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Thread: Graduated Neutral-Density Filters in the Digital Age

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    Graduated Neutral-Density Filters in the Digital Age

    It's been a while since I posted a somewhat educational post on my blog, but the topic of GND filters has been on my list for a while, so I decided to publish an introduction to GND filters.

    I've reproduced it here for everyone's benefit, and hope that it will be useful.


    Introduction to Graduated Neutral-Density Filters

    Graduated neutral-density (GND) filters were used in the days of film to lower the contrast (sometimes expressed as 'dynamic range') in a scene.

    When shooting a landscape or seascape image (especially when shooting towards a rising or setting sun), the difference in brightness between land (or sea) and sky can be significantly different, in the order of up to seven or eight stops.

    The solution to this problem is GND filters, which are positioned in front of the lens, and optically even out the brightness levels between sky and foreground by darkening the much brighter sky via a semi-opaque darkened portion of the filter and transitioning to a non-filtered (ie, 100% transparent) portion of the filter.

    Neutral refers to the grey, non-colour-altering property of the filter.

    By positioning the filter such that the darker portion covers the sky and transitions to unfiltered where sky and land meet, the dynamic range in the scene can be reduced, which makes exposure easier.

    GND filters come in various grades of darkness, measured in stops.

    • GND2 or 0.3 = one stop.
    • GND4 or 0.6 = two stops.
    • GND8 or 0.9 = three stops.

    One major brand even offers intermediate GND filters, such as 0.75 (2.5 stops).

    Transitions are 'soft' or 'hard', with soft GND filters transitioning subtly from dark to light, and hard filters transitioning more abruptly.

    Soft filters are best used for uneven landscapes (eg, mountains) and hard filters for horizons (eg, oceans or flat landscapes).

    So, what does 'GND8' mean?

    There is a simple formula for translating the filter nomenclature into the number of stops of filtration offered by the filter. The formula is as follows:

    GNDx = 2 ^ y stops of darkness

    Examples:

    • GND2 = 2 ^ 1 (ie, one stop)
    • GND4 = 2 ^ 2 (ie, two stops)
    • GND8 = 2 ^ 3 (ie, three stops)


    Are GND Filters Necessary?

    In the digital age, some people might propose, as an alternative to optical filters, exposure bracketing and blending of multiple exposures either manually, or using Photoshop's own gradient filters.

    My own philosophy is that while you can do this type of work in post-production, attempting to decrease the dynamic range in a scene during the capture phase makes capture and post-processing easier in the long term.

    Depending on the nature and intensity of the light and cloud cover, the use of a GND filter at the capture phase may eliminate the need to employ exposure bracketing and blending in post-processing at a later stage. In other cases, even stacking multiple GND filters may not produce a balanced single-frame exposure. I have certainly experienced cases where the sky is still blown out despite me having stacked my two-stop and three-stop GND filters.

    My approach is to use both GND filters at the capture phase, and blending during the post-processing phase. I want to give myself the most flexibility and ensure I have a good range of exposures to cater for the dynamic range in the scene I have captured.


    Recommended GND Filters

    I personally use and recommend the Lee creative filter system. It is a modular system, consisting of a filter holder, an adapter ring (for mounting the filter holder onto the lens) and the filters themselves. Lee GND filters are 4 x 6" (100 x 150mm) in size, and made of resin.

    A filter system such as this is quite handy, as the filters are large enough to cover ultra-wide lenses without introducing vignetting, and if you have lenses with different filter thread sizes, all you need to do is buy an adapter ring of the appropriate size. Adapter rings are quite inexpensive.

    Unfortunately, the filters themselves are very expensive. I chose the more expensive Lee filters because I had heard good things about Lee filters, and I had also heard about, and seen, the magenta colour cast introduced by Cokin filters. Unfortunately the magenta colour cast issue is far from a simple case of brand, as I have personally experienced a magenta colour cast with my Lee filters when stacking GND and ND filters (both Lee-branded). It may be a combination of the colour of the light, the white balance, the filters and even the camera. The jury seems to be hung, but in my experience with Lee filters, colour casts have not been problematic for me with the exception of one dawn shoot.

    Many people use the much less costly Cokin filters, which are more readily available, and have also shown themselves to work quite well. Someone using the Cokin system may never experience magenta colour casts. In my case, I decided not to risk it, so I opted for the Lee brand, which generally had much better feedback.


    In Conclusion

    My recommendation is always to give yourself the most options when it comes to capturing images. You cannot easily add what wasn't captured, and in my experience, using filters can eliminate the need for exposure blending. However, I still bracket so that I have the most options, and I will mostly continue to blend exposures that were captured with filters.

    Where filters can also help is in cases where there is movement in a scene. Wind has a nasty habit of blowing branches and leaves, and if these are in the sky portion of a scene, blending multiple exposures will be somewhat tricky, whereas the use of a filter can eliminate that problem.

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    Account Closed Wayne's Avatar
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    I'm still waiting on a heap of Lee gear from Nov 2010, and word is it won't arrive until at least April, but to me they will be worth the wait.

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    Assuming I use a GND mainly for sunrise/sunset shots, is there a rough rule of thumb as to which filter (eg. GND2, GND4, GND8) would be most useful to start off with? I realise the contrast can vary a lot, but I probably cant afford to buy 3-4 of these.

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    A nice summary Xenedis.

    I recently splurged on my first set of filters, opting for the Lee Foundation kit holder system, but using the Hitech filters (I think inbetween the Cokins and Lees in terms of quality), primarily chosen because the wait for the Lee filters was ridiculous.

    cfm - I have found the 3stop to be most useful so if I only bought one it would be this.

    I also bought a Hitech Reverse Grad (3 stop), which has the darkest part in the middle, and is ideal for sunsets and sunrises where the horizon is the brightest part of the scene.
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    Quote Originally Posted by cfm View Post
    Assuming I use a GND mainly for sunrise/sunset shots, is there a rough rule of thumb as to which filter (eg. GND2, GND4, GND8) would be most useful to start off with? I realise the contrast can vary a lot, but I probably cant afford to buy 3-4 of these.
    The advice I was given was not to bother with the one-stop filter; the Australian light is too harsh.

    I have two-stop and three-stop soft grads. My first port of call is my three-stop GND; if I need further filtration due to contrasty light, I stack my two-stop filter on top.

    I rarely (if ever) use my two-stop filter in isolation.

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    Quote Originally Posted by Wayne View Post
    I'm still waiting on a heap of Lee gear from Nov 2010, and word is it won't arrive until at least April, but to me they will be worth the wait.
    From where did you order it?

    I ordered my Lee filters (two separate occasions) from Studio Kit Direct in the UK. I had no waiting periods, but admittedly my orders were back in 2009.

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    A royal pain in the bum! arthurking83's Avatar
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    the other two well know brands of grad(and other) filter makers are Hi Tech/Formatt and Singh Ray.
    Many folks swear by the quality of Singh Ray as one of the best, if not the best, and they have a selection of handy reverse grads that work better than straight grads such as the Cokin/Lee type.. for use when the bright light source is on the horizon and such.
    Even tho there ways around the magneta cast, it's still an issue to have to deal with, and I think it's more to do with the stacking of filters, than the filter brand itself. Cokins can induce a slight brownish cast when used singularly, but have never produced a magneta cast when used as a single item. For me the only times I see the magenta cast is when two or more have been stacked.
    Hi Tech/Formatt filters apparently manufacture the only glass type GND(that I know of), where all others are a poly/resin/plastic type, still good by more susceptible to wear than is glass.

    Even tho I have all the necessary holders and adapters to make it hassle free, I still prefer to handhold my filters in most cases due to the quicker workflow. But this involves a lot of wear and tear on the filter itself, and I've worn out at least 5 or 6 GNDs now, all of Cokin manufacture. Had I used them in their holders they'd be fine, but the scratches are easily induced when handholding. One day I'll get a larger set to suite my needs and will then cease to hold them by hand and no longer waste money on the wear factor.

    I'm always seeing or hearing of delays in getting Lee filters, I asked wayyy back at Vanbar if they had any(at all) and they only had filters that I'd never personally use(NDs and such) but no stock of single GNDs or even of the kits that Lee also sell, you can buy starter kits where you get a selection of filters and a holder and so forth. I went in at every opportunity for about 6months(approx a year ago) and simply gave up trying.
    Never thought to try purchasing online tho. Maybe Lee are having supply issues or something?

    Anyhow.. FWIW, even tho John mentions that Lee are expensive, Singh Ray's are even more so!
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    Quote Originally Posted by arthurking83 View Post
    the other two well know brands of grad(and other) filter makers are Hi Tech/Formatt and Singh Ray.
    Very true. I was aware of both brands, and did consider Singh-Ray before I went with Lee.

    I don't think any of the four major creative filter vendors produce inherently bad filters.

    Quote Originally Posted by arthurking83 View Post
    Even tho there ways around the magneta cast, it's still an issue to have to deal with, and I think it's more to do with the stacking of filters, than the filter brand itself. Cokins can induce a slight brownish cast when used singularly, but have never produced a magneta cast when used as a single item. For me the only times I see the magenta cast is when two or more have been stacked.
    In the one case I reported, my experience mirrors your observation, in that I experienced a horrible purple cast when I had at least one GND stacked with a regular ND. Both filters were Lee filters.

    However, I've stacked filters on many occasions and have not experienced a colour cast, so there has to be more to it than stacking multiple filters.

    Quote Originally Posted by arthurking83 View Post
    Even tho I have all the necessary holders and adapters to make it hassle free, I still prefer to handhold my filters in most cases due to the quicker workflow. But this involves a lot of wear and tear on the filter itself, and I've worn out at least 5 or 6 GNDs now, all of Cokin manufacture.
    Egads. I gather wear-and-tear is from dropping filters; they otherwise shouldn't deteriorate!

    I'd find holding them too cumbersome, and on the one or two occasions on which I did hold filters, it was a PITA.

    Quote Originally Posted by arthurking83 View Post
    I'm always seeing or hearing of delays in getting Lee filters, I asked wayyy back at Vanbar
    Maybe there are delays when ordering from local suppliers.

    When I was in the market for filters, I found Vanbar too expensive, and I literally saved $200 by ordering from a UK-based supplier (Lee filters are in fact British-made).

    I suspect UK-based suppliers have a much easier time when it comes to stocking gear.

    Quote Originally Posted by arthurking83 View Post
    Never thought to try purchasing online tho. Maybe Lee are having supply issues or something?
    As per my experience, you can save substantial money by ordering online. I'm past the point of being willing to pay Australian retail costs.

    Quote Originally Posted by arthurking83 View Post
    Anyhow.. FWIW, even tho John mentions that Lee are expensive, Singh Ray's are even more so!
    I cannot say I've compared prices, but yes, both are premium brands.

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    Ordered from Robert White in UK, and also had a chat with Studio Direct prior to ordering, and they too have the huge backorders. There is currently a worldwide shortage of Lee filters due to huge growth in demand, particularly because they are hand made, so take some time, skill and patience, along with the utmost strict quality controls.

    I'll wait...

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    Quote Originally Posted by Wayne View Post
    There is currently a worldwide shortage of Lee filters due to huge growth in demand
    Very interesting. I guess I got in before demand sky-rocketed.

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