Rollei Pro Square Filter Mark II - Reverse Graduated Neutral Density Filter (GND)
A reverse GND rectangular filter, also known as a grey graduated filter, has the greatest degree of darkening in its centre. The reverse GND filter quickly (concisely) attenuates to transparency from the centre downwards. Upwards, the filter attenuates to light grey.
High colour fidelity for your photos
Rollei Pro Square Filters Mark II have no colour distortion that is perceptible to the naked eye, and no colour casts. This has been confirmed in independent testing by Chip magazine and experienced by professional photographers who usually work with filter systems from different manufacturers.
Rollei Pro Square Filters Mark II have a (graduated) coating that uniformly lets in light (from ultraviolet almost up to infrared) through the filter. Unlike plastic resin filters and laminated filters, whose colour fades over time and whose bonding can easily come apart, the glass in Rollei Filters is extremely durable and does not fade.
If the light obscuration does not cover the whole spectrum of visible light, colour faults appear. With cameras, the visible light lies between 420 nm ~ 680 nm. The flat spectrum curve means that the light attenuation rate is relatively high and thus less visible light penetrates the filter. If light can penetrate the filter uniformly there are no colour casts. Rollei Filters meet this important requirement.
Reverse GND Filter Mark II – Versions and Sizes
There are different versions of the Pro Square Filter Reverse GND Mark II from Rollei available: GND4, GND8, GND16 and GND32
The number indicates the degree of darkening and the number of f stop reductions, also termed the gradient.
This Reverse GND Filter is available for filter holder sets from different manufacturers in widths of 100 mm, 150 mm and 180 mm.
Using Reverse GND Filters Mark II
A Reverse GND Filter is used for subjects that are very bright at the focal point in the centre. Take, for example, a sunset by the sea where the sun is close to the horizon. The same thing applies with a sunrise of course.
The very bright focal point of the image is darkened using a reverse GND filter. The sun is able to be given full expression, the sky and the water are well exposed, and the contours can be clearly seen. Even with photo processing, you cannot correct when the sun is over-exposed and the image information is lost in the over-exposure. For landscape photographs of professional quality, a reverse GND filter is indispensable and really works wonders. When using filter holder systems from Rollei or other manufacturers, you can use one or two Reverse GND Filters at the same time for creative and impressive picture art works.
If the American specialist manufacturer, Corning Inc., which, after all, can look back on more than 160 years of experience in the manufacture and coating of high-quality glass, calls its premium material “Gorilla®* Glass”, you can certainly assume from that that you will hardly find anything more resistant. For this reason, with immediate effect, Rollei professional filters in a rectangular form will be made from 2-mm thin Gorilla®* Glass. This small material thickness is only possible, because the blanks are exposed to a boiling hot alkaline solution, which engenders an ion exchange on the molecular level that, among other things, has a positive effect on the surface tension. Scratches, persistent contamination and even ruptures can do hardly any harm to the coated glass. Even more profound damage caused by points or sharp-edged objects cause no further splintering of the material on the edges.
What predestines Gorilla®* Glass further for our professional rectangular filters, is its impressive colour neutrality and extremely high degree of light transmission. Homogeneously coloured ND and GND filters can only unleash their complete effect if the glass material in itself doesn’t already change their colourfulness or impair their transparency. With the internally developed coating, Corning Inc. creates the very best conditions for you to be able to use Rollei rectangular filters productively for a long time for the implementation of your creative photography ideas. The small material thickness has an extremely positive effect on the total weight of your filter equipment particularly if you tackle expanded photo safaris.
“Luminance” is the photometric unit for light density - an essential quality factor for filters. This coating, which was developed in accordance with strict Rollei specifications, considerably reduces undesired reflections and optical distortions. Anyone, who doesn’t only take studio photographs but who engages extensively with the subject of “long-term exposure”, is aware of the relevant problem. Various sources of light, which you cannot affect, produce reflections, which clearly are intensified by longer exposure times. Either you change the camera location, which is quite often accompanied by a less than ideal perspective, or you use the specially coated Rollei rectangular filters from the outset.
An essential test criterion of the strict Rollei quality tests affects colour neutrality and light transmission, which must still be guaranteed to the greatest extent after the glass is coated. The colour curves of the filter glass must behave in an exemplary manner within the range of 400 to 800nm with respect to these two parameters. Due to their combination with the already extremely translucent, colour neutral and resistant Gorilla®* Glass from the traditional American manufacturer, Corning Inc., Rollei professional rectangular filters of the newest generation exhibit outstanding characteristics, which predestine them for daily use under difficult conditions.
Even with rough treatment and the worst kind of contamination, due to careful coating in accordance with Rollei specifications, no impairment of the optical quality occurs. After taking your photograph you can undertake colour variants, reflection effects and other creative digital image editing options. You will obtain the neutral, distortion-free raw files with Rollei’s professional rectangular filters.
Engineered and Quality Controlled in Germany
Rollei is setting new standards in the photography sector with the extraordinarily stringent multi-level quality assurance initiative: “engineered and quality controlled in Germany”. All Rollei professional rectangular filters of the newest generation must be subjected with immediate effect to these unyielding testing criteria before being put on sale. In the process, several steps that are precisely coordinated with each other guarantee adherence to the extremely high (essentially contradictory) quality requirements of the optical characteristics of Rollei professional filters:
In the first step the Rollei filter experts define all optical and technical, material requirements, which are then considered as the exclusive basis of the following production phases. In this way backward-looking weakening or falsifications of the original specifications are prevented.
Directly after actual production - and before delivery to Rollei - the individual manufacturing batches are quality-tested according to the AQL (acceptance quality limit) principle. This principle, which is known in German-speaking countries as "Annehmbare Qualitätsgrenzlage" goes far beyond the usual random tests. It is only if all the random samples selected are in compliance with the previously, precisely specified tolerance values that the production batch can be delivered. If the samples fall below the requirements, the entire unit is returned.
If the approved supply subsets are received by Rollei, then the procedure is repeated with the same consequences. It is only by means of this uncompromising process, which is linked to substantial costs and effort for Rollei, that we can guarantee you the nearly already proverbial merit and optical quality of Rollei rectangular filters of the professional class.