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EX1/3 focal length question


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#1 Alex Aust

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Posted 25 August 2009 - 04:18 AM

i'm a bit confused. the ex1/3 cameras have a 1/2" chip, so the width of the chip should be 11mm. so the widest focal length of the lens, 5.8mm, should equal ~19mm on a 35mm still frame. however sony states that the widest focal length equals 31mm on 35 still and it actually looks much more like that and not 19mm. so where is the mistake in my logic guys?? :unsure:
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#2 Stephen Williams

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Posted 25 August 2009 - 05:35 AM

i'm a bit confused. the ex1/3 cameras have a 1/2" chip, so the width of the chip should be 11mm. so the widest focal length of the lens, 5.8mm, should equal ~19mm on a 35mm still frame. however sony states that the widest focal length equals 31mm on 35 still and it actually looks much more like that and not 19mm. so where is the mistake in my logic guys?? :unsure:


Hi,

The active area of a 3x4 2/3" CCD was 6.6mm x 8.8mm. Can't imagine a smaller chip has a width of 11mm.
5.8mm would be wide for a 2/3" camera.
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#3 Alex Aust

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Posted 25 August 2009 - 06:10 AM

Hi,

The active area of a 3x4 2/3" CCD was 6.6mm x 8.8mm. Can't imagine a smaller chip has a width of 11mm.
5.8mm would be wide for a 2/3" camera.



so it looks like 2/3" in fact is less than real 2/3". does anybody know why??
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#4 Stephen Williams

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Posted 25 August 2009 - 06:15 AM

so it looks like 2/3" in fact is less than real 2/3". does anybody know why??


Hi,

It's a diaganol measurement, originally tube cameras were used so there needed to be some area 'cut off'. It's a bit like a 4K raw camera that is neither 4k nor records raw data.
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#5 Will Earl

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Posted 25 August 2009 - 06:57 AM

With the numbers you've given and assuming Sony has measured the AoV correctly and have compared it with a full-frame 35mm filmback, I've come up with a roughly judged (I matched it to 60.62 degrees rather than 60.28 degrees) 6.7818mm x 3.8147mm as the dimensions of the sensor.
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#6 Alex Aust

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Posted 25 August 2009 - 08:24 AM

ok guys i think i got it. with those numbers it all makes sense. so these attributes <2/3"> and the like, they are not real sizes but refer to a pimped scale. i understand that now. thanks guys.
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#7 K Borowski

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Posted 25 August 2009 - 12:39 PM

It's just like how a silent frame used to be " 1"x3/4" ", when it was actually 24x18mm.

So, there is more than a 5% loss from the actual quoted dimensions.

At least here in the U.S., you are generally allowed +/-10% on a quoted measurement before weights and measures comes after you.


I saw a test chart once on lenses, think they were for 35mm still cameras, and they were all consistently short of the quoted focal lengths. Some were off by even more than 10%.

One thing that is bothersome to me is that, while 10% error is allowable, it is not allowable for a measurement to be consistantly short of what is quoted.

Technically, overstating a length or size by even 5% consistently is illegal, but apparently in some arenas this fact is simply overlooked, like with camera lenses.
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#8 Mark August SOC

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Posted 25 August 2009 - 05:53 PM

If you would a Camera Aperture and Image Formats the below link should be of help.

http://media.panavis...atSpecs2008.pdf

If this link does not work go to www.panavision.com and click on "media Center" >Reference Library > Techinical Reference > Format Specifications... the chart is in a PDF format to save if needed.

The Format for 2/3" CCD with a Aspect ratio 1.78:1 the dimensions are .3775 x .2123 in or 9.59 x5.39 mm 2/3 CCD area or 51.7mm
for a 2.40:1 Aspect ratio the dimensions are .3586 x 1500 in or 9.11 x 3.81 mm 2/3 CDD area for 2.40:1 or 34.7mm


Mark August, SOC
Panavision Hollywood, CA
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#9 John Sprung

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Posted 25 August 2009 - 07:01 PM

so it looks like 2/3" in fact is less than real 2/3". does anybody know why??


Yes. These oddball fractions of an inch go back to the days of tube cameras. They were the actual outside diameters of the glass tubes. The images are always considerably smaller.

There are a lot of things where what used to be real dimensions are now just names. The nominal "2x4" at any lumber yard today is actually 1.5" x 3.5", and a nominal 3/4" steel pipe is 1.050" in diameter. A 26 foot extension ladder might if you're lucky be 23 - 24 ft. long. Go figure.




-- J.S.
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