Originally posted by Wheatfield I think the problem is the flange to focal plane distace. It's around 45mm on the K mount. Anything shorter than that has the rear nodal point outside the lens. The shorter the focal length the more difficult (and expensive) it becomes to put some properties into the design.
A fast 50 is relatively easy.
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Not that this explains the DA*55/1.4 which is pretty gargantuan.
Had to google "gargantuan"...
Originally posted by Spock Exactly!
I don't subscribe to the argument that such a lens would have to be big and heavy. Firstly, old film SLR 50mm f1.4 lenses were compact - and secondly, isn't the whole idea of a smaller sensor size that lenses can be made smaller and lighter and faster?
(Olympus has certainly proved that to be true - have you seen how fast their lenses are?)
As Wheatfield explains, it is getting complicated to make lenses once you go to a focal length shorter than the registration distance (about 45mm in Pentax case), especially when there is also a mirror to consider. To make a wide angle lens sort of requires breaking some of the basic optical rules (or getting around them), especially if it also has to be a fast wide angle. Some early wide angle SLR lenses required that the mirror was locked up to leave room for the last lens elements. I think the retrofocus lenses were the first way around this, invented for cinema cameras but first applied for SLRs in the 50's by a
French lens designer followed by Pentax
Auto-Takumar 35mm f2.3 (scroll down), one of the first fast 35mm lenses. A beast with a hugh front element. Despite that the lensmakers now have more tricks in their bag than back in the 50's, such as aspherical lens elements, it is still a challenge to build a fast and/or compact wide angle lens. The DA15ltd is a fine little miracle in it's compactness.
Olympus? You mean their f2 zooms? So hugh that they make the tiny 4/rd cameras look rediculous?
Originally posted by smc Perhaps it's the advancement of technology and I'm presuming that the quality is better....but my 1957 lenses start at F1.9? Why are they all so small? I guess there is autofocus....aperature....advancements in quality.....but I'm not so sure it's better quality after using them.....why does a modern F4 need to have 10X the surface glass to the older f1.9 lenses?
Because they try to correct for abberations, distorsions etc with more lens elements. Optically better lenses. Pentax old 28/3.5 and 35/3.5 are among the sharpest and most distorsin free wide angles I've seen, moderately sized. But if you make it faster the lens elements gets wider, you get more optical problems to correct for, so you need more lens groups, and if we are talking about a zoom, you need to add some group to be able to change the focal length. And some lenses to correct for the optical flaws you creat when you zoom. Then add some electronics and autofocus gears and/pr engines...and the lens is getting rather heavy. The Pentax limited lenses are not the fastest or optically most perfect lenses. But they are miracles of optimized compromises between optical quality and small size, pared with a great build quality. But if the priority is fast lenses, such as the DA* lenses, they at once get bigger.
Originally posted by Wheatfield And which one is a 30/1.4?
Have patience. I think it is comming (you remember the 30mm that was on the lens route and then dissapeared...hopefully that was because Hoya wanted to be more secret, not because we will never see it). Meanwhile, there are other options.
Originally posted by Class A It is quite obvious that Pentax would have to compete with other lens manufacturers on such a market.
If customers only bought Pentax lenses to go with their Pentax cameras then, yes, Pentax would need to address some holes in the line up. However, customers have a wider range to choose from, although I get the feeling that many involved in this thread here are not looking elsewhere at all.
Definitely. And Sigma offers some fast wide angle options. What you will have to live with is some optical flaws (soft corners etc), but you get the speed with their 20/24/28mm f1.8 and 30mm f1.4 lenses.