[pentexas]

I just bought an M42 50mm F1.4 for my K-50 and really like it so far. For a few things it feels a little too close up to my subject, so I'm thinking about getting something like a 28mm.

However, looking at the various options out there, it seems like they mostly go to F4 or F3.5. Occasionally I see an F2, but nothing faster.

Why is it more common to see a lens as fast as F1.4 in a 50mm focal range but it seems like things slow down quite a bit when you move to a shorter focal length?

[dadipentak]

Physics. It's easy to make a fast fifty but harder for longer or shorter lenses.

[misomosi]

50 is normal focal length and it is relatively easy to do a f1.x aperture.

For longer focal lengths the problem is the size of the lens: think of a 300mm. If one would design a 300mm f2, the max aperture would be 300/2=150mm which is quite big. The front element would be even bigger.

For short focal lengths the problem is not weight obviously. Maybe there is a technical reason to it but I suspect it has more to do with the demand:
- wide angles are usually for landscape and in landscape you use f8 f11 f16 anyway on tripod using ND filters etc. - fast is not necessarily a problem
- it's hard to get shallow DOF with wide-angles anyway. f1.x could help but it's still easier with a ~50mm or anything around and above

[drypenn]

As dadipentak has mentioned, the natural laws of light and physics dictate that wider and faster lenses will require more glass, thus they will be more difficult to design, costlier to produce, and will be very expensive and heavy.

Besides, we normally use wide lenses for scenery, where we normally stop them down for better DOF, thus there is not much need for a fast lens for wide glasses.

[Lowell Goudge]

you need to start with the definition of aperture. Diameter / focal length.

For a short lens the curvature of the front element needed is much higher and leads to distortion and other problems, which have only been resolved reviently by better optical glasses

There are new very fast short lenses, but for legacy lenses below 50mm F3.5 was the norm, and F2 was fast

[Hamiltom]

The only normal way to increase the aperture is to physically increase the diameter of the lens.This allows a greater amount of light in for any given focal length. Unfortunately, this increases costs and weight.

So the basic answer is price.

[UncleVanya]

Registration distance matters... 50mm is close to the registration distance which makes the design simpler optically.

[Lowell Goudge]

The only normal way to increase the aperture is to physically increase the diameter of the lens.This allows a greater amount of light in for any given focal length. Unfortunately, this increases costs and weight.

So the basic answer is price.

While this is true for long lenses, fast short lenses don't require big diameters necessarily. Think about it, at 24mm for example, F2 only requires 12 mm diameter. It is about the ability to make a small diameter lens with high curvature needed etc....

[BrianR]

I don't have one, but there's Sigma 30mm F1.4 DC HSM (Art) Lens Reviews - Sigma Lenses - Pentax Lens Review Database

For longer focal lengths the problem is the size of the lens: think of a 300mm. If one would design a 300mm f2, the max aperture would be 300/2=150mm which is quite big. The front element would be even bigger.

There is a Nikon version: Company Seven | Nikon 300mm f/2.0 ED IF & Tochigi Nikon T2.2 Lenses Description Page. Big, but hand holdable according to one of the pictures

[TomTom]

I don't have one, but there's Sigma 30mm F1.4 DC HSM (Art) Lens Reviews - Sigma Lenses - Pentax Lens Review Database



There is a Nikon version: Company Seven | Nikon 300mm f/2.0 ED IF & Tochigi Nikon T2.2 Lenses Description Page. Big, but hand holdable according to one of the pictures

I believe that's a young Arnold Schwarzenegger in that picture.

[yucatanPentax]

There's also the MF Samyang 35mm, F1.4: Samyang 35mm f/1.4 AS UMC Lens for Pentax K SY35M-P B&H Photo

Gives an idea how large lenses get to have wide apertures at focal lengths other than around 50.

Oh, and Samyang has a 24mm at 1.4 also: https://www.pentaxforums.com/userreviews/samyang-24mm-f1-4.html

[formercanuck]

28mm f/2.8's aren't hard to come by - at least manual lenses aren't
I will agree though - 50mm has been the typical (ff at least) focal length - and easy to get 'fast' lenses.

35mm / 43mm / 50 mm / 55mm / 71mm are about what they have. Anything longer / shorter requires 'work'

[AquaDome]

I believe that's a young Arnold Schwarzenegger in that picture.

He comes with the 300/f2. Its a heavy beast.