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Sony HVR-V1 / HDR-FX7
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Old September 11th, 2008, 07:36 AM   #1
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Values for DoF calculations

There are several apps for the iPhone that work as Depth of Field calculators. You set the parameters (aperture, focal length, distance, circle of confusion) and get a read-out of depth of field info (hyperfocal distance, near and far points etc). I'd love to be able to use one, or indeed any other DoF calculator, with the V1.
The first part of my question is: What Circle of Confusion (CoC) value should be used for the V1?

I've seen several different formulae for CoC, (e.g CoC = d / 1500 , where d is the diagonal measure of the original image) but my understanding of CoC is that it takes into account both the format dimensions and the "normal" viewing circumstances of the image for an "acceptable" degree of focus. e.g The criticalness of sharpness for a 10x8" photographic print viewed at arm's length is different to a billboard viewed across the street. The above formula is specific to photography with an assumption of the desired print resolution and enlargement factor built in. I'm guessing that SD or HD resolution is a limiting factor in any formulae for video image CoC, so should be taken into account.
For my purposes I'd be interested in two distinct viewing circumstances:
1. watching on a tv monitor.
2. viewing projected onto a screen in a cinema.
I'm guessing I need to work with a different CoC value if I know the piece is aimed for projection rather than tv screen.
Any light on a CoC formulae for video production would be very much appreciated.

Wrt format size: in this thread http://www.dvinfo.net/conf/sony-hvr-...allow-dof.html Tim Le uses a CoC value of 0.003mm for a 1/4" sensor. I'm not sure how he's arrived at this figure. I must admit I'm confused as to whether 1/4" measures the width of the sensor or its diagonal. To make matters even more confusing, it says in Sony's V1 Manual that the 1/4" type (sic) CMOS sensor is 4.5mm. That's significantly less than a quarter of an inch. Can anyone clarify actual dimensions?

The second part of my question relates to focal length:
The focal length of the V1 lens ranges from 3.9 - 78 mm. You can't actually get these figures in the viewfinder readout, but the numerical scale goes from 0 - 99, and I'm hoping to figure out an index to retrieve the actual focal length. (i.e 0=3.9mm, 10=5mm (normal) etc)
Should I assume that the numerical zoom scale works linearly? Or is it exponential?
I guess as a last measure i can do a through-the-lens comparison with a 35mm stills camera and figure it out from there.

Of course I'm not expecting to get absolute precision here; If I was, I wouldn't be using this camera! But a rough guide to the DoF would be very useful to the kind of stuff I'm doing. Thanks in advance for any help, and if you're interested, the iPhone apps are DoF, DoF Calculator, and iSee4K (free and geared to Red) available via the iTunes store.
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Old September 13th, 2008, 08:17 AM   #2
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Sorry I don't have answer but thanks for the post and please report back if and when you find the answer.

I would really like to know the DOF of my V1E!
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Old September 13th, 2008, 10:24 AM   #3
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Well, no concrete answers yet!
But here's an update to the thread:

the iPhone "DoF" application uses a CoC value of 0.008mm for a 1/4" sensor. I've emailed the developers to find out what is assumed to be "normal" viewing circumstances.

Once I get round to indexing the focal length values by comparing through-the-lens with a 35mm stills camera, I'll post the results.
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Old September 13th, 2008, 11:25 AM   #4
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Wow, that was an old thread. To be honest, I don't remember exactly where I got the 0.003 value for the COC for a 1/4" type sensor. I suspect I did some googling and estimated the value from different sources.

What I can tell you is that a 1/4" type sensor is not literally 1/4" across. It's a just a designation that originated from the old vacuum tube diameter designations and is still used today. Here's an explanation: Making (some) sense out of sensor sizes: Digital Photography Review

Sorry I guess I wasn't much help. What you can do is back out the COC value from your calculator by making real life measurements of the DOF at different aperture settings and focal lengths and then by trial and error, replicate those values on your calculator.
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Old September 13th, 2008, 11:45 AM   #5
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Tim,
Thanks for the link. At least that's clarified the 1/4" vs 4.5mm issue.
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Old September 14th, 2008, 03:45 AM   #6
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In Apple application store i can only see 2 Dof apps - iSee4k and Dof Calculator?

Where you find the other one?
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Old September 14th, 2008, 04:24 AM   #7
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Brendan,

You're right, for some reason iPhone "Dof" app doesn't come up in an iTunes search (maybe too new?) but you can find it in the Photography catagory. I've found it to be well designed and quick to use in the field. Here's the link:

http://phobos.apple.com/WebObjects/M...71550&mt=8

There's also a free "DoF Calc" webapp by Digital Rebellion: It's optimized to be browsed on iPhone, but i expect it will work with any mobile browser. It works on Safari on my Mac. Clearly the disadvantage is that you have to get online to use it: But check it out, you don't need an iPhone:

Depth of Field Calculator (iPhone version) - Digital Rebellion

This one also uses CoC 0.008mm for a 1/4" sensor.

Good luck!

Last edited by Alnoor Dewshi; September 14th, 2008 at 05:48 AM.
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