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Forum: Pentax SLR Lens Discussion
01-04-2014, 04:49 PM
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Something else I just thought of is that the light rays will be reaching the film at very acute angle relative to the film plane on the outer limits due to the shorter focal plane distance of 35mm compared to the longer focal plane distance of medium foumat. This will no doubt also degrade image quality on the outer limits and you will probably see a loss of contrast in outer limits
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Forum: Pentax SLR Lens Discussion
01-04-2014, 04:35 PM
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The standard design furmula for teleconverters is really very simple maths - 'cheapo = poor image quality'. However for your initial experiments they will proove the concept.
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Forum: Pentax SLR Lens Discussion
01-04-2014, 04:12 PM
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Yes it does increase the size if the image circle. However image quality may be an issue around the edges and cormers. When a TC is designed the manufacturers only design it with the central image area sharpness in mind as this is the only area of TC projected image that gets used in normal use. Light that is spread to the outer limits of the image circle normaly 'gets lost' and is given no consideration when designing lens distortions / corrections. Assuming you are producing a 6x7 negative your center 36x24mm of image will be the same image quality produced with the TC on a standard negative and will degrade radialy out from there. Your focal plane distance will remain the standard 45.46mm as it is for Pentax 35mm cameras.
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