When shooting with the 5D outdoors some recommend using a variable ND filter. Philip Bloom recommends a lSO below 1600, Shutter of 1/60 and low Aperture for a shallow depth of field. Of course you then need another method of controlling the light. Enter the Variable ND. I have tried the less expensive filters from ebay. One caused everything to be out of focus, the other caused dark bands in various patterns across the frame. Tried to return but no response from the seller.
Posts on this web site and others report equal success with both the Singh Ray and the less expensive foreign ebay models. Is it possible that I could be doing something wrong. The process seems straight forward. Attach the filter to the end of lens, depress the light meter, adjust the filter by turning the movable glass, to get the desired exposure reading.
I ordered and received two different filters. One caused everything to be out of focus the other works in lower light situations but when used with bright sun in a snow covered environment causes banding in a variety of shapes and forms.
The seller will not respond to my emails.
I wonder if others are having similar experiences.
Thanks
Kent

much complex is the gradient ND filter on the front of the lens, as you change how the light travels through the lens that your using you change the area of the filter your hitting.
so a closer zoom or lens itself your right up on gradient changes few bands, back a bit further your going through more of the filter, and therfore more changes effect the light.

A poor gradient with banding change, might look ok with a wider or closer view, or in a situation where the Glass itself is very out of focus, and would cause major problems when using less of its area , or where the glass itself on the front of the lens comes into focus.
then add in that cheap glass in general has no anti-reflective coatings, so you can get some bounces, and you now have a pattern on the glass that can be light up by any stray lighting hittin it at different angles.

now i know why a good one is $70-400 they have huge boxes controlling the light around them, and are used only within the realm that the filter, or use of that filter was designed.
Try it with a different shot type , and avoid ones that are just cheaply spray painted on in visable bands of change.

Any ND filtration gradient or not changes the iris setting you will use (or other settings to adjust to the darkening), as the iris goes from "pinhole" to "Dof" it will effect your ability to focus, adjust your settings according to the quantity of "DOF" you desire vrses having a small iris opening that will provide the pinhole effect which will have many more things in focus.

hey its Art :-) if you want everything out of focus, AND cutting back your light, and dont have enough light, and dont have the settings right, your going to have to re-paint the picture.

Kent,

The black-cross effect is well-known and is unavoidable with the variable ND filters. Singh Ray admits to them on their website and the only way to avoid that is to use a focal length of longer than 28mm. You can try wider but 16mm-20mm definitely will not work with the VND. You can of course use the lower densities with any focal length, it's the higher densities that shows the issue.

Thanks for the post. I had no idea that Fader ND's do not work with a wide angle lens.

Good news. The Fader ND arrived today and the seller returned my email. I am anxious to try the replacement filter tomorrow.
My concerns about the sellers integrity were somewhat put to rest as he offered to either send me another filter or return my money. I received his email before I got the filter.
Enjoy

Kent

if you mean the Fader ND, his seller name is 'bonifaceleung' on ebay and he seems a pleasant guy to deal with..
theres apparently some imitation 'fader nds' around at the moment so it may be best to search by the above name..

Good luck!

I got the fader ND from here Light Craft Workshop - Fader ND adjustable ND filter (ND2~400) (http://www.lightcraftworkshop.com/site/page1000.aspx)
It was 115€. I tried it with max and min, it works great, no crosses. But, if I go over the max, I see the cross coming.