How center filters are made?

[yong_shin1]

Does anyone know how center filters are made? Does it have to be mass

produced or can an individual attempt to fit a particular lens with a

custome-made center filter? I want ceter filters made, one for

Notilux, GR28, etc. I hope I am making sense. Thanks in advance.

[james_elwing]

Think I know what you mean; all graduated centre filters are made for larger format, so I am told. The Hoya version, I think, is worth only one stop, from centre to edge, and is quite expensive. In addition, they are made for larger filter sizes, so you might need a filter adaptor. For the Noctilux, you could use 2 filters?????????

If you wanted to make one yourself, look at Goerz's Hypergon, then work out how much black mist you would need to float onto the centre/center of a UV filter to do the job.

Then work out why you wanted to lose two stops and get to the light collecting ability of a Summicron in the first place,

Be of good cheer; the short depth of field would be awesome

[stephen_w.]

Expariment:

 

Take a Sharpie and place some dots on a UV. I may just try that myself. It's completely reversible.

[stephen_w.]

Black-out 50% in the center and gradually reduce the marking out to the edge to zero.

[Rob F.]

A one-stop ND in the center of the Noctilux field will turn it into an f/1.4 lens. What you need is a Summilux.

[joe_fikes]

One way that good ones are made is by cementing a plano-concave lens to a plano-convex lens that is made of absorptive glass... the same glass neutral density filters are made of. The thick middle part of the convex lens absorbs more light than the edges, while the concave lens absorbs essentially none of the light. The curved sides of the two lenses are cemented together. For this to work, the curvature of the concave lens must accurately match that of the convex lens so that they fit together without a gap. The index of refraction of both elements must also match. Otherwise, the cemented lens pair would exhibit some amount of optical power. It's not something that most folks could make home.

 

If you enjoy tinkering, you might come up with a scheme to get the ND pattern you want on a piece of film with a clear base and then cement that between two pieces of glass. Sounds like lots of work.

[stephen hazelton]

I've thought of Joe's idea before. Take the lens that NEEDS the center filter, aim at a blank uniformly lit wall, fire off a shot, develop the negative, and there's your center filter. May have to enlarge or adjust contrast, but the basic pattern is there.

[jean_christophe_barnoud1]

Black dots on a filter will result in a lot of diffraction. Pictures will be softer if more evenly lit.

[watts]

<i>A one-stop ND in the center of the Noctilux field will turn it into

an f/1.4 lens. What you need is a Summilux.</i><br><br>I can't

speak for the original poster but I guess, like me, he is

interested in the unusual optical characteristics of this lens wide

open and not its light gathering ability per se. I routinely use an

8x ND filter on my Noct so that I can use the lens in normal

lighting conditions at as wide an aperture as possible. I would

certainly be interested in a centre filter to reduce the vignetting

(even better would be something like a 16X ND centre biased

filter). I actually like the vignetting in many circumstances but it

would be nice to have the choice to reduce it when desired.