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I am trying to achieve the type of photo where the people/moving parts of the photograph are virtually invisible, but the static background is perfectly sharp.

For example, I am taking a photo inside of Saint Peter's Basilica, and I want the photo to be of the beautiful architecture and decoration, not the other tourists. To achieve the effect where the people are like ghosts, I set the shutter speed to 4 seconds and let the camera figure the rest out itself.

Because of the limited lighting in the basilica, the 4 seconds are permissible and the photo comes out as desired. Here it is:

photo of desired effect

(Sorry about the image quality. It is a photo of a photo.)

How I can achieve this effect in an area with more light, like outdoors? Lowering the shutter speed alone will not help, for it will either give me a photo without the effect, or a white photo. I thought that maybe I could put a polarized filter over the lens to limit the amount of light that can enter. I also thought that maybe I can put a light gray filter on the lens to limit the amount of light but that might just make it grayer and not really help at all.

How can I achieve this effect in lighter conditions?

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  • @Olivier - while the effect that that post is trying to achieve is something that I would also like to know how to skillfully capture, that is something different. I am getting an example photo.
    – Daniel
    Aug 24 '15 at 18:25
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    It's exactly what you can do with a ND filter. I added a picture made with a ND1000 to illustrate what you want to achieve :)
    – Olivier
    Aug 24 '15 at 18:53
  • Another option, which will not blur people as in your example, but can completely remove them: photo.stackexchange.com/questions/20953/…
    – MikeW ♦
    Aug 24 '15 at 19:52
  • @MikeW - I know about this and you are not the first on this post to mention it. It is not what I am looking for.
    – Daniel
    Aug 24 '15 at 21:21
  • Even though you want to keep the "ghosts" in the picture when in bright light the same as when you were in lower light here, the answer is the same: Use an ND filter of the correct strength to allow you to use the same Tv/Av/ISO in the brighter light outside as in the dimmer light in the basilica.
    – Michael C
    Aug 24 '15 at 21:34
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What you are looking for is a ND (Neutral Density) filter.

To illustrate, here is an example of a photo taken in daylight in a street with a ND1000 filter. The filter allowed a shutter speed of 6 seconds. With no filter, with the same aperture and ISO, the shutter speed would have been approximately 6/1000 = 0.006 seconds (no "ghosts" effect).

enter image description here

Contrary to what you may think, a "good" ND filter is by definition "neutral". You will have exactly the same color with it, your sensor will simply need more time gathering light to produce an image with the same luminosity.

To put some science behind, basically, a ND filter is gray in appearance because gray absorb all radiations (all colors) more or less equally to the human eye.

You will find more information about how it works and its effects in the following posts :

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  • Do you know what the 1000 after ND indicates? Does it have to do with the shutter speed, aperture, or other stuff?
    – Daniel
    Aug 24 '15 at 18:55
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    @Dopapp It means the light passing through is reduced by a factor of 1000
    – user1207217
    Aug 24 '15 at 19:05
  • @Dopapp the number after "ND" indicates by how much the light intensity reaching your sensor is divided. With a fixed aperture and iso, you have to multiply the shutter speed by the same number to have the same exposure. By daylight, if you need 1/1000 of a second with no filter, you will need 1s with it.
    – Olivier
    Aug 24 '15 at 19:06
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    @Dopapp ND filters have three different numbering standards which may be kind of confusing. Wikipedia has a good overview of the different numbering schemes.
    – You
    Aug 24 '15 at 20:22
  • An ND1000 is a "10 stop" filter, so your 4 second shutter speed would need to be extended to 4,096 seconds (or 68 minutes 16 seconds) for the same aperture/ISO settings in the same light!
    – Michael C
    Aug 24 '15 at 21:31
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Apart from using an ND filter, you might be able to achieve the desired effect by taking multiple photos and then blending them in post processing. Either an automatic blend with "ghost removal" might work, or layering the images and manually masking/unmasking selectively (in effect "painting out" the people).

All of this pretty much requires a tripod for nicely aligned pictures, but that's the same for long exposures, of course.

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  • I added a photo example to my question. Will it be achieved with an ND filter? Can the shutter speed still be 4 seconds or does it have to be lower?
    – Daniel
    Aug 24 '15 at 18:37
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    The effect of an ND filter is just as if there was less light. How long your exposure needs to be depends on the desired effect. You choose a matching ND filter to achieve that speed.
    – ths
    Aug 24 '15 at 18:42
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Just to add a bit of links to the other (good) answers, if you do not want to use a ND filter, you can use multiple exposure and

  1. use an averaging method to simulate a long exposure --- basically, 20 exposures at 1/10 of seconds will be more or less equivalent to a 2 seconds exposures, or

  2. use a median filter, which can even be better --- in the right conditions, the people can just disappear.

PS --- I am not, nor related to, Pat David. I just like his tutorials.

Notice however that to have the same effect than a ND1000 filter with averaging, without changing the other exposure parameters (only the shutter time), you'll need 1000 exposures... which is around 1% of your average camera shutter life. If there aren't too much people around, you can go with much less shots in the median case; the trick here is to guess how much you need (partial success is not so nice as the "averaged ghosts").

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    I've not tried this but if you want the "ghosts" effect you could probably have a layer containing the average image under a median layer and adjust the opacity of the median layer. The median approach won't help too much if the people linger too long, or are in too many frames, as the median pixel value will have too much chance of being part of a person.
    – Chris H
    Aug 25 '15 at 8:17
  • The averaging method is a really nice idea, with it there's no need for an expensive neutral filter.
    – A.L
    Aug 25 '15 at 8:26
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As mentioned in Oliver's answer, you can use a neutral density filter, this let's through only a small fraction of the light, but it doesn't affect the color. You can then shoot at large aperture and yet have long exposure times.

Another solution is to take many pictures and then use image stacking methods. This method can be used under favorable conditions to completely remove all the moving objects. What you then do is you align the pictures and either use the median or remove the pixelwise maximum and minimum and take the average, or use some hybrid between these two extremes. If for each background point there is always an image for which that point in not obscured, it is in principle possible to reconstruct the scene with all the people removed. If the overlap between the obscured parts is typically not large, then it's easy to do automatically by taking the median or the average with the maximum and minimum image removed.

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Another option is, if you're happy with the resolution your DSLR can create videos, is to record the scene for a few seconds (or even a few minutes), and later blur the frames together. Pros of this approach compared to the multiple image one is that you'll have usually much more frames to blur, and the result will be much smoother, the cons is that the image quality (especially resolution) won't be as good as with the single image approach.

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