[ScooterMaxi Jim]

Most 50mm lenses are very good. Even a three element triplet can be remarkably good. The famous Tessar is a triplet of sorts with the last element made of two pieces glued together to help flatten the field, and the results from Tessars are excellent. The M50/f2 has five bits of glass because f2.8 is as big as a Tessar can handle. The M50/1.7 was too much for 5 elements, so a sixth was added. The f1.4 needs 7 lenses, but one should remember that every bit of glass impedes and reflects light from where you want it to go. Glass that isn't there has 100% transmission.
About the fungus in your lens, you may not be aware that fungus spoors are everywhere in the air, and will eventually enter lens-space. This is only a problem if you give them the conditions to grow - moisture and darkness for example. Yur lens is not likely to contaminate other lenses, and if it is in low humidity, growth will shut down completely. Some fungus, when it is active, produces an acid that eats into the glass. For aesthetic reasons I hate the idea of fungus in my lenses, but leave it to those more experienced to open the lens and clean it.

That's correct. The three m-series lenses are distinct. The f/1.7 clearly the best of the lot (and I should have gone that route four decades ago when given the chance within the Pentax affiliate purchasing program - but anyone buying an LX pretty much opted for the deal with the f/1.4 because that was the thing we did). The f/2 is a fine lens, but clearly the least of the lot. By f/4 typically you can't tell them apart (except for very slight lower contrast for the f/2).

Also right, don't toss the f/1.7 because you're expecting it might infect your other lenses with fungus - unless you are literally placing your lenses together in a steam bath. A bit of spider looking fungus (not haze) has nearly no impact on the optical quality. Test the f/1.7 against the f/2 in both wide aperture situations and at maximum acuity (typically f/5.6 on APS-c). Don't be a bit surprised if you find the f/1.7 is slightly stronger.

[ChristianRock]

Having had a couple of copies of both, the 50 1.7 is far superior where it matters: large apertures. F4 and smaller, you won't see much of a difference.

[niceshot]

He IS worried bout fungus spreading to his other lens.

[niceshot]

SEND THAT LENS TO ME ,so as to not worry you to death.FUNGUS SMUNGUS. Sent to me I am NOT AFRAID OF FUNGUS

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Last edited by MarkJerling; 04-04-2017 at 09:35 PM. Reason: Masked profanity removed.

[gofour3]

What I heard was that back in the Takumar M42 days, Asahi produced two versions of the same lens (55mm f1.8 and f2), the second of which had a baffle inserted to reduce the max aperture to f2, so they could claim it was a 'budget' lens for provision with 'budget' bodies such as the Spotty 500 - but the lenses were optically identical. Now, I don't know whether this practice continued into the bayonet era, or whether the lenses were optically different - does anyone know? (Brian?)

Same goes for the K55/1.8 and K55/2. They are the same optically, just the maximum aperture is different.

Phil.

[pinholecam]

Get the lens cleaned.
I had one that looked bad, but cleaned up nicely.

The 50/2 and 50/1.7 are both good lenses (esp for the price).
In real use shooting, there is really little between them.

The 50/2 does lose out on the value proposition though.
The f1.7 is as small, faster and as cheap.

Only thing I really dislike about both lenses is that the aperture closes down to a hexagonal shape from f2.8 to f5.6.

[butangmucat]

Get the lens cleaned.
I had one that looked bad, but cleaned up nicely.

The 50/2 and 50/1.7 are both good lenses (esp for the price).
In real use shooting, there is really little between them.

The 50/2 does lose out on the value proposition though.
The f1.7 is as small, faster and as cheap.

Only thing I really dislike about both lenses is that the aperture closes down to a hexagonal shape from f2.8 to f5.6.

I have realized that for ergonomics, I almost prefer my FA43 or Zenitar-K2 any day. Do use them sometimes, but I have chosen to use my FA43 more and more recently as it just feels awesome.

*On a Sony NEX-6 with Lens Turbo II, on my K-S2 I will take my Super-Tak 35/2 or FA35/2 any day, depending whether I feel like using MF or back-button AF.

[Pioneer]

I have been shooting the M50/2 for a very long time. It is a terrific lens.

It is a tiny bit soft (think beautiful portraits) at f/2.0 and, under the right circumstances, will show some chromatic aberration at f/2. By f/2.8 the lens sharpens up very nicely and from f/4 through f/8 you will not be able to see any difference between the f/2.0 lens and its slightly faster brothers.

Mechanically this lens is a beautiful example of the lens builder's art and you will never have to worry about it coming apart or letting you down.

I laugh every time I see one of these types of threads. Below f/2.0 it becomes amazingly tough to focus exactly where you want to. F/2 is probably the practical limit for most people. I own a LOT of lenses, and I truly do enjoy them all. But of all the lenses I own, this M50/2.0 and my Sigma 50mm f/2.8 EX DG Macro are far and away the most used lenses I own.

I own the K50/1.2, the M50/1.4, the A50/1.7 and this M50/2.0. In the real world I can't pick out which lens took which picture, with the exception of some of my wide open photos with the 50/1.2.

The real trick is to walk away from all these useless comparisons, pick a lens, and then go shoot it until you know exactly how it will react under any lighting condition you can possibly encounter. Once you can honestly do that then you will know how to use your camera and lens. And you will also know if you do need a different lens and why you need it. Until then you are just shooting in the dark.