SMC Pentax-F Zoom 1:3.5-4.5 35-70mm

Cost: 15$ (average market price $45)

This was a real find... 15$ and that included a film-era Pentax body. This time in an SPCA thrift store.

Image quality is excellent. Pretty sharp for an older lens, and nice Pentax SMC colors. But...

This is again a lens made completely from plastic. Combined with the green/gray color, it looks pretty cheap, although not really that light for such a small lens. On this lens, the aperture ring was difficult to move, but that might be the age and specific to the lens. The zoom was much looser, but did not have the typical Pentax smooth feel to it. But the biggest problem was in the focus ring. It was soft alright, but the with of the ring itself was very small, making it sometimes hard to find, and even when found, not practical to use.

The APS-C crop factor of 1.5 results in 52.5-105mm, making it a nice portrait lens. And I was pretty impressed with the image quality for portraits. Although it has a macro setting, I was not to impressed with the sharpness when in macro.

In summary, good color quality and sharpness when not used as Macro, but difficult to use due to the small focus ring (it is a manual lens after all). But if you can get it at a low cost, it's still a good deal.

It seems the community is giving this lens very good reviews, so my issues might be just my own taste... 

To combat partial reflection, Pentax developed chemical coatings for the lens surfaces with minimum light loss. SMC is "a remarkable seven-layer lens coating process that cuts the reflection ratio down to just 0.2% per lens surface. The result is a dramatic improvement in both color fidelity and brightness and the elimination of flare and ghost images."
SMC was patented and first applied in 1971, when Pentax was still making screw mount equipment. The multi-coated lens lines changed from Takumar and Super-Takumar to Super-Multi-Coated Takumar and later on to SMC Takumar. SMC Pentax was used for the newly introduced K-mount lenses. Pentax's SMC is still today considered as one of the best lens coatings on the market.

Lens Specification:

Focal Length: 35-70mm
Maximum Aperture: F3.5
Minimum Aperture: F22
Image Format: 35mm
Lens Mount: Pentax K
Optics: 8 elements, 8 groups
Blades: 6 blades
Focussing: Manual
Minimum Focus: 32cm
Maximum Magnification: 0.25x
Filter Size: 49mm
Weight: 235g
Length: 50mm
Production: 1987 until 1991
Serial Number: 1318855

More information on Pentax

Samples:

1/320 sec - ISO640

1/250 sec - ISO100

1/60 sec - ISO250

1/80 sec - ISO100

1/60 sec - ISO100

1/60 sec - ISO500

1/125 sec - ISO400

1/1250 sec - ISO800

Sources:
Wikipedia - Pentax
Pentax Forums
The Northcoast Photographer
All Photolenses