Variable ND Filters at 7 day shop

I received the email myself and was just going to ask the same question, they look very well priced, but price unfortunately isn't everything
 
How do variable ND filters actually work?

It seems like witchcraft.... Or is it made up of 2 x straight polarising filters?
 
it looks like cpl to me
 
HuntMike said:
How do variable ND filters actually work?

It seems like witchcraft.... Or is it made up of 2 x straight polarising filters?
Click to expand...

Linear polariser on the front of a circular polariser.

There's already a couple of threads opened dicussing these filters.
 
i just ordered one ill let nyou now if its allright
looks like a nd fader copy
 
Jpandyp - I would be interested to hear your comments on this please

thanks
 
I've just gotone. On a quick test it seems to vignette to a greater or lesser degree below 35mm on a full frame camera but is OK after that. It's impossible to determine exactly how much ND you are applying (just less or more:) ) but on the plus side there doesn't seem to be any colour cast.

For my needs and the money I'm quite pleased with it.
 
parkmoy said:
I've just gotone. On a quick test it seems to vignette to a greater or lesser degree below 35mm on a full frame camera but is OK after that. It's impossible to determine exactly how much ND you are applying (just less or more:) ) but on the plus side there doesn't seem to be any colour cast.

For my needs and the money I'm quite pleased with it.
Click to expand...


Thanks for updating the thread.
Does the vignetting disappear at smaller apperture?
 
See this thread, but I think it's alright for the money and apart from a little loss of contrast (which may be caused by the polorisation) I haven't noticed much difference!

100% crop from the 24-105L at 24mm, f11 1/50th no filter

24mm100cropNF.jpg


100% crop from the 24-105L at 24mm, f11 1/20th

24mm100crop.jpg
 
i bought one in 77mm for my siggy 10 -20mm
at the wide end of the scale and up on the max on the filter its unusable
the nd effect is far from uniform
same on my 17-85 at 17 aswell
at the lower settings(lighter) it seems allright
 
jpandyp said:
i bought one in 77mm for my siggy 10 -20mm
at the wide end of the scale and up on the max on the filter its unusable
the nd effect is far from uniform
same on my 17-85 at 17 aswell
at the lower settings(lighter) it seems allright
Click to expand...
A variable ND has the same limitations as the constituent parts, i.e. the effect become non-uniform in the same way that the effect from a circular polariser becomes non-uniform on an UWA.
 
Thanks guys, I've decided to give this a miss. I'll just stick with my hoya hd poloriser for now.
 
Alastair said:
A variable ND has the same limitations as the constituent parts, i.e. the effect become non-uniform in the same way that the effect from a circular polariser becomes non-uniform on an UWA.
Click to expand...

Er, nope.

The effect of a polariser only varies across the sky, and is really bad only when the sun is near the horizon. A polariser's ability to cut-down on glare from reflections is fairly uniform.

The cross-pattern on a VND is much, much, worse than using a polariser alone - even in the worst possible case.
 
hollis_f said:
Er, nope.

The effect of a polariser only varies across the sky, and is really bad only when the sun is near the horizon. A polariser's ability to cut-down on glare from reflections is fairly uniform.

The cross-pattern on a VND is much, much, worse than using a polariser alone - even in the worst possible case.
Click to expand...

Because you're using two polarisers, for double the trouble and then some..

I've never seen a cross-pattern interference with a variable ND, usually it's two extremely dark parallel bands, sometimes slightly curved. Are you using a CPL/LPL, CPL/CPL or LPL/LPL variable filter?

I use a DIY variable ND and with the ability to rotate the circular and linear indepenently (which I don't think you'll get with the 7DS version) I've been able to experiment with the orientations of the filters relative to the scene and each other. From my own experience with variable ND filters, the uneveness of the effect at short focal lengths and maximum filtering is most easily described as being very similar to the banding issues you'll see using a polarising filter for a sky shot with an UWA. It's not exactly the same, it's down the interference between the two polarisers and it's constant for a fixed orientation of the filters regardless of your orientation to the sun. The effect is more pronounced with a shorter focal length (I tend to stick in the 30-50mm range).

Parkmoy.. using these filters is slightly a*** about t**. You don't need to know the strength of the effect. Pick the exposure you want (shutter speed, aperture and ISO) and then adjust the *filter* until the metering comes right. In full sun I've found it best to stick around 2-5 seconds on the exposure to avoid any unevenness.
 
Alastair said:
Because you're using two polarisers, for double the trouble and then some..

I've never seen a cross-pattern interference with a variable ND, usually it's two extremely dark parallel bands, sometimes slightly curved. Are you using a CPL/LPL, CPL/CPL or LPL/LPL variable filter?
Click to expand...

OK, I've just been out and took two shots, one with the CPL and t'other with the VND.

CPL_vs_VND.jpg


Both are taken pointng 90º away from the Sun - where the polarising effect should be maximised. The cross-pattern is the same regardless of the direction.


As you can see, the cross-pattern makes this shot unusable.
 
Odd, I've never had an effect like that with a VND. I only ever get banding (on opposed corners/edges) when I push the effect too hard and it's noticable worse on wider lenses.

I know I'm using lens-CPL-LPL when I'm shooting VND, I wonder if some of the off-the-shelf units are using CPL-CPL or LPl-LPL? (both of which are cautioned against when DIYing a VND).
 
Parkmoy.. using these filters is slightly a*** about t**. You don't need to know the strength of the effect. Pick the exposure you want (shutter speed, aperture and ISO) and then adjust the *filter* until the metering comes right. In full sun I've found it best to stick around 2-5 seconds on the exposure to avoid any unevenness.
Click to expand...

Yep, that's what I discovered:)
 
Some people in here I don't think have a clue what an Nd filters used for well it's simply to enable you to slow down your shutter speeds so that you can capture movement like a river or dramatic cloud movement why the hell is people posting pictures of flowers ????????????
 
born-shooter said:
Some people in here I don't think have a clue what an Nd filters used for well it's simply to enable you to slow down your shutter speeds so that you can capture movement like a river or dramatic cloud movement why the hell is people posting pictures of flowers ????????????
Click to expand...

Er. Link
 
born-shooter said:
Some people in here I don't think have a clue what an Nd filters used for well it's simply to enable you to slow down your shutter speeds so that you can capture movement like a river or dramatic cloud movement why the hell is people posting pictures of flowers ????????????
Click to expand...

Mabye if you read the post that had the photographs you may gain a little bit of information :)
 
born-shooter said:
Some people in here I don't think have a clue what an Nd filters used for well it's simply to enable you to slow down your shutter speeds so that you can capture movement like a river or dramatic cloud movement why the hell is people posting pictures of flowers ????????????
Click to expand...

READ first before accusing people. You might be a veteran with cameras etc but, read and understand what the poster's intention is first. nuff said.
 
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