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Forum: General Photography
04-20-2018, 03:37 PM
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Not me, but I know photogs that might. As for dim light, here in my area some of the skate parks are under bridges to allow all-weather skating and even when its not raining, cloudy skies are pretty much the rule for about 7-8 months out of the year.
Steve
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Forum: General Photography
04-20-2018, 03:13 PM
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Yep...very true, though not fully appreciated unless one has such a lens in hand.
Those that shoot skate park would strongly disagree, though fast ISO may provide an out.
Steve
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Forum: General Photography
04-20-2018, 02:51 PM
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As noted above, there are design challenges that are particularly prominent with wide angle lenses. Those include vignette, geometric and volumetric distortion (assuming rectilinear projection), optical aberration (all types), flatness of field, and accommodation of the camera with which they are mated. I don't have any rectilinear ultra-wides, but I do have a small collection of 35mm, 28mm, and 24mm lenses as well as 15mm and 8mm fisheyes.* A few generalities may be helpful:- Physical size does not correlate with maximum aperture. My largest lens is also the slowest.
- Size of front lens element does not correlate with maximum aperture
- Focal length does not correlate with maximum aperture. The shortest is also one of the two slowest at f/3.5.
- Image circle does not correlate with maximum aperture
- Performance does not correlate with physical size, front element size, focal length, or image circle. None of my wide angles suck and all but one (a 28mm taking 67mm filters) offer very decent performance.
I take the variety on my shelf to be evidence that there is more than one way to meet design goals. I also take it to mean that compromise is a fact of life at the short end of things. Now about the practical aspects driving and influencing design decisions:- Almost all wide-angle lenses employ some degree of retro-telephoto (aka retro-focus) design. This comes with the price of complexity and erosion of performance along with difficulty supporting wider maximum aperture. This is even true for mirrorless camera lenses where symmetrical designs are practically non-existent at shorter than 35mm due to the lens center being well within the camera body.
- There is little incentive for designers to offer the fast/wide combination, even for crop-sensor. Consider:
- The use cases for fast and wide are limited to low magnification compositions having limited DOF. How many photos of a king and queen on a chess board with rooks either side and nothing sharp beyond one's own pawns does the world need? BTW...flatness of field counts double here.
- The common use cases involve a need for deep DOF, something that is difficult even at f/2.8 at 16mm. Why waste good glass making an f/1.7 lens when the shooting will be done at f/11 or f/16?
- Fine focus at 28mm (20mm on APS-C) and wider using manual technique is not easy even with live view or focus aides. Everything in the frame is simply too tiny to detect out-of-focus. It is even harder for AF to consistently perform when magnification is low and the sensor has a "baseline" tuned for f/2.8 and narrower. The machine needs something to work with. Anticipating the loud chorus of objection...no, ultra-wide does not provide infinite DOF, it just makes missed focus harder to see.** I have to work double hard with my fisheyes to get attain critical focus than with longer focal lengths.
- Ditto the preceding point
- There is a strong incentive to simplify design where possible to keep size/weight/costs down while maintaining adequate flatness of field, resistance to vignette, and sharpness across the frame. A wider maximum aperture works against all of those.
Reasons to not go slow at the wide end?
There is a strong case for giving manual and AF systems something to work with. Increased DOF, full open, cuts both ways. Simply put, f3.5 and f/4 are both unacceptably dim for many lighting conditions, particularly when the view is wide. There is a reason why most wide-angles are clustered around f/2.8. I own the highly-regarded S-M-C Takumar 28/3.5 and it is not a fun lens to use in other than bright light. There, I said it.
Summary...there may well be design constraints resulting in slower wide-angles, but if there is a design benefit, it is not being widely leveraged.
Steve
* I suppose I could extend the discussion to include my 90mm f/6.8 for 4x5" film, but I won't.
** The unlimited DOF discussion is a difficult one, particular since shooting the hyperfocal is both valid and useful. Some lens designs complicate the matter. My Rokinon 8/3.5 Fisheye is a prime example. DOF rules for the focal length apply (go figure), but focus throw is incredibly short and hard to work with. The rule of thumb for owners of that lens is to set the distance scale at 6' with aperture at f/8 and shoot at will...works like a charm :o OTOH, my Zenitar 16/2.8 Fisheye snaps focus easily and rewards efforts at proper focus.
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