Inverted Graduated Centre (center) Filter

[Ed Bray]

I an just wondering if anyone is aware of an Inverse Graduated Centre Filter, that is one that is clear in the centre and then graduated outwards to give less exposure at the edges. Ideally this would be in the form of a square filter of 125mm to fit my Lens hood or even a 100mm square which I could then adapt to 125mm as I have already done with my Lee contrast filters. A large circular filter would also work but may be more difficult to work with.

Failing that, does anyone know where I could buy some clear optical grade resin 1.5mm x 125mm (100mm at a push) so I can attempt to make one myself?

TIA

[Sevo]

Why don't you cut a circular hole into an plastics ND filter?

[Bob Salomon]

One of the square filter makers, Lee, HiTech had some in the past.

[Mark Woods]

Panchro mirror in Los Angeles makes these filters. I own 3 of them.

[DrTang]

Lindahl does too - for their shade system


One of the square filter makers, Lee, HiTech had some in the past.

[Ed Bray]

Why don't you cut a circular hole into an plastics ND filter?

Because that would not give a graduated effect.

Thanks for all the responses, i have tried Lee and Hitech but they do not seem to list them in their current ranges. I shall try the others suggested when I return from my holiday.

[Sevo]

Because that would not give a graduated effect.


That is just a matter of the appropriate distance between filter and lens. But you will need a graduated clear centre filter to create soft vignette effects on very wide lenses (where you cannot place a classic opaque cut-out vignette close enough that its edges blur) - is it that what you intend to do?

If their description is right, Cokin still have one gradual centre spot without extra softness, colours or fancy effects, #141 on that page: http://www.cokin.co.uk/pages/cspot3.htm

[Ed Bray]

That is just a matter of the appropriate distance between filter and lens. But you will need a graduated clear centre filter to create soft vignette effects on very wide lenses (where you cannot place a classic opaque cut-out vignette close enough that its edges blur) - is it that what you intend to do?

If their description is right, Cokin still have one gradual centre spot without extra softness, colours or fancy effects, #141 on that page: http://www.cokin.co.uk/pages/cspot3.htm

I want to introduce a light vignetting effect on longer lenses such as a 240mm or 360mm similar to what typically happens when not using a centre filter with an extreme wide angle lens.

I realise I can (and normally) do this either in Photoshop or by giving the edges and corners a greater exposure under the enlarger if wet printing, but I am considering moving up in size and contact printing so would prefer for it to happen in camera.

Thanks for the link, I will have a look at the Cokin offerings.

[Carsten Wolff]

photograph an ordinary Center-filter and use the negative :)

[Ed Bray]

photograph an ordinary Center-filter and use the negative :)

That may be quite a good idea, I might actually try that with my center filter for my 72mm XL. Judging the exposure required may be an issue though.

[Struan Gray]

There are high-quality inverse-centre filters available for certain sorts of imaging applications. They're not cheap though, as the density profile is accurately calibrated, and the glass is of optical quality and flatness. Still, if you need them, they're there:

http://www.edmundoptics.com/optics/optical-filters/neutral-density-filters/continuously-variable-apodizing-filters/3121

You could try just using too long a lens hood, or a round vignette mounted on the end of a properly-specced hood, but I suspect the cutoff will be too sharp for what you've described. If, however, you have a drop-in filter system like Lee or Cokin, you can experiment with star-shaped holes, which will progressively darken the outer edges of the scene. With the longer lenses you mention there's little danger of the star shape itself coming into focus.

[John Olsen]

If you make a negative of an ordinary center filter it has to be on a glass negative, as film substrates are not of optical quality. Pete Palmer used to make these for me back in the early 70's.

[Mark Woods]

Be careful with the star cut out idea. At a certain point your bokeh highlights will all be star shaped.

[Struan Gray]

You can always spin the star in its mount, a la Hypergon :-)

I don't know whether layers of screen material or mesh could be combined to give a soft edge to the vignette without having to invest in optical-quality glass filters. Worth a try if you're the tinkering sort. I'd start with a hole in a bit of black card, but that'll be a bit hard-edged at f22.

[Mark Woods]

I've had students use the cut card in front of the lens, not to the point of vignetting, just for the bokeh effect. I'd give it a shot. What the heck.