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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 12 Jan 2011 (Wednesday) 18:19
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"normal" lenses usually have the widests apertures, right?

 
krb
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Jan 12, 2011 18:19 |  #1

I'm not generally one for starting "what if..." or "why not..." type threads but I've been wondering about this and cannot find an answer.

Whatever the platform, a lens that is normal is usually the fastest available such as the f/1.0 and f/0.95 lenses that have been made for 35mm. Does it follow then that an EF-S (or DX if you will) 30mm f/1.0 is an equally realistic possibility? Obviously there are economic and marketing issues that are likely to prevent it from ever happening, just like the ultra-fast 50s are not in current production, but on the engineering front is there any reason it couldn't be done?


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wunhang
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Jan 12, 2011 18:23 |  #2

The widest apertures are on the wider lenses for one simple reason... size. The front element on lenses get real big REAL fast the longer the lens gets.

Edit:
Sorry, accidentally posted before finishing.

So the EF-S would lend itself to being faster but then you run into issues on depth of field for faster lenses as many on this forum can attest to on the 85L and 50L


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KCMO ­ Al
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Jan 12, 2011 18:25 |  #3

Generally, yes. It is possible to make single FL lenses with wider apertures due to the ability to make them within size/weight tolerances. Lenses with apertures of f/1.0 or lower generally require very large elements at the front. If you've ever seen the Canon rangefinder 50mm f/0.95 lens it has a huge front element that actually partially blocks the rangefinder.
Attempting to build zoom lens with an aperture larger than about f/2.8 would produce a very large, heavy lens.
The lenses produced today, imo, are about optimal. Therefore, 24/35 f/1.4, 50 f/1.0, f/1.2, 85 f/1.2 are probably on the theoretical edge of the price/weight continuum.


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wunhang
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Jan 12, 2011 18:29 |  #4

krb wrote in post #11627444 (external link)
....but on the engineering front is there any reason it couldn't be done?

None whatsoever. The big issue is who is willing to pay and how many friends does that guy have?


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gasrocks
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Jan 12, 2011 18:40 |  #5

The longer the lens, the bigger the front element has to be to be, say, f/1.2. So shorter is easier - however, getting good quality all the way across the frame is a big issue with WA lenses. Normal seems to be the best compromise.


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Jan 12, 2011 20:19 |  #6

KCMO Al wrote in post #11627478 (external link)
The lenses produced today, imo, are about optimal. Therefore, 24/35 f/1.4, 50 f/1.0, f/1.2, 85 f/1.2 are probably on the theoretical edge of the price/weight continuum.

Is this a factor of the space/time continuum? Lokks like it to me. ;)


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The ­ Ran
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Jan 12, 2011 20:53 |  #7

So far the Canon 1200mm f/5.6 has the largest physical aperture (equivalent to a 50mm f/0.2), and the Canon 50mm f/1.0 is the fastest lens. So, buy a 1200mm, pull out a few elements, make a custom lens barrel, and then you have a lens over twice as fast as the commercially available one :lol: .


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krb
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Jan 12, 2011 21:05 |  #8

wunhang wrote in post #11627471 (external link)
The widest apertures are on the wider lenses for one simple reason... size.

A simple answer that is simply wrong. Between the retrofocal designs and the need to create a wide angle that doesn't have monster vignetting, wider lenses are generally slower than normal or telephoto desings.

So the EF-S would lend itself to being faster but then you run into issues on depth of field for faster lenses as many on this forum can attest to on the 85L and 50L

If you'd bothered to check the numbers you'd know that 30mm f/1.0 on crop has the same DOF as a 50mm 1.8 on full frame if focus distance is kept the same.


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wunhang
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Jan 12, 2011 21:09 |  #9

I stand corrected, sir.


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krb
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Jan 12, 2011 21:16 |  #10

KCMO Al wrote in post #11627478 (external link)
Generally, yes. It is possible to make single FL lenses with wider apertures due to the ability to make them within size/weight tolerances. Lenses with apertures of f/1.0 or lower generally require very large elements at the front. If you've ever seen the Canon rangefinder 50mm f/0.95 lens it has a huge front element that actually partially blocks the rangefinder.
Attempting to build zoom lens with an aperture larger than about f/2.8 would produce a very large, heavy lens.

I realize you are trying to be helpful, but did you read my question? I made no reference to primes nor to zooms. You are answering questions that were not asked and are so basic that even if I didn't already know what you've typed then I would have been able to easily find the info on my own since it is so well covered on numerous web sites and comes up in one form or another at least once a week on these forums.


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RDKirk
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Jan 12, 2011 21:18 as a reply to  @ wunhang's post |  #11

A simple answer that is simply wrong. Between the retrofocal designs and the need to create a wide angle that doesn't have monster vignetting, wider lenses are generally slower than normal or telephoto desings.

To emphasize that point: The "normal" lens for a format (approximately the length of the format diagonal) is usually of the simplest optical design. In fact, the design of the 50mm f/1.8 has been virtually unchanged for over half a century--they had achieved f/2 with that design before WWII.

Getting much farther from the "normal" focal length, designers have to use special design tricks to gain image quality and any speed at all, keep lenses to a managable size and price, plus work around design constraints like the depth of the mirror box on an SLR. That's when you get into "retrofocus" designs for wide-angle lenses and "telephoto" designs for long lenses.

It's possible to make a very fast non-retrofocus wide angle lens, but it would have to extend deeply into the mirror box and the mirror would have to be locked up. It's possible to make a very fast non-telephoto "long lens," but it would be extremely heavy and physically quite long.


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"normal" lenses usually have the widests apertures, right?
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