Jump to content


Photo

Smaller format zooms more efficient


  • Please log in to reply
2 replies to this topic

#1 Benjamin G

Benjamin G
  • Basic Members
  • PipPip
  • 25 posts
  • Cinematographer
  • Victoria, BC

Posted 29 March 2011 - 07:51 PM

I've noticed that the smaller the format the faster the zooms are.

For example the Fujinon 5.5-88mm that came with my 1/3" camera is a T1.4. I've seen 16mm Angenieux zooms under T2. Yet when you get to 35mm T2 is about as fast as you can get for a zoom.

Is it just because more glass is needed to cover the sensor and more glass equals more light loss? Or is there something more to it than that?
  • 0

#2 M Joel W

M Joel W
  • Basic Members
  • PipPipPipPip
  • 268 posts
  • Student

Posted 29 March 2011 - 11:11 PM

More glass is one factor, but not to the extent that more glass means more light loss (with modern coatings you lose very little light and contrast even with complex designs); it's mostly a factor of more glass costing more money and resulting in an enormous lens. The front element has to be as large as the maximum aperture and so a 240mm f1.4 lens would need a 171mm-wide front element, which is HUGE and very expensive and would likely result in tons of flare. Image circle is another factor. I shoot some large format and lens designs list coverage in degrees (so the longer a lens the more coverage) and the word is that the widest lenses of a given design are also the sharpest over their (more limited) image circle. So it gets really hard designing fast, wide, sharp lenses for bigger sensors. I have a 135mm f5.6 plasmat that weighs half a pound (and is disgustingly amazing); its 240mm f5.6 brother weighs more than four times as much and seems even bigger than that.

Equally important is the fact that you need some depth of field to shoot. Imagine pulling focus at ultra-telephoto t1.4 on super35. No one could do it! I assume it would be possible to make a t1.4 zoom for super35, but it would be incredibly expensive and probably have rather poor image quality (flare, spherical aberration, etc.) and be almost unusable in terms of size.

You'll notice it's the same with stills. For 35mm still cameras you usually get primes in the f1.4 range; for 6x7 and 6x6 cameras f2.8 is about as fast as it gets; for 4x5 and 8x10 f5.6 is fast (f2.8 exists and by most accounts is amazing), for ULF Schneider makes f11-f22 lenses. The limitation seems to be related to the size of the front element and depth of field. Despite normal aperture values of f16-f64, focusing in 4x5 is an art and a science.

This is mostly second hand and maybe full of fuzzy science. I have a book on lens design but am scared to read it. It's full of real science. I'm just repeating what I've been told and have found from experience.

Edited by M Joel Wauhkonen, 29 March 2011 - 11:15 PM.

  • 0

#3 Benjamin G

Benjamin G
  • Basic Members
  • PipPip
  • 25 posts
  • Cinematographer
  • Victoria, BC

Posted 03 April 2011 - 07:41 PM

I had noticed it in still lenses as well as I recently got a 35mm adaptor with a Nikon Mount (and a PL mount). This is what actually led to me noticing the big difference as I was comparing cine lenses and still lenses as well as lenses from smaller formats.

What is the title of that book on lens design? I would like (to try) and read it and see if I can get a better understanding of why things are the way they are.

Thanks
  • 0


rebotnix Technologies

Technodolly

Rig Wheels Passport

Tai Audio

Ritter Battery

Willys Widgets

Paralinx LLC

Glidecam

Abel Cine

Media Blackout - Custom Cables and AKS

Broadcast Solutions Inc

Gamma Ray Digital Inc

The Slider

New Pro Video - New and Used Equipment

FJS International, LLC

CineLab

Aerial Filmworks

Visual Products

Metropolis Post

Wooden Camera

CineTape

FJS International, LLC

Ritter Battery

CineTape

Willys Widgets

Rig Wheels Passport

Aerial Filmworks

The Slider

Tai Audio

Technodolly

Metropolis Post

Glidecam

CineLab

New Pro Video - New and Used Equipment

rebotnix Technologies

Gamma Ray Digital Inc

Abel Cine

Wooden Camera

Visual Products

Paralinx LLC

Media Blackout - Custom Cables and AKS

Broadcast Solutions Inc