How far have we come?

Every now and then, I get the chance to look over something that was rare and expensive, back in its day.
For example, I’ve just finished sprucing up an old Pentax M42 mount 20mm lens. We may not get too excited at such a modest offering in this day of 14-24mm zooms, but back when it was introduced, it was probably something only one in a thousand Pentax owners might purchase.
So there aren’t many of them out there, for sure.
In 1970 the widest Pentax screw mount lens was a 24mm, unless you count the 17mm fisheye. But the next year the 20mm F4.5 arrived, in the single-coated Super-Takumar version. However the lens I have in hand is the Super-Multi-Coated Takumar version that arrived in 1973 and supposedly lasted until 1979. However, price guides from 1979 no longer show it, as Pentax had switched all premium optics over to the K bayonet mount by then. That guide does show a 20mm F4.0 compact “M” lens for the bayonet cameras. By 1982 ultra-wide 18mm, and uber-wide 15mm offerings were available.
But in the early ‘70s, a super-wide with 94 degrees angle of view on 35mm film was cutting-edge optical technology. If you had one, fellow camera clubbers might mention your name in hushed tones. “He’s got a 20mm.…”
Old magazine ads show the lens available for around $200 in ’73. Nikon’s 20mm F3.5, which was much bulkier in comparison, could be had for around $250.
That might not sound like much, but consider you could buy Pentax’s top-line camera, with a 50mm F1.4 for less than $200.
But, yikes, we’re talking about an F4.5 lens here. And if you’ve never tried such a slow wide angle on an SLR before, you’re in for a rude awakening. For some reason, F4.5 telephotos project a bright snappy viewfinder image, while F4.5 wide angles make you feel the light is coming from a small opening at the far end of a cave.
What I can’t fathom is if the two lenses have such different appearance to the naked eye, how is it the light meter still reads perfectly?


I used to have a Nikon 20mm F4, and while it was a good lens, it was almost impossible to focus manually by sharpness alone. A split image screen was best, but on my old autofocus body, I found I could only get sharp focus by using the AF assist. Eyeballing it left me with quite a few out of focus images, despite the depth of field of a 20mm.
So this equally-ancient Pentax should be even worse at F4.5, and putting it on a 35mm body confirmed that. I suspect most users might have simply focused by using the scale – probably more accurate than viewing through the finder.
The rest of the stats on the SMCT 20mm F4.5 are illuminating (pun intended). There are 11 elements in the design. There’s only five aperture blades in the diaphragm, which is situated eerily close to the back of the lens. It takes a 58mm lens cap, but officially 77mm filters are supposed to attached to the supplied lens hood mount to avoid vignetting. That makes sense, because my newer 20mm 2.8 Nikkor will vignette its corners with a thickish 62mm polarizer mounted.
The Pentax lens hood is also surprisingly complex, having some five main parts and sundry screws. After screwing it on, it allows you to orient its rectangular frame. However, it’s so shallow, it’s doubtful it does much good shading from flare.
This particular lens is unusual in that its barrel and exterior were well worn, with ugly engraving around it from its original institutional owner. But the glass was virtually pristine. Apparently it wasn’t loaned out to anyone who might be rough with it. I’m guessing the photo department had bunches of 28mm’s around, and the odd 24mm too – but that 20mm was the only one they had.
And let’s not forget the mount around which the lens was built – the venerable M42 screw mount. No doubt going with a screw-it-in body mount helped keep costs down for Pentax for many years. But even if a Pentax Spotmatic cost a good bit less than its Nikon contemporary, there’s no denying that Asahi Optical did their very best to compete with the best optics
So if I were to dare to compare this 40 year old lens with something more modern, one contender comes straight to mind, my 21mm F3.4 Pentax Limited.
It’s not really a fair fight, one might argue, in that the newer lens isn’t designed to cover a full frame – and the old one does. But, that being said, Pentax hasn’t seen fit to give us a full-frame digital yet. If we wanted to try the old 20mm on a full-frame sensor, the easiest way would be to adapt it to a Canon 6D or something similar.
One also notes the newer lens has only eight elements, not eleven. But then again, it’s not really as wide a lens as the old one – designed for just 68 degrees on the APS-C sized sensor.
So, even if it’s not a fair fight, let the battle begin.
I didn’t know it at the time, but I took both lenses out for a test on one of the last nice days of fall, before it got cold around here. I used the K-01 mirrorless body, with screw mount adapter, which allowed for easy focus-peaking focus on that slow old F4.5 lens. Both lenses delivered up a few nice looking shots. I tried to see if the old lens would flare badly against the light, but those multi-coatings lived up to their promise. It did well.
Colour issues, distortion weren’t a problem. All images looked quite usable from both lenses, at least on the camera back, and browsing on the computer.
But no, it wasn’t a tie. A close look at details, both distant and close show the newer 21mm wins hands down for sharpness. Check my attached photos.
So, we’ve come a long way since the early ‘70s in lens design? Well, I have nagging thoughts about the fact this wasn’t a fair fight. The old lens can do 94 degrees of coverage. The new one only goes 68 degrees.
A fairer test would be to mount the old optic on a full-frame Canon body, and then use a Pentax 15mm on a crop sensor. At least the angles of view would be similar – but then you’d be battling two sensor types. What would we learn then, I wonder?
Fortunately, that’s not going to happen. The vintage lens has been returned to its owner after getting its clean bill of health, and I don’t have a 15mm Limited handy anyway.
In case you blindly assume that any 40-year old lens will be beaten by a newcomer, I can assure you that isn’t always the case. I’ve tested quite a few vintage moderate wide angles, normals, and telephotos that are just as good as anything made today. The trick, of course, is finding a modern camera that can make use of them.

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~ by windsorphotooutfitters on January 31, 2015.

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