Why aren't ultrawides really fast

Jim_Tod

Jim_Tod

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Out of interest question mostly and hoping I can get some clarity.

I'm struggling to understand why ultrawide lenses don't come in really fast apertures naturally. I can understand the difficulties associated with a focal length being inside the camera body and getting the glass correct to achieve this but as the speed is simply the ratio of aperture size to focal length I'm not sure why putting a 14mm aperture on a 14mm lens or an 11mm aperture on an 11mm lens isn't quite simple. 20mm 1.4's are achievable at reasonable cost and that's a physical aperture of about 14mm wide open.

Can anyone help educate me in this matter.
 
Eh?

14mm aperture?

You can get fast ultrawides?
 
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Controlling chromatic aberrations would be a problem. The lens diameter would be large and the transmission of light from the sides to focus at the same point as light going through the centre would be difficult.
Matt
 
MatBin said:
Controlling chromatic aberrations would be a problem. The lens diameter would be large and the transmission of light from the sides to focus at the same point as light going through the centre would be difficult.
Matt
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Ok i think that makes sense for me- it's not so much about achieving the physical aperture and more about what you have to do to converge light - thanks
 
A lens's max aperture is not simply focal length divided by aperture diameter. It is actually focal length divided by the entrance pupil diameter, which is how wide the aperture appears when viewing the lens from the front. Fast teles have large front elements to magnify the aperture and create an entrance pupil that is actually wider than the true aperture diameter, however as the main purpose of an ultra wide is to shrink the image into a wide field of view, by their very nature this also shrinks the entrance leading to a relatively slow max aperture. Hope this helps.
 
Also ultra wides don't really have such a requirement to have large apertures, most of the time when shooting ultra wide you want everything in focus and because they are so wide then a slow shutter speed can be used with less risk of blurring the image from camera shake. Telephoto lenses are the opposite where you want a high shutter speed to freeze motion so wide apertures are desirable.
 
Jayst84 said:
20/1.4 = 14 (give or take)



Can you? They're few and far between. Especially if you want something good. Mainly because physics, as Matt says.
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It depends what you mean by really fast? There are plenty of f/2.8's but I suppose faster than that there aren't many options.

But then as already said, other than for Astro most people shoot UWAs stopped down anyway.
 
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Jim_Tod said:
Out of interest question mostly and hoping I can get some clarity.

I'm struggling to understand why ultrawide lenses don't come in really fast apertures naturally. I can understand the difficulties associated with a focal length being inside the camera body and getting the glass correct to achieve this but as the speed is simply the ratio of aperture size to focal length I'm not sure why putting a 14mm aperture on a 14mm lens or an 11mm aperture on an 11mm lens isn't quite simple. 20mm 1.4's are achievable at reasonable cost and that's a physical aperture of about 14mm wide open.

Can anyone help educate me in this matter.
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Fast wide-angles, like f/2 and f/1.4, are just hard to make. Many aspects of lens design are in direct conflict. Tricky areas are fast apertures, format coverage with good edge sharpness and minimal vignetting (full-frame is much harder than say M4/3 with one quarter the sensor area), extremes of focal length at either end of the range, zooms, size and weight, cost.

And fast aperture wide-angles are not in so much demand these days. Low f/numbers are less necessary with the high ISO performance of modern cameras, and it's hard to get shallow depth-of-field effects (even if you want them, and landscapers for example, usually don't) when DoF is naturally much deeper with wide-angles at normal shooting distances.
 
Brachytron said:
A lens's max aperture is not simply focal length divided by aperture diameter. It is actually focal length divided by the entrance pupil diameter, which is how wide the aperture appears when viewing the lens from the front. Fast teles have large front elements to magnify the aperture and create an entrance pupil that is actually wider than the true aperture diameter, however as the main purpose of an ultra wide is to shrink the image into a wide field of view, by their very nature this also shrinks the entrance leading to a relatively slow max aperture. Hope this helps.
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Had to do a bit of googling on entrance pupil but I I understand this now.

odd jim said:
But then as already said, other than for Astro most people shoot UWAs stopped down anyway.
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I was looking at these specifically in respect to getting into astro which is why I was thinking about the issue.

HoppyUK said:
Fast wide-angles, like f/2 and f/1.4, are just hard to make. Many aspects of lens design are in direct conflict.
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Thanks.

Thank you all- I feel a little more educated today than I was yesterday so (y)
 
Jim_Tod said:
Had to do a bit of googling on entrance pupil but I I understand this now.



I was looking at these specifically in respect to getting into astro which is why I was thinking about the issue.



Thanks.

Thank you all- I feel a little more educated today than I was yesterday so (y)
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If Astro is what you're looking to do, perhaps the 20mm f/1.4 Siggy would be the way to go, especially on FF?
 
odd jim said:
If Astro is what you're looking to do, perhaps the 20mm f/1.4 Siggy would be the way to go, especially on FF?[/QUOTE

Pressed the button on a Samyang 14mm to ease me in on the low cost approach
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Its a good lens :)
 
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