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Canon EOS Crop Sensor for HD
APS-C sensor cameras including the 80D, 70D, 7D Mk. II, 7D, EOS M and Rebel models for HD video recording.

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Old March 7th, 2011, 06:00 AM   #1
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600d / T3i questions (Zoom)

So this camera has me intrigued. I have a 7d and I'm currently using it on various pro wildlife shoots as well as personal work. (Remotes, easy carry/use and some specialist situations.)

The new zoom feature would obviously very useful when it comes to wildlife. But I'm trying to get my head around how to think about this.

Firstly the standard sensor crop is 1.6, is the 3x crop, 3x the 1.6 or 3x full frame ?

After that has anyone worked out how much of the sensor (in size) is being used when at 3x. Of course an answer to my first question will help work this out. But what I mean is. At 3x crop are we shooting the equiv of a 1/2 inch , 1/3 inch etc ? - It would be good to know this as I've shot lots of 1/3 and 2/3 rd's format and when engaging this function if you can have in your head that your now shooting an equiv of x it would certainly be useful.
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Old March 7th, 2011, 07:12 AM   #2
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Re: 600d / T3i questions (Zoom)

I'm also interested in the T3i for wildlife, so I downloaded the manual and this is what I've been able to gather.

Canon doesn't refer to it as a crop, but as a "zoom". So it's a 3x "zoom" on top of the 1.6 crop, that works out to a 4.8x factor when you're trying to figure the effective focal length of your telephoto.

Given that the GH2 is a 2.6x on top of a 2x = effective 5.2x factor, and that's just a bit bigger than a 2/3" sensor, it would seem that the T3i will be using a slightly larger area.

It would be also good to note that the T3i zoom seems to be more variable than the GH2, and Canon only states that it's "approx 3x - 10x". It also seems that the zoom function is only available in 1080p mode, not 720p... I often shoot in 720p/60 for wildlife/birds.
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Old March 7th, 2011, 11:42 AM   #3
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Re: 600d / T3i questions (Zoom)

Hi Kin Lau

Ok then so at x3 you are shooting a x4.8 crop which equates to 1/1.8" inch sensor. So slightly bigger than a 1/2 inch EX chip.

And at about 4.5x zoom you are shooting the equiv of a 1/3rd sensor camera. Crop of x7.2

AND - I'm sure someone can shoot me down in flames here but in terms of pixels. Even at a 7.2 crop the way I work it (which is probably wrong)...you still have pixels to spare. In other words you don't start upscaling until about 5x zoom which is when I guess the quality would start to get hit.

hhmmm, now I want to see the same framed shot at 0, 3 and 4.5x crop. I'm hoping there won't be much difference in quality! I might try and do this test at the camera shop tomorrow :-)

Last edited by Mat Thompson; March 7th, 2011 at 02:47 PM.
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Old March 7th, 2011, 12:47 PM   #4
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Re: 600d / T3i questions (Zoom)

x3 would really be interesting on a full frame camera. An EF 14mm f/2.8L would be a 42mm equivalent. The sensor size would be roughly 13mm x 7.3mm, which is nearly identical to Super 16mm.

In fact, one could probably use a fisheye, do a slight correction in post and get an even wider shot without too many artifacts.

The irony about the x3 getting rid of aliasing is this: I don't generally have a problem with aliasing with long lenses. If the subject is a face, aliasing doesn't tend to harm the image too much, and an out of focus background will show no aliasing at all. It's really the wide, establishing shots where aliasing is an issue. A cityscape will have deep focus, lots of details, and lots of near-horizontal lines.

That said, reducing jello would be great for medium handheld shots.
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Old March 7th, 2011, 02:47 PM   #5
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Re: 600d / T3i questions (Zoom)

Originally Posted by Mat Thompson View Post
the way I work it (which is probably wrong)...
Yup, you are wrong.
At 3X you are about there, the 18MP sensor has 9 times more resolution than Full HD (1920X1080) and that equals to 3X magnification (square root 9 = 3).

Everything above 3X is through interpolation, maybe you can get away with zoom up to 4.5X were you get at the limits of HD (~1280X720) above that it will be noticeably soft.

The total multiplying factor at 3X is ~ 4.55X. i.e. a 17mm lens equals to aproximately 28mm at normal mode and ~78 at 3X mode and a 50mm turns from ~78mm to ~235mm at 3X.
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Old March 8th, 2011, 04:07 PM   #6
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Re: 600d / T3i questions (Zoom)

Yeah, the 3x zoom is 3x on top of the 1.6x crop. So, I took a frame grab unzoomed, and then took a framegrab from a 3x zoom shot. If I shrink the 3x zoom shot to 1/3 size, it fits into the middle of a 3x3 grid of the unzoomed shot. I just did it in passing and it lined up well enough to satisfy my curiosity about it. I didn't do a literal pixel specific test.

However, after some short use, I will try to only ever use the 3x zoom and not push it towards 10x at all. Not even 4x. 3x already appears to very slightly soften the image. Anything towards 10x is digital zoom and degrades the image. Even at 3x I don't think it is a literal 1920x1080 capture from the sensor. It is most likely slightly less, 1700 pixels across or something, upscaled to 1080p. That is just my unscientific guess, but the pixel count on the T3i sensor is in fact insufficient to produce 3 1920 horizontal line units.
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