We used a 5x4 camera with a pinhole ‘lens’ at the front. We
measured the diameter of the aperture at 0.5 mm. I chose a focal length of
150mm, which is equivalent to a short telephoto lens on a regular 35mm or
digital camera.
To work out the f/stop you use a simple equation which is Focal length DIVIDED by Aperture.
To work out the f/stop you use a simple equation which is Focal length DIVIDED by Aperture.
My aperture was f/300 (150mm / 0.5mm)
I then had to work out my shutter speed. Using the light meter I measured using the ISO of 4 (the sensitivity of the paper), the light meter measured that at f/22 I would need a shutter speed of 1 second. I then had to scale this up to reach my f/stop of f/300; as the f/stop increases the shutter speed doubles in length so as to keep the exposure the same.
The f/stop increases in set increments as follows with my shutter speeds listed above:
1s 2s 4s 8s 16s 32s 64s 128s 256s
f/22 f/32 f/45 f/64 f/90 f/128 f/180 f/256 f/360
I then had to work out my shutter speed. Using the light meter I measured using the ISO of 4 (the sensitivity of the paper), the light meter measured that at f/22 I would need a shutter speed of 1 second. I then had to scale this up to reach my f/stop of f/300; as the f/stop increases the shutter speed doubles in length so as to keep the exposure the same.
The f/stop increases in set increments as follows with my shutter speeds listed above:
1s 2s 4s 8s 16s 32s 64s 128s 256s
f/22 f/32 f/45 f/64 f/90 f/128 f/180 f/256 f/360
My f/stop lay between two values (f/256 and f/368) from the
scale above, I chose a shutter of approx. 200 seconds (3 min 20 seconds).
Due to reciprocity failure I had to double this time to 6min 40.
Reciprocity is the relationship between aperture and shutter speed that determine exposure time. As one changes the other must also change to achieve the same exposure, they reciprocate.
For example, say you wanted to gain an exposure of 0 EV (exposure value) on a scene you started with a shutter speed of 1/125 sec and an f/stop of f/5.6.
You then decided you wanted some motion blur, and so changed your shutter speed to 1/60 sec (double the length of time), you would then have to halve your f/stop to f/8 to compensate and keep an EV of 0.
Reciprocity failure is the point when the relationship between aperture and shutter speed deteriorates, many films and papers are tested to find the point of reciprocity failure and can be as fast as 1 second and as long as 2 minutes (‘better’ films having longer times before failure).
With extremely small apertures such as f/300, only a very small amount of light reaches the paper which is weakened as it has to travel a relatively long distance (300 times the aperture in this case); luckily Dave had had experience with this paper and knew that typically that to double the exposure time would rectify the problem. If you are using film or paper that you are unsure about, the best thing to do is to use a technique called bracketing. Bracketing is when you take multiple exposures at different lengths to try and ensure you get a correct exposure, when you find out the most suitable time to add for a particular aperture then you’re good to go!
Due to reciprocity failure I had to double this time to 6min 40.
Reciprocity is the relationship between aperture and shutter speed that determine exposure time. As one changes the other must also change to achieve the same exposure, they reciprocate.
For example, say you wanted to gain an exposure of 0 EV (exposure value) on a scene you started with a shutter speed of 1/125 sec and an f/stop of f/5.6.
You then decided you wanted some motion blur, and so changed your shutter speed to 1/60 sec (double the length of time), you would then have to halve your f/stop to f/8 to compensate and keep an EV of 0.
Reciprocity failure is the point when the relationship between aperture and shutter speed deteriorates, many films and papers are tested to find the point of reciprocity failure and can be as fast as 1 second and as long as 2 minutes (‘better’ films having longer times before failure).
With extremely small apertures such as f/300, only a very small amount of light reaches the paper which is weakened as it has to travel a relatively long distance (300 times the aperture in this case); luckily Dave had had experience with this paper and knew that typically that to double the exposure time would rectify the problem. If you are using film or paper that you are unsure about, the best thing to do is to use a technique called bracketing. Bracketing is when you take multiple exposures at different lengths to try and ensure you get a correct exposure, when you find out the most suitable time to add for a particular aperture then you’re good to go!
(I used curves and gamma correction on the positive image as it was slightly over exposed.)
After this task I was inspired to make my own pinhole camera and opted for a Match Box Pin Hole Camera in which can be seen in this post.
I also turned my bedroom in to a Camera Obscura, details of which can be seen in this post.
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