When and why are grey graduated filters such as soft, hard or reverse GND filters a good idea? The human eye is a genuine high-performance system that surpasses any image sensor. It perceives the most delicate differences in brightness and colour contrasts, as well as the smallest details in a subject like a bustling city centre or an extensive landscape panorama in the sunset and, using the retina and cones, sets these sensory impressions perfectly in the scene, as the information is passed on to the visual centre and converted into razor sharp images. All of that is called the dynamic range of a subject. For us and our eye, handling the high dynamic range and thus the correct exposure and the perception of all of the contrasts in our environment is obvious, so to speak. For a camera and its image sensor, it is not. Neither is it for modern DSLR (digital mirror reflex cameras) or DSLM cameras (system cameras). Therefore, beautiful subjects are certainly found quickly in landscape photography. But without appropriate filters you often have to wait a long time for the (almost) perfect picture. What appears to us to be high in contrast and diverse on site is often not captured on camera as it has been seen in reality. Good DSLR cameras have a dynamic range of approx. 9-12 and thus can deal with a maximum of 12 brightness differences in apertures, whereas a high-contrast subject in landscape photography can be captured by the human eye with approx. 20 aperture stops. And if it was impossible to capture the appearance of the sky in a subject, for example, then even digital processing of the RAW file can no longer help. Although HDR offers possibilities here but even multiple exposure has its limits, particularly with moving subjects like waves on the sea. Therefore grey process filters are used to compensate for this disadvantage in handling differences in brightness and contrasts that the image sensor has in comparison to the human eye. In order to capture a subject preferably in precisely the same way as the eye of a landscape or travel photographer perceives it.
In professional landscape photography our grey graduated filters that are made from durable Gorilla® glass with a neutral grey gradient on the filter glass are used as an indispensable aid - so-called GND filters (graduated neutral density filters), which are suitable as plug-in filters for 100-mm, 150-mm and 180-mm systems. Above all, for the simultaneous ideal exposure of the sky and a foreground with high subject contrast, thus many excessively bright and excessively dark areas at the same time. Ideally, you can quite simply combine our plug-in filters in a user-friendly manner with a CPL filter (circular polarizing filter), which intensifies the colour contrasts more and filters out reflections on non-metallic surfaces. We also recommend the use of our adaptor rings for different lens sizes, in order to connect the filter holder to the particular lens. The high-quality durable Gorilla® glass makes the grey graduated filters scratch-proof and prevents optical distortions. At the same time the rugged filter glass guarantees a high degree of light transmission as well as great colour neutrality. It is absolutely colour neutral even with up to three combined filters. In this way you can also use yet another normal ND filter to execute longer exposure times even in daylight and you will achieve particularly lively, professional and authentic results in landscape photography.
Everything about grey graduated filters:
- What are grey graduated filters & why do we need them?
- The design of Rollei’s grey graduated filters – which strength and which transition?
- When are grey graduated filters useful in landscape photography?
- What is distinctive about Rollei’s grey graduated filters?
- What should I look for when purchasing a grey graduated filter?
- Using & cleaning grey graduated filters properly
What are grey graduated filters & why do we need them?
What is a grey graduated filter? In contrast to normal grey filters / ND filters grey graduated filters darken only the area of a subject, which is too bright.
Due to one darkened and one transparent half of the filter glass of a GND filter (graduated neutrally density filter) this allows both enough light of the foreground of a subject in the lower area through, which would otherwise have been too dimly photographed, while the darkened section in the upper area ensures that the very bright components of the subject are not too brightly photographed without an outline. Thus, graduated filters are intended primarily for photography of the sky in contrast to the landscape. Here it is important that the neutrally darkened part does not affect the colour, which we can guarantee by our coated Gorilla® glass. The transition from the neutral grey darkened area to the transparent area of the grey graduated filter is hard (hard GND), soft (soft GND), reversed (Reverse GND) or from the centre of the filter out (medium GND). In the case of plug-in filters you can adapt the gradient to the horizon by shifting them up and down. However, normal ND filters reduce the quantity of light of a photo on the whole surface, in order to use longer exposure times. With grey graduated filters you can optimally adjust differences in brightness above all in that way. In certain situations you can obtain particularly beautiful results with a combination of ND and GND filters. You can choose to add still another circular polarising filter in order to emphasise the individual colour contrasts even better. CPL filters remove reflections from non-metallic surfaces. For example, in this way you can photograph a river through its surface and capture the stones on the bottom.
Sunset in Hamburg’s Speicherstadt with CPL, soft GND8 and ND8 filters - image: Thomas Güttler
Why do we need grey graduated filters? A camera or the camera sensor cannot process and reflect high contrasts and differences in brightness like the human eye, something which is noticeable for example in the case of photographs of a sunset or a sunrise, or the blue sky and its beautiful line in the cloud structures. Or in the photograph of a lake surrounded by high mountains and a bright blue sky on the horizon. Here over-exposure or under-exposure of individual areas with great differences in brightness leads to the fact that either the beautiful landscape is wonderfully lit, while the bright blue sky with its impressive cloud towers degenerates into a uniformly grey-white “soup”, or the other way round; the sky looks great, while the actual subject in the foreground can barely be seen since it was much too dark in the photograph. This is where the grey graduated filters come into play.
The design of Rollei’s grey graduated filters - which strength & which transition?
Our grey graduated filters from Rollei are rectangular plug-in filters in design and are made out of durable, absolutely colour neutral, translucent Gorilla® glass. They are compatible with 100-mm, 150-mm and 180-mm plug-in systems, into which you can push several types of filters one after the other in order to be able to cope with different lighting situations. The glass of the Rollei grey graduated filters is manufactured with a soft or hard transition of the grey gradient, which decreases from top to bottom, except in the case of our Reverse GND Filter. Reverse grey graduated filters also consist of a transparent half and a half with a grey gradient. However, this is darkest in the centre, decreases towards the top and is completely transparent on the bottom. This is suitable therefore particularly for photographs of subjects, where the brightest area is located exactly at the level of the horizon, e.g. in the case of sunrises and sunsets. Since in landscape photography the sky, in particular, should be darkened by the optical density of the neutral grey, only the upper half of the filter glass is darkened neutrally. In this way the difference in brightness of the horizon can be balanced, by pushing the rectangular filter up or down. That is also their greatest advantage over screw-in filters.
Grey graduated filters - which strength?
The strengths of the GND filters are graduated according to how strongly the upper part of the glass of a grey graduated filter is darkened, thus how high the optical density is and to how many apertures / f-stops it corresponds. We recommend grey graduated filters of the strength GND8. You can obtain the following grey graduated filters from Rollei.
Grey graduated filters of the strengths, GND4, GND8, GND16 and GND32 from RolleiSimilarly to ND filters the optical density or the GND value determines by how many apertures the incidence of light within the darkened area is reduced.
Rock Solid in the 100-mm system:
- Rock Solid Soft GND8 filters (strength: GND8 to GND16)
- Rock Solid Hard GND filters (strength: GND4 to GND8)
- Rock Solid Medium GND filters (strength: GND8)
- Rock Solid Reverse GND filters (strength: GND4 to GND8)
Mark II Professional Rectangular Filters in the 100, 150 and 180-mm system:
- Mark II Professional Rectangular soft grey graduated filters (strength: GND4 to GND32)
- Mark II Professional Rectangular hard grey graduated filters (strength: GND4 to GND32)
- Mark II Professional Rectangular reverse grey graduated filters (strength: GND4 to GND32)
Both series of the Rollei rectangular filters are equipped with Gorilla® glass, which has a high degree of light transmission and is absolutely colour neutral. The Rock Solid series is distinctive particularly due to the coating of the Mark II professional rectangular filter series. The Mark II series is finished with Luminance Coating, which renders the graduated filters shatterproof as a rule if they fall from a height of up to 1.2 metres. The high-quality filter glass protects both series against scratches and other external influences.
The difference between hard & soft transitions of the grey gradient
The difference refers to the hard or soft transition of the grey gradient, thus the phasing out of the shading up to the straight line/horizon, which separates the neutral grey darkened area and the transparent area of the glass of the GND filters.
Hard transition of the grey graduated filters (Hard GND)
Soft transition of the grey graduated filter (Soft GND)
The more clearly the individual differences in brightness in a subject should be defined and the more uniform or more straight-lined the horizon is, the more likely it is that the use of a hard transition is recommended. For example for a cloudless blue sky or for landscape photography at the sea or on flat land, thus with clearly defined horizon lines.
If the horizon is rather irregular, as high mountains or buildings project into the horizon, for example, or the subject contrast has a very large dynamic range e.g. a cloudy sky with a very dynamic outline and differences in brightness, urban subjects and rugged mountain landscapes or pristine woodland with the appropriate heterogeneous vegetation and without a clear horizon, then the use of a soft transition is probably recommended.
The reverse grey gradient (Reverse GND)
Then there is still the reverse grey gradient which exhibits the highest optical density in the centre and not at the upper edge of the filter glass.
This is suitable in particular if the brightest area of the subject is clear on the level of the horizon, e.g. in the case of sunrises and sunsets. If you are committed to only one normal grey graduated filter here, then the top of the clouds would be darkened too much. This is exactly where Reverse GND filters, whose glass was darkened most right at the transition, are used.
Medium transition of the grey graduated filter (Medium GND)
A medium GND filter combines a hard and a soft grey graduated filter with one another. The grey gradient in the upper third of the filter runs quite hard, while it phases out softly downward, in a soft transition. The bottom third is completely transparent. This filter is particularly suitable for places where there are no clear horizon lines to be seen. Thus, for example, for landscape or city photography, in which the sun is dazzling and should be darkened and at the same time photographs of a landscape with trees or the houses of a city should be captured with a wealth of detail.
When does it make sense to use a grey graduated filter in landscape photography?
Many photographers, who are starting to concern themselves with landscape photography and the challenges associated therewith, know this. A great subject with a wonderful play of colours, incidental light and impressive cloud structures is soon found thanks to that wonder tool, “the human eye”. Hence with a great dynamic range and excessively bright and excessively dark areas at the same time. Indeed after shooting with the reflex camera, the histogram of the image then indicates that brightness levels are cut off at the edges
Thus, when are grey graduated filters useful? What is distinguished by our eye and appears to it to be high in contrast, like a blue sky, can nevertheless look like a grey nothing in the image file. Because if a subject has a high dynamic range and/or a subject contrast and thus excessively bright and excessively dark areas at the same time, then a grey graduated filter can adjust this high contrast range immediately when the shot is taken. Yes, there is the option of digital post-processing with the keyword, HDR (high dynamic range). In the process, several photographs are taken without filters and with different exposure times. One picture captures the sky almost perfectly and another does the same for a subject in the foreground. Via digital image editing these pictures then merge on your PC into an HDR picture. But in the case of strongly over-exposed areas not much can still be saved by means of standard image editing if a sequence of exposures was not created, since they don’t contain any more outlines. In addition, in the case of HDR beginners, pictures often become too ”flashy” since the controls are often gladly overwound. Also with moving subjects multiple shooting with several exposures quickly reaches its limits because you have to take several pictures of the same subject. If the latter moves, e.g. in a strong wind or with a strong swell in the case of shots by the sea, then you can’t use multiple exposure, as the subject changes too much. In addition, we also always recommend the use of a stand for filter photography. Also, anyone who would like a genuine photo with feeling and an artistic trade-off, should select grey gradient filters. Anyone looking for the absolutely perfect final result on a computer would probably be better off with HDR photos.
In addition, the attraction for most professional photographers lies precisely in capturing an almost perfect picture with only one shot. It isn’t half as fascinating to achieve this result by piecing together different pictures because the attraction of photography has also always lain in the best possible creative compromise.
What is distinctive about Rollei’s grey graduated filters?
Resistant, colour neutral filter glass
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 the Rollei grey graduated filters - both the Mark II professional rectangular filters and the Rock Solid filters - are made of 2-mm-thick Gorilla®* glass. This small material thickness with simultaneous ruggedness 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.
Also, the impressive colour neutrality and extremely high light transmission of the special filter glass regularly convince photographers of the value of our grey process filters. 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.
Also: It is not only our grey graduated filters that are made from Gorilla®* glass. All our filters (both screw-in and rectangular filters) are committed to the sturdy colour neutral filter glass:
- CPL Filters
- UV Filters
- ND Filters
- GND Filters
Mark II Professional Rectangular Filter Series with Luminance Coating
“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. Anyone, who doesn’t only take studio photographs but who engages extensively with the subject of long exposure, is aware of the relevant problems. Various sources of light, which one cannot affect, produce reflections, which are clearly 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 800 nm 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 options of digital picture editing. You will obtain the neutral, distortion-free raw files with Rollei’s professional grey graduated filters.
Grey graduated 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 grey graduated filters, as well as all other rectangular and screw-on filters from our company, must be subjected to these unyielding test criteria, before they are 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 grey graduated and ND 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 production phases below. 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 process, which is known in German-speaking countries under the name “Annehmbare Qualitätsgrenzlage” goes far beyond the usual sample testing. It is only when all of the selected random samples of the grey graduated filters are in compliance with the previously stipulated 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 efforts for Rollei, that we can guarantee you the already almost proverbial merit and optical quality (colour neutrality and light transmission) of Rollei rectangular filters of the professional class.
What should I look for when purchasing a grey graduated filter?
- Which subject: The type of grey graduated filter that is recommended for use also varies based on the subject. Particularly with respect to a hard or soft transition and the optical density. If I would like to take shots of sunrises and sunsets where the sun is located on the horizon and the brightest part of the picture is therefore to be located in the centre, the use of Reverse GND filters is recommended.
- Hard or soft transition: If the differences in brightness in the image are clearly delineated from one another, e.g. in the shot of a relatively even to very straight horizon (sea & lakes in the flat country), then a hard transition is recommended. If the demarcations are rather irregular, e.g. in the case of a skyline from the middle distance or a very dynamic mountain gradient, then I should preferably use a soft transition. In order to be prepared for all eventualities, you should get a grey graduated filter of the particular strength in each case with both a hard and a soft transition.
- Which strength: the greater the difference in brightness, the more light there is that has to be darkened, in order to capture contrasts and outlines in the picture, the greater the optical density and thus the strength of the grey gradient should be.
- Screw-in or plug-in filters: we are exclusively committed to plug-in filters when it comes to grey graduated filters since the horizon is not movable with the use of screw-in filters.
- Which size: You must buy an appropriate adaptor ring for the plug-in system for your lens diameter. This is available in different sizes in the set.
Using and cleaning grey graduated filters properly
Handling grey graduated filters requires a little practice. Particularly concerning the correct placement of the horizon, thus the straight-line transition between the grey gradient and the transparent half of the filter glass. Before you travel to a distant nature reserve in order to take breathtaking pictures, practice using your filter first in a natural setting near home in order not to be disappointed in the end. However, digital cameras always show a result immediately and thus facilitate a quick correction of the settings. This greatly simplifies training with grey graduated filters.
- Selecting the right strength: This requires empirical data, which you have to collect. The histogram can help, in order to arrange the range of contrast in a scene. It is only in this way that you can select the correct strength and optical density (GND4, GND8, GND16 or GND32). If you decide on an excessively strong and/or dark filter, then the subject will possibly be photographed as “unnatural” or with too little contrast. On the other hand, if you select an excessively small optical density and an f-stop reduction that is too slight, the dynamic range of an image will be lost. In short: the greater the differences in brightness and/or the dynamic rang are, the darker the GND filter is.
- Selecting the transition & positioning it correctly: Positioning the transition correctly in front of the lens and adjusting it to the more or less clear horizon of a subject probably requires experience most of all. You have to try it out yourself. However there are already a few basic rules. The clearer and straighter the horizon is, the harder the transition should be. If bright and dark areas cannot be separated along a straight line, for example, in the case of urban photography, skylines or rugged mountains, then a soft transition should be selected. If you would like to take a shot of a subject, whose brightest area is on the level of the horizon, you should select a Reverse GND with a reverse grey gradient for example in the case of sunrises and sunsets by the sea. For best results, place the lowest part of the darkened half of the filter glass best a little bit above the landscape in the foreground, so that you create a clean transition to bright areas.
Cleaning grey graduated filters
- Rollei filters are dirt-repellent due to their special coating. Therefore cleaning them with a micro fibre cloth is sufficient in most cases. If the filters are heavily soiled some lens cleaning fluid can be put on the cloth and afterwards an air blower can be used. For photography tours we recommend our travel camera cleaning set, with which you are prepared for typical kinds of contamination of the camera and the filters when you are on the road.
- Before any trip or photography tour, check whether the grey graduated filter is free from spots and fluff. It is really very annoying to discover the latter just briefly before your planned use of the filters in landscape photography. Also check again whether the plug-in filter is completely devoid of fluff, etc. especially in its central area before pushing it into the holder system. Simply blow it free once more provisionally and always look again to see whether a fly or something similar has landed on it. Because any irregularity will immediately become apparent in the finished picture.
- Thanks to the very rugged Gorilla®* filter glass scratches and other damage can be effectively avoided. Thus, if you clean your grey graduated filter regularly and thoroughly, it will reliably supply you with authentic landscape shots with a high dynamic range over a very long period of time and will photograph both foreground and sky virtually perfectly.