Jump to content




Photo

Lens quality for 4K acquisition

lens quality 4K

  • Please log in to reply
9 replies to this topic

#1 Kim Bolan

Kim Bolan

    New

  • Sustaining Members
  • 6 posts
  • Cinematographer
  • Seattle

Posted 08 November 2015 - 12:27 PM

With the advent of the 4/3 mount system a wide variety of lenses are now availble for use in HD and 4K acquisition. Lenses produced prior to the digital era may provide a specific look but for general production may not provide adequate resolution for HD or 4K production. Is there a standard suggested minimum resolution for lenses used for 4K acquisition?

 

Are lower end lenses such as the Bower series and still lenses such as the Canon EF series of significant resolution to meet the requirements of 4K?

 

 

 

 


  • 0




#2 Phil Rhodes

Phil Rhodes
  • Sustaining Members
  • 11230 posts
  • Other

Posted 08 November 2015 - 12:44 PM

This sounds a bit like a homework question!

 

 Is there a standard suggested minimum resolution

 

There isn't really any such thing as a quotable resolution figure for a lens - well - there is, but it's more complex than just a number. The way lens resolution is usually measured is to shoot progressively finer and finer patches of alternating black and white stripes, often "soft" stripes of sinusoidal profile. Any lens will, at some point, diffuse the two together to the point where they are no longer distinguishable. Before that, though, there's a point where the contrast between black and white is so compromised that we can assume the lens is not producing a usable image of the stripes at that scale. The term for this is modulation transfer function, or MTF, which describes the relationship between contrast and stripe width. It's a graph, where the contrast falls toward zero as the resolution increases. What's an acceptably usable point on that graph is up to you.

 

Art complicates this even more. Lenses with comparatively poor MTF may be selected for the way they look, because they all produce softness in various ways. There is no formal requirement that a 4K image actually contain 4K of information. Using the pixels to store lens aberrations is fine, if that's the look you're after.

 

 still lenses such as the Canon EF series of significant resolution to meet the requirements of 4K

 

Stills lenses are often quite contrasty. Remember that a 4K video frame is only 12 megapixels. A lot of stills cameras have more resolution than that.

 

P


  • 0

#3 Kim Bolan

Kim Bolan

    New

  • Sustaining Members
  • 6 posts
  • Cinematographer
  • Seattle

Posted 08 November 2015 - 01:32 PM

Thank you Phil

Film does require more contrast and I did not consider that factor so I appreciate you bringing this to my attention. 


  • 0

#4 Phil Rhodes

Phil Rhodes
  • Sustaining Members
  • 11230 posts
  • Other

Posted 08 November 2015 - 02:21 PM

Does it? How d'you figure?


  • 0

#5 Dom Jaeger

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

Posted 08 November 2015 - 06:56 PM

Here's an interesting article from the Cooke website that discusses the resolution requirements of 4K:
http://www.cookeopti...tion camera.pdf
According to that, 35 line pairs per mm is about as fine a detail as a 4K sensor can make out. Virtually every lens I've ever tested can easily resolve that, often it's more than 5 times that in the centre.
But of course Phil is right that resolution is a more complex thing than one measurement can describe - MTF charts for lenses will have different curves for varying contrast percentages and line pair detail, whether it's the centre or the corners of the frame, and whether the line pair is sagittal or meridional.
All very complicated sounding, but the point being, the performance of a lens is a multifaceted thing. Usually what lets a lens down is the aberration correction, how well things like colour fringing, astigmatism, coma and flare have been controlled. Often these aberrations are worse towards the edge of frame. On zooms, anamorphics and wide angles distortion can be an issue. Sometimes it can be the out of focus areas that people like to assess, or the way a sharp area rolls off into blur. The colour rendition between lenses can vary, very important in cinematography where sequential images need to match. The image can change magnification as you rack focus, or subtly shift. Very often it's the physical constraints that make a lens unsuitable - the poor markings, the minimum focus, the size, the mechanics.
Generally resolution itself is not the problem with low cost or vintage or stills lenses.
  • 0

#6 Kim Bolan

Kim Bolan

    New

  • Sustaining Members
  • 6 posts
  • Cinematographer
  • Seattle

Posted 09 November 2015 - 01:07 AM

Thank you Dom I found the article informative. Today i tested my 4K camera with lenses from several manufacturers and discovered all of them produced good images. With regard to color rendition I remember as a young still phtographer (when film was our mainstay) being told that manufacturers spend considerable time and expense matching the output color of their lenses so that film would have the same consistant color appearance regardless of focal length. My tests indicated that this was true and regardless of the focal length the color was consistent. Your point is well taken and the more important factor may be to select a series of the lenses from the same manufacturer. 

 

In response to Phil, it is my understanding that still camera lenses were producd with a greater contrast primarily for black and white film. 

 

Thank you


  • 0

#7 stewart addison

stewart addison

    New

  • Basic Members
  • Pip
  • 4 posts
  • Cinematographer
  • London and Los Angeles

Posted 09 November 2015 - 05:54 PM

What 4K camera / lenses are you using currently Kim?


  • 0

#8 Kim Bolan

Kim Bolan

    New

  • Sustaining Members
  • 6 posts
  • Cinematographer
  • Seattle

Posted 09 November 2015 - 10:12 PM

Stewart,

 

Thank you for asking. My first venture into 4K is with a Panasonic GH4. I am using Canon EF lenses, Panasonic lenses and also a set of Bower EF mount lenses. I have a set of Lecia R lenses and also Canon FL series from my younger days. 


  • 0

#9 Robert Houllahan

Robert Houllahan
  • Sustaining Members
  • 1511 posts
  • Industry Rep
  • Providence R.I.

Posted 10 November 2015 - 12:06 AM

Well just remember that a "4K" bayer mask imager generally only resolves 2/3 of it's boilerplate resolution, also still lenses were generally designed to cover a full frame 35mm negative which is Vista-Vision sized in movie terms and Vista is commonly scanned to true RGB 8k.


  • 0

#10 Satsuki Murashige

Satsuki Murashige
  • Sustaining Members
  • 3081 posts
  • Cinematographer
  • San Francisco, CA

Posted 10 November 2015 - 12:35 AM

Also keep in mind that there are very few if any '4K' prosumer cameras that are actually capable of recording a high fidelity image at that resolution. A highly compressed 4K 8bit h264 file is not going to take advantage of high MTF glass in the same way as a 4K 12bit raw file. So I would just use glass that looks pleasing to the eye. There's more to lens quality than just MTF. Those Leica R's should look great!
  • 1



Visual Products

CineTape

Zylight

Pro 8mm

CineLab

rebotnix Technologies

Ritter Battery

Abel Cine

Broadcast Solutions Inc

Glidecam

Tai Audio

Paralinx LLC

Technodolly

Rig Wheels Passport

Willys Widgets

The Slider

Aerial Filmworks

Rig Wheels Passport

Technodolly

Paralinx LLC

CineLab

Glidecam

Aerial Filmworks

Visual Products

Abel Cine

The Slider

Tai Audio

rebotnix Technologies

Broadcast Solutions Inc

Zylight

CineTape

Pro 8mm

Ritter Battery

Willys Widgets