I arrived on site, Riverside Gillingham at about 10am and there was bright Winter sun giving a light meter reading of 1s at f22. This was translated to judge the exposures used in the photos.
This time the photos I have scanned the negatives in grey scale rather than colour (and then the colour removed).
Camera One: 3 minute exposure with yellow filter still evidence of the bright over exposed centre
Camera One: 4 minute exposure with yellow filter
In my opinion slight general over exposure.
Oops finger marks or something on the negative !!!
Camera One: 3 minute exposure with yellow filter but using a fresher paper
In my opinion less over exposure in the centre
Camera One: 4 minute exposure with yellow filter but using a fresher paper a general over exposure
Camera One: 6 minute total exposure but carried out as a test strip with yellow filter but using a fresher paper. The strip suggest an exposure between 3 and 4 minutes.
Camera One: one and half minute exposure but with NO yellow filter but using a fresher paper. This show considerable over exposure due to Multigrade IV paper being very responsive to blue light.
Camera Two: with 120mm focal length and graduated neutral density filter and yellow filter 4 minute exposure
The over exposure at the centre has all by gone and the generally tonal quality is good overall.
The difference between the two cameras is the focal length and the filter systems but what a difference in results.
However from all that I have read having the centre area over exposed is a trait of pinhole photographs when using a flat negative plane as the light drop off from centre to edge is of the order of 0.5 to 1 stop due to the greater distance between the edge of the paper and the pin hole than between the centre and the pinhole. As the focal length is made longer the drop off is less as the difference in lengths is not as marked.
I have made a re-design to my pin hole camera to test the idea that the greater focal length reduced vignetting.
No comments:
Post a Comment