Is Focal Length Objective of Sensor Size?

T

tommygdawg

Well-known member
Hey all,

This question may seem confusing, but there's one thing on which I'm confused when it comes to focal length and field of view. How do they measure it for different lenses? For instance, if they're developing a 50mm lens for a full frame camera such as the 5DMkII, will it have the same field of view as a 50mm developed for an APS-C sized sensor? I have a Canon 50mm FD, were these designed for full frame cameras? If so, it would effectively be 100mm-ish on M4/3, correct? But if I bought a 50mm lens designed for M4/3, would it have the same field of view as a 50mm designed for a full frame? I'm not sure if this makes sense, but let's hope so!
 
A 50 is a 50 is a 50. For field of view, it doesn't matter what format a lens was initially designed for, it will always have the field of view permitted by the sensor size for that focal length. To clarify - a 50mm designed for FF35 and a 50mm designed for Micro 4/3 will both have identical fields of view when put on the same camera. The difference between lenses designed for different sensor/film formats is in terms of image circle. Going back to my example, the 50mm designed for a m4/3 format may vignette on a FF35 camera.

I've always disliked the "crop factor" idea, because it just invites confusion. Your 50mm FD lens, when put on a micro 4/3 camera, will have the same field of view as a 100mm would on a FF35 sensor - but it is still a 50mm lens. "Crop Factors" are just a way for someone familiar with shooting on FF35 to estimate field of view on differently-sized formats. For me (and I imagine a lot of people in film), my frame of reference is Super-35, not FF35, so "crop factors" become even more meaningless.
 
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I realize that a 25mm on a GH2, for instance, will have the same field of view as a 50mm on a Canon 5D. The image perception and characteristics would still be like a 25mm though right? Basically, if I wanted to *exactly* simulate the look of a 50mm on a 5D, I'd have to put a 50mm on a GH2 and back up however many feet?
 
So basically, if you take a 50mm designed for a full frame and stick it on a GH2, it's like taking a photo on a full frame, bringing it into Photoshop, and cropping off the edges?
 
tommygdawg said:
So basically, if you take a 50mm designed for a full frame and stick it on a GH2, it's like taking a photo on a full frame, bringing it into Photoshop, and cropping off the edges?
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That's exactly what it's like. And a 50mm designed for M4/3 would look exactly the same. A 50mm designed for Super-16mm would also look exactly the same, except it would likely vignette pretty heavily.
 
Kevin's spot on.
It's all about making sure you know what you're getting despite the equipment you own.
Whilst it's a pain, I'm glad that the manufacturers have at least TRIED to have a semblance of interoperability between their equipment.
 
Kevin Marshall said:
I've always disliked the "crop factor" idea, because it just invites confusion.
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Agreed, confusing as hell. I am of the firm belief that the standard of reference in filmmaking should be super35, but the majority of the internet disagrees with me - even people who have never shot with a full frame camera.

Instead of wasting effort trying to figure out a meaningless crop factor, instead concentrate on learning how sensor size affects FOV and you will be comfortable choosing lenses for ANY camera.
 
So just to make sure I understand correctly, crop factor also applies to lenses made for a smaller sensor that are put on a larger sensor? If I put an M4/3 lens on a full frame, will it be cropped because of the smaller image circle? Essentially not seeing the whole image? I'm not sure if that makes sense. I also agree that the idea of crop factor is really confusing. Especially when trying to communicate it via text over message boards.
 
nothing said:
Agreed, confusing as hell. I am of the firm belief that the standard of reference in filmmaking should be super35, but the majority of the internet disagrees with me - even people who have never shot with a full frame camera.Instead of wasting effort trying to figure out a meaningless crop factor, instead concentrate on learning how sensor size affects FOV and you will be comfortable choosing lenses for ANY camera.
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Can all the folks who have normalized their thinking around the FF 35 sensor size and field of view go sit down in the far corner and talk amongst themselves?.FF "still" photography sized sensor whether film or electronic has very limited application in the film making world as we know it. In the motion picture world the 36x24mm sized film neg is called "vista vision" and is used primarily for VFX background plates. There's a every small world of film cameras that shoot this format, none or very few to my knowledge are sound sync, AND NOBODY USES THEM TO SHOOT ANYTHING BUT VFX SHOTS. if you go to about 99% of the rental houses and try to rent a lens for a motion picture camera that covers vista vision you will be incredibly disappointed because there aint any of those lenses for rent. I can agree that S35 should be considered the default imaging sensor size be the sensor digital or photochemical for motion picture capture because at this point in time this is actually the case.
 
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Mark Smith said:
Can all the folks who have normalized their thinking around the FF 35 sensor size and filed of view go sit down in the far corner and talk amongst themselves?.FF "still" photography sized sensor whether film or electronic has very limited application in the film making world as we know it. In the motion picture world the 36x24mm sized film neg is called "vista vision" and is used primarily for VFX background plates. There's a every small world of film cameras that shoot this format, none or very few to my knowledge are sound sync, AND NOBODY USES THEM TO SHOOT ANYTHING BUT VFX SHOTS. if you go to about 99% of the rental houses and try to rent a lens for a motion picture camera that covers vista vision you will be incredibly disappointed because there aint any of those lenses for rent.I can agree that S35 should be considered the default imaging sensor size be the sensor digital or photochemicalt for motion picture capture because at this point in time this is actually the case.
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Amen.
 
J Davis said:
Yes. The word for that is vignetting
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I just wasn't sure if vignetting meant you get the entire image of the lens except with a black circle around it, or if part of the image was cropped out (basically the reverse of a large lens on a small sensor). This thread has been very useful, everyone. Thanks so much :)
 
http://www.flickr.com/photos/smaedli/3790629725/

this is an example of a lens designed for 16mm being used on a G1. because the image circle for 16mm is smaller than micro 4/3, the lens does not fully cover the sensor. if this had been a lens of identical focal length, but designed for micro 4/3 (or a larger format), it would look the same - except the vignetting would be gone in exchange for more image.

for reference, according to the page, that's a (approx) 13mm lens (converted from the 1/2" given)

EDIT: apparently it's getting too late for me. originally read it as GH1. fixed now. still 4/3, though
 
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DBP said:
I realize that a 25mm on a GH2, for instance, will have the same field of view as a 50mm on a Canon 5D. The image perception and characteristics would still be like a 25mm though right? Basically, if I wanted to *exactly* simulate the look of a 50mm on a 5D, I'd have to put a 50mm on a GH2 and back up however many feet?
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No no no no no. The image perception characteristics are determined by the camera's position, not by the focal length! If you want to match a 5d at 50mm, you must NOT back the Gh2 up! Stand at exactly the same spot with your 25mm, open up the iris 2 stops, and your shot will look identical to the 5d at 50mm (as far as perspective and depth go).
 
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