Why is it impossible to make a really fast zoom?

[hdco1209]

There must be some technical impossibility to making, say, an f1.4 zoom, or even 1.8. It can't be about money, because you know that if Canon made a f1.4 28-70L and charged 6K for it a lot of people on this forum would line up.

Just curious.

[crn3371]

Size and weight. (And cost)

[cjm]

Have you ever seen a Canon F2.8 300mm prime? It is massive. That is a f2.8 probably double it in size for a 70-200 f1.4 L zoom. Then at a cost of $10,000+ who is buying it?

It can't be done unless Canon wishes to go broke.

[angryhampster]

Sigma's 200-500 f/2.8 is ungodly huge. I don't think anyone actually wants anything that big to carry around.

[CoolToolGuy]

Olympus has at least 2 f/2.0 zoom lenses for the Four Thirds format. The sensor size is smaller, so the lens has a smaller circle of confusion, which may reduce development and manufacturing costs. I'm hoping that spurs Canon on to make at least one f/2.0 zoom - in EF-S, perhaps?

Have Fun,

[Control Group]

Because the f-stop is the ratio of the lens' focal length to the width of the aperture. For an f-stop of 2.8 on a 100mm lens, you need an aperture of 35mm. At 200mm, it's 70mm, and so forth.

Drop that to a really fast f-stop, like 1.4, and you're at a 70mm aperture for the 100mm lens. The lenses just become giant blobs of glass, with all the potential for aberration involved with giant lens sizes.

It's not that there's a strict reason that it can't be done, it's just that it's a more successful compromise to have the slower lens in the more manageable size.

[KevC]

It's not impossible. There are no physical boundaries to bend or break to make a wide aperture zoom. It's just not feasible. Why do it? Canon is a business. Their sole purpose is to make money. So much R&D funds and time would be poured into designing and making an f/2 zoom, there would be no market for something that large and cumbersome. It probably wont be so sharp either.

[hdco1209]

Some of these seem like very good arguments, particularly the one about dividing the specular opening by the radius of the third element etc etc etc.

And those points are probably being made by engineers or others with a lot more experience than I have in designing lenses for Canon (which consists solely of this thread).

I STILL think that, all of your good arguments notwithstanding, if someone were to come up with a zoom lens along the following specs, there would be some takers:

THE CONTROL LENS (now available):
EF 24-70 f2.8L
Weight: 2.1 lbs
Length: 4.9"
Max Diam: 3.3"
Price: $1139.00 (B&H)

THE NEW 1.4L MONSTER:
EF 24-70 1.4L
Weight: 5.5 lbs
Length: 6.5"
Max Diam: 5.5"
Speculative price: $6000

Wouldn't there be some wedding photographers who would want it? Or journalists assigned to cover senate hearings with no flash? I'm perfectly happy with my 17-85 IS (OK...somewhat happy, until I get the 17-55 2.8 and a 24 1.4L).

[Crashoran]

spending $6000 on a 24-70 wont justify the kind of work anybody does.

[kevinsyn]

Some of these seem like very good arguments, particularly the one about dividing the specular opening by the radius of the third element etc etc etc.

And those points are probably being made by engineers or others with a lot more experience than I have in designing lenses for Canon (which consists solely of this thread).

I STILL think that, all of your good arguments notwithstanding, if someone were to come up with a zoom lens along the following specs, there would be some takers:

THE CONTROL LENS (now available):
EF 24-70 f2.8L
Weight: 2.1 lbs
Length: 4.9"
Max Diam: 3.3"
Price: $1139.00 (B&H)

THE NEW 1.4L MONSTER:
EF 24-70 1.4L
Weight: 5.5 lbs
Length: 6.5"
Max Diam: 5.5"
Speculative price: $6000

Wouldn't there be some wedding photographers who would want it? Or journalists assigned to cover senate hearings with no flash? I'm perfectly happy with my 17-85 IS (OK...somewhat happy, until I get the 17-55 2.8 and a 24 1.4L).

While we're add it throw IS on there :P Then i'd buy it.

[calicokat]

Monsterous Size

[echo]

I don't think it's really needed, if you need faster then a prime does the job?

[liza]

I don't think it's really needed, if you need faster then a prime does the job?

Pretty much. :)

[DC9]

Make it to be an EF 24-135mm f1.4L IS and then count me in (so long as it is $1500 usd)

[joshandlauri]

spending $6000 on a 24-70 wont justify the kind of work anybody does.


then again some of us spends thousands on 400/500/600 primes and all we have is an unpaid hobby, I'm sure someone would buy it after all it would be an L

[Double Negative]

Simple; cost, weight and size. Canon (and everyone else) knows they'll sell more f/4 lenses that are lighter and cheaper than f/1.8 that are more expensive and heavier (which are also more of a niche product). If you really need the speed, use a prime. Also, as mentioned - it gets harder and harder to maintain a good image the more glass is involved, requiring special elements such as aspherical, UD, flourite, etc. which further adds to the cost.

If you're will to pay for it and carry it around - it CAN be done. But the numbers just aren't there to entice anyone to make it for you.

[Tapeman]

If the marketing people at Canon thought it could be profitable they would have one.

If a person had the money they could have one custom built. Canon builds the 1200 5.6 for around $90K. Why not a fast zoom?

[manipula]

It can be done but isn't for the reasons mentioned. But for reference a gent who shoots extensively with a colleague works for the BBC here and showed me recently a lens they have for their TV cameras. 9-1100mm f/1.8. It takes two people to move it, and it ISN'T soft! I did, however, drool lots lol!