Jump to content




Photo

Focal length prospective and crop factor confusion (help)

focal length lens prospective

  • Please log in to reply
7 replies to this topic

#1 Kendrick Gray

Kendrick Gray
  • Basic Members
  • PipPip
  • 23 posts
  • Cinematographer
  • Detroit, MI

Posted 28 August 2016 - 10:28 PM

I wanted to upload some examples but I can't for some reason. I have screenshots not urls. I can't seem to search the answer to this question considering I wouldn't exactly know how to search it. I don't know what to look for.

 

So my question is about perspective (I think this is the proper term to use). I noticed that 16mm, 35mm, and 85mm lenses not only have different field of views, but they have a different look. 16mm makes the face look skinnier, and the higher focal lengths made the faces wider. This I already knew but my question requires that I bring this up.

 

The Question: If I am using a camera with a super35 sensor with a 85mm FF lens attached, will the 85mm FF lens give me the same prospective of the face considering the crop factor from the sensor? I hope this is not a dumb question.

 

Usually somebody may get a 50mm lens or something close to that to have the same field of view as the 85mm on the crop sensor. Im afraid that doing this will make my picture change thats all. 


Edited by Kendrick Gray, 28 August 2016 - 10:41 PM.

  • 0




#2 Dom Jaeger

Dom Jaeger
  • Basic Members
  • PipPipPipPip
  • 1200 posts
  • Other
  • Melbourne, Australia

Posted 29 August 2016 - 12:09 AM

If you're worried that on a S35 sensor camera an 85mm lens designed to cover full frame will look different to an 85mm designed for S35, they won't. On the same size sensor, the lenses will produce the same sort of image, with the same field of view. The FF lens simply has a larger image circle than is needed for the S35 sensor, but whether the image circle is cropped by the lens design or the sensor, it's still an 85mm lens.

 

The distortion you're talking about is due to the distance from the subject, it's not a function of the lens itself. With a longer focal length you can fill the frame with a subject from a relatively far distance. With a shorter focal length you have to get closer to make the subject appear the same size in the frame, and that's what causes things to look different.

 


  • 0

#3 Kendrick Gray

Kendrick Gray
  • Basic Members
  • PipPip
  • 23 posts
  • Cinematographer
  • Detroit, MI

Posted 29 August 2016 - 04:08 AM

Thank you for your answer. So let me get this straight, 85mm is 85mm. But what if I wanted the same field of view of the full frame camera with an 85mm lens. Getting a smaller prime lens is ok and is only widening the image on the super35 right?


  • 0

#4 Stuart Brereton

Stuart Brereton
  • Basic Members
  • PipPipPipPip
  • 2575 posts
  • Cinematographer
  • Los Angeles

Posted 29 August 2016 - 04:31 AM

If you wanted to match the FOV of an 85mm on a s35mm sensor with a full frame sensor, you'd need something like a 120mm lens so maybe a 135mm would be the closest solution. Going the other way, matching an 85mm on a full frame sensor with s35mm, you'd need a 58mm, so either a 50mm or 65mm would be closest.


  • 0

#5 Robin R Probyn

Robin R Probyn
  • Basic Members
  • PipPipPipPip
  • 1045 posts
  • Cinematographer
  • Tokyo

Posted 29 August 2016 - 05:02 AM

have a look at this site.. it shows very clearly the difference between FF and other sensor sizes..

 

http://www.abelcine.com/fov/

 

Crop factor is about 1.6 s35 -FF35..  the lens itself of course stays the same but the FOV changes..  all started with DSLR camera,s shooting video.. 


Edited by Robin R Probyn, 29 August 2016 - 05:06 AM.

  • 0

#6 Kendrick Gray

Kendrick Gray
  • Basic Members
  • PipPip
  • 23 posts
  • Cinematographer
  • Detroit, MI

Posted 29 August 2016 - 12:23 PM

Thanks, I was just making sure that distortion wasn't a lens issue. I appreciate the info. 


  • 0

#7 David Mullen ASC

David Mullen ASC
  • Sustaining Members
  • 18789 posts
  • Cinematographer
  • Los Angeles

Posted 29 August 2016 - 12:59 PM

It's the field of view and whether it creates a wide-angle view that is linked to the distortion, not the focal length number in the abstract.  But in terms of wider-angle lenses, some distort more than others even if they have the same focal length and are on the same format -- distortion in terms of artifacts like barrel distortion, corner fall-off, etc. -- not distortion in terms of shooting a face with a wider-angle lens.


  • 0

#8 Kendrick Gray

Kendrick Gray
  • Basic Members
  • PipPip
  • 23 posts
  • Cinematographer
  • Detroit, MI

Posted 29 August 2016 - 05:51 PM

Ahh ok I understand. 


  • 0



Pro 8mm

Rig Wheels Passport

Broadcast Solutions Inc

Abel Cine

Zylight

CineLab

Glidecam

Technodolly

CineTape

Tai Audio

The Slider

Ritter Battery

Visual Products

Aerial Filmworks

Paralinx LLC

rebotnix Technologies

Willys Widgets

Tai Audio

CineTape

Rig Wheels Passport

Technodolly

Aerial Filmworks

Abel Cine

Broadcast Solutions Inc

Willys Widgets

Pro 8mm

Glidecam

The Slider

Ritter Battery

CineLab

Paralinx LLC

rebotnix Technologies

Zylight

Visual Products