Night pinholes

I recently came across some long exposure night pictures – taken with a conventional camera – whilst flicking through what I think may have been a book, rather than an Instagram feed. In any case, I can’t remember exactly what picture inspired me to start on this project, but it must have been quite impressive.

An Ilford Obscura Pinhole Camera
The Ilford Obscura. Find one on eBay*

I’ve had this Ilford Obscura Pinhole Camera for a while, but haven’t really made much use of it, other than a few paper negatives and some experiments with Harman Direct Positive Paper.


Film

A box of Ilford FP4 sheet film
A box of Ilford Fp4 of uncertain vintage

I knew I’d have to acquire some 5×4 sheet film, as the single-digit ISO ratings of photo paper mean that exposure times can be several minutes long during the day, never mind on a dimly lit street at night.

The problem, of course, is that sheet film is expensive – at the time of writing Ilford FP4 Plus is about £40 for 25 sheets, which seemed a bit much for an experiment that would almost certainly end in mediocrity, if not worse.

Due to the current mania for expired film, it took me a couple of weeks to find an affordable pack on eBay; I ended up paying £20 for “about 30” sheets of very expired Ilford FP4 (note the lack of “Plus”; original FP4 was apparently discontinued in 1990, and I suspect the box I have is rather older than that). This turned out to be a bargain – I made a test exposure during the day, which turned out fine.

Ilford FP4 is rated at ISO 125; I was fairly confident the film had been pretty well stored over the decades – it came from a school darkroom – so I didn’t worry too much about increasing exposure to compensate for age. In any case, for night photography the effect of ISO film speed is dwarfed by the effect of reciprocity failure.


Metering

Having already scouted the first location with my iPhone, I knew the EV would be about 4. I confirmed this with a glance at an EV chart, which indicated an EV of 4-5 for “Christmas Tree Lights” and 3-5 for “Floodlit buildings, monuments, and fountains”.

As noted, the most important factor in calculating exposure for night photography is reciprocity failure. This refers to the phenomenon whereby the reciprocal relationship between aperture size and shutter speed – that doubling one and halving the other gives an equivalent exposure – breaks down, or “fails”. This occurs when the exposure time is very long, meaning more than a second or so, or very short, meaning some fraction of a second that is irrelevant for most photography.

The practical effect of this is that for longer exposures you have to allow additional exposure time, and the amount of exposure time you have to add increases exponentially as the base exposure increases. Ilford publish a table of reciprocity factors, or exponents, for all their films here. From this table we can see that the exponent to use for Ilford FP4 Plus is 1.26, and the formula for calculating the revised exposure time is

\[Tc = Tm^p\]

Where Tm is the uncorrected, or metered, exposure time, p is the reciprocity factor, in this case 1.26, and Tc is the corrected exposure time. Again, given the approximate nature of the experiment, I assumed that the reciprocity characteristics of old FP4 were comparable to those of modern FP4 Plus.

So, assuming a constant EV of 4, , which is what I do in practice, we can pre-calculate the exposure times for a range of Exposure Indexes as follows:

Exposure IndexAperture (Doesn’t change!)Uncorrected Exposure Time (Tm)Corrected Exposure Time (Tc)
400f/24815m 46s93m 39s
500f/24812m 31s70m 0s
800f/2487m 53s39m 6s
1600f/2483m 56s16m 17s
Calculated exposure times at EV4 for Ilford Obscura with Ilford FP4 Plus

I used the Pinhole Assist app for IOS to generate these exposure times, and then used it again at the scene just before making the exposure to check that EV4 was “about right”, which it invariably was.

The three EI values I have found myself using the most are 400, 500, and 800. The Exposure Index for a given photo tends to depend on how much time I have available to stand around in the cold rather than any artistic consideration about grain or contrast. In general, situations where there is a bench available near the camera position lend themselves to longer exposures and correspondingly smaller EI values.

Given the age of the film and the approximate metering, these times can all be taken as guidelines, a minute or five either way doesn’t make much difference to an exposure time of an hour and a half.


Making the exposure

The photograph that accompanies this post is the first one I made; I have made a few more since and I will be posting the more successful ones in this gallery. I’d planned to go on a midweek evening when the place would be less crowded, but life got in the way and I ended up arriving at about 7 o’clock on a busy Friday evening. Given that super-long exposures erase moving objects I wasn’t too worried about people getting in the way of the shot, my concerns were more about pre-Christmas revellers inadvertently walking into the tripod.

Having found a suitable vantage point – with a bench – I got everything set up. I use a trio of iPhone apps for this: Pinhole Assist to check the exposure, Focal Viewfinder to check the framing, and the built-in spirit level to get the camera level. Conveniently, I can lie my phone on its back on top of the camera whilst levelling with the tripod. With the Viewfinder app, I tend to check with the phone just to the left and just to the right of the camera position, mostly to exclude unwanted objects at the edges of the frame. The camera also has sight-lines printed on the top, which you can use to check where the edges of the frame will be.

I had originally intended to make a 90 minute exposure, for an Exposure Index of 400, but I arrived at the scene a little later than planned and had to settle for 70 minutes. In fact, I hadn’t worked out this row of the table in advance, but fortunately I had 70 minutes in which to calculate the resulting EI for my exposure time.

Making this kind of photograph certainly makes you more aware of your surroundings – it’s a rare experience to be standing around in the city centre for an hour or more with exactly nothing to do. I originally thought the cluster of white spots near the centre of the frame were artefacts on the negative, but with hindsight they are the head torches of a group of carol singers who showed up outside the town hall. Some kids arrived to smoke weed on the benches opposite me for a while, they were so motionless that I was worried they might end up in the photograph but fortunately they wandered off after 40 minutes or so.

During this particular exposure I had a few more interactions with the public, there were a lot of people taking photos of each other in front of the Christmas lights, and I ended up acting as the cameraman for quite a few couples. There were also a few people who stopped before walking through the frame so they wouldn’t “spoil the photo” – I decided to reassure these people that this was “fine” without offering a more detailed explanation.

I also spent some time with a homeless guy who was retrieving partly eaten food from the benches, as well as the coins from the fountain. He wanted to be in the photograph too, but I spent some time explaining why this wasn’t really possible, all the while defending the tripod legs from his curiosity. That particular evening was bitterly cold, and I felt bad that like so many other people, I rarely have any cash these days. The number of homeless people wandering around is certainly something I’ve become more aware of during this project, and I now try to make sure I have a bit of change in my pocket when going out to make these photos.

I’ve made a few of these photographs now, with mixed results, and on every occasion I’ve stood around in the dark there’s been exactly one member of the public who knew what it was I was doing and came to talk about it. In all cases, this person has also been holding a camera, though never a pinhole. In a city with a population of about 350,000, I suppose that’s not a bad average.

I’ve only ever had one hostile interaction, and it wasn’t during this exposure. On that occasion I was approached by a bunch of kids on mountain bikes who demanded to know why I was filming them. Without too much explanation I reassured them that I wasn’t filming, so naturally one of them asked what I was doing. When I replied that I was taking a photograph, the next question was “What are you taking a photo of?”, to which I gestured towards the lights. The final question was “What are you taking photos for?”, to which I didn’t have an easy answer. After an awkward silence, they rode off into the darkness. I’m not sure exactly what these photos are for, but I’m fairly confident I take fewer photos than those kids do.


I’m quite pleased with how these turned out, I like the effect of making the people disappear from the scene. I’ll be looking for more locations in the future, possibly broadening the scope beyond Christmas decorations. One thing I have learned from the reject pile is to be conscious of the need to have some foreground interest apart from the lights.

Development Notes

Rodinal, mainly because I already had an open bottle. Having gone to the effort of metering the scene correctly and standing around in the cold for nearly an hour and a half, I wasn’t going to go for the one-size-fits-all of stand development. Accordingly, I decided on “normal” development using Rodinal at 1:25.

I’d previously had a bit of a disaster trying to develop sheet film in my somewhat inadequate trays, so I decided to develop this exposure in my Paterson Universal tank. A single sheet just fits inside the tank in “landscape” orientation, arranged around the outside of the tank with the emulsion side facing in.

It’s necessary to overfill the tank in order to cover the negative, this required about 800ml of liquid. I ended up using 775ml of water and 31ml of Rodinal per sheet, which makes this a pretty expensive proposition. I used the development times from the Emulsive FP4 cheat sheet, giving a development time of 18 minutes and 30 seconds for an EI of 500.

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