Lens Spotlight: M100 Macro & 1.4x-S - Jason Doss

Lens Spotlight

smc Pentax-M 100mm f/4 Macro

& 1.4x-S Teleconverter


The Pentax SMC-M 100mm f/4 Macro was the first macro lens I acquired.  The lens is, of course, all manual with an aperture ring and manual focus ring.  Unlike most modern day 100mm macro lenses, this one and older versions have only a 1/2 life size, which means for a full frame or film camera, the smallest field of view is only 48mm x 72mm.


Macro lenses are designed for more than just close focusing.  The lenses do best at close distances and have optics with minimized distortions.  The lens is a fairly slow f/4 which saves a bit of size and weight compared to its newer A version, which will be reviewed later.


The lens is 355g and 77.5mm long (0.8# and 3 inches) and has 49mm filter threads like most M-series lenses.  There are markings on the lens to indicate the magnification ratio.  The M-series macro lenses have recessed front elements, therefore lens hoods are not required.  


In my collection, I work thru lenses in a random order, and I treat the addition of teleconverters as a separate lens.  So, this time, the M100 Macro is paired with the 1.4x Pentax teleconverter of the day, which was the Converter A 1.4x-S.  The teleconverter adds 0.85 inches and 5.1 ounces to the package.  The fit is tight and comfortable.  Magnification is increased by 1.4x without decreasing the minimum focus distance.  The combination behaves as a 140mm f/5.6 lens with 3/4 life size magnification.



The two shots up top are from a trip to Pedestal Rocks, national parkland just south of glorious Newton County, Arkansas.  These two were done to show some contrast between close and infinity focus capability.  The shelf fungus on the left is shows decent detail at lower resolution, but zooming in will show operator error in manual focusing.  Sometimes, optics of a macro lens aren't as good at infinity focus because, well, they're generally used for something else.  Here, you can see that despite the haze in the air, this landscape image to the upper right shows decent detail... about what could be expected under the circumstances.


Below, we see a flash-illuminated, tripod-mounted, underwater (yes) shot of my second favorite gemstone, a piece of tigerseye.  I put the stone underwater in a clear plastic container, and sent the flash beam in from the top of the frame.  Of course, the flash unit was off-camera, controlled by an on-camera master unit that was turned off.  The water smoothed out the frame, and helped reduced glare and distracting reflections


That's all I have for now... See you next time.


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