Long Exposures with an NDx1000 Filter
By Karl Williams, February 2011
Most photographers are familiar with the use of neutral density (ND) filters, which are essentially “sunglasses for cameras” in that their sole purpose is to reduce the amount of light passing through the lens. They are used in situations where the side effects of the “normal” methods of coping with excessive light – combinations of closing down the lens, reducing the exposure time or reducing the ISO (i.e. the sensitivity) of the sensor – may be, for a variety of reasons, undesirable.
The most common types are the circular screw-in NDx2, NDx4 and NDx8 filters which reduce the light by factors of 2 (1 stop), 4 (2 stops) and 8 (3 stops) respectively and are readily available from camera shops and online suppliers.
There are, however, situations in which the photographer requires to reduce the amount of light passing through the lens by far more than the factors available with these ND filters either individually or in combination. Yes, I imagine there are a handful of industrial photographers in this world who wish to take photographs of the inside of blast furnaces and/or incinerators from time to time but there are many more “normal” (i.e. like you and me) photographers who wish to use long-exposure techniques for artistic and creative purposes such as blurring the motion of individuals in a crowded shopping precinct or, as shown, producing silky surfaces on lakes and rivers.
For these photographers, the solution is the NDx1000 filter which, as the name suggests, reduces the light passing through the lens by a factor of 1000 (approximately 10 stops).
These filters come in two varieties: the screw-in ND-110 (3.0) filter produced by B+W and the flat Big Stopper produced by Lee Filters, both of which are available from Wex Photographic. Whilst each has its good and bad points (see below), they are both expensive and, by virtue of their comparative rarity, occasionally in short supply – so their purchase is something you need to think seriously about before committing yourself. If you’re anything like me, your camera bag is full of expensive gadgets which, at the time, you couldn’t possibly live without but which, in hindsight, you could all too easily live without!
Using the NDx1000 Filter
As far as the use of the filter goes, it’s a little bit more complicated than just attaching the filter, letting the camera work out the exposure and then pressing the button, largely because this filter is so dark that it has all the light transmission properties of a welder’s mask – you can see the sun through it, but that’s about it! Not only can YOU not see through it, but your autofocus gizmo can’t see through it either; furthermore, given the sort of exposure times you’ll be dealing with (30 – 200 secs), your Live View screen will struggle as well.
This means that all your composing, focussing and exposure measurements have to be done before you put the filter on the lens, and a wee bit of calculation (don’t panic – we’re not into “Ph.D. in Mathematics” territory here!) has to be done to convert the “unfiltered” exposure time to the “filtered” exposure time.
So, here’s what to do:
1. CHECK YOUR BATTERY; believe me, you do NOT want it going dead in the middle of a long exposure! Yes, I know, teach your grandmother to suck eggs and all that – but, if you’re anything like me, the reality is that the first time you even think your battery might be on the way out is when you see the little flashing red message on your screen telling you that you’d better do something quickly!
2. Remove any UV or protection filter which you may have on your lens (if you want to avoid the possibility of vignetting with the screw-in version of the ND filter), SET THE LENS TO “MANUAL FOCUS” (emboldened, upper-cased and underlined deliberately – see below) connect up your cable release, set the exposure mode to MANUAL and set the camera up on the tripod.
- If you forget to set the lens to “manual focus” (which, suffering from the usual memory deficiencies of advancing age, I do on a regrettably regular basis .. but that’s another story!), the first time you’ll realise this is when you press the shutter release in step 7 below and nothing happens – other than that you become aware of a strange humming sound coming from the camera. Don’t panic – all this indicates is that your autofocus gizmo, rendered virtually blind by the filter, is trying desperately to focus on something but can’t. Before it drains all the power out of your battery, say “#### it!” the requisite number of times, take your thumb off the button and rectify the omission. The fact that the “AF-MF” switch will inevitably be in the most awkward position possible on the set up camera serves to emphasise the importance of not forgetting this step – hence the highlighting above!
- A number of DSLRs have an in-camera long-exposure noise reduction facility which, irrespective of the type of DSLR you have, will operate on the basis of “Dark Frame Subtraction”. This process requires the camera to make a second identical exposure with the shutter closed to enable it to determine how much noise there is and where in the image it occurs. The camera then subtracts the dark frame image from the shot you’ve just made and saves the result. Whether or not you wish to avail yourself of this facility is entirely up to you; in making that decision, though, imagine that you have just taken an exposure of 100 secs and, while the camera is in the middle of its subsequent 100 sec dark frame exposure, the shot of a lifetime materialises in front of your eyes and you can’t do a thing about it: your call! Personally, I prefer to disable the NR facility; if there is any noise, I’ll either live with it or correct it at the processing stage.
3. Do the “composing and focussing” bit, set the shutter speed on 1/10 sec (bear with me, there’s a reason for this) and adjust the aperture until you get “correct” exposure.
4. Put the filter on the lens. Yes, I know this step is blindingly obvious, but it can be so blindingly obvious that it’s easily overlooked – I know, I’ve done it more than once (see the previous comments on advancing age)!
5. Cover up the camera eyepiece to avoid stray light leaking through the eyepiece onto the sensor. Some cameras come with a wee rubber mask for this purpose, but, since this requires the eyecup to be removed, it’s sometimes a lot easier (and just as effective) to stick a piece of insulating tape over the eyecup.
6. Activate your “Live View” facility. Yes, I know I told you it would be virtually useless but there is a reason (see below). Apart from anything else, it locks up the mirror (at least it does on my Canon) and that’s always good practice for tripod shots.
7. Set the shutter speed to BULB and expose for 100 secs (which is 1000 x 1/10 – now you can see the reason for choosing an easy “unfiltered” shutter speed). For those of you new to long exposures, the time will count off either on the LCD monitor on the back of the camera (the Live View screen) or on the wee LCD screen on the top of the camera – so there’s no need for all this “1 potato, 2 potato, 3 potato ..” stuff we used to do in the old days.
- On some cameras (the Canon EOS 450D for example), BULB is (sensibly) a single click of the exposure dial from 30 secs in MANUAL mode. On other cameras (the Canon EOS 7D for example), the manufacturers, in their wisdom (for reasons which completely escape me), have decided that BULB should be a separate exposure mode from MANUAL. There is, therefore, the potential for the BULB aperture setting to be different from the one you used in MANUAL mode to do your exposure calculations: you have been warned!
8. Check the result; if it’s under-exposed, increase the exposure time by half a stop (multiply by 1½ ) or a full stop (multiply by 2) as appropriate and re-shoot; if it’s overexposed, reduce the exposure time by ⅓ (half a stop) or ½ (a full stop).
9. Finally, some “rememberable” unfiltered/filtered exposure conversions if the light is too bright (in step 3) to get an “unfiltered” exposure of 1/10 sec:
- 1/15 sec ~ 60 secs (more or less);
- 1/20 sec ~ 50 secs (exactly);
- 1/30 sec ~ 30 secs (more or less);
So – which filter do you go for – the screw-in B+W filter or the flat Lee Big Stopper? Here are a few comparative points to help you decide:
I hesitate to put my neck on the block by making a definitive statement about the relative optical qualities of the two filters because, almost inevitably, someone will find a “geek” website which uses a variety of charts, diagrams and largely unintelligible technical jargon to prove me wrong. Suffice it to say, though, that, in the photographic “real world”, I haven’t noticed any difference between the two filters and I haven’t met anyone who has. What you WILL notice, however, is that, because of its “higher transmission in the red beyond 600 nm” (no, I don’t know what that means either), the B+W filter tends to give a noticeable red/magenta cast to images; this, however, can be easily corrected (if required) at the processing stage (using, for example, the White Balance Tool in Adobe Camera Raw).
Ease of Use:
Given the necessity to carry out the “composing and focussing” bit before attaching the filter, attaching the screw-in B+W filter to a set up camera can be a bit of a pain on the odd occasion on which it gets cross-threaded – which almost inevitably seems to occur when you are in a rush and/or have cold useless fingers. Apart from giving rise to the possibility of dropping the filter (can you hear the voice of bitter experience here?), there is always the possibility of inadvertently changing the field of view or the zoom setting of your lens. If you’ve activated the Live View facility as advised above, this can be corrected (more or less) – but only if detected! The “avoidance strategy”, by the way, is to use two hands (one to hold the filter, one to hold the lens), don’t rush, and screw the filter in just enough to hold it reasonably firmly but no more! The Lee Big Stopper doesn’t have this problem – it can just be slid into the filter holder when required. That said, however, the holder has been known to lose its “holding ability” with long use and that in itself can be something of an irritant.
You will, fairly obviously, require a separate screw-in B+W filter for each lens on which you propose to use it which can be a bit expensive given the cost of the individual filters. An alternative would be to buy a single filter for your largest diameter lens and then use step-rings (if available in the sizes you require) to attach it to your other lenses. You won’t be able to attach a lens hood to the other lenses with this arrangement, though, but that may only be a problem if the sun is shining directly on the face of the lens and a judiciously positioned hand can’t block it out! Whilst the Lee Big Stopper is a bit dearer than a screw-in B+W filter, a single filter will suffice for all your lenses – that is, of course, providing you have the basic filter holder kit (about £50) and the necessary adaptor rings (at anything between £18 and £40 a shot, depending on size) to fit this to each of your lenses. If you don’t, and you don’t plan to make use of the range of Lee filters generally, this alone will probably rule out the Big Stopper as a viable option for a one-off purchase.