One of the things that I believe will help anyone with their photography is to understand the basics. In this day and age cameras will work it all out for us and give correct exposures. Just set to automatic mode and press the shutter button and a correctly exposed image will just happen. Trouble is that this doesn't allow the creative juices to flow.
Where I can see detail in the dark/shadow areas and details in the bright/highlight areas my camera may not have the dynamic range to collect all of that data. A standard light meter will average all of the light in the image field and will give a correctly exposed image but the shadows will be muddy and the whites will tend to be a little grey.
Understanding this and how to make the adjustments properly is relatively simple but people never seem to learn it. Oh well, if mediocrity is what you are trying to achieve...
Pinhole imaging takes these basics to a whole new level...
First you need a light meter to collect an "average" for the image (ISO, aperture, shutter speed). Then you need to work out what size the aperture (pinhole) is for the focal length you are using. Then you need to work out what shutter speed is required for that aperture relative to the light meter reading. Then you need to understand "reciprocity failure" (the longer film is exposed to light the less sensitive it becomes) and factor that in.
Here's an example: I'm using a film with an ISO/ASA rating of 125 (Ilford FP4+) so I set my meter to 125 and get a reading of 1/60th of a second at f/8. I then find that my aperture for the 75mm pinhole is f/216 so I have to then use a scale to see what shutter speed is required (I could work it out in my head if I had a better brain). The scale shows that I need an exposure of (about) 10 seconds. A 10 second exposure means that I need to factor in reciprocity failure and I need to multiply the 10 second exposure time x 10 = 100 seconds which means I need a tripod and a cable release.
My very first attempt at a pinhole image was taken in my kitchen and it's a photo of some seed pods on a black background. The exposure I calculated needed a 90 minute shutter speed. I actually went shopping and came back to close the shutter... The image is here. I was amazed at how good this image was (technically) and just how much detail was available in the negative. It remains one of my favourite images.
Next: Some images - stay tuned...
Next: Some images - stay tuned...
3 comments:
Mal, Fuji Arco is your friend. No reciprocity until the 2 min mark, even then Ive pushed it to 5 min with worrying.
Cheers
Shane
Ha! There are so many film types to choose from and so little time! Thanks Shane.
Each film will have it's own reciprocity "factor" (problems, challenges, joys). There are charts out there that will give you all of the answers but one of the things I like about pinhole photography is that it's always just a little bit random.
The other thing I want to know is whether a 15 minute and 30 second exposure is going to look that much different to a 16 minute exposure (or 14 minutes and 25 seconds). I'm thinking that the longer the exposure the greater the reciprocity failure but the greater the leeway (fudge factor) before you can see the difference.
Well when you consider a 14min exp a extra stop is another 14min so a 1min extra/less is hardly going to make much difference. So your last statement is pretty much right
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