mean if you move your shutter speed dial 1 click you are altering the shutter speed by 1/3 stop. If you move it 3 clicks you have just altered your shutter speed by 1 full stop. So that means that it takes 30 clicks of your shutter dial to change the exposure 10 full stops. If you have your camera exposure increments set to 1/2 then it would only take 20 clicks of the shutter dial to increase or decrease your shutter speed by 10 stops.
So let's say you have your camera on a tripod in Full Manual mode and your exposure for the scene at ISO 100 and an aperture of say f/11 gives you a shutter speed of 1/250 sec. Your camera is set to 1/3 increments, and you are going to put a 10 stop filter on the front which will drastically reduce the amount of light hitting the sensor. In order to compensate to get the exposure back to the right level you are going to have to adjust the shutter speed 30 clicks until it's shows the correct exposure again (on the exposure meter). Now of course the camera can do this automatically in some modes, BUT since most cameras will only allow a 30 second exposure in manual mode and you may want to do some night photography where the shutter might be open for much longer time periods that the camera can't calculate you're going to have to know how to figure the correct time for exposure doing the math...and using Bulb Mode.
Dave
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09/15/2011 05:13:56 PM · #9 |
Originally posted by gcoulson:
My question is: assuming that both images are exposed exactly the same (for the sake of this discussion), will the images have the same amount of detail/texture or will the longer exposure result in more detail? |
You can certainly gain detail by decreasing the aperture or iso. As for changing exposure time alone (with the use of ND grads to compensate), I guess that would be on a case-specific basis, as others have already said. |
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09/15/2011 05:18:27 PM · #10 |
Originally posted by Cory:
That would be why I qualified it as "more accurate".. I've noticed that the lines on buildings will straighten out, at the cost of contrast... maybe I'm just nuts though.. |
Oh yes, surely the long exposure will yield straight (but blurrier) lines, because you are "averaging" the position of the edge across the exposure time. So, less distortion, but also less detail.
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