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First Stab

As mentioned in the last post – I wanted to put this up yesterday but had to find/buy cables to scan the test images and so this lunch time I bought a new cable for HK$ 25 and here is the post that starts yesterday morning at 6am when I got to try out for the first time the 4×5 Zero Image using a Polaroid 550 back and Fuji C45 100 colour pack film.

The set up I went for was with the 75mm focal length and the smallest and sharpest of the three pin hole options – f216.

Pack film isn’t new to me as I have used the Fuji film before in a Holgaroid but the Pinhole is very different to any other camera I use.

The particular science for creating an exposure time is as much art as science and even though you get an exposure calculator with the camera – you still need to employ a whole range of educated guesses for the following reasons;

– you need to use a meter to get a reading and then use the exposure calculator to give you the reading at a high f value that your meter won’t manage. Even great meters won’t go above f99 and so this is either a little mental arithmatic or a quick look at the calculator.

– Then as I was taking shots at 6am with the sun getting brighter by the minute – I had to guess-timate the reading at the end of the exposure and guess a reading for that too – and then decide on an average time between the two answers.

– Unfortunately it is never that simple – as there is such a thing as Reciprocity Failure that needs to be taken into account for very shot or very long exposures.

Here is how Wikipedia defines Reciprocity – In photography reciprocity refers to the inverse relationship between the intensity and duration of light that determines the reaction of light-sensitive material. Within a normal exposure range for film stock, for example, the reciprocity law states that the film response will be determined by the total exposure, defined as intensity × time. Therefore, the same response (for example, the optical density of the developed film) can result from reducing duration and increasing light intensity, and vice versa.

So what does this mean?   Exposure = Intensity x Time and so for the same exposure, if the Intensity of the Light Doubles the Time required halves and so on for any multiple you want.

For very small Intensity figures (i.e. when it is restricted by a tiny pinhole) you need a lot of Time to get sufficient Exposure for the film you are using and to add difficulty to the correction you need to use, each film fails at different levels.

In general terms however if your calculated exposure is longer than 1 second – you should double the actual value you use and if it is over 5 seconds, multiply by 5 and by 12 for anything over 50 seconds.

– So back to my dilemma – I now had calculated that I wanted around 8 minutes for the exposure – but if I multiplied that by 12 then the sun would be up and shining directly at the camera and I would also be late in catching the train to work. So I did what anyone would do and that is make a complete and utter guess based on the fact that I was using Pack Film and so would see the result 90 seconds after removing it from the camera back.

Having seen this exposure and the fact that it was already over exposed at 20 minutes, I quickly took another at 8 minutes with the sun getting stronger and burning into the film and got a less blue image but still slightly washed out.

and then I brought the time right down to 4 minutes and got a better image with a nice patch of yellow where the sun reflected on the sea but unfortunately a white and blue mess where the sun was.

I guess I shouldn’t be taking pictures into the sun unless I expect some blow out on the film.

So after this initial lesson yesterday morning I realized that if I wanted to take some long exposure images of the night sky with the pinhole, that for a reading of 1/4 second at f2.8 – I need over 25 hours of exposure at f216 without adding the x12 bit for failure….and so I guess I won’t need to waste my time trying.

As this is also a day late I have had a bit more of a play with the camera inside in the evening with a more stable light source and this is what I managed after an 80 minute exposure at f216 and 75mm…..and learnt another lesson – in insufficient light, you need one hell of a lot more light than you think.

I had planned to go to my favourite building tomorrow morning with some B/W sheet film but at a tropical typhoon is coming towards us quickly I guess that is going to be an unwise choice – especially if I can’t even expose the film yet….

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Posted by simon on July 28, 2011

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