Interesting ND filter, Anyone tried?

Manlatiger · Jan 23, 2009

Dear all,

I found this interesting ND filter in Ebay, seems to be a new product.
Did anyone tried with this? I'm Planning to get one.

Fader ND Filter (from ND2 to ND400) 77mm - eBay (item 140296353178 end time Jan-28-09 00:21:40 PST)

Cheers

Pure · Jan 23, 2009

Judging by the crappy English, and it's from china, it's probably low quality glass with a even crappier coating.

dEARlEADER · Jan 23, 2009

i especially enjoyed the "high quality professional photography" seal of endorsement on the add...

$200 bones??

i dunno.... it's unproven....

i'd rather waste my money on the more affordable cokin p series....

if you buy it let us know how it works out..

Joves · Jan 23, 2009

Lokks like they are trying to do a knock off of the Singh Rays. Their 77mm is only $340 and well worth it if you use one enough. Singh-Ray Filters: Vari-ND Variable Neutral Density Filter I personally though prefer stacking filters over paying alot for a filter that does it for me.

Eldrich · Jan 23, 2009

if you just stacked two polarizing filters, you'd get the same control. you might have AF issues if you're not using circular polarizers, but as long as there are no strongly polarized light sources (i.e. reflections or sky at 90 degrees to the sun) they would behave just like a ND filter with variable control (spinning one polarizer with respect to the other) and since you already probably own one polarizer, a second one would be much cheaper than the filter mentioned in the OP.

Eldrich · Jan 23, 2009

actually, now that i think about it, as long as you kept the circular polarizer as the inner filter, that is the filter just before the light entering the camera, you would not have any AF problems. So you could get a cheap regular polarizer for the second one to go on top of the circular polarizer and have a very cheap variable ND filter, as long as you were okay with getting the effects of polarizing filters as well.

dEARlEADER · Jan 23, 2009

Eldrich said:
actually, now that i think about it, as long as you kept the circular polarizer as the inner filter, that is the filter just before the light entering the camera, you would not have any AF problems. So you could get a cheap regular polarizer for the second one to go on top of the circular polarizer and have a very cheap variable ND filter, as long as you were okay with getting the effects of polarizing filters as well.

you will most likely introduce vignetting when stacking polarizers...

plus two polarizers only gets four stops.... whereas the cheap p.o.s. listed would give you up to 8 stops

or make the 8 EASY STOPS!!

Joves · Jan 23, 2009

dEARlEADER said:
you will most likely introduce vignetting when stacking polarizers...

plus two polarizers only gets four stops.... whereas the cheap p.o.s. listed would give you up to 8 stops

or make the 8 EASY STOPS!!

Supposedly easy stops. :lol:

Eldrich · Jan 23, 2009

dEARlEADER said:
you will most likely introduce vignetting when stacking polarizers...

plus two polarizers only gets four stops.... whereas the cheap p.o.s. listed would give you up to 8 stops

or make the 8 EASY STOPS!!

yes, stacking filters may give you vignetting, but I mentioned it in response to someone saying they would stack ND filters.

and actually, using two polarizing filters you could go from 1 stop, all the way to having absolutely no light making it to the camera. That is as long as the first polarizer was not a circular polarizer. If it was a circular polarizer, then you could only take it down 2 stops I think, not 4 (?) how do you figure 4?

The way I see it, with completely random polarization, the first filter can polarize all light say, vertically, which would effectively be 1 stop, then if the second polarizer were oriented 90 degrees to the first, no light would get through. And as I said, if the first filter were a circular polarizer, then it would circularly polarize the light, and the most stop you could get from the second polarizer would be one more stop.

tirediron · Jan 23, 2009

Eldrich said:
... using two polarizing filters you could go from 1 stop, all the way to having absolutely no light making it to the camera...

Interesting theory; not exactly sure I understand the physics you're talking about however.

Eldrich · Jan 23, 2009

tirediron said:
Interesting theory; not exactly sure I understand the physics you're talking about however.

Basically, if you imagine light traveling directly at you, the electric field of that light can vibrate in two different polarizations (for instance, horizontally or vertically), or it can be in a combination of the two different polarizations. In general, random light will be a random combination of the two directions.

A polarizing filter, if oriented in the horizontal direction, will block all light that oscillates in the horizontal direction. If you were to rotate the polarizer by 90 degrees, it would block all vertically polarized light.

So a polarizer will work as a 1 stop ND filter on completely randomly polarized light, it will block on average, half of the light.

Since the polarizer blocks all light that is horizontally polarized, all light that goes through the polarizer is polarized vertically. Then, the second polarizer can be oriented to block any amount of the light which you want it to. If the second polarizer is aligned the same way as the first it would let all light through, because all of the light that made it through the first is already polarized vertically. If you then rotated the second polarizer, you would see things get darker until the two polarizers were at 90 degrees to one another and then since the first polarizer only let vertical light through, the second polarizer would be oriented to only let horizontal light through, and so none would get through.

since light is a quantum system, there is a gradation between the two different polarizations, so you can get anything between half of the original light, to no light going through.

This website has a description of cross polarization:
Light and Polarization

but really, any optics book or physics book that discusses polarization will address the same thing.

If you want I can describe my comment about the circular polarizers having a limitation to 2 stops of ND, but only if you're interested, it would take a little more explanation.

tirediron · Jan 23, 2009

Hmmmm... have to give that a try.

Manlatiger · Jan 23, 2009

well, true.
seems made in china products are still not having a good reputation.
however I asked the seller bout the glasses and they replied me, saying the filter glasses are from Polaroid and they are using imported glasses rather than made in china.
LOL, I think they know pretty well how bad China glasses are.
Looks like price dropped, I think I will give it a try.
Cheers

Eldrich · Jan 23, 2009

Manlatiger, sorry the thread was somewhat hijacked into a discussion of polarization!

I only meant to convey that the effect of a variable ND filter could be achieved much cheaper than 300$ with two polarizing filters, but if the price dropped to 100$ and you are interested in having the ability to change a ND filter over a range, then perhaps it is worth it to buy a single filter that can do the job.

I cant say for certain, (in some circles 'polaroid' means a polarizing filter) but I suspect that this variable neutral density filter simply IS two polarizing filters mounted together, utilizing the effect I've been talking about. If someone were to ask me how to design a variable ND filter, i would give them two polarizing filters.

Anyway, I would still be a little hesitant to spend 100$ for an effect I think you could get buying a second 20$ polarizing filter (assuming you already have one) but it's up to you.