Are the limits on lens aperture, image stabilization, and ultra-wide focal lengths physical or just practical?
Asked 9/22/2016
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I’m trying to understand whether some apparent lens limits are due to physics or mainly due to cost and current engineering.
For example:
- I read that the Canon 35mm f/2 IS is the fastest lens with image stabilization. Is stabilization at wider apertures impossible, or just harder and more expensive?
- Telephoto lenses often seem to be f/2.8 or slower. Are faster telephoto lenses physically impossible, or just uncommon because they become very large and expensive?
- For wide-angle lenses, how close can a non-fisheye (rectilinear) design get to 180°? Is there a hard limit on making lenses wider than 11mm without becoming fisheye?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
7
There are several questions mashed up here, most of them based on false assumptions.
Rectilinear lenses and fisheye lenses are different and they can have focal-lengths that overlap. As in, there is an 11mm rectilinear but a 15mm fisheye. One does not simply switch below a certain focal. A rectilinear lens has a practical limit though since one cannot have it project 180 degrees, how close it can get to 180 is a matter of cost and design. One on the other hand fisheye lenses can view up 220 degrees wide at least.
A quick search on my site shows there are currently 31 telephoto lenses with F/2 maximum aperture. So telephoto lenses can have brighter than F/2.8 aperture. Remember that the aperture is a ratio of focal-length, so the longer the lens, the wider it has to be for having the same aperture. This makes brighter aperture telephoto lenses more bulky, so if you look at 200mm with F/2 aperture, there are only 3 and they all weigh at least 2.5kg (5 lbs).
Regarding stabilization, there are 17 stabilized lenses with F/1.2 to F/2 maximum aperture, so it is possible even for F/1.2 lenses to be stabilized. It is not a technology limit but an issue of lesser need. The brighter the lens, the more light it lets in, so stabilization becomes less important.
Originally by user1620. Source · Licensed CC BY-SA 4.0
user1620
9y ago
0
Generated from our catalog & community — verify before relying on it.
These are mostly practical design limits, not absolute physical impossibilities.
Aperture is a ratio: f-number = focal length / entrance pupil diameter. So for the same f-number, longer lenses need a much larger front opening. That makes very fast telephotos possible, but bigger, heavier, and more expensive. They do exist; f/2 telephoto lenses are available.
Image stabilization is also not fundamentally blocked by a wide aperture. Stabilization and maximum aperture are separate design challenges, and combining both can add size, complexity, and cost.
For ultra-wide lenses, fisheye and rectilinear are different projections, not steps on a single scale. Their focal lengths can overlap. A fisheye can be longer than a rectilinear lens and still look much wider because it bends straight lines.
A rectilinear lens has a practical limit because it cannot show a full 180° field of view while keeping straight lines straight. It can approach 180°, but doing so becomes increasingly difficult and expensive. Fisheye designs can exceed that and reach around 220° in some cases.
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