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Lens question? sensor cropping

Joel Arvidsson

Joel Arvidsson

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Ok today I had to investigate something that have bugging me for a while.
If you have a canon t2i (550) with a 18-135 lens and set it to 50mm. Then you get very close to the subject compared to my old analog system cameras. The old anlalog cameras have one prime 50mm and one 28-70 set to 50mm.

On both of the analog cameras you can fit more in the frame with 50mm. Is this due to the chipsize of the t2i? I mean if it had bean a fulllframe you would se more right?

I have not yet understanded if this has to do with the sensor is cropping it. If I want to shoot with the canon t2i and get the feel of 50mm. How do yo calculate that?
How can you calculate what lens I need to use to get the same as a fullframe?

Sorry If the explanation is abit blurry

/Joel
 
Joel Arvidsson said:
I have not yet understanded if this has to do with the sensor is cropping it. If I want to shoot with the canon t2i and get the feel of 50mm. How do yo calculate that?
How can you calculate what lens I need to use to get the same as a fullframe?
Click to expand...

In short, yes. This is because of the t2i sensor being significantly smaller than a piece of full-frame 35mm film or a full-frame 35mm sensor.

APS-C sensors are sometimes called "1.6x Crop" sensors. This is because a given focal length, multiplied by 1.6x, will equate to another focal length on a full frame 35mm camera in terms of field of view.

For example:

[35mm lens] x [1.6] = [56mm lens]

So a 35mm lens on your t2i will give you approximately the same field of view as would a 56mm lens on your film camera.
 
Michael Olsen said:
In short, yes. This is because of the t2i sensor being significantly smaller than a piece of full-frame 35mm film or a full-frame 35mm sensor.

APS-C sensors are sometimes called "1.6x Crop" sensors. This is because a given focal length, multiplied by 1.6x, will equate to another focal length on a full frame 35mm camera in terms of field of view.

For example:

[35mm lens] x [1.6] = [56mm lens]

So a 35mm lens on your t2i will give you approximately the same field of view as would a 56mm lens on your film camera.
Click to expand...


Thanks. Do you know how to calculate this for the Scarlet 2/3 to?
 
Joel Arvidsson said:
Thanks. Do you know how to calculate this for the Scarlet 2/3 to?
Click to expand...

2/3" video is about 2.5X to match Super-35, which in turn is about 1.6X or 1.5X to match FF35.

It's simpler if you just compare horizontal view and thus can ignore differences in aspect ratio that a diagonal view would be affected by.

A FF35 camera is 36mm wide, a Super-35 camera is 24mm wide, a 2/3" sensor is usually about 9.6mm wide. So that's a 1.5X difference between FF35 and S35, and a 2.5X difference between S35 and 2/3", and a 3.75X difference between FF35 and 2/3". So you'd need a 13.33mm lens on a 2/3" camera to match the field of view of a 50mm lens on a FF35 camera. And you'd need a 33.33mm lens on a S35 camera to match the field of view of a FF35 camera.

Now keep in mind that Red is calling the M-X sensor "Super-35" even though it is 30mm wide, not 24mm wide.
 
At what focal length would the fixed-lens Scarlet not have any perspective distortion or the same as with the human eye? Would this be at 13.33mm on a 2/3" camera?
 
Joel Arvidsson said:
At what focal length would the fixed-lens Scarlet not have any perspective distortion or the same as with the human eye? Would this be at 13.33mm on a 2/3" camera?
Click to expand...

"normal" lens focal length is usually defined as equal to the diagonal, which would be around 11mm. Something in the 13-14mm range gets you to a 40 degree AOV, which is probably closer to what most would consider a normal lens on a still camera.
Perspective is a different matter I think. Being pretty near sighted, "normal" perspective for me falls around 80mm focal length regardless of format, even corrected. For others it is probably different.
 
David Rasberry said:
"normal" lens focal length is usually defined as equal to the diagonal, which would be around 11mm. Something in the 13-14mm range gets you to a 40 degree AOV, which is probably closer to what most would consider a normal lens on a still camera.
Perspective is a different matter I think. Being pretty near sighted, "normal" perspective for me falls around 80mm focal length regardless of format, even corrected. For others it is probably different.
Click to expand...

Hehe funny my vision would be somewhere between 28-35mm wide angle eyes!
 
It's confusing to toss in notions of "human perspective" because we have peripheral vision, which to emulate would require very wide-angle photography projected on a very large screen (which is the basis of Cinerama back in the 1950's and IMAX in general.) The image is shown large enough that we concentrate on what would be a medium focal-length image in the center of a wide-angle image.

So when most people talk about "normal" lenses, they are talking about lenses which don't exaggerate the size of the object and the space around it, but ignore peripheral vision issues. In other words, you set up the camera and look quickly at the subject and then through an optical viewfinder and the size of the subject in your field of view doesn't really change. Hard to do that with an EVF or small LCD however.

In FF35 photography, that has traditionally been a 50mm lens. In 35mm cine, it would be a 35mm lens though in the past, most Hollywood directors thought that it was still the 50mm lens (Hitchcock insisted that most of "Vertigo" and "Psycho" be shot on a 50mm lens, but only "Vertigo" was shot in FF35, i.e. VistaVision, where the 50mm would be "normal" in perspective.) To some extent, part of the problem was also that most directors started out in the silent era back then where the 4-perf 35mm Full Aperture was 1.33 and had a longer diagonal than later when cropping to 1.85 became common and the focal length had to shorten a bit to compensate if you wanted the same diagonal view.

So a 13mm would be the equivalent in 2/3" photography.

I agree that it's more of a range rather than a specific focal length. There's nothing magic about the number 50 in FF35 photography.

I would consider 27mm to 50mm as being a "neutral" range in Super-35, 40mm to 75mm in FF35, 10mm to 14mm in 2/3".
 
I was thinking more of perspective as perception of depth relationships between objects at different distances rather than angle of view.
 
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