Variable ND Filters

[E.J. Peiker]

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

You do have a point there, I wasn't thinking about this correctly! 

The other two uses I cited that can't be simulated in post still hold though, basically if there is too much light to attain a slow enough shutter speed in video and if you are recording something that requires a slower shutter speed than attainable given the exposure parameters and light available to you and where multiple exposures isn't an option - for example a pan blur of a car or animal or anything where you just can't handle the momentary stoppage of recording that multiple frames would result in.

[Wayne Fox]

I've heard of this, though I've never actually tried it. Theoretically if the stack is merged the right way it should yield something to the effect of a long exposure, and since each shot is correctly exposed individually there isn't a clipping problem. Here's one article I bookmarked some time ago ... made me a little curious.

Simulate a long exposure in Photoshop

[Paulo Bizarro]

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).

This reminds me of the multiple exposure modes in film cameras. Same principle I think? I would select the number of shots, adjust the exposure compensation accordingly (a bit of trial and error, normally 1 more stop for each shot); then the camera would expose the same frame by the number of shots that was set.

With digital is easier, and more controllable. But I still prefer to use filters:)

[dwswager]

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).

The disadvantage of motion blur when trying to blend multiple exposures is true.  But the thing here is that this is and argument for Split ND to reduce the overall DR requirement and obviate the need for multiple exposure stacking.  Variable ND operate on the entire image and so I do not think it applies in this situation.

[Enda Cavanagh]

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

If you are living in the Uk you will be crippled by B&H shipping costs. I live in Ireland. I stopped using them for the same reason. I bought my p Singh Ray filters direct from the manufacturer for about $50 shipping for a couple of 130mm square filters

[orc73]

if you go to Switzerland buy your stuff there. Photography equipment and electronics are very cheap due to so much competition between online shops.
I'm yet to find a cheaper place to buy stuff. In addition you can get Tax refunded when returning on the airport.
Try digitec.ch or digifuchs.ch. They offer pickup at their shop as well(you should place the order online in most cases though).
You might find other options in google.