Our aim is a perfect image and for this reason Schneider-Kreuznach and Nurizon, a well known specialist for imaging software, have created a digital centerfilter, a Photoshop®
Plug-in (CS 2 and later) for MacIntosh.

The software correction of the image based
on the exact lens date and gives best results.

With May, 3rd each Schneider-Kreuznach wide-angle lens will be supplied with this new digital centerfilter at no extra charge. Along with the lens the customer will get a license code for release at the internet.

What is a CENTERFILTER?

Wide-angle lenses are characterised by decreasing light intensity towards the edge with increasing angle of view, which makes the corners appear darker and is unwelcome in many cases. In conventional film photography concentric gradient filters referred to as CENTERFILTERs were developed. These filters have a higher density in the centre of the image and increase transmission towards the edge.

CENTERFILTER for analogue photography have to be mounted on the lens before the film is exposed. They correct the brightness reduction by a fixed value – usually 1.5 or 2 aperture stops. ANALOGUE CENTERFILTERs consist of a glass plate that is coated with a special ND grading in a complex production process and a filter ring that positions the plate at an exactly calculated position in front of the first lens.

Disadvantages of an ANALOGUE CENTERFILTER:

• Possible vignetting at ultra-wide angles > 100°
• Several filters may be required, e.g. an additional polarising filter
• Risk of reflexes, reflections and “ghost images” on the filter surface under unfavourable lighting conditions
• Loss of brightness during focusing
• Symmetry interference with high-resolution lens systems

Why use a DIGITAL CENTERFILTER?

In contrast to analogue photography, in digital photography each image is stored in a file and can be (post-)processed using suitable software. If the brightness reduction of the lens over the whole image circle is known, it can be corrected – provided the edges of the image were sufficiently exposed – with the aid of special software, the DIGITAL CENTERFILTER.  A DIGITAL CENTERFILTER can also be used for correcting the edge brightness reduction in analogue images after they have been digitised for processing.

Fig. 1: Digital Centerfilter as Photoshop^® Plug-in

Advantages of a DIGITAL CENTERFILTER:

• The filter is applied after the image has been taken, so that the full brightness of the lens is retained
• Virtually 100% edge shading correction available, even with offsets (offset values xy can be entered in the software)
• Continuously variable correction of the exposure value – aperture 0.1, 0.5 or 1.5, anything is possible.
• A correction can be discarded and repeated, if necessary
• No additional glass in front of the lens system that may cause reflections and reduce the resolution.
• No risk of vignetting of centerfilter holder

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