What can go wrong with extreme long term exposure?

Question

Ok, maybe I'm crazy, but I'm curious what will happen when I combine a ND400 filter (9 stops) with a zone plate or zone sieve "lens."

If I'm shooting a sunset, it I might get a 30 second exposure with the zone sieve in place. (I have two, they are about f50 and f100). So if I tape the ND400 in front of it, do I multiply the 30 seconds by 512? (2 to the 9 is 512). This will yield about a 4 hour exposure.

With a 4 hour exposure, what can go wrong? I expect some overheating on the sensor, but how bad will it be?

And yes, I know I need to experiment but at hours per shot, a bit of advance planning will go a long way.

(Note, I have a power adapter for the camera, so I could use a car battery and an inverter to give me 4 hours of power in the field.)

Asked by Paul Cezanne

Answer

I really like the idea but in my opinion anything can go wrong with a 4 hour exposure.

Firstly, you may be right about the sensor. It might overheat, although opinions are divided on this issue. CMOS sensors are really energy efficient and I've never experienced sensor overheating while taking pictures or recording videos. However, my longest exposures were 3 consecutive 30min exposures, captured with a Nikon D7000. Some people claim that the reason why you can only capture 20min videos on most DSLR cameras relates to sensor overheating. I personally believe that this isn't really a problem. Most advanced DSLR cameras are probably equipped with a thermal cut-off system that simply turns the sensor off when it reaches critical temperatures (please don't quote me on that). Besides, overheating also depends on a variety of outside factors like the weather.

Secondly, with a 4 hour exposure it would be difficult to determine the light conditions and calculate other settings such as ISO and aperture. I realise that you want to use the zone sieve so the aperture is already determined. However, with such 'extreme' setup, your built-in light meter will become inaccurate or even unusable. Therefore, if you are wrong with your calculations, your pictures can be either overexposed or underexposed. I personally think that a 4 hour exposure is just like a stab in the dark. You never know what to expect as the light conditions can drastically change in 4 hours.

Next, the images may be completely unusable due to the amount of noise. My experience is limited to APS-C sensors but I can tell you that a 30min exposure I took was very noisy. It took me a long time and effort to reduce the noise and the image quality wasn't great.

Finally, you have to think about image stabilisation. Like I said, anything can happen during 4 hours so you have to stabilise your tripod and protect it from outside influences such as a strong wind or even rain.

I hope I managed to answer your question and I'm looking forward to seeing your 4 hour exposure soon.

Best Greg

Answered by Greg

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Will stacked ND filters perform as well as a single 10 stop ND filter?

Question

I have the Tiffen 0.9 ND filter which gives me approximately 3f stops reduction. I like to really slow things down and although it's sufficient in low light it just won't do in daylight.

Should I get a pair of 2 more 0.9 ND filters to stack or should I would a single say 10 stop filter be a better solution? Will the stacked ND filters perform as well as a single 10 stop filter?

I would like to be able to slow things down to the point where I get similar results to this photo which was shot at f4, ISO 200 and 75 seconds.

Asked by Jakub

Answer

From a functional standpoint, yes, you could essentially achieve the same effect with multiple stacked filters as a single high-density filter (say a 10-stopper.) There are a variety of concerns to be aware of, however, regarding stacking multiple filters.

1. Filter quality:
   • The Lee "Big Stopper" 10-stop ND filter is pretty high quality glass filter
   • There are two Lee ProGlass filters (0.6 and 0.9) of the same quality
   • The full range of standard Lee ND filters, (0.3, 0.45, 0.6, 0.75, 0.9) are resin
   • Many third-party filters are resin, a very few are glass
2. Color cast:
   • Stacking lots of resin filters can cause strange color casts
   • With digital, color cast is usually an easy post-process fix
3. Vignetting:
   • Stacking enough resin filters means a pretty thick hunk of junk on the end of the lens
   • At least four resin ND filters (0.3/1stop, 0.6/2, 0.9/3, 1.2/4) are needed to match a single 10-stop filter
   • On wider-angle lenses, you can barely get away with two stacked filters let alone four without vignetting
4. Flaring:
   • Any additional optical device added to the light path adds the potential for flare and ghosting
   • Stacking four ND filters adds a total of 8 additional surfaces which can reflect
   • To my knowledge, no 4x4/100mm filters are multicoated, so their chances of flaring/ghosting are high
5. Versatility:
   • A single 10-stop filter still leaves you some room to also stack on a graduated ND filter to balance contrast

If you want to do some serious ND work, such as 5 minute exposures of sunset along the coast, you should get a 10-stop filter. You'll probably also need at least one GND to normalize scene contrast if you are photographing a sunset/sunrise, which would usually require a setup like the Lee base filter kit with a tandem adapter and an additional independent filter holder (for a total of up to 8 filters)...that is pretty much guaranteed to add vignetting on anything other than a telephoto lens.

Answered by jrista

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Will a variable neutral density filter produce similar results to a fixed neutral density filter?

Question

I've decided to look at experimenting with neutral density filters and I found this variable neutral density filter on Amazon here in the UK.

It's a lot cheaper than buying a set of filters of different densities, so I was wondering if it would produce similar results to a fixed filter when set appropriately? I realise I have the added complication of setting the filter to the desired density, but as this would be my first foray into this area I don't want to spend a lot of money if I'm not going to use it a lot or get serious with the effect.

Asked by ChrisF

Answer

I have just trialled a variable ND filter and have written a review about it

Yes, it will produce similar results. It's very handy in photographing things like waterfalls, as you can dial in whatever effect you need.

The drawback is that it acts like a polarising filters, so if you have large expanses of sky, the sky will not be uniform - the polarising effect is such that parts of the sky will be darker than others. With a fixed ND filter, you should get uniform darkening across the image.

Also with some of the less expensive variable ND filters, you can get color casts or dark bands in the image. I didn't experience much of that under most operating conditions - you will tend to see those at very wide angles (i.e. under 18mm DX) and at maximum density. You can also get color casts with some brands of fixed ND filters, especially when stacked with other ND filters, or with polarising filters.

Answered by MikeW

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Why are doubled polarization filters as continuous ND not popular?

Question

One thing I was always wondering when it comes to ND filters is why there's need for such a large amount of different strengths, when two linear polarization filters would do the trick just fine. Assuming a light loss of 1/sqrt(2) per filter, one could easily create a ND "1 to infinity" filter. Why is that not in everyone's camera bag?

Unfortunately, all the filter companies offer only LCPL (linear, then circular), so I can't simply make one myself. Apart from cases where I do not want to take polarized light into account while having a ND filter (architecture photography maybe), I can't think of a reason not to do this.

Edit: More specifically, I'd like to know why there's nothing like this at all, or how I could get my hands on such a filter.

Answer

Does Singh-Ray's VariND filter not count?

Note, though, that even in their own product advertising, they point out the fundamental problem with this filter arrangement: it's still a polarizer, so it's still going to give unsatisfactory results on skies when used with a wide-angle lens. And there's that little thickness problem as well; vignetting is going to be an issue on wide lenses or on lenses that don't have a lot of wiggle room between the front element's edge and the filter thread.

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Is ND400 insufficient for some sun moments?

Question

I've taken a shot of the sun using my Tamron 70-300 (at 300) on my Nikon D5000 at 1/4000 and F40 and had attached the ND400 filter.

The shot was taken mostly to test the filter so I ignored the dirty window through which I shot.

However I was surprised to find out that even with all the controls turned to minimum luminosity and having the filter installed the sun was too bright. Maybe the time of day (local time around 09:00 AM, today, November 29th) was inappropriate for taking such pictures?

Or maybe the filter is not enough?

Answer

The pixels are not overexposed in any channel, and applying a heavy curve will reveal the darker edges and some dark spots. What you have is an exposed-to-the-right image of how the sun looks like - it is a big shiny ball. IMHO you should have enough data in RAW to tweak this into a usable image.

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Why should I use a Graduated ND filter as opposed to the digital equivalent(software)?

Question

With options like Nik’s Color Efex Pro 4 allowing me to digitally apply a Graduated Neutral Density filter, why would I choose to use a piece of equipment that I have to buy and carry around?

Related Questions:

How do I use Graduated Neutral Density filters?

What are neutral density filters and how do I use them to create long exposures in daylight?

What types of filter cannot be emulated by post-processing? -This points out that exposure time or aperture can be altered and not reproduced with software.

Answer

There are two ways to simulate a Graduated ND filter by software and they both have different disadvantages and advantages, compared to an physical filter:

H/W Filter

• Pro: A H/W filer gives you results immediately which you can see while you compose.
• Con: On the other hand, the effect is fixed in gradation and shape.

Software Effect

• Pro: Adjustable in strength, size, shape and direction.
• Con: Cannot recover clipped details. Blown out areas wont get details with a software effect while the H/W filter would have prevented over-exposure.

Exposure Fusion / HDR

• Pro: Completely adjustable. Can simulate any strength, shape and size of ND filter.
• Con: Anything that moves between exposures can cause problems.

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Do ND filters increase the dynamic range that a camera can 'see'?

Question

I am attempting to work out, conceptually, how the use of a neutral density filter effects the resulting captured image.

Do ND filters allow a camera to capture higher contrast scenes (without clipping the highlights) than would otherwise be possible? Or do they just decrease the amount of light uniformly so that highlight detail is gained at the expense of shadow detail being lost?

Put more technically, is the effect of a ND filter more like a linear mapping or a clipping of the low light levels? See the figure below for examples of each.

Answer

Simple answer: no, ND filters don't increase dynamic range.

In zone system, an ND filter just moves exposure of scene elements n stops lower. Everything that was in the lowest n zones captured without the filter, gets clipped off as black.

I can think of two scenarios where an ND filter might increase dynamic range, but I wouldn't use it for that:

• low quality ND filters will reduce contrast, so dynamic range increases a little (on expense of image quality)
• film is somewhat forgiving of underexposure, so you might gain more highlights and still preserve some shadow detail by underexposing; often you could achieve the same by simply adjusting exposure parameters

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What are neutral density filters and how do I use them to create long exposures in daylight?

Question

I've seen a few related posts on the site but nothing specifically on this point:

I'd like to be able to take long exposure photos during daylight (like the examples in this Flickr group). I'm told that you can do this by using a neutral density filter. So my question is: what is a neutral density filter exactly, and how is it used to achieve that smooth long exposure effect?

Answer

A Neutral Density (ND) filter is a filter that reduces the amount of light captured by the camera evenly across the visible spectrum. As such, it looks grey to black (depending on the filtration power) and does not cast color on the received image (like blue or yellow, e.g., filters will do).

When using a ND filter, there is a need to compensate for the reduction in light by using longer exposures (or higher ISO, but it usually defies the intention of ND filtration). This way, one can capture long-exposure images that are not possible w/o the filter as the camera (set to its lowest ISO and possibly smallest acceptable aperture) is at its slowest speed for a good exposure.

Examples for such situation is when shooting waterfalls in a fairly lit location. Then, the speed for correct exposure is not slow enough to create the required streaming water effect. Using a ND filter, one can reach slower speeds, as if the scene lighting was dimmer.

Note that a uniform ND filter does not change the Dynamic Range of the scene, as the bright areas get darker in the same amount as the dark areas.

Another type of ND filters is the graduate ND filters. These filters usually attenuate the light only at one half of the frame and gradually get clearer on the second half. These filters are used when shooting landscapes, where the sky is much more bright than the scenery and using good exposure for the ground will overexpose the sky. A graduate ND filter lets one reduce the brightness of the sky and get it captured nicely with the ground.

ND filters are marked in multiplies or stops. An 8X ND filter is similar to ND3. Both cut 3 stops of the light. If the camera's meter tells that 1/500 sec is required for the given aperture, then using a ND3 filter will allow an exposure of 1/64 sec with similar outcome.

There are some (expensive) variable ND filters. These are made from two polarizers, where the front element rotates and thus let you set the amount of light being cut (up to virtually no light passing through).

The image below, from Wikipedia, shows the effect of an ND filter:

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Whats the difference between Singh-Ray Vari-ND and cheap Fader-ND filters?

Question

I think the Singh-Ray Vari-ND variable ND filter sounds great, but is really expensive.

There are way cheaper variable ND filters from some chinese sites.

I wonder: are the cheap ones worth the money? Is the vari-ND worth the premium you pay for it?

or: what's the difference between cheap knock-offs and the Singh-Ray?

Answer

The mechanism is likely a combination of a linear polarizer and a circular polarizer (which itself is a linear polarizer followed by a quarter wave plate). Thus the differences you can expect between high-quality and cheaper variable ND filters ought to be similar to the differences found among polarizers which include flare, vignetting, inhomogeneity, and color shifts. You can avoid flare in many cases by not including bright lights in the photo; vignetting can be compensated in software and sometimes is desirable; I suspect the inhomogeneities are usually not noticeable; but color shifts can be pronounced. Typically a set of crossed polarizers (which is what you're using to get the heaviest ND settings) pass essentially no colors except violet. Therefore, I would expect cheaper variable ND filters to work OK except at the heaviest settings (more than about 4 stops) where the violet shift will become pronounced.

You can see evidence of vignetting and a violet shift on this dealer's website. Compare the bottom two photos: the one taken with their ND filter has pronounced vignetting (many stops) and a strong blue cast. In contrast, look at the photos on the Singh-Ray site. If you look closely you can see the vignetting, but there's little evidence of a violet shift: look at the grays of the rocks in the stream. Maybe those were post-processed to remove the blue, so the comparison is not definitive, but these two sites nicely illustrate the difference we would expect between good and bad variable ND filters.

I did a quick test using a high-end, top-rated Marumi circular polarizing filter and an old low-end Vivitar linear filter. In combination they made a fine variable ND filter, although there were some color shifts (first to yellow, surprisingly), but below about 3-4 stops a yellow incandescent light started to take a distinctly blue hue. At the maximum density, probably around 6 - 8 stops (I only looked, I didn't measure), only the light was visible and it was a brilliant blue, the color of a Wratten 80b filter.

Your best bet for a cheap solution, then, is actually to look through one of the inexpensive filters and pay special attention to the apparent color at the densest ND settings. While you're at it, look at a bright light through the filter to check for flare and scattering. If everything's acceptable you probably have a great deal.

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How do I use Graduated Neutral Density filters?

Question

I want to improve my photos of landscapes with high contrast (sunset/sunrise). What are good selections for GND filters and what are some techniques for using them correctly?

Answer

Filter Types

There are essentially 3 kinds of GND filter: Soft, Hard, and Sunrise/Set. All these come in various 'strengths'.

Soft GND filters have a gentle gradient from dark to transparent and so are good for landscapes with irregular horizons such as mountains, hills and to some extent buildings.

Hard GND filters have a more sudden change between dark and transparent and so suit landscapes with level horizons, like desert or seascapes.

Sunrise/Set GND filters have a band of 'dark' across the centre of the filter, leaving the upper sky and the foreground unfiltered. This allows you to pull back detail in the brightest part of the sky at sunrise and sunset.

Just because there are dedicated Sunrise/Set filters does not mean they will always be suitable for every sunrise or set. They are most suited to relatively clear situations: if you have a fantastic cloudscape lighting up the whole sky, they'll be no good.

Filter Strengths

The different strength filters reduce the amount of light in the dark part of the filter by a set number of stops. Most filters are sold with designations such as 'ND2'. These translate to stops as follows:

• ND2 - 1 stop
• ND4 - 2 stops
• ND8 - 3 stops
• ND16 - 4 stops

Determining which filter to use

The most accurate method for using GND filters is to make use of your camera's metering system. In Aperture Priority mode (you can do it any mode, but A or Manual is the most common landscape mode) point your camera at the foreground, or the 'land' in your landscape, and make a note of the exposure the camera calculates, e.g. @f16 1/60. Now point your camera at the sky (in the case of sunsets, at a point above or either side of the sun) and again note the exposure, e.g. 1/500.

Now you just need to calculate the difference between the two exposures: in this case a 3-stop difference (1/60: 1/125, 1/250, 1/500). So you need a 3-stop filter in order to get the correct exposure for the sky and the ground. You can then either re-meter for the ground and lock the exposure, or head into Manual and dial in the 'ground' exposure settings.

The next step is positioning the filter. Hard filters are easier to position as the difference in light is easier to see. Soft filters are harder, but the positioning is also less critical than the hard filter. If you have a Depth of Field preview button this can make the position clearer, or you can simply take a test shot and adjust. If you are using Manual mode you will also see if you have the filter too low in the scene as the light meter will start to show underexposure.

Choosing your filters

In terms of buying filters, as ever, go for the best you can afford: Lee and Hoya are respected brands. Personally I think there's little use for a 1-stop filter but if money is no object it won't hurt to have it. If you are on a budget I would go for 2 and 3 stop filters, soft and hard edged if possible, as well as a sunset filter or two, but it will depend on your location and the type of shot you plan on taking - if you're 300 miles from the sea, you might not want to bother with a hard filter for example.

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What's the result of stacking ND filters?

Question

If you stack two 3-stop neutral density filters, does it reduce the exposure by 6 stops or 9 stops?

Answer

It's six.

Remember, the stops are already logarithmic. That is, a 3-stop reduction (as from a 3-stop ND filter) is a 2³× loss of light — ¹⁄₈ of the light gets through. A one stop filter halves light, since 2¹ is just 2 (→ ¹⁄₂), and two stop filter is 2² (→ ¹⁄₄ the light). When you stack them together, you're adding the exponents, so 2³ stacked with 2³ is 2⁶ — or ¹⁄₆₄th the light. That's the same as thinking "three stops is one over 2³, or ¹⁄₈, and ¹⁄₈ × ¹⁄₈ = ¹⁄₆₄ — which is one over 2⁶".

But, fortunately (and in fact partly why it's done that way), you don't have to remember all this. Just remember that 2³ + 2³ = 2⁶ — or, 3 stops plus 3 stops is 6 stops.

Of course, this is just the math. In the real world, there may be other practical effects, like vignetting in the corners (due to the increased thickness) or color casts — you're adding more layers for the light to go through, and that takes a toll on image quality. See the comments below.

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Is it possible to use a polarizer and a ND filter at the same time?

Question

Is is possible to use two filters (one polarizing and one ND) at the same time on a 18-55 kit lens from Canon. I am new to photography and wanted to work with filters. Do you suggest me buy these filters?

Answer

The front element of the 18-55 rotates when focusing, which makes using polarizing filters a bit irksome. But other than that, yes, it should work, although using multiple filters on a lens is something that should be avoided as far as possible on general principles because of the added risk of flare, internal reflections, vignetting and other optical nasties.

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