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Author Topic: Variable ND Filters  (Read 4878 times)

Neil Williams

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Variable ND Filters
« on: June 26, 2016, 05:52:23 pm »

Lastnight I was looking at buying the Singh Ray variable ND filter from B&H for my Switzerland trip (landscape photography) but when I saw that the shipping at tax was nearly 200 bucks to the UK I decided that 90% of what they can do can be done in post processing........Am I thinks straight??
Neil
« Last Edit: June 26, 2016, 05:56:42 pm by ndwgolf »
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E.J. Peiker

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Re: Variable ND Filters
« Reply #1 on: June 26, 2016, 06:50:00 pm »

No they can't.  Variable ND filters are used to slow down the exposure when you need a slower shutter speed than the combination of exposure parameters and light will allow - examples are to render a waterfall that is silky or to get a shallow DOF in bright conditions, or in the video world to get your exposure to 1/60s or whatever 1/(2 x Frame rate) is.  How do you do that in post?

That said, variable ND's can leave some weird cross polarization artifacts especially on wide angle lenses as you dial up the strength.  Personally I much prefer carrying a 6 stop and 10 stop pure ND filter rather than a variable as the results are much more predictable.

BTW, Cokin makes screw on variable ND's that you should be able to get in Europe - also B&W and Heliopan - all European filters. 
« Last Edit: June 26, 2016, 06:54:59 pm by E.J. Peiker »
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dwswager

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Re: Variable ND Filters
« Reply #2 on: June 26, 2016, 07:29:33 pm »

...I decided that 90% of what they can do can be done in post processing........Am I thinks straight??
Neil

No.  ND and Polarizers are 2 things you can't do in post.  ND because it will affect the Shutter Speed and/or Aperture which most certainly cannot be changed in post.

Also be warned that most variable NDs cannot be utilized at full strength.  Normally between a stop or 2 from the top has been the limit due to getting a visible X in the image where the two polarization  screens interact. 

I own 2, 3, 6 and 10 stop ND filters.  The 3 stop is my most versatile.  The 10 would be the next one I would want.
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SrMi

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Re: Variable ND Filters
« Reply #3 on: June 26, 2016, 11:19:51 pm »

ND filter can be simulated by using multiple exposures and blending it in camera or in Photoshop. Sony A7rII has even an in-camera app that does that.

I prefer using ND filters instead of multiple exposure. Had good experience with Heliopan's Vari-ND filters. The advantage is that you can focus and frame with a bright setting and then darken it as much as needed. You may not see much in the viewfinder once you screw-in a fixed strength ND filter. Vari-ND is also very useful for video.

Nonetheless, I prefer using Lee's system with fixed strength filters.
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Shiftworker

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Re: Variable ND Filters
« Reply #4 on: June 27, 2016, 03:17:20 am »

You will also find that most variable ND filters will take the edge of resolution. Top end ones are better like Heliopan and B&W but be prepared to pay for it.
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Otto Phocus

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Re: Variable ND Filters
« Reply #5 on: June 27, 2016, 06:46:24 am »

Check out the Marumi Variable ND filters.  I have found them to be of high quality at a reasonable cost. 
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dwswager

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Re: Variable ND Filters
« Reply #6 on: June 27, 2016, 07:35:37 am »

I prefer using ND filters instead of multiple exposure. Had good experience with Heliopan's Vari-ND filters.

Now I'm baffled.  How does using a ND filter have anything do with exposure stacking?  I can see if you are using split ND instead of compositing two or more exposures. Normally ND is used to obtain a single proper exposure while providing slower shutter speeds and/or wider apertures for a variety of reasons. 

You will also find that most variable ND filters will take the edge of resolution.

Are you saying a Variable ND set at 6 stops degrades the image less than a straight 6 stop ND of the same make and quality? 
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Neil Williams

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Re: Variable ND Filters
« Reply #7 on: June 27, 2016, 08:09:41 am »

I bought myself a Singh Ray CPL and will just continue to use my Lee filter system and my 3 stop ND for waterfalls


Sent from my iPhone using Tapatalk
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E.J. Peiker

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Re: Variable ND Filters
« Reply #8 on: June 27, 2016, 09:02:31 am »


Are you saying a Variable ND set at 6 stops degrades the image less than a straight 6 stop ND of the same make and quality?
The variable filter uses two pieces of glass rather than one so in theory it would degrade the image more and that's before any weird cross polarization effects.
« Last Edit: June 27, 2016, 09:20:52 am by E.J. Peiker »
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dwswager

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Re: Variable ND Filters
« Reply #9 on: June 27, 2016, 09:06:04 am »

It does use two pieces of glass rather than one so in theory the answer would be yes and that's before any weird cross polarization effects.

Why would 2 pieces of glass with a gap in the middle be less degrading than a single piece of glass?  That seems counterintuitive!
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E.J. Peiker

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Re: Variable ND Filters
« Reply #10 on: June 27, 2016, 09:17:14 am »

Why would 2 pieces of glass with a gap in the middle be less degrading than a single piece of glass?  That seems counterintuitive!
It wouldn't, I misread your question and answered it opposite  :-[. It would obviously, at least on paper, be worse with a variable filter with more glass surfaces than with a single multi coated ND filter.

I edited my original answer above.
« Last Edit: June 27, 2016, 09:21:12 am by E.J. Peiker »
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SrMi

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Re: Variable ND Filters
« Reply #11 on: June 27, 2016, 11:10:48 am »

Now I'm baffled.  How does using a ND filter have anything do with exposure stacking?  I can see if you are using split ND instead of compositing two or more exposures. Normally ND is used to obtain a single proper exposure while providing slower shutter speeds and/or wider apertures for a variety of reasons. 
...

Let's say you set 5 shot multiple exposure in your camera (e.g., Nikon), each shot with 1 second shutter speed. The resulting image should be the same as one shot that takes 5 seconds, for which you would have needed an ND filter.
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dwswager

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Re: Variable ND Filters
« Reply #12 on: June 27, 2016, 01:09:27 pm »

Let's say you set 5 shot multiple exposure in your camera (e.g., Nikon), each shot with 1 second shutter speed. The resulting image should be the same as one shot that takes 5 seconds, for which you would have needed an ND filter.

Trying to follow.  Assuming you want a 5 second shutter speed for some reason.  Further assuming aperture and ISO remain constant.  Then shooting 5 1s exposures will result in 5 identical images.  If I block up the shadows with this underexposed set then no way to get it back and I still don't get the benefit of the slow shutter speed.

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Shiftworker

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Re: Variable ND Filters
« Reply #13 on: June 27, 2016, 01:23:55 pm »



Are you saying a Variable ND set at 6 stops degrades the image less than a straight 6 stop ND of the same make and quality?
Yes - not sure why but there can be quite a significant resolution loss with some variable ND filters esp with longer focal length lenses. Do an internet search on the topic.
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SrMi

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Re: Variable ND Filters
« Reply #14 on: June 27, 2016, 03:02:28 pm »

Trying to follow.  Assuming you want a 5 second shutter speed for some reason.  Further assuming aperture and ISO remain constant.  Then shooting 5 1s exposures will result in 5 identical images.  If I block up the shadows with this underexposed set then no way to get it back and I still don't get the benefit of the slow shutter speed.

I apologize for not being able to explain it properly. Maybe Moose's post makes it clear: http://www.imagechaser.com/creating-long-exposure-look-without-wait-nd-filter/

Multiple exposure setting in a camera like Nikon creates only one image (RAW if wanted). That one image has all 5 captures blended. There is a way to blend 5 distinct images in PS as well. The key is that those 5 images are not identical if they contain moving elements in them (e.g., sky, water).
 
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E.J. Peiker

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Re: Variable ND Filters
« Reply #15 on: June 27, 2016, 03:48:45 pm »

Yes - not sure why but there can be quite a significant resolution loss with some variable ND filters esp with longer focal length lenses. Do an internet search on the topic.
He misread your statement exactly the same way I did ;)
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E.J. Peiker

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Re: Variable ND Filters
« Reply #16 on: June 27, 2016, 03:51:11 pm »

I apologize for not being able to explain it properly. Maybe Moose's post makes it clear: http://www.imagechaser.com/creating-long-exposure-look-without-wait-nd-filter/

Multiple exposure setting in a camera like Nikon creates only one image (RAW if wanted). That one image has all 5 captures blended. There is a way to blend 5 distinct images in PS as well. The key is that those 5 images are not identical if they contain moving elements in them (e.g., sky, water).
I think you are missing the point.  If those one second exposures have an area that is blocked up black, stacking 5 images will still have it blocked up black where the single 5 second exposure won't.  What you say works for some motion but it does nothing to solve this issue.  Simply said, you cannot replace 5 one second exposures with a single 5 second exposures in every case.
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SrMi

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Re: Variable ND Filters
« Reply #17 on: June 27, 2016, 05:01:19 pm »

I think you are missing the point.  If those one second exposures have an area that is blocked up black, stacking 5 images will still have it blocked up black where the single 5 second exposure won't.  What you say works for some motion but it does nothing to solve this issue.  Simply said, you cannot replace 5 one second exposures with a single 5 second exposures in every case.

If a single image of 1 second does not have enough dynamic range to reveal detail in the black part, then the 5 second exposure would neither, would it? Each of the five 1 second images must be properly exposed before blending. What am I missing? Thanks!
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E.J. Peiker

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Re: Variable ND Filters
« Reply #18 on: June 27, 2016, 05:11:19 pm »

If a single image of 1 second does not have enough dynamic range to reveal detail in the black part, then the 5 second exposure would neither, would it? Each of the five 1 second images must be properly exposed before blending. What am I missing? Thanks!
Absolutely not true because sensors aren't able to collect every photon as there is a noise floor.  If sensors were perfect and there were absolutely zero noise with 100% photon collection efficiency then your statement would be true but we don't live in that world ;)  You need to cross a threshold of photon collection before a sensor can record it in our imperfect world.  If you don't cross that threshold in 1 second exposures, 5 times zero is still zero.  But in the 5 second exposure you do cross it then you are actually recording shadow detail.
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fdisilvestro

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Re: Variable ND Filters
« Reply #19 on: June 27, 2016, 08:09:14 pm »

One second exposure without a ND filter would collect the same amount of photons as a 4 seconds exposure though a 2 f-stops ND filter. If you cannot get enough detail in the shadows with one second exposure without the ND filter you will not be able to record them either with the 4 seconds exposure through a 2 f-stops ND
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