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04/08/2013 12:59:10 PM · #1
I want to buy a ND filter so I can shoot in the daylight and still get that soft water motion. I'm looking at the Tiffen Solid Neutral Density 1.5 Filter (5 stops). Would this be sufficient or do I need to go higher or lower?

04/08/2013 01:15:02 PM · #2
Depends on the lighting conditions. I currently have 6 stops worth, and that works early morning or evening, but not midday.
04/08/2013 01:32:20 PM · #3
you would need minimum 10 stop
04/08/2013 01:34:15 PM · #4
Depends on how much light you're dealing with, and also what kind of effect you're looking for.
04/08/2013 01:35:25 PM · #5
Five stops will leave you with relatively short exposures in bright daylight (sunny conditions). For instance, if the lighting approximates "sunny 16" (1/ISO at f/16) you'd need 1/100s @ f/16 (the smallest aperture you're going to want to use to avoid too much softness from diffraction) without ND, then five stops gets you to 1/3s. You really want 1 second or more, so you need almost two additional stops.
If you can shoot in less than mid-day light, you may find that five stops is adequate. Because you are presumably shooting on a tripod, you can also take several images at 1/3s, then stack and average them. This process gives you *exactly* the same result as the longer exposure, with the following advantages:
- It's much easier to compose through a five-stop filter than something much darker
- Random noise is reduced. Not that you have much noise to begin with, but still...
- You can choose, in post, how much exposure time is enough (!)
The process is more work, but it does provide a lot of flexibility. the ability to choose the level of "smoothness" to the water in post is a really crazy benefit of doing things this way.
The process for stacking and averaging works like this (I assume a Photoshop-based process):
- Shoot on a tripod, with remote release and mirror lockup to avoid any camera movement. Lock down all settings including white balance (don't use auto WB). Ideally, shoot in RAW mode.
- If processing in a program like Lightroom or Aperture, convert each file using the same settings. If you shot RAW, make sure that the WB for the conversion is locked down. Export the developed RAWs.
- In Photoshop, choose File>Sripts>Load Files Into Stack. Once files are loaded, you will have a single Ps document with one image on each layer.
- On the bottom-most layer, leave opacity set to 100%
- On the next layer up, set opacity to 50%
- On the next layer up, set opacity to 33%
- Continue setting opacities on the layers until complete. The opacity (in percent) for each layer is (1/N)*100 where N is the number of the layer, counting from the bottom.
Once you have completed the above process, you will see that the image looks as if the exposure time was the same as the total exposure of the sub-exposures. Now you can turn off visibility of the layers (start from the top) to change the effective exposure time in post!
One more thing... if you find that one or more frames are not useable someone walked into the frame, for example), you just don't use them in the stack; delete the layer, and readjust the opacities of the layer(s) above.

ETA Example:
Here is a 10-second shot in mid-day light (used 10-stop ND):
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The above was the first frame in a 10-shot series, taken in rapid succession. The result of stacking and averaging the individual shots looks like this, and is equivalent to a "synthetic" 100-second exposure in mid-day light:
' . substr('//images.dpchallenge.com/images_portfolio/0-4999/2333/120/Copyrighted_Image_Reuse_Prohibited_881344.jpg', strrpos('//images.dpchallenge.com/images_portfolio/0-4999/2333/120/Copyrighted_Image_Reuse_Prohibited_881344.jpg', '/') + 1) . '

And finally, if we put the individual frames into an animation, it looks like this:
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The *only* difference between the "synthetic" 100 second exposure and a real 100-second exposure is the short gaps that would be caused by the delay between the shutter closing on one shot and opening for the next. In most cases, this is not observable.

Message edited by author 2013-04-08 13:47:59.
04/08/2013 01:36:30 PM · #6
All good advice. Also, take a look at making your own pinhole lenses, it may or may not suit your desires, but it will be cheap. (unlike a 10 stop ND filter of any reasonable quality)
04/08/2013 01:38:34 PM · #7
Another item of note for long exposures that require you to stop down to small apertures:

Clean your sensor - I know you're kinda new to this, and it's probably scary - but go take a look at the Copperhill cleaning method and kit - once you stop down to f/9 or more you start to see all the little tiny bits of dust on your sensor. Unless you LOVE spot editing, this is a great time to look into cleaning your own camera sensor.

Message edited by author 2013-04-08 13:40:04.
04/08/2013 02:20:16 PM · #8
Of course if you are cheap or just not sure you love this technique enough to justify the cost, you can buy some welding glass and play around. The colors can take some adjustment to get right in Photoshop, but for B&W work they work fine.
04/08/2013 03:01:35 PM · #9
I prefer stacking weaker ND (3,6 and 9 stop) filters. Yes, it gives all the effects of multiple layers of glass, might be more expensive and it means carrying more filters. However, it's far more flexible. I can get to 18 stops, or I can just go with 3 or almost anywhere in between.
04/08/2013 03:13:39 PM · #10
Great tip, ' . substr('//www.dpchallenge.com/images/user_icon/21.gif', strrpos('//www.dpchallenge.com/images/user_icon/21.gif', '/') + 1) . ' Kirbic. FWIW, Hoya makes a very reasonable 9-stop ND filter.
04/08/2013 03:27:28 PM · #11
Originally posted by Spork99:

I prefer stacking weaker ND (3,6 and 9 stop) filters. Yes, it gives all the effects of multiple layers of glass, might be more expensive and it means carrying more filters. However, it's far more flexible. I can get to 18 stops, or I can just go with 3 or almost anywhere in between.


I just run with a 6-stop and 10-stop. I can pretty much get what I want with one or the other or rarely both of them. As a rule, I don't stack filters if I can avoid it, due to potential problems with image degradation and/or vignetting.
04/08/2013 04:50:50 PM · #12
You can also stack two polarizers to create a variable ND filter effect, though sometimes you can also get a weird color-shift which may or may not be artistically desirable.

These early experimental shots were made with one linear and one circular polarizer stacked -- I was able to get as long as a 4-second exposure on a July afternoon at f/8 ISO 80 and it still seems under-exposed ...
04/08/2013 05:32:27 PM · #13
I have a B+W ND110 filter (10 stops) and most of my landscapes are taken with that filter. I absolutely love it. In any case even with that kind of filters it's better to take landscape shots when the light is not too strong.
04/08/2013 05:38:08 PM · #14
Originally posted by BrennanOB:

Of course if you are cheap or just not sure you love this technique enough to justify the cost, you can buy some welding glass and play around. The colors can take some adjustment to get right in Photoshop, but for B&W work they work fine.


' . substr('//images.dpchallenge.com/images_portfolio/5000-9999/6519/120/Copyrighted_Image_Reuse_Prohibited_666313.jpg', strrpos('//images.dpchallenge.com/images_portfolio/5000-9999/6519/120/Copyrighted_Image_Reuse_Prohibited_666313.jpg', '/') + 1) . ' ' . substr('//images.dpchallenge.com/images_portfolio/5000-9999/6519/120/Copyrighted_Image_Reuse_Prohibited_666314.jpg', strrpos('//images.dpchallenge.com/images_portfolio/5000-9999/6519/120/Copyrighted_Image_Reuse_Prohibited_666314.jpg', '/') + 1) . '

I got hubby to cut mine the same size as a Cokin filter, to fit into the holder.
04/08/2013 11:25:23 PM · #15
Originally posted by Cory:

Another item of note for long exposures that require you to stop down to small apertures:

Clean your sensor - I know you're kinda new to this, and it's probably scary - but go take a look at the Copperhill cleaning method and kit - once you stop down to f/9 or more you start to see all the little tiny bits of dust on your sensor. Unless you LOVE spot editing, this is a great time to look into cleaning your own camera sensor.


Great advise!
04/08/2013 11:26:42 PM · #16
Originally posted by kirbic:

Originally posted by Spork99:

I prefer stacking weaker ND (3,6 and 9 stop) filters. Yes, it gives all the effects of multiple layers of glass, might be more expensive and it means carrying more filters. However, it's far more flexible. I can get to 18 stops, or I can just go with 3 or almost anywhere in between.


I just run with a 6-stop and 10-stop. I can pretty much get what I want with one or the other or rarely both of them. As a rule, I don't stack filters if I can avoid it, due to potential problems with image degradation and/or vignetting.


What about color shifts. Does the ND cause any color casts?

Message edited by author 2013-04-08 23:27:59.
04/08/2013 11:35:54 PM · #17
Originally posted by Purplerose:


What about color shifts. Does the ND cause any color casts?


The nicer ND filters will not have any color cast. The cheaper ones will sometimes have a very minor color cast, but it's easily fixable in post.
04/08/2013 11:40:39 PM · #18
Adding to the confusion what is the difference in these ND filters. I'm assuming I should be looking at the solid ND filters.

Neutral Density Filters

Neutral Density (Solid)
Graduated Neutral Density
Center ND Filters
04/08/2013 11:45:57 PM · #19
Originally posted by Purplerose:

I'm assuming I should be looking at the solid ND filters.

Correct. Graduated ND filters are normally used to balance the contrast of a bright sky against darker ground while a center ND filter produces a vignette around the edge of the photo.
04/08/2013 11:48:28 PM · #20
Originally posted by Purplerose:

Adding to the confusion what is the difference in these ND filters. I'm assuming I should be looking at the solid ND filters.

Neutral Density Filters

Neutral Density (Solid)
Graduated Neutral Density
Center ND Filters


Solid are what people typically refer to. These provide a uniform amount of light reduction across the whole filter.

Graduated filters only have half of the filter darkened. People often use these for sunset photos where they only want to darken the sky while leaving the beach bright.

I've never heard of anyone using a center ND filter before. My only guess is that this can be used to counteract a lens that has a heavy vignette.
04/09/2013 12:14:00 AM · #21
Originally posted by bhuge:

I've never heard of anyone using a center ND filter before. My only guess is that this can be used to counteract a lens that has a heavy vignette.

They aren't generally used for SLRs. The purpose is to correct falloff inherent to medium and large format wide angle lenses as you suspected.

Message edited by author 2013-04-09 00:14:59.
04/09/2013 07:53:50 AM · #22
question for kirbic:

does image stacking really create EXACTLY the same result as one long exposure? for motion, maybe, but what about for making a dim object brighter? would multiple averaged short exposures really capture as much light as one long one? I have a hard time seeing how that's possible.
04/09/2013 08:14:05 AM · #23
Originally posted by LanndonKane:

question for kirbic:

does image stacking really create EXACTLY the same result as one long exposure? for motion, maybe, but what about for making a dim object brighter? would multiple averaged short exposures really capture as much light as one long one? I have a hard time seeing how that's possible.


Good question!
Yes, you are correct that if in my example I had taken a single 100-second exposure, it would have been over exposed by more than three stops. Because I used ten 10-second exposures, I avoided the over exposure, making a shot which was impossible under the conditions possible. So I should clarify that the result will be the same with the exception of avoiding the over-exposure.
04/09/2013 12:13:39 PM · #24
Thank you everyone for all the great posts. I feel like I have a better understanding now, which will help me with my purchase.
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