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Anonymous
Why are all lenses pretty much the same with regard to their specifications? Like, why are standard zooms pretty much 17/18-50/55, f/2.8 or f/3.5-something? Or there being a bunch of 24mm lenses? Why are not a 19-62/3.6 or a 26mm lens?

Pic related in that it's a lens that kinda deviates from this, although 58mm isn't terribly unusual if old lenses and the Noct-Nikkor are taken into account.
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>> Anonymous
>>153401
Fuck my 4 A.M. typing.

"Why is there not a..."
>> Anonymous
Same reason they sell shoes in pairs.
>> Anonymous
the main reason is most likely that certain designs are easier to create and build... i.e. a 50mm lens will have fewer and less complex elements than a 42mm lens.
Then there is the fact that many users of cameras like to have focal lengths that they instantly know will cover the FOV they want them to... most people will know how much a 50mm can take in vs a 28 or 18mm lens, but again... not how much a 62mm will cover.
Lastly there is the issue of competition, if Tamron bring out a new 18-55mm lens which is better than all other offerings, and people buy it in their thousands, then sigma and tokina are going to respond buy improving their own lens designs of that specefic focal length to be in direct competition, rather than loosing out on a significant sector of the market. This doesn't allow much scope for new and bizzare focal lengths.

However, there are exceptions, like the 58mm nokton as you mentioned, the pentax 40mm pancake, the 60mm nikkor micro and the sigma 20mm f/1.8, to name but a few.

tl;dr
Some lenses easier to build
people like certain focal lengths and stick to them
market favours these standard focal lengths
>> Anonymous
>>153408
tl;dr
inertia
>> Anonymous
The known working lens designs are all optimal at the same few focal lengths. Look at element diagrams, and they'll reveal big similarities in all the brands. True Sonnar type lenses are best at 50 and 85mm, so that's why pre-war Zeiss Sonnars are those lengths (Newer ones aren't actually Sonnars, so there's a much bigger range of focal lengths they cover). Tessars work with pretty much every length longer than 50mm (35mm with modern glass formulas), so you can find Tessars up to 300mm - but one limitation of the Tessar design is that they never go faster than f/3.5. Since the Tessar design is a good performer and pretty cheap otherwise, that's why most companies had cheap long lenses (200/4) that were almost identical Tessar (four elements, three groups) designs, as well as identical slow kit standard lenses (CZ Tessar 3.5 for Contax, Leitz Elmar 3.5 for Leica)

SLRs became popular as the Planar design for standard lenses became popular. Fast Sonnars tend to be f/1.5, so you can often recognize an old lens by that speed. Planars, on the other hand, are either f/1.4 or f/2, and back then they seemed to work better at slightly longer lengths (hence all the 55 and 58 kit lenses of the first SLRs)

The Nokton in OP is a conscious copy of an old Tokyo Kogaku lens that CV released with permission in conjunction with a new Topcon. That's why it's got the really normal symmetrical Planar design and the longer length. It probably gives a similar "look" as the old lens too.

I think I started rambling there, but I hope the gist gets through.
>> Anonymous
>>153437
argh okay on second thought it made no sense

tl;dr version:
There honestly aren't that many working lens designs (give or take subtle variations), and everybody uses them. Links with moar:
http://www.taunusreiter.de/Cameras/Canon_RF_e.html#SONNAR_PLANAR
http://keppler.popphoto.com/blog/2007/04/inside_straight.html
http://keppler.popphoto.com/blog/2006/11/inside_straight.html

Also there are Planars at f/1.8 as well - such as the modern Nifty Fifty from every brand.
>> Butterfly !xlgRMYva6s
>>153441
I thought it made sense actually, but then I have a lot of exp reading bad english etc.

Minolta used to make a bunch of weird lenses that sony have dropped, but I dont have a list of them anywhere, 72mm anyone?
>> Anonymous
>>153444
http://members.aol.com/xkaes/slrlens.htm
>> Anonymous
>>153437
>>153441
But then why do so many lenses have distinctive looks to them? I know lots of designs are similar, but most lenses look different than others. Bokeh, how it draws the image, etc. Just for a quick and easy example, the Canon and Nikon 50/1.8s look noticably different.

Wouldn't designers go for the best aesthetic design, instead of trying to nail it to some specific specifications?

>>153408
>Some lenses easier to build
>people like certain focal lengths and stick to them

I'm one of them, but that's not really relevent in a zoom.

>market favours these standard focal lengths

Would a kit lens off from the standard by a few millimeters really negatively affect sales?
>> Anonymous
>>153444
>72mm anyone?

Yeah, like this. Why 75mm and not 72?
>> Anonymous
>>153449
They're optically identical, pretty much. Must be the fairy dust one puts into theirs.

>>153450
Actually there are many 72mm lenses. Lens angle of view tolerances are actually enough so that a "50mm" lens is often a 48 or a 52 (of course this doesn't work for wides). That's why old lenses from Leicas to Russian copies packed certificates signed by a tester with a certified "true" focal length. Also if you take apart some older lenses (don't do this unless you're sure you can put it back together to the correct tolerances, or it's a junker), the real focal length is penciled in by the craftsman who made it. They tried to make the best performing lens possible, which with minor imperfections in glass shape and alignment sometimes meant the exact focal length desired could not be achieved.

Of course, nowadays nobody gives a shit, and robots are probably pretty good at getting this stuff right.
>> des
>>153449
The look of a lens isn't just a function of lens configuration. Element type and construction, aperture blade number and even coatings can affect it.
>> Anonymous
Two more points:
a) Most lenses change the angle of view (and therefore, focal distance) when focusing, so your usual 50mm lens may actually behave like a 50mm one when focused to infinity and a 60mm one when focused to 1 m. This effect is usually most evident with macro and superzoom lenses.
b) There is a "standard" sequence of focal lengths everyone is used to - 50, 85, 100, 135, 180, 200mm etc. Sometimes deviating focal lengths were consciously rounded to the nearest "standard" number - a lens with a focal length of 80mm by design could be sold as a 85mm, for example.