Why are Canon compact zooms faster than EF zooms?

Pascal Parvex · Jun 14, 2006

I'm new to the SLR world, the EOS 5D is my first SLR. I have been wondering, why Canon can manufacture faster compact zooms than EF zooms. For example, the classic PowerShot G2 features a fast f/2.0 to f/2.5 three times zoom, whereas even the most expensive EF L glas never gets under f/2.8. I suppose this can only mean that compact 2.8 is not the same as EF 2.8 aperture.

steve1984 · Jun 14, 2006

Someone here can probably give you a more scientific answer but it's basically because it's a lot easier (and much, much cheaper) to build a small lens for a small sensor than a large lens (with the same aperture) for a larger sensor.

Pascal Parvex said:
I'm new to the SLR world, the EOS 5D is my first SLR. I have been
wondering, why Canon can manufacture faster compact zooms than EF
zooms. For example, the classic PowerShot G2 features a fast f/2.0
to f/2.5 three times zoom, whereas even the most expensive EF L
glas never gets under f/2.8. I suppose this can only mean that
compact 2.8 is not the same as EF 2.8 aperture.

NoName130552 · Jun 14, 2006

But it should be remembered that the DOF on a digicam at f/2.8 is much bigger than the DOF on a 5D at f/2.8.

PalmsWestPhoto · Jun 14, 2006

the difference is the actual focal length

compact cameras have a sensor that is much smaller which means the lens's actual focal length is a lot shorter

campact cam lenses are in the neighborhood of something like 5mm on the wide end and between 30 and 100mm on the long end.

That means the physical size of the lens even though it is also f2.8 is a lot smaller

--
Michael Salzlechner
http://www.PalmsWestPhoto.com

PalmsWestPhoto · Jun 14, 2006

just to add you can calculate the size of the front element by dividing the actual focal length by the aperture

for example 300 / 2.8 = 107

means for a 300mm lens at F2.8 you need a front element of 107mm. The lens will also be about 300mm long

if as mentioned with compact cams you use a smaller sensor say a fourth in order to build a lens that covers the same FOV you would only need a 75mm F2.8 lens which would only need a 27mm front element and only be 75mm long

--
Michael Salzlechner
http://www.PalmsWestPhoto.com

Lemming51 · Jun 14, 2006

The G2 lens is 7mm-21mm f/2-2.5.

The fact that SLR lenses have to be mounted a fair distance from the sensor/film plane is a significant optical design problem that limits maximum aperture.

Pascal Parvex said:
I'm new to the SLR world, the EOS 5D is my first SLR. I have been
wondering, why Canon can manufacture faster compact zooms than EF
zooms. For example, the classic PowerShot G2 features a fast f/2.0
to f/2.5 three times zoom, whereas even the most expensive EF L
glas never gets under f/2.8. I suppose this can only mean that
compact 2.8 is not the same as EF 2.8 aperture.

avidday · Jun 14, 2006

PalmsWestPhoto said:
just to add you can calculate the size of the front element by
dividing the actual focal length by the aperture

Not really. The aperture formula you are abusing relates the focal length to the entrance pupil diameter. The entrance pupil diameter almost never the front element diameter. It is normally the maximum diaphragm diameter, or in some the cases the minimum diameter of the lens before the diaphragm.

Pascal Parvex · Jun 15, 2006

So, would it be possible then to see something like a EF-S 24-105 f/2.0L in the future?

avidday · Jun 15, 2006

EF-S has basically nothing to do with it. A 105mm f/2.0 lens is always a 105mm f/2.0 lens, irrespective of what size image circle it is designed to project. An EF-S lens can have a smaller internal diameter behind the diaphragm, which can make it a bit smaller and lighter, but fundamentally nothing changes with respect to the size of the entry pupil of the lens, and what that means for the size and complexity of the front objectives of the lens.

Lemming51 · Jun 15, 2006

Pascal Parvex said:
So, would it be possible then to see something like a EF-S 24-105
f/2.0L in the future?

Olympus has exploited their even smaller 4/3 system (with much shorter back-focus than EF-S) and created a 35-100 f/2 zoom. It is unlikely that Canon (or Nikon/Pentax/Sony) will be able to do an f/2 zoom for the significantly larger APS-C DSLRs.

Lemming51 · Jun 15, 2006

Especially considering that the Oly 35-100 f/2 is larger, heavier, and 2x as expensive than EF 70-200 f/2.8L USM.

Lemming51 said:
Pascal Parvex said:

So, would it be possible then to see something like a EF-S 24-105
f/2.0L in the future?

Click to expand...

Lemming51 said:
Olympus has exploited their even smaller 4/3 system (with much
shorter back-focus than EF-S) and created a 35-100 f/2 zoom. It is
unlikely that Canon (or Nikon/Pentax/Sony) will be able to do an
f/2 zoom for the significantly larger APS-C DSLRs.

nickleback · Jun 15, 2006

avidday said:
PalmsWestPhoto said:

just to add you can calculate the size of the front element by
dividing the actual focal length by the aperture

Click to expand...

Not really. The aperture formula you are abusing relates the focal
length to the entrance pupil diameter. The entrance pupil diameter
almost never the front element diameter.

The front element can be larger than the entrance pupil, but it cannot be smaller.

--
Seen in a fortune cookie:
Fear is the darkroom where negatives are developed

Robert 55 · Jun 15, 2006

nickleback said:
--
Seen in a fortune cookie:
Fear is the darkroom where negatives are developed

JJMacks · Jun 15, 2006

Lets look at Canon Lens lineup note the weight of the fast lens to me it seems to make a lens faster you need to increase the size of the Glass to gather more light. Then answer my questions.
Canon EF 50mm F1.0 2.2 Lbs
Canon EF 85mm F1.2 2.3 Lbs
Canon EF 85mm F1.2 2.25 Lbs
Canon EF 24mm F1.4 1.21 Lbs
Canon EF 35mm F1.4 1.28 Lbs
Canon EF 200mm F1.8 6.6 Lbs
Canon EF 135mm F2.0 1.64 Lbs

If a Canon 200mm F1.8 is 6.6 lbs what would the weight of the following lens be if they would be made larger to increase their speed to f2.0?
Canon EF 300mm F2.8 6.0 Lbs
Canon EF 400mm F2.8 11.7 Lbs
Canon EF 1200mm F5.6 36.3 Lbs
Canon EF 28-300mm F3.5-5.6 3.7 Lbs
Would you carry one?

--
JJMack

avidday · Jun 15, 2006

That was kind of my point...

carlk · Jun 15, 2006

Just note it actually letting in less amount of light than 70-200/2.8.

Lemming51 said:
Lemming51 said:

Pascal Parvex said:

So, would it be possible then to see something like a EF-S 24-105
f/2.0L in the future?

Click to expand...

Click to expand...

Lemming51 said:

Olympus has exploited their even smaller 4/3 system (with much
shorter back-focus than EF-S) and created a 35-100 f/2 zoom. It is
unlikely that Canon (or Nikon/Pentax/Sony) will be able to do an
f/2 zoom for the significantly larger APS-C DSLRs.

Click to expand...

dr_mat · Jun 15, 2006

There's no reason why they couldn't make such lenses for SLRs. They do make lenses with some silly apertures. The largest one seems to be the legendary 1200/f5.6 lens with it's 214mm aperture...

But as has been pointed out, there's likely a huge cost and weight penalty. That 1200/5.6 weighs 12kg and costs about as much as a small continent...

JJMacks said:
Canon EF 300mm F2.8 6.0 Lbs
Canon EF 400mm F2.8 11.7 Lbs
Canon EF 1200mm F5.6 36.3 Lbs
Canon EF 28-300mm F3.5-5.6 3.7 Lbs

...

--
Why is the universe filled with shiny things I want to buy?

keithallenlaw · Jun 15, 2006

Compacts come no where near the spead of primes. I have a 50 f/1.4.
I think theres even a Canon 50 f/1.0. Am I missing something here?

--
don't surround yourself with yourself...
move on back two squares

Come visit me at:
http://www.pbase.com/keithallenlaw
See my profile for what i shoot with.

misha · Jun 15, 2006

keithallenlaw said:
Compacts come no where near the spead of primes. I have a 50 f/1.4.
I think theres even a Canon 50 f/1.0. Am I missing something here?

Yes -- the question was about zoom lenses.
--
Misha

nickleback · Jun 15, 2006

dr_mat said:
There's no reason why they couldn't make such lenses for SLRs.

Sure there is. Geometry of the EOS mount doesn't allow 300mm f/2, unless you like massive vignetting. Quick guess would be around f/2.2 max for 300mm.

dr_mat said:
But as has been pointed out, there's likely a huge cost and weight
penalty. That 1200/5.6 weighs 12kg and costs about as much as a
small continent...

A 1200/2 lens cover could do double duty as a trash can lid.

--
Seen in a fortune cookie:
Fear is the darkroom where negatives are developed

Why are Canon compact zooms faster than EF zooms?

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