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Focal Length Conversions


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#1 Michael Collier

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Posted 15 November 2005 - 08:09 PM

Ok, so I know target size affects angle of veiw at a given focal length.

Heres my question: I am so used to using lenses marked for 2/3" CCDs that in planning which lenses I need for a mini-35 setup is making me a bit uneasy. I am looking for a range similar to an ENG news lens, something around 7.5-110mm (calculated for the 2/3" chip) but need that to work with the 35mm target of the mini-35. I think we are going with some primes so this is all the more important for me.

is it a linear conversion? IE if the diagonal is aprox twice as big on the 35mm to the chip, does that mean that a 25mm 35mm prime equates to a 12.5mm chip?

If anyone knows how to calculate that I would be very thankful.

(not looking for actual focal length, just equal angle of view. these wont be anamorphic or anything complicated like that, just standard round lenses.)
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#2 John Allardice

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Posted 15 November 2005 - 08:29 PM

IIRC, its a multiple of 2.5 to convert 2/3" to 35mm academy...

in other words a 25mm cooke s4 would have the equivalent FOV to a 10mm fujinon on a 2/3" eng setup

J
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