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Old November 18th, 2016, 07:16 PM   #1
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Sony FS7, F5, F55 Centre Crop resolution calculations

After using MTF’s B4 to Super 16 adapter on a Sony FS7 a couple of us were quite surprised at the quality and resolution of the 1920 HD image. We expected less. Why did it look better than we expected?

Generally speaking a 1920 HD image after being demosaiced (Debayered) is considered to have a resolution of about 1.5K. The image we were getting looked to be a very decent full HD image. This prompted me to do a bit of investigation as to what we were actually looking at. Roughly this is what I discovered. Not as good as the full sensor sampled down to HD but surprisingly good. In fact good enough for one our our local DPs to use it on the F55 for shooting a TVC on Bentley's new 16MY Bentley Continental GT Speed. He said:

“There’s more to this camera too. The F55 centre crop function allowed us to use high quality cine glass for most of the shoot and then activate centre crop to be able to record direct to camera with a much more telephoto feel. The camera also delivered pictures that could be distributed quickly to media during the three day event and then used for a more finessed clip released a month after the shoot.”

http://www.content-technology.com/as...cnews/?p=11433

Sony’s Super 16 crop sensor dimensions are 12.7mm x 6.75mm for 2178 x 1148 which results in a diagonal of 14.5mm, a fair bit larger, 32% larger than the 11mm diagonal of a 1920 HD sensor.
2178 x 1148 gives us total of 2,500,344, a resolution of approximately 2.5K.

The generally accepted figure is a Bayer sensor loses about 20% of its resolution after demosaicing. For example a 4K sensor has a resolution of 3.2 K a 2K sensor has a resolution of 1.6K and a 1920 sensor has a resolution of 1.5K

Based on Sony’s Super 16 figures of 2178 x 1148 the centre crop function results in a 2.5K crop. One could then argue the following. After applying a 20% loss in resolution after demosaicing the image produced is in the order of 2,000,275. Very close to 2K in other words.

Following these deductions leads me to the conclusion that the Super 16 Centre Crop function in the Sony FS7 / F5 / F55 after demosaicing when down sampled or cropped, whichever way Sony do it, can actually deliver a TRUE full resolution 1920 x 1080 HD image.

Is this correct? Can anyone point out any major flaw in my calculations here? Happily stand corrected if I’m off the mark.

I may be totally wrong but I don’t think so. Anyway always curious as to the why.

Sony’s Super 16 sensor crop dimensions were obtained here:

Using Super16 Lenses on the Sony F55 in 2K Center Scan Mode | CineTechnica

Chris Young
CYV Productions
Sydney

Last edited by Christopher Young; November 18th, 2016 at 11:54 PM. Reason: Additional info
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Old January 30th, 2017, 06:04 PM   #2
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Re: Sony FS7, F5, F55 Centre Crop resolution calculations

Hi Chris,

Interesting post. Thanks for doing all that brain busting.

I have used the centre scan function with a true Super 16 lens on my FS7 and found it to be a very nice image, especially with the cine optics.

In fact apart from the DOF difference between a S35 and S16 sensor, the differences take a lot of finding.

I took this material with a Nikon 17-55mm f2.8 as a comparison.

password is: 8264

If you zoom the image in by a factor of 4 in post, the edges on the Centre Scan seem a little fluffier. But then who zooms 1080 footage in that much.... nobody.

After years of struggling with stills glass and seeing decent B4 HD lenses way out of reach and also not feeling like the B4 option was really adequate for a S35 sensor, my Canon 8-64 Super 16 lens is an object of beauty.

You can get wide, 24mm (35mm Equivalent) and close 192mm (35mm equivalent).

All this with a minimum aperture of f2.4.

For doco work this is now my Go To lens.

S16 lenses have had almost no value for the last 20 or so years. There are some bargains around and they do turn up on eBay from time to time but word is starting to get out that they are a better alternative to B4 if you don't already have that lens format, and the majority of S16 lenses are PL mount, which is nice too.

Shallow depth of field is lovely, but it's also a pain in the ass a lot of the time when you don't need it. Especially for what the Yanks call "Run and Gun".

I think Sony must have a few old film guys who said, "we can, so we should". There are people out there with tens of thousands of dollars worth of B4 and Super 16 glass who all now have these "F" cameras. I'm sure, like me, they have been dusting off a few old road cases and going.. "I Wonder....? OH YEAH!!!!!" :-))

I.
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Old January 31st, 2017, 12:08 AM   #3
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Re: Sony FS7, F5, F55 Centre Crop resolution calculations

No argument from me Ian, looks good.

If that lens is the Canon SC 8x8 T2.4 then they were a lovely lens. They and other brand S16 lenses are going up in price since the advent of S16 centre crop in S35 cameras and I think will continue to do so as the word spreads. I think this will be my next investigation, to see what is around in S16 cine glass at a reasonable cost. Could prove to be a worthwhile exercise as you are already finding out.

Chris Young
CYV Productions
Sydney
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