C100: Focal length interpretations for various lenses on the C100

J

jthabel

Well-known member
I've always been confused by what my "true focal lengths" are for my various lenses on Super-35 sensors. Most of my lenses are designed for APS-C formats, but of course work perfectly well on my C100. Example: the new Sigma 50-100 lens claims to 80-160mm for a 35mm equivalent, since it's an APS-C lens. How do I interpret what that'll be on my C-100? Or is it actually 80-160?

What about my Canon 24-105, which is a non-APS-C lens? It's comparable APS-C focal length is 38.4 -168. What will the focal length fall to on a C100?
 
APS-C is a 1.6 crop factor in relation to full-frame. C-series cameras are a 1.53 crop factor. Speaking semantics, focal length stays the same no matter what sensor size you put it on, while focal equivalent (not really a technical term) changes.

A lot of photographers compare focal lengths to full-frame, but videographers tend to not since videographers (thankfully) don't use full-frame anymore (except those poor souls still using 5Ds for video).
 
Your focal length stays the same no matter what. A 50mm lens is a 50mm lens no matter what camera it's on. The FIELD OF VIEW changes for a given focal length based on the size of the sensor.
 
What they said. So basically a 50mm lens, for example, will look more "zoomed in" when used on a C100 vs say a 5D.
 
I look at it like this, my C100 has a Super 35mm sensor that is almost exactly the same dimensions of Super35mm film which is what most lenses are designed for because that was more or less the standard.


So with that in mind, A 24-105mm on my C100 is a 24-105mm, the field of view is exactly what it was supposed to be. I don’t apply a crop to it because as I see it, there is no crop on Super35 because that was the standard. If anything, I apply the crop to the Full frame cameras (in the opposite way of course) because they are more uncommon in motion pictures.


So for me, a 50mm lens on a Super35mm camera would be 50mm and a 50mm lens on a full frame camera would be 42.5mm.

But that's me.
 
With my 24-70/70-200 both 2.8 Canon L lenses I own, I also owned a Rokinon 85mm T1.5 Cine lens and I wanted something wider that was "cine" to use with my FS7. So, I decided on a Rokinon 24mm T1.5 Cine lens because this is how it works out (if shooting 1080) as far as focal length without speed boosting and with speed booster, PLUS center scan.

~17
~24
~34
~48
~60
~85
~120
~170

All from 2 primes, all super fast. Amazing times we live in.
 
Its been 12 years or so and I have been doing the "crop" calculations. First I used to use the DSLR side by side with my EOS 1V HS, so it was very important to know using a lens in DSLR and its equivalent focal length in a film SLR. Then I moved completely into DLSRs having two bodies with two different sensor sizes. APS-H (1.3 crop factor) and APS-C (1.6). So in wildlife safari situations I had to visualise where the tiger is probably going to be and accordingly shift my lenses to different bodies. I never crop after shooting a still shot. I compose in camera. So for me the focal length/ equivalent focal length is more important. I am comfortable with the concept and when explained people easily get it as compared to "field of view".

I find it easy to calculate by using 1.6 than 1.53 even when I am using the C300. :)

I don't care what a Hollywood ASC thinks about crop factor calculation. I do what is suitable for me. People will judge me based on my work rather than whether I call it crop factor or field of view, whether I call it aperture or iris. It may matter to a youngster trying to get a job in a production where someone is rigid about such nomenclatures.

Some videographers do use full frame like 1DC and are not "limited" by 5D. Finally getting the 1DXII. So I will also be using a full frame.
 
If you are going back and forth between Full Frame and Super-35 then it is helpful to understand how they compare. Otherwise I would say it is best to force yourself to start thinking in terms of the sensor size of your current camera as this will get much easier and quicker for you as time goes on. I had to do this back in the day when I moved from Super-16 to Super-35, which essentially doubled all the numbers. But I quickly adapted.

Don't feel bad about it, this is an issue that's been going on for some time. So much so that years ago at AbelCine I participated in the creation of some tools to help people better understand. The first was a video I produced called "A lens is a lens is a lens" that I created just to explain what the heck was going on to people. Then I made a comparative chart showing a bunch of different camera sensor sizes along with their relative size both in physical measurement as well as a percentage comparison. Lastly Andrew Shipsides created a Field of View Comparator tool that would show what different lenses did on different sensor sizes. These tools have proven quite popular over the years ad each has its place.

A lens is a lens
http://blog.abelcine.com/2010/05/14/a-lens-is-a-lens-is-a-lens/

Sensor chart
http://blog.abelcine.com/2010/08/30/35mm-digital-sensor-comparison-chart-2/

FOV comparator
http://blog.abelcine.com/2010/10/08/field-of-view-comparator/
 
A 50mm lens on a Cx00 will look like a 75mm on a 5D (50mm*1.5 = 75mm. A 35mm on a Cx00 would look like a ~50mm on a 5D (35*1.5=52.5)). For folks only shooting Super35, crop factor may not be useful; for those shooting multiple sensor sizes, it's very useful. Red Dragon, ARRI 65, are cinema cameras where crop sensor math is also useful (+GH4, A7x, 1DC, 1DX II, BM Pocket, Speed Booster, etc.). Crop factor was initially used for 35mm full frame still cameras, so that's now the standard as the base reference.

Note that crop factor is based on the diagonal sensor length, so comparing a 5D stills frame at 4:3 to 16:9 for video takes slightly different math.
 
Last edited:
You must log in or register to reply here.
Back
Top