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Old July 2nd, 2015, 10:12 AM   #1
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Trying to understand FOV of the X70

For photos, I exclusively use a 50mm lens on a full frame camera. I attempted to compute what focal length I would need to be on the X70 to get the same field of view (distance to subject the same). But all my calculations don't make any sense.

So I did a "physical" test and found I needed to be around 33 to 34% zoom which would be 44mm (or 132mm 35mm equivalent). I believe the equivalent rating specified is a 35mm film frame and not a 35mm photo frame.

So how does one compute the horizontal field of few equivalent from a 3:2 35mm full frame photo frame to a 16:9 1-inch frame on the X70?
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Old July 2nd, 2015, 11:16 AM   #2
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Re: Trying to understand FOV of the X70

The Sony page about this camera ( PXW-X70 (PXWX70) : Specifications : United Kingdom : Sony Professional ) says the following (section labelled "lens"):


f=9.3 - 111.6 mm
equivalent to f=29.0 - 348.0 mm on 35 mm lens (16:9)


So if 29mm on a ff 35mm camera gives the same angle of view as this lens/camera at 9.3mm, it follows that the actual focal length that corresponds to ff50mm must be 50/29 x9.3 = 16mm

Note this is presumably giving figures based on diagonals - to get equivalent figures for horizontal fields of view, you'll need to take the 3:2/16:9 into account.
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Old July 2nd, 2015, 02:36 PM   #3
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Re: Trying to understand FOV of the X70

...except that if using Active Stabilization, it crops in slightly more to allow the extra space for the in-camera smoothing. So you lose a bit of the wide end but gain a bit of reach. Watch as you make the shift and you'll see it happen.
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Old July 3rd, 2015, 01:14 AM   #4
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Re: Trying to understand FOV of the X70

Hopefully when you talk about 35mm film frame etc., your simply talking about your 3:2 full frame sensor -> X70's 16:9 1" Sensor? - keep it simple & just crop the top & bottom of your full frame footage making the FOV match 50mm in the horizontal.

Davids correct above & it makes the crop factor of the X70 3.12 (A standard 1" sensor crop factor is allegedly 2.7 - so 3.12 does allow for the Stabiliser). That would make an equivalent 50mm FOV at just 6.55% of the zoom range.........

However I've duplicated your test & you're correct that a 50mm equivalent FOV falls in the 32 - 34 range as indicated on the X70's zoom indicator - the discrepancy is that the X70 doesn't have a sensor marker that I can see, so the correct figure is a bit of a guess.
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Old July 3rd, 2015, 06:19 AM   #5
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Re: Trying to understand FOV of the X70

Thanks all. And thank you Paul for duplicating my test. I suppose one assumption I've had is that the zoom range scale is linear (each 1% equaling the same increase in focal length). Perhaps near the wide end, percentages vary greatly for little change in focal length. And the opposite of that on the tele end.

Speaking of scales, I sure wish the X70 had a labeled audio meter. Been thinking of putting some kind of sticker along the LCD frame so I know where -12dB and other points are. Maybe Sony could add that in a firmware update and while their at it, allow one more display option for zoom: focal length (along with the current 'bar' and 'percentage' options).
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Old July 4th, 2015, 01:35 AM   #6
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Re: Trying to understand FOV of the X70

Quote:
Originally Posted by Ricky Sharp View Post
Speaking of scales, I sure wish the X70 had a labeled audio meter. Been thinking of putting some kind of sticker along the LCD frame so I know where -12dB and other points are. Maybe Sony could add that in a firmware update and while their at it, allow one more display option for zoom: focal length (along with the current 'bar' and 'percentage' options).
Press the 'status check' button & go to screen 1, that'll give you audio meters with labeled levels!

enjoy!
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Old July 4th, 2015, 06:48 AM   #7
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Re: Trying to understand FOV of the X70

Quote:
Originally Posted by Paul Hardy View Post
Press the 'status check' button & go to screen 1, that'll give you audio meters with labeled levels!

enjoy!
Thank you!
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