T3i Zoom? Doing the math :)

C

c3hammer

Well-known member
Does anyone know exactly how the zoom/crop math works on the T3i?

I'm trying to calculate field of view numbers for different lenses with this zoom effect.

I'm assuming that to calculate angle of view I would need to divide the sensors width of 22.3mm by the effective number of pixels on the sensor and then multiply by 1920 to get the width of the sensor when getting a 1:1 crop out of the center.

This makes each pixel 0.00430mm and the width of the 1920 crop to be 8.2593mm.

Here's the "angle of view" formula

c9652413291248e3eb7413571cadb79c.png


d=8.2593 f=600mm

angle of view = 0.78869 degrees at 1:1 crop and a 600mm lens

I believe that equals about 12 feet wide field of view at 1000 yards and about 1.2 feet at 100 yards.

Does that sound like I'm doing the math correctly?

I'm trying to get a setup to film wildlife at 1/2 to 3/4 of a mile away. It is to compete with digiscoping setups. My current one is a camcorder on a Nikon FieldScope EDIII 60mm spotting scope with a 20x eyepiece. It's ok video but I'm trying to do some thing that is perfect and the new zoom function on the T3i may just be the thing that brings this techology into the fore.

By pure luck a family memeber is sending me an old Nikkor 600mm ED f5.6 lens to play with.

Here's the type of footage I've been getting that I'm trying to better :)

http://www.youtube.com/watch?v=RrRPe4mjzjE

Cheers,
PEte
 
I can't help with the math, but I've been doing some T3i zoom tests at the 3x setting. I don't think the 3x zoom is a 1:1 crop. The image looks very subtlely softer and the T3i sensor doesn't enough pixels across to crop it by 1/3 for true 1920x1080.

Still, it is a very cool feature.

http://vimeo.com/20719440
 
you may want to visit my FoV+DoF calculator, and use 4.8 (if you believe 3x actually means 3x) or 4.3 (if you believe a 1920x1080 subsection of photosites are used, and 3x actually means 2.7x) as crop factor:
http://www.similaar.com/foto/dof/dof.php

you get FoV measured both in angle and in height and width of focus plane at a given distance, plus DoF
(everything is done in meters, though)
 
Thanks for the link Norm !!! The caclulator will save me significant time here. All this does beg the question again though. What is the T3i actually doing here with it's zoom function?

I'm not too worried about a slight softening of the image at these distances. Compared to what I'm currently getting the sharpness and abberation will be orders of magnitude better :)

Cheers,
Pete
 
Had the chance to play with the T3i and a 100-400mm L zoom today. The zoom number equals the increase in effective lens focal length.

Thus a 100mm lens * 3x zoom is equivalent field of view to 300m lens * 0x zoom.

This gives you a 35mm equivalent of the lens * 3 - 10 * 1.6 crop factor.

I would consider at first glance, on a 30" Mac Cinema display the 5x zoom to be usable video. The 10x with the 400mm lens at an equivalent focal length of 6400mm was surprisingly detailed. It gave a field of view of about 15" at 150 yards just for reference.

Cheers,
Pete
 
I stopped in Bestbuy today, and ended buying a new t3i. I had the t2i, which was a great little camera. But I have to say the upgrade is worth while. It's an all around nicer camera. It even feels heavier than the t2i. Plus is has adjustable audio, crop mode, and a bunch of other added features, some good, some gimmicky. Overall im happy with it. I was gonna go with a 60d, but there's not much reason to at this point. The T3i does almost everything the 60d does and more. The only thing it really lacks is in between iso settings, and adjustable kelvin temps by way of actual numbers. Doesn't mean you still cant get the same white balance, it just takes a little longer to work around.

I was going to go with a gh2, but unfortunetly panisonic can't get product out to the stores, Must suck to lose sales due to low supply. It's not like there's so much demand they can't keep up, because their readily available in othe countries if you want to buy one. I still think their having quality issues. I have read at least a dozen or so people complaining of hot, or stuck pixels, therefore adding wasted post time to fix. Plus I have seen lots and lots of banding, and pixelated skies.
 
c3hammer said:
Had the chance to play with the T3i and a 100-400mm L zoom today. The zoom number equals the increase in effective lens focal length.

Thus a 100mm lens * 3x zoom is equivalent field of view to 300m lens * 0x zoom.

This gives you a 35mm equivalent of the lens * 3 - 10 * 1.6 crop factor.

I would consider at first glance, on a 30" Mac Cinema display the 5x zoom to be usable video. The 10x with the 400mm lens at an equivalent focal length of 6400mm was surprisingly detailed. It gave a field of view of about 15" at 150 yards just for reference.

Cheers,
Pete
Click to expand...

So, when you're not filming this stuff, are you by chance a sniper? :)

Cool that teven at 5x its good enough for what you're doing. I bought a 2x teleconverter a year ago, thinking it was the most amazing thing in the world, light loss included. These sensor crop features are so amazing now, I need to go spend some serious money on stabilizing the lens to be able to use them.
 
No not a sniper. I've also found I'm not a good enough indian to get close to wildlife so I'm taking technology into my own hands :)

At these magnification levels there's no tripod or stabilizer that will allow following a subject or panning. With my spotting scope setups, I simply have to start recording and not touch it again until the subject leaves the field of view or your get bored with that shot.

Hopefully later this week I'll be able to post some new super high quality video through a 600mm lens and the 3x zoom :)

Cheers,
Pete
 
Very cool. What are those dark patterns all over? Is that the lens?

Here is another test I've done with the T3i. Directly comparing the 3x zoom feature to an equivalent focal length with the zoom.

 
I see a veil of softness on the 3x samples, but maybe it's just that I'm missing the "artificial sharpening" of the line-skipping artifacts, which are definitely gone

a 2x option might be the optimal setting: use a 3K bayer pattern to retrieve a 2K final image
it's not there, is it?



EDIT: for the vimeo ones, everybody please download the original clip before watching, it looks worlds better, both with and without the digital zoom; I still see some softness on one side and some artifacts on the other, but both probems are much smaller in the original footage than on what you see in vimeo
 
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Ryan, I don't see any dark patterns unless you're refering to the sparkling effects of the out of focus bushes in the snow on the hill in the shade another 500 yards behind the elk. It is strange effect for sure.

Norm, the zoom function for video on the T3i is only 3x - 10x. I don't think it can be taking even a 2k bayer pattern. I believe that it is simply their focus aid for stills function ported to the video mode. I have no idea how they do that funtion, but they look identical on the lcd screen.

Maybe some day we'll find out what this thing is doing but for now the results have met my highest expectations for this set up!

Cheers,
Pete
 
c3hammer said:
Ryan, I don't see any dark patterns unless you're refering to the sparkling effects of the out of focus bushes in the snow on the hill in the shade another 500 yards behind the elk. It is strange effect for sure.
Click to expand...

Yeah, must be a weird perspective of the bushes out of focus.

I'm loving this feature too. Need to get a real tripod now though. :-)
 
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