Jump to content

Rookie focal length question


Pete Huffman

Recommended Posts

Question: Lets say Spielberg uses a 21 mm lens on a S35 sized reel of film, now if you take that 21mm and attach it to a full frame DSLR, does that give you an equivalent of a full frame sensor with a 16mm lens on it (assuming a 1.5 crop factor)?

 

Is a 50mm photo lens (for full frame cameras) the same as a 50mm for real cine lens (made to be used on film)?

 

Thanks

Pete

Link to comment
Share on other sites

  • Premium Member

Is a 50mm photo lens (for full frame cameras) the same as a 50mm for real cine lens (made to be used on film)?

 

If you mean 36 mm × 24 mm by full frame, it isn’t. The standard sound image aperture is 22 mm by 16 mm, the standard silent image area is 24 by 18. The can of worms you’re opening with the question has to do with perspective. Photos enlarged from 36 × 24 images on paper are viewed at quite different distances from those enlarged in a cinema from 35-mm. film. Here you have an arm’s length as maximum stretch, there it can be a hundred feet easily. The eye base is an other with each situation and hence the perceived spatial angle.

 

In other words, the cinema normal lens in general is of a longer focal length compared to the stills one.

Link to comment
Share on other sites

OK cool, i think I'm getting this... So theoretically, if Spielberg says use a 21mm lens (and he's shooting on film, not anamorphic). that would be similar/close to me using a 21mm on a sony A7R3 in crop mode or a 14mm lens in FF mode?

 

Thanks

Link to comment
Share on other sites

Say you have 2 A7s side by side, and one is in crop mode, and the other in Full Frame mode. If you put the 21mm lens on the crop camera, you'd need to put a 35mm (roughly) lens on the full frame camera to match. If you put the 21mm lens on the full frame camera, you'd need to put a 14mm on the crop camera to match.

 

The bigger the sensor, the wider the FoV for any given focal length.

Link to comment
Share on other sites

OK cool, i think I'm getting this... So theoretically, if Spielberg says use a 21mm lens (and he's shooting on film, not anamorphic). that would be similar/close to me using a 21mm on a sony A7R3 in crop mode or a 14mm lens in FF mode?

 

Thanks

The Sony A7r3 super 35 "crop mode" is super 35 sized, so there should be no difference between our friend, Mr. Speilberg, and his film camera shooting super 35mm.

 

In full frame mode, a 21mm lens will look similar to a 14mm lens, when placed on a super 35mm camera.

  • Upvote 1
Link to comment
Share on other sites

  • Premium Member

 

In other words, the cinema normal lens in general is of a longer focal length compared to the stills one.

You mean the same focal length has a narrower view in Super-35 rather than Full Frame due to the lens image being cropped — so the net result is that cinema lenses tend to use shorter focal lengths than FF still cameras do to get the same fields of view.

 

To keep things simple, I use a 1.5X crop factor figure for horizontal field of view differences between Super-35 (24mm) and Full-Frame (36mm). Not using the diagonal measurement avoids dealing with aspect ratio differences. So to match the view of a 50mm lens on a Full-Frame camera, you’d have to use a 33mm lens in Super-35.

  • Upvote 1
Link to comment
Share on other sites

  • Premium Member

OK cool, i think I'm getting this... So theoretically, if Spielberg says use a 21mm lens (and he's shooting on film, not anamorphic). that would be similar/close to me using a 21mm on a sony A7R3 in crop mode or a 14mm lens in FF mode?

 

Thanks

The equivalent to the field of view of a 21mm lens on a Super-35 camera would be nearly a 32mm lens on a Full-Frame camera.

  • Upvote 1
Link to comment
Share on other sites

  • Premium Member

“50mm” is a physical measurement so yes, a 50mm lens is 50mm whether it is made for cinema or stills and whether it is put on a Super-8 camera or an IMAX camera. It’s 50mm!

 

The only differences, other than some mechanical issues with cinema lenses (like a longer barrel rotation to go from minimum distance to infinity to allow larger and further-spaced distance marks, less breathing, etc.) is that some lenses aren't designed to cover a larger format without vignetting, so a 50mm cinema lens made for Super-35 might start to vignette in the corners on a Full-Frame camera. If you're designing a lens for a small format, there is no reason to make it big enough to cover a larger format.

Link to comment
Share on other sites

  • Premium Member

You mean the same focal length has a narrower view in Super-35 rather than Full Frame due to the lens image being cropped — so the net result is that cinema lenses tend to use shorter focal lengths than FF still cameras do to get the same fields of view.

 

To keep things simple, I use a 1.5X crop factor figure for horizontal field of view differences between Super-35 (24mm) and Full-Frame (36mm). Not using the diagonal measurement avoids dealing with aspect ratio differences. So to match the view of a 50mm lens on a Full-Frame camera, you’d have to use a 33mm lens in Super-35.

 

Yes, in my non-native speaker English. Different aspect ratios complicate the matter, I agree, too. As an unneccesary sidenote I’d like to state that my favourite movie image format is 3:4.

Link to comment
Share on other sites

  • Premium Member

Question: Lets say Spielberg uses a 21 mm lens on a S35 sized reel of film, now if you take that 21mm and attach it to a full frame DSLR, does that give you an equivalent of a full frame sensor with a 16mm lens on it (assuming a 1.5 crop factor)?

 

Is a 50mm photo lens (for full frame cameras) the same as a 50mm for real cine lens (made to be used on film)?

 

Thanks

Pete

 

I think what's a bit confusing about the original question is that "equivalency" is generally expressed in terms of equivalent to full-frame 35mm, though of course when talking about cinema, one probably should just make 35mm cine the base for equivalency. But marketing for lenses and formats today is all about equivalency to full-frame 35mm.

 

If you put that 21mm on a full-frame camera, it's still a 21mm obviously... though if designed for a 35mm cine camera, it may vignette on a full-frame camera. So it's weird to say that the 21mm put onto a full-frame camera is the equivalent to putting a 16mm lens on it -- you'd express it more as a 21mm lens on a 35mm cine camera is like using a 16mm on a full-frame camera in terms of field of view. Which is wrong of course, it's the opposite -- the 21mm on a full-frame camera is like a 16mm on a 35mm cinema camera in terms of equivalence of view. But if you said "a 21mm lens moved from a 35mm cine camera to a full-frame camera gives me a wider field of view" you'd be correct.

 

I guess the proper way to say it is that putting a 21mm lens onto a full-frame camera would give you the equivalent field of view of a 16mm lens on a 35mm cine camera. But given the 1.5X factor, it's actually 14mm, not 16mm (21÷1.5 = 14). And the equivalent to a 21mm on a 35mm cine camera would be a 31.5mm on a full-frame camera (21x1.5 = 31.5).

Link to comment
Share on other sites

Ive got a horrible feeling the next big thing its going to be FF on all video cameras.. not just the high end..probably with a built in 1.5 crop mode like the Sony A7III stills/video cameras have .. so as not to make all s35 lenses redundant over night.. its coming for sure.. they have sold all the C300 mk II,s .. well all 10 of them.. all the fs7,s/f55/5.. no one bought the C700 anyway..the Alexa mini is more popular than the big one.. marketing and "buzz" is all going they way..Bro..

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...