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Is there a formula to convert digital lens focal length to 35mm focal length ?



 
 
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  #1  
Old February 28th 05, 10:34 AM
narke
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Default Is there a formula to convert digital lens focal length to 35mm focal length ?

Does it relative to CCD size?

  #2  
Old February 28th 05, 10:45 AM
Justin Thyme
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"narke" wrote in message
ups.com...
Does it relative to CCD size?

Yes it is entirely dependent on CCD size. For DSLR's, most are close enough
to 1.5x. The Olympus E1/E300 are the only lowish-priced SLR's that are
significantly different, with a 2x equivalence factor.



  #3  
Old February 28th 05, 01:28 PM
Chris Brown
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In article . com,
narke wrote:
Does it relative to CCD size?


Yes. To a first approximation, divide 43 by the diagonal of the sensor in
millimetres. This will give you the multiplication factor for field of
view/focal length (differing aspect rations will make this something of an
inexact sicence, but it should be close).

(43mm is the diagonal of a 35mm frame).
  #4  
Old February 28th 05, 05:05 PM
Alan Browne
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narke wrote:

Does it relative to CCD size?



The focal length does not change at all.

The 'cropping' factor gives a final image similar to the effect of using a
longer lens of FL * cropfactor.

So, a camera with a 50mm lens and a 1.5 cropped sensor is said to be equivalent
to a 75mm lens. (But the focal length does not change, the sensor is just smaller.)

Cheers,
Alan



--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
-- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
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  #5  
Old February 28th 05, 05:11 PM
Alan Browne
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Chris Brown wrote:

In article . com,
narke wrote:

Does it relative to CCD size?



Yes. To a first approximation, divide 43 by the diagonal of the sensor in
millimetres. This will give you the multiplication factor for field of
view/focal length (differing aspect rations will make this something of an
inexact sicence, but it should be close).

(43mm is the diagonal of a 35mm frame).


Just divide 36 by the width of the sensor. eg: the Canon 20D at 22.5 mm (x):

36 / 22.5 = 1.6

(Quicker than (36^2+24^2)^0.5 / (22.5^2+15^2)^0.5 and same result).

Cheers,
Alan.

--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
-- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
-- [SI] gallery & rulz: http://www.pbase.com/shootin
-- e-meil: there's no such thing as a FreeLunch.
  #6  
Old March 1st 05, 01:31 AM
narke
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understand. Thank You All

 




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