An idea to reduce vignetting

Hi. I 've just been thinking about the so called "hot spot" found to various degrees in all the mirror lenses, while at it I also thought of all the dreaded vignetting present with almost all lenses at the widest apertures. Why would one not manufacture computer designed filters of the appropriate size to compensate exactly for the difference ? Take your 50 / 1,4, put on your 55mm filter which will be neutral grey in the center just the right amount, and clearing up progressively towards the corners. OK, your f1,4 will become a f2 or 2,8, but you save the depth of field and bokeh of the original F stop. Of course if you stopped down you get a darker centre... but for us fast lenses freaks ? Same with the mirror lenses. The f8 will become something around f 11 or 16, but you get an evenly exposed pic. What do you think ? Is it worth it commercially ? I suppose not. Those who edit pictures with computers probably already have some programme doing just that...

I think it has been done with radially dyed filters in the old days, but such an item would have to be matched to a particular lens and aperture, since different ones have different degrees of vignetting and also are different at different apertures

 

These days it's so easy to correct vignetting in post processing (such as in Adobe Camera Raw) that there surely wouldn't be much market for a glass-and-metal filter...

Agreed. Thank you JDM !

Many large format wide angle lenses had filters like this available, but they were (are) pricey. When I shot interiors with my 65 mm f/4.5 Grandagon N on 4x5 film I would set up lighting to be a stop brighter at the edges than in the center of the image, which also worked to minimize vignetting on transparency film.

I have a 72mm Hoya centre ND filter that grades from about 0.45D in the centre to transparent at the edges. I bought it in the mid 1980s or thereabouts, and it was 'end of line' remaindered then.

 

It was apparently designed as a generic anti-vignetting filter, and was available in several diameters.

 

Schneider and Rodenstock also supplied such filters specifically for some of their large format wideangles for many years. However, the high price of such filters meant that many users forwent their use and put up with the vignetting, or just held back the corners during enlarging.

 

In addition, the amount of vignetting of any lens varies quite considerably with the aperture used. Therefore it's impossible to design a centre filter that fully compensates for vignetting at all apertures.

 

Having said that, the Hoya centre filter I have has been quite useful on a few occasions, across all formats. And on an aesthetic note; a degree of vignetting can draw the eye into the centre of a picture and hold it there.

Here's a 65mm Super Angulon lens wearing a Rodenstock CWNDF, or Centre Weighted Neutral Density Filter. They are not cheap items...

 

Impressive indeed. Thanks to all.

See http://www.galerie-photo.com/center-filters-for-large-format-lenses.pdf

 

Old idea, the earliest one was mechanical. See the historical note.

 

JDM, not radially dyed. Two pieces of glass of the same refractive index and dispersion, one with a colorant. The colored piece is ground to give the density gradient needed, the clear piece is ground to match and the two are cemented. The first one, Rodenstock's Enixantos, used greenish-yellow glass.

The Hasselblad Xpan came with anti-vignetting "center filters" designed for the 45mm and 30mm lenses.

65mm Super Angulon lens wearing a Rodenstock CWNDF

 

Thanks, Impressive!