cine lens crop factor

Deniz Zagra · February 18, 2023

I'm currently working on a student film production, and our director is looking for premium cine lenses to rent. Since most cine lenses cover S35 or 4 perf image sizes, are the focal lengths numbers in s35 terms or in full frame terms? For example, if I put a Panavision Primo 50mm lens on a film camera that shoots 3 perf s35, would the focal length be 50mm or (50 x 1.4 = ) 70mm?

Daniel Klockenkemper · February 18, 2023

This topic again... ?

Lenses do not have crop factors. Period. The focal length of a lens is always what it says it is. It does not matter if the lens does or does not have the ability to cover a particular sensor or piece of film completely. A lens cannot become a different lens when placed in front of a different format; that would violate the laws of physics.

"Crop factor" only relates to the size of one format compared to another format. The ratio between two formats is always the same, even with no lens involved.

The combination: format ⋆ focal length ⇒ angle of view.

Which means:

If you keep the format the same and change the lens, you get a different angle of view.
If you keep the lens the same and change the format, you get a different angle of view.

So to get around to your question... ?

A S35-sensor camera might be paired with a typical set of focal lengths, such as: 16mm, 24mm, 35mm, 50mm, 85mm.
To choose lenses for a full frame camera that have the same angle of view as the above set, you'd multiply by the 1.4x crop factor - the difference between the two formats - which would tell you to pick these focal lengths: 22.4mm, 33.6mm, 49mm, 70mm, 119mm. But in practice this would probably get rounded to more common numbers: 24mm, 35mm, 50mm, 75mm (or 85mm), 135mm.

There are quite a few "Super 35" lenses that can cover a full frame sensor. And an excellent set of "full frame" lenses will work just fine on Super 35 formats, too. So start by determining what angles of view are needed for the particular story or style, then choose a format, and pick the lenses from there!

David Mullen ASC · February 18, 2023

To add to what Daniel is saying...

If you had a 50mm full-frame lens, it would be a 50mm on a Super 35 camera, a Super 16 camera, a Super 8 camera, etc. It would be a 50mm on an IMAX camera but it might not fill the IMAX negative area. If you put that 50mm full-frame lens on the Super 16 camera and then switched to a 50mm lens made for Super 16, you'd get the same field of view.

To get the exact difference in size between two recorded areas of a sensor, you have to know the actual specs. And it's easier to figure out if you pick just one dimension like the horizontal size.

For example, Open Gate on a regular Alexa is a bit larger than traditional Super 35 (24mm wide). So while the difference between generic Super 35 (24mm wide) and Full-Frame 35 (36mm wide) would be 1.5X (divide 36 by 24), the difference between Open Gate on an Alexa (28.25mm) and an Alexa LF (36.7mm) is only 1.3X.

The focal lengths tend to get longer as the format gets larger to get an equivalent field of view (which is also why larger formats tend to have less depth of field.). So if your crop factor is 1.5X, let's say, and you liked the horizontal field of view on a 25mm lens on the smaller of the two formats, then a 37.5mm lens (25 x 1.5X) would give you an equivalent horizontal field of view on the larger of the two formats.

Joerg Polzfusz · February 18, 2023

Hi!

I fear that you have misunderstood Deniz’ question:

Let’s take this example from the attached screenshot: the lens is 8.8-132mm no matter what mode you’re using it. However, at 4:3, this zoom-range would be equivalent to 26-390mm on a 35mm still camera.

Deniz’ question would be (if he referred to this lens): would you expect this lens to be marked as 8.8-132mm or as 26-390mm?

Or to come back to a cine-lens: is the real value listed? Or is it the „equivalent to … on a 35mm camera“ value or something else?

Dom Jaeger · February 18, 2023

51 minutes ago, Joerg Polzfusz said:

Deniz’ question would be (if he referred to this lens): would you expect this lens to be marked as 8.8-132mm or as 26-390mm?

Or to come back to a cine-lens: is the real value listed? Or is it the „equivalent to … on a 35mm camera“ value or something else?

No cine lens will ever be marked as anything other than the focal length it is.

There will be a multitude of different angles of view (“equivalent to x on y format”) depending on the camera and sensor mode you might shoot with. If someone feels the need to refer that back to a format they’re familiar with they just have to do the crop factor calculation.

As David mentioned earlier, S35 and Open Gate on a nominally S35 camera like Alexa Mini are different sizes and will give different views with the same focal length. An Alexa 35 or Sony Venice or Alexa LF or RED whatever will all be different again, depending on the sensor mode you choose.

There are other factors to consider as well, such as whether a particular lens covers a format larger than the one is was designed for. Not every lens in a S35 kit might adequately cover Open Gate mode on a S35 camera for instance. And some S35 lenses will actually cover full frame.

The only constant is that a particular lens will always be the focal length that it is.

(You can alter a lens focal length and image circle by adding focal length extenders or speed boosters, but in this case you’re adding optics to the lens, so it’s a different scenario.)

Deniz Zagra · March 2, 2023

On 2/18/2023 at 5:21 PM, Dom Jaeger said:

No cine lens will ever be marked as anything other than the focal length it is.

On 2/18/2023 at 5:21 PM, Dom Jaeger said:

There are other factors to consider as well, such as whether a particular lens covers a format larger than the one is was designed for.

On 2/18/2023 at 3:51 PM, Joerg Polzfusz said:

Deniz’ question would be (if he referred to this lens): would you expect this lens to be marked as 8.8-132mm or as 26-390mm?

Thanks a lot for clearing my mind. This has been bugging my mind for a long time.