Why f/1.8?

[digitaldave]

Does anyone know why f/1.8 lenses seem to be so common, particularly in the SLR world? Most systems both old and new I've seen have a 50mm f/1.8 lens available, even my old Skoda of a Praktica has one 😉. The logical progression of apertures would be 1, 1.4, 2 (assuming you start from 1 of course), so why 1.8? Was it just a compromise between 1.4 and 2 to give a large enough wide open aperture at a reasonable cost?

Thanks 🙂.

 

[Crasis]

Does anyone know why f/1.8 lenses seem to be so common, particularly in the SLR world? Most systems both old and new I've seen have a 50mm f/1.8 lens available, even my old Skoda of a Praktica has one 😉. The logical progression of apertures would be 1, 1.4, 2 (assuming you start from 1 of course), so why 1.8? Was it just a compromise between 1.4 and 2 to give a large enough wide open aperture at a reasonable cost?

Thanks 🙂.

I'd make a cynical guess that it was merely to be able to say "Hah! The fastest the competition has is f/2. Well we have f/1.8!"

Then everyone else made f/1.8 lenses and it just became a common thing due to that. Pretty cynical. Wonder if there's truth in it? 🙂

 

[telenous]

Could be because f1.8 is the widest aperture you can get in a 50 lens and still have it optimised in terms of performance and cost. Most 50 f1.4 optical designs call for a compromise in performance unless cost is no object (in which case tolerances can go skyhigh).

 

[Socke]

I'd make a cynical guess that it was merely to be able to say "Hah! The fastest the competition has is f/2. Well we have f/1.8!"

Then everyone else made f/1.8 lenses and it just became a common thing due to that. Pretty cynical. Wonder if there's truth in it? 🙂

Hm, could be. My Zeiss Planar 50 is f1.7.

 

[rxmd]

It's not uncommon to have lenses aligned to half a stop somewhere. I regularly use a 50/f1.8, a 35/2.5, a 90/2.5 macro and a 135/2.5. Now 1.8 is technically about third of a stop, but then people considered 1.5 to be the f-stop above 2 for a while when now it's usually 1.4, so these differences are pretty negligible in practice. In practice, an 1.8 is half a stop brighter than a 2. I guess it's a compromise between economy, speed, and the marketing bonus to have an 1 before the decimal point.

Philipp

 

[ClaremontPhoto]

Marketing.

That's why the Fuji Natura is f1.9, and they say that it's a specialist night time camera, no flash required and so on. Still a nice camera but f1.9 is really no different from f2 in the real world.

 

[Spyderman]

I have a Zuiko 50/1.8, but in PopPhoto test they once measured it's in fact a 1.9 🙂

And for example Minolta used to offer 50/2, 50/1.7, 50/1.4 and I think even 50/1.2 in MD mount 😀

 

[HansDerHase]

Pure marketing.

Same as with 10.3 Megapixel. The .3 makes ABSOLUTELY NO practical difference in quality of the final result. Especially when taking into account all other steps of the image making chain. The .3 is totally worthless information from a technical point of view. But it makes the ad look nicer.

Actually even the practical difference between 8 and 10 MP is questionable. A typical 8MP gives you a file with around 2400 vertical pixel. A typical 10MP gives around 2600. Thats a barely noticable 200 vertical pixel difference. - OK it's obvious on screen 1:1, but you don't shoot a 10MP-Image to display 1:1 on a computer screen, do you?

But "more megapixel" seems to be more sexy for the casual consumer than "less noise".

Speaking of differences in pixel count:
Anyone to explain why Leica squeezes out some extra horizontal pixel in JPEG while losing some vertical?

From the M8-Spec:
"DNG : 3916 x 2634 pixels (10.31 MP), JPG : 3936 x 2630 pixels (10.35 MP),"

.. Wow now I'm way off topic .. 🙂

 

[Pherdinand]

not only a matter of marketing. Also a matter of lens design.
50/2 lenses can be made relatively easily. 50/1.8 and 50/1.7 lenses usually have one extra element if you look at their construction, and are not very different in design. 50/1.4 lenses are a bigger step, more complicated, meaning larger anbd more expensive. The step below f/1.4 is even larger.

 

[jaapv]

Speaking of differences in pixel count:
Anyone to explain why Leica squeezes out some extra horizontal pixel in JPEG while losing some vertical?

From the M8-Spec:
"DNG : 3916 x 2634 pixels (10.31 MP), JPG : 3936 x 2630 pixels (10.35 MP),"

.. Wow now I'm way off topic .. 🙂

Just a speculation: sensors do have more pixels that used for actual pictorial rendering. The surplus pixels have a function in the software. Maybe DNG compression needs some different edge pixels than Jpeg does... But let the experts call me a fool....

 

[Benjamin Marks]

As you all probably know (and to complicate things), an f-stop is a ratio of the actual focal length to the physical opening of the lens iris. Most 50's are not actually 50mm in focal length. So there is some slop factor there. I think marketing also helps explains the answer. I find it unlikely that anyone could notice the difference between f2 and f1.8 (or f1.4 and f1.5) in actual practice. The marketing works, though. My very first lens was a Pentax 50/1.7 and I chose it because it was "faster" than the 50/2.

 

[Benjamin Marks]

Also, while half stop can easily be compensated by faster of pushed film, there is a major difference in OOF behavior.

Roland.

Very true. But, alas, what did I know of such subtleties in 1984? I can remember pouring through the tiny-print ads in the backs of photo mags looking for the longest, cheapest zoom I could find. I wound up with an 80-300/4.5 two-ring Soligor with a macro-feature. Yikes, what a monster. Now I own no zooms.

Ben