Before the rush

Before the rush
by evan-pak

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I can understand that a zoom below f/2.8 would be difficult and costly, but it seems like something pros would kill for. Surely it can't be more expensive (if its possible) than some of the $10k+ lenses and they exist to sell in limited quantities. Is it just near impossible or is there another reason we don't see zoom lenses below f/2.8?

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Olympus makes an f/2.0 zoom for Four Thirds, although arguably the smaller sensor format means an f/4 lens is a more apt comparison on full-frame. – mattdm Apr 2 '12 at 15:49
Weight and cost are the biggest reasons. – nwcs Apr 2 '12 at 16:41
I have to suspect that the number of element & groups plays a part, as well -- inasmuch as each of these elements contributes to the amount of light the lens can transmit, at some level, the increased count typically seen in zooms would seem to be a factor. – D. Lambert Apr 2 '12 at 16:44
Sigma now makes a full frame 24-35mm f2.0 zoom lens!… – Goldorak84 Nov 19 '15 at 14:10
up vote 38 down vote accepted

Angenieux (for one) makes some f/2 zooms. They're used primarily for movie making. The Optimo 17-80, for example, is an f/2 (T2.2) lens, covering, obviously enough, the 17-80mm range.

As for why these aren't common, consider that this particular lens weighs 11 pounds and costs about $50,000US.

Going even more extreme would be the Optimo 24-290, which is f/2.5 (T2.8), and constant aperture across that entire range. It weighs 24 pounds, and though I don't know a price on this one, I think: "more than most houses I've lived in" would be a safe guess.

Yes, you undoubtedly could build an f/2 zoom that was smaller, lighter, and less expensive, especially if you restricted it to APS-C. Nonetheless, this may give some idea of the direction really fast zooms would go. Yes, they can be considerably more than expensive than $10K, and they can be unreasonably large and heavy as well.

Edit: As for why this is from an optical viewpoint, it largely comes down to correcting aberrations. Just for example, for any particular design spherical aberration grows approximately quadratically with aperture.

Along with that, you run into size and weight problems: to get one stop faster, you multiply the diameter by ~1.4. That doubles the area, which multiplies the volume of each element by 2.8. With each element weighing about three times as much, the mechanical parts to mount those elements end up bigger and heavier as well.

So, let's consider one of the most popular fast zoom categories: the 70-200 f/2.8. Most current ones way about 3 pounds. Based on simple geometry, scaling up to f/2 should increase the weight to about 9 pounds. At 3 pounds, you're right at the border between hand holding and really wishing for a monopod. At 9 pounds, most people pretty nearly need a tripod for any more than one or two shots at a time.

Along with that, 9 pound lenses just don't sell in large quantities. Reasonably dedicated photographers buy a lot of 3 pound lenses (including the aforementioned 70-200/2.8). When you get to the 5-6 pound lenses like a 300/2.8, the quantity has already dropped a lot -- only a few of the most dedicated will even consider them. Going up a step from there (e.g., to a 400/2.8) the number drops precipitously.

Let me try to put that drop into perspective. When I go to one of my kids' sporting events, chances are pretty good at least three or four of the parents will have a 70-200/2.8, or something around the same size/weight (and at a larger event, I might easily see a dozen).

For 300/2.8, that drops a lot. On any given weekend at my local photo-friendly wildlife refuge, I might or might not see one. During mating season (for example) seeing two or three wouldn't be all that unusual.

In twenty years of shooting, I could probably just about count on my fingers the total number of times I've seen people out shooting a 400/2.8, 500/4, 600/4, etc.

Based just on size and weight, a 70-200 f/2 would be pretty much in that last category -- so rare it would hardly be used even if somebody put it in their catalog.

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Is that cinema lens in f-stops or t-stops? Cinema lenses are often rated for transmission rather than maximum aperture, and quite often a t-stop of 2 requires a wider f-stop, so that lens might actually be f/1.8 or wider. It should also be noted that many of the really expensive cinema lenses have CONSTANT apertures throughout their very wide zoom ranges. – jrista Apr 2 '12 at 17:39
@jrista: It's f/2, T/2.2, and yes, it's constant aperture. – Jerry Coffin Apr 2 '12 at 17:44
But why? I think that's the question - why must a zoom lens be so much bigger, heavier and expensive than a fixed focal length lens? Something to do with the number of elements, transmission of light? Or that at that price you don't want to compromise on IQ? – MikeW Apr 2 '12 at 18:08
A bit of googling shows a Optimo 24-290 going for around $60k. (…) It wasn't clear to me if this was new or used. – Paul Cezanne Apr 2 '12 at 18:15
@DanNeely: I've yet to see such a thing at a star party. Refractors are pretty rare to start with, and those I do see are mostly the usual suspects: Celestron, Meade, Orion, Vixen, Televue, one home-built job, etc., not anything like a Nikon or Canon with (for example) a controllable aperture. – Jerry Coffin Apr 2 '12 at 19:36

Olympus makes f2 zooms.

I disagree with another poster who said this was like f4 because of the smaller sensor size.

Sure, the size of the sensor has an impact on ultimate image quality, particularly with depth-of-field effects, but you still get to shoot an f2 in lighting that would be impossible with an f4.

I don't see any postings sneering at the cited cine f2 lenses, although they surely have a smaller "sensor" than 35mm full-frame, as well!

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I'm not sneering. For DoF, see this. For low-light: The twice-the-area full-frame sensor format theoretically allows twice the light to be gathered overall, and I think it's generally safe to say that full-frame cameras have a one-stop noise advantage over four-thirds — same as f/2 to f/4. Note the crop-factor correspondence of the focal length the Olympus lens I linked, too: it's a 35-100mm, giving a field of view roughly like the traditional 70-200mm. – mattdm Apr 5 '12 at 21:17
I can see that full-frame confers a noise advantage, but I think you missed my point that it confers no shutter-speed advantage. – Jan Steinman Apr 19 '12 at 18:39
Same thing — if you can go up a stop in ISO for the same image quality, you can use a faster shutter. – mattdm Apr 19 '12 at 19:09
In this context we have to treat m43 f/2 as FF f/2 equivalent - the question was about the f/2 zoom feasibility, and yes, if the Olympus zoom is scaled 2x we would get the f/2 FF zoom (having 4x more aperture area and 8x the weight) – szulat Jun 16 '15 at 9:44
The size of the entrance pupil, which defines the minimum diameter of the front element also does not change with sensor/image circle size. But the focal length needed to get the same field of view does change. If you only need 1/2 the focal length, then for the same f-number you only need half the diameter and 1/8 the weight. – Michael Clark Jan 8 at 5:18

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