July 25, 2014, 07:49:39 AM

Author Topic: Why aren't zoom lenses faster than 2.8?  (Read 18429 times)


canon rumors FORUM

Re: Why aren't zoom lenses faster than 2.8?
« Reply #60 on: April 18, 2013, 06:01:53 AM »

Malte_P

  • Guest
Re: Why aren't zoom lenses faster than 2.8?
« Reply #61 on: April 18, 2013, 06:27:23 AM »
they are.. from now on.  ;)

infared

  • 1D Mark IV
  • ******
  • Posts: 792
  • Kodak Brownie!
    • View Profile
5D Mark III, Canon 15mm f/2.8 Fisheye, Canon 17mm f/4L TS-E, Canon 16-35mm f/4L IS, 21mm f/2.8 Zeiss, Sigma 35mm f/1.4, 24-70mm f/2.8 II, 50mm f/1.4 Sigma, 85mm f/1.2L, 100mm f/2.8L Macro,70-200mm f/2.8L IS II...1.4x converter III, and some other stuff.....

woollybear

  • Guest
Re: Why aren't zoom lenses faster than 2.8?
« Reply #63 on: April 18, 2013, 06:45:33 AM »
It is quite easy actually. If you want to know what size it would require just divide the focal length with the required f-stop and you'll see what size the front element diameter would be. So, for a 100-400mm f/1.2 the front element would be 33,3cm in diameter.  :D

If you divide the focal length with the diameter of the front element you'll get the maximum f-stop for that lens.

33,3 cm...wow!!! 

Malte_P

  • Guest
Re: Why aren't zoom lenses faster than 2.8?
« Reply #64 on: April 18, 2013, 07:30:30 AM »
It is quite easy actually. If you want to know what size it would require just divide the focal length with the required f-stop and you'll see what size the front element diameter would be. So, for a 100-400mm f/1.2 the front element would be 33,3cm in diameter.  :D

If you divide the focal length with the diameter of the front element you'll get the maximum f-stop for that lens.

33,3 cm...wow!!!

i don´t quite get the math....  8)

can you show how f1.2 gives 33,33 cm on a 100-400mm lens?

it´s more like 83mm for the 100mm end.

by the way:

Quote
The number for lens f/stop in photography (for example, f/8) is the ratio of lens focal length divided by the effective lens aperture. Aperture is not the obvious physical diameter, but instead is the apparent "working" diameter as seen through the magnification of the front lens element.
« Last Edit: April 18, 2013, 07:43:23 AM by Malte_P »

danski0224

  • 6D
  • *****
  • Posts: 510
    • View Profile
    • Some of my Work in Progress
Some of my Work in Progress..... www.dftimages.com

rs

  • 6D
  • *****
  • Posts: 579
    • View Profile
Re: Why aren't zoom lenses faster than 2.8?
« Reply #66 on: April 18, 2013, 08:13:08 AM »
There are now:
http://www.dpreview.com/news/2013/04/18/Sigma-announces-worlds-first-F1-8-constant-aperture-zoom-lens

Equivalent of f2.7 FF on a Nikon 1.5x crop, or f2.9 FF on a Canon 1.6x crop. So on Nikon it is faster than an equivalent of f2.8 FF, but not by much. I'd still prefer a Canon 24-70 II on FF, even if it is 'only' f2.8
5D II | 24-70 II | 70-200 II | 100L | 40 | Sigma 50/1.4 | 40D | 10-22 | 17-55 | 580 EX II | 1.4x TC II

canon rumors FORUM

Re: Why aren't zoom lenses faster than 2.8?
« Reply #66 on: April 18, 2013, 08:13:08 AM »

neuroanatomist

  • CR GEEK
  • ********
  • Posts: 13539
    • View Profile
Re: Why aren't zoom lenses faster than 2.8?
« Reply #67 on: April 18, 2013, 08:20:38 AM »
It is quite easy actually. If you want to know what size it would require just divide the focal length with the required f-stop and you'll see what size the front element diameter would be. So, for a 100-400mm f/1.2 the front element would be 33,3cm in diameter.  :D

If you divide the focal length with the diameter of the front element you'll get the maximum f-stop for that lens.


33,3 cm...wow!!!


i don´t quite get the math....  8)

can you show how f1.2 gives 33,33 cm on a 100-400mm lens?

it´s more like 83mm for the 100mm end.


A 100-400mm f/1.2 lens (which will never exist) would need to have a 333.3 mm (13") front element - a practical impossibility.  Your comment about needing an 83mm front element for the 100mm end isn't relevant - the front element can't change size so the optics must be sized for the long end.  That's why the 100-400mm lens is a variable aperture zoom with an f/5.6 long end - if it was f/4.5 throught the zoom range, it would need an 89mm front element.

by the way:

Quote
The number for lens f/stop in photography (for example, f/8) is the ratio of lens focal length divided by the effective lens aperture. Aperture is not the obvious physical diameter, but instead is the apparent "working" diameter as seen through the magnification of the front lens element.



While the above is true, it actually depends on the design of the lens (Roger Cicala has an article on lens designs that's worth a read).  With a telephoto design, the 'apparent working diameter' or 'virtual aperture' of the lens actually sits right at or just behind the front element.

Put another way, the front element generally needs to be at least as large as (focal length ÷ f/number), and with many lens designs the front element is significantly larger than that. 
EOS 1D X, EOS M, and lots of lenses
______________________________
Flickr | TDP Profile/Gear List

Malte_P

  • Guest
Re: Why aren't zoom lenses faster than 2.8?
« Reply #68 on: April 18, 2013, 08:23:57 AM »
Quote
A 100-400mm f/1.2 lens (which will never exist) would need to have a 333.3 mm (13") front element - a practical impossibility.  Your comment about needing an 83mm front element for the 100mm end isn't relevant - the front element can't change size so the optics must be sized for the long end.  That's why the 100-400mm lens is a variable aperture zoom with an f/5.6 long end - if it was f/4.5 throught the zoom range, it would need an 89mm front element.

so what he meant is a CONSTANT aperture 100-400mm f1.2?

yeah sorry,  then i was stuck to much in reality...  ;)

CamKrist

  • SX50 HS
  • **
  • Posts: 1
    • View Profile
Re: Why aren't zoom lenses faster than 2.8?
« Reply #69 on: April 18, 2013, 10:35:14 AM »
I sent you in pm

RGF

  • 1D X
  • *******
  • Posts: 1231
  • How you relate to the issue, is the issue.
    • View Profile
Re: Why aren't zoom lenses faster than 2.8?
« Reply #70 on: April 18, 2013, 02:06:44 PM »
every time you add a stop, the size of the lens more than doubles - 70-200 F4 to 70-200 F2.8.  imagine the size of 70-200 F2.0, it would weigh 5-6 pounds.  And since L lenses cost more than $1000/lb, this monster would be close to $10,000 (USD). Still interested?  I am not.

dolina

  • 1D Mark IV
  • ******
  • Posts: 969
    • View Profile
Re: Why aren't zoom lenses faster than 2.8?
« Reply #71 on: April 18, 2013, 02:29:35 PM »
Weight, technology, materials and price.

The trend today have bodies increasing ISO so the need for faster glass lessens.
Visit my Flickr, Facebook & 500px and see my photos. :)

jrista

  • Canon EF 300mm f/2.8L IS II
  • *******
  • Posts: 3733
  • POTATO
    • View Profile
    • Nature Photography
Re: Why aren't zoom lenses faster than 2.8?
« Reply #72 on: April 18, 2013, 02:53:19 PM »
Weight, technology, materials and price.

The trend today have bodies increasing ISO so the need for faster glass lessens.

The need is not always for "faster". Sometimes the need is for thinner DOF, which you can only get with a wider aperture.

The fact is, it IS more difficult to develop high quality lenses that perform well at apertures wider than f/2.8. The wider you go, the harder it is to control optical aberrations...and controlling them means more glass, glass with more precise characteristics, and often higher grade materials (high end optical glass, aspheric elements, fluorite or DO elements, etc.) Throw in "zoom", and those issues become even harder to control, as you have to control them such that they balance out at all of the key focal lengths along the zoom range.

I don't think there really is a trend towards lenses with slower apertures. I think f/3.5-5.6 and f/4.5-5.6 lenses, and even at times f/5.6-6.3 lenses, have been used in consumer-grade lenses for decades, by both brand names as well as off-brands. I don't think there are generally more of them now that we have cleaner higher ISO than there was before. I think they just become a little more relevant now that we have clean higher ISO...they are more useful in a broader range of use cases than they were before.
My Photography
Current Gear: Canon 7D | Canon EF 600mm f/4 L IS II | EF 100-400mm f/4.5-5.6 L IS | EF 16-35mm f/2.8 L | EF 100mm f/2.8 Macro | 50mm f/1.4
New Gear List: Canon 5D III/7D II | Canon EF 300mm f/2.8 L II

canon rumors FORUM

Re: Why aren't zoom lenses faster than 2.8?
« Reply #72 on: April 18, 2013, 02:53:19 PM »

noisejammer

  • EOS M2
  • ****
  • Posts: 157
    • View Profile
Re: Why aren't zoom lenses faster than 2.8?
« Reply #73 on: April 18, 2013, 03:19:26 PM »
To get an idea on the weight - I'll make a wild assumption and say we scale the optical formula. This doesn't really work in practice... whatever :D

Say you go from f/2.8 to f/2. Achieving this means the aperture has to increase by 41.4%. Keeping the same slope on the glass means the glass means the thickness increases by 41.4% too. The result is that the weight of the glass must increase by 1.414^3 = 2.83x.

The structure that supports each lens has to be stiffer, and since it's going to be bigger, the mechanical bits get a lot heavier.

but that's not all....
Optical glass increases in price at roughly the fourth power of the aperture. This means the cost of glass has increased by 4x. Similarly, faster lenses demand tighter tolerances so the manufacturing costs increase. Say this quadruples too.

Suddenly a 70-200 weighs at least 10 lbs and material / manufacture costs $8000.

The price is very high, so the market size is now about 1/100 of the market size for the f/2.8 model. Amortise the development cost makes the lens even more expensive... say $10k.

If you think the numbers are wild, take a look at the Sigma 200-500 / 2.8. $26k and 35 lbs. Compare this with the 120-400/4.5-6. 10x as heavy and 26x more expensive.


TW

  • PowerShot G1 X II
  • ***
  • Posts: 55
    • View Profile
Re: Why aren't zoom lenses faster than 2.8?
« Reply #74 on: April 18, 2013, 04:09:22 PM »
Well, as of today, they are! Way to go Sigma. Again!
35+ years of Canon gear...good grief! Still have 2 FTb cameras in working order, too!

canon rumors FORUM

Re: Why aren't zoom lenses faster than 2.8?
« Reply #74 on: April 18, 2013, 04:09:22 PM »