Idle question for a Friday night

Ok, so we expect long lenses to be slower since it's expensive to make glass elements the size they'd have to be for the lens to be faster.

So how come it's the 50mm lenses that are the fastest?

Why, for instance, would a 28mm lens not be easier to make faster than a 50mm?

Because wide-angle is another extreme. 50mm is in the middle, like a sort of optical Liberal.

G

It also gives a similar perspective to the human eye, even if the field of view is different. It has been a very popular choice for many reasons and because of its wide use and ease of manufacture fast lenses have been made.

The easiest lens to make for the 35mm frame would be around 58mm.

Some of the early fast standard lenses were in fact 58mm. Then 55mm became the standard, but as the lens makers got better 50mm took over.

i wasnt aware of that, thank you John

I still have a F 1,8 55 mm lens for my (retired) K2. It's a beauty of a lens. Whish it would have a KA-mount...

some good information which brings up a question i had recently. does anyone know a fast wide angle for the k10 i mostly see like f4. i know the 35 f2 is good but it becomes around 50mm on digital...

Sigma makes a 20/1.8
http://www.bhphotovideo.com/c/product/217800-USA/Sigma_411109_Super_W_A_20mm_f_1...
I have no idea how good it is though.

-- MW

thank you magnus, ive heard some things about aspherical lenses though, something along the lines of crap quality.

I've no experience of the Sigma 20mm F1.8 but I'd be very surprised if it's crap. The Sigma prime lenses I've played with or owned (I used to have one of their 28mm F1.8 manual focus primes) were good performers optically and also well made. Ok their cheap consumer lenses might not be very good (but then are anyones?) but it'd be a mistake to think the same is true of the rest of the their range.

Are you talking specifically about Sigma aspherics, or just lenses with aspheric lenses in general?

You'd be fairly hard pressed to find any modern zooms that didn't contain one or more, including the new DA*s.

Dan

Well, to answer my own post; a Swedish photo-forum is of the opinion that if you get a good specimen, it is a quite lovley lens. Somewhat soft on full aperture, but much better at 2.8 and up. The nice thing is that it covers 24x36, for us analog-shooters. The test at PhotoZone (on a Canon EOS 350D), however, is less than convincing, but maybe they got one of the lemons.

-- MW