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December 13th, 2006, 01:22 PM
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#1 |
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Wrangler
Join Date: May 2003
Location: Eagle River, AK
Posts: 4,100
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XL H1 20X Zoom Number vs 35mm Equivalent Focal Length
The relationship between Zoom Number and focal length in Canon cameras is curvilinear. Method:
- Measured the width of the field of view (FOV) every ten Z Numbers. - Plotted the Z=0 and Z=99 FOV against the published focal lengths in an Excel chart, and let Excel calculate the linear regression for the expected FOV intermediate focal lengths. - Used the regression to convert intermediate FOV numbers to focal lengths. - Also converted actual camera focal lengths to 35mm equivalents (7.00 conversion factor). - Replotted focal lengths against Z Number. Here is the XL H1 chart.
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Pete Bauer The most beautiful thing we can experience is the mysterious. It is the source of all true art and science. Albert Einstein Trying to solve a DV mystery? You may find the answer behind the SEARCH function ... or be able to join a discussion already in progress! |
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May 27th, 2007, 05:23 AM
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#2 |
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Major Player
Join Date: Jan 2006
Location: The Netherlands
Posts: 993
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Using this chart, is it possible to get the Z numbers for the most commonly used prime lenses that they use in film production? Like 50mm, 85mm, 100mm, 150mm, 200mm? I am not a great performer in Excel, but if I remember well Excel can calculate those things quite easily if you know the formula.
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May 27th, 2007, 10:25 AM
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#3 |
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Regular Crew
Join Date: Sep 2006
Location: Miami Florida
Posts: 70
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Can you explain this better ?
Thanks, CQ. |
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May 27th, 2007, 11:59 AM
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#4 |
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Inner Circle
Join Date: Feb 2006
Location: Belfast, UK
Posts: 6,152
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You can calculate the equivalent focal lengths for different formats here:
http://www.panavision.co.nz/main/kba...enseqvform.asp |
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June 3rd, 2007, 11:24 AM
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#5 |
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Major Player
Join Date: Jan 2006
Location: The Netherlands
Posts: 993
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What I really would like to see is the equivalent focus value in 35mm terms for each zoom number. I have the sheet but I can't remember how to have Excel output and interpret the numbers for each given value.
If someone can help me with this it would be greatly appreciated. It has to do with interpolation I believe. But I am really not good in maths. |
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June 4th, 2007, 09:59 AM
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#6 |
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Major Player
Join Date: Jun 2004
Location: McLean, VA United States
Posts: 749
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38.2/2.72 = 14.044 != 20. ???
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June 5th, 2007, 03:15 PM
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#7 |
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Major Player
Join Date: Jan 2004
Location: Ventura, California, USA
Posts: 255
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The XH A1 has a 20X zoom lens, and in the specifications, it states:
"32.5mm-650mm; 35mm photo equivalent" I don't for sure that it's the same for the XL H1 20X, but it should be close.
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Don DesJardin |
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June 5th, 2007, 06:54 PM
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#8 |
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Major Player
Join Date: Jun 2004
Location: McLean, VA United States
Posts: 749
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I took the direct approach: ask the camera. Interestingly enough the camera reports the same focal length (9.9mm) for indicator settings of 30 and 35 (I went in 5 unit steps) even though the focal length did clearly change. It also reported 18.4 mm for indications of 55 and 60 and 44.8mm for 80 and 85 though the image size does change over those ranges. There is some sort of quantization issue at work here. That aside the log of the focal length is modeled pretty well by
log(fl) = 0.75569 + 0.00425*I + 0.00008231*I*I where I is the indicator value (0-99) |
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